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8607073

D uffy, W a lte r G ilb e rt

THE POPULATION ECOLOGY OF THE DAMSELFLY LESTES DISJUNCTUS
DISJUNCTUS (ZYGOPTERA: ODONATA) IN THE ST. MARYS RIVER,
MICHIGAN

Michigan State U niversity

University
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Ph.D.

1985

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THE POPULATION ECOLOGY OF THE DAMSELFLY
LESTES DISJUNCTUS DISJUNCTUS (ZYGOPTERA:ODONATA)
IN THE ST. MARYS RIVER, MICHIGAN
By
Walter Gilbert Duffy

A DISSERTATION

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

DOCTOR OF PHILOSOPHY

Department of Fisheries and Wildlife

1985

ABSTRACT
THE POPULATION ECOLOGY OF THE DAMSELFLY
LESTES DISJUNCTUS DISJUNCTUS (ZYGOPTERA:ODONATA)
IN THE ST. MARYS RIVER, MICHIGAN
By
Walter Gilbert Duffy

A demographic investigation of a natural population of Lestes
disjunctus
was

disjunctus

inhabiting

conducted during 1982

life history, distribution,
examined

the

the

St.

and 1983.

Marys

Laboratory studies

temperature on egg development,

the influence of water temperature,
predators on growth and survival

Michigan

Field studies investigated

and demographics.

influence of water

River,

prey density,

and coexisting

of nymphs and the influence of

fish on survival and habitat selection.
The

1982

cohort

oviposited

the 4.03 ha study area.
to be

77.2%.

anthropogenic
difficulty

(6.0%),

and

estimated 3,202,000

eggs

in

Mortality in the egg stage was estimated

Egg mortality
sources

an

factors

(18.9%),

were:

habitat loss through

overwintering

unexplained

sources

(16.7%),

hatching

(35.6%).

Relative

mortality among 10 nymphal instars varied and was greatest in the
final
stages

instar
was

(71.4%).

94.7%.

study

area yielding

adult

stage

of

An
an

1.2%.

Relative
estimated

mortality
35,800

all

nymphal

adults emerged from the

estimated survival rate from the egg to
Lower

potential

_i

eggs‘9

through

fecundity

in

1983

(45.2

_i

) than in 1982

(73.5

eggs*9

) combined with

increased

mortality

in

1983

to

produce

a

negative

population

rate

of

increase (A) value of -0.612.
Growth of nymphs in the laboratory was significantly greater
at

20.0°C

density
did

than

at

treatments

16.0°C.
were

significantly

Differences

in

not significant.

influence

survival

growth

However,
of

nymphs

among

prey

prey density
while

water

temperature did not.
Survival of nymphs in the laboratory was significantly lower
in the presence of nymphs of the dragonfly Aeshna canadensis than
in the presence of other coexisting predators.
may

also

influence

significant.

survival,

Growth

although

Other predators

differences

were

not

of nymphs was not influenced by coexisting

predators.
In

the

absence

of

bluegill

sunfish

(Lepomis

macrochirus)

nymphs exhibited little discrimination among three cover densities
or three

cover types

In the presence

of

(macrophytes, aquarium bottom,

fish,

nymphs

selected or were restricted in

distribution to macrophytes at all cover densities.
of

nymphs

bluegill.

was

significantly

and sides).

affected

and

survival

Distribution
reduced

by

ACKNOWLEDGMENTS

Ecological

investigations

of areas

distant

from university

facilities are difficult and require the cooperation and effort of
many people.

I gratefully acknowledge the students and staff of

the Dunbar Research Station and the Department of Fisheries and
Wildlife,

Michigan State University,

for their encouragement and

assistance during this investigation.
I especially thank Dr.

Charles R.

Liston for his continued

interest and support during this investigation.

Other members of

the

Donald

Doctoral

Committee,

Clarence D. McNabb,

Drs.

Edward

Grafius,

and Richard W. Merritt,

J.

Hall,

counseled me during

the program and critically reviewed the manuscript.
I am particularly grateful to Diane E. Ashton, my spouse and
colleague,
this

for her unselfishness,

period

of

investigation.

understanding,
In

dialogue on littoral zone ecology,

addition

and help during

to

maintaining

a

her encouragement, biological

insight, and editorial expertise were most welcome.
Rob

Allard

collections
some of the

and

provided

able

laboratory work.

field work.

laboratory duties.

assistance
Michael

in

both

field

Schirripa helped with

Robert Day and Mark Hart assisted with

Dr.
from

Ted R.

the

study

Batterson
area.

graciously provided limnological data

Paul

illustrating macrophyte

E.

Roettger

distribution.

drafted

the

John R. Craig,

figure

George W.

Knocklein, and Dr. Mehdi Siami collected and analyzed limnological
data.
Dr. Niles R. Kevern provided equipment, laboratory and office
space.

This work was

Service

and the U.S.

Drs.

Charles R.

supported by

the U.S.

Fish

and Wildlife

Army Corps of Engineers through grants to

Liston

and Clarence

D.

McNabb and by the U.S.

Geological Survey through a grant to Dr. William Taylor.
support

was

provided

by

the

Agricultural

Michigan State University.

ii

Experiment

Partial
Station,

TABLE OF CONTENTS

page
ACKNOWLEDGMENTS

....................

i

LIST OF TABLES

vi

LIST OF FIGURES

........................................

viii

CHAPTER ONE
Demographics and Life History of the damselfly
Lestes disjunctus disjunctus,
in the St.Marys River, Michigan

...

INTRODUCTION
AREA OF STUDY

1
2

........................................

MATERIALS AND METHODS

..................................

Physical-Chemical Measurements

..................

4
12
12

......................................

13

Population Sampling... ...............................

14

Area of Cover

Egg Stage
Nymph Stage

....................................

14

..................................

17

Exuvia

21

Adult S t a g e ...................................

21

Data Analysis

......................................

23

Age Specific Life T a b l e .......................

23

Population Rateof I n c r e a s e ...................

25

iii

page
R E S U L T S ................................................
Physical-Chemical Measurements

26
26

Area of Cover

......................................

26

Demographics

......................................

29

Egg S t a g e ......................................

29

Nymph Stage

31

. .. .............................

Exuvia

38

Adult Stage

..................................

38

Age Specific Life T a b l e .......................

41

DISCUSSION

.............................

45

Life History

......................................

45

Demographics

......................................

49

CHAPTER TWO
The Influence of Environmental and Biological Factors
on Growth, Survival, and Habitat Selection in
Lestes disjunctus

INTRODUCTION

disjunctus

. . . .

..........................................

MATERIALS AND METHODS

...............................

Water Temperature-Prey Density
Competition-Predation
Habitat Selection

55

56
59

..................

59

...........................

61

..................................

Field Data

63
64

iv

page
R E S U L T S .................................................
Length-Dry Weight

..................................

Water Temperature-Prey Density
Competition-Predation
Habitat Selection

.............................

..................................

Field-Laboratory Comparisons
DISCUSSION

.....................

66
66
66
75
81

.......................

81

............................................

86

Water Temperature-Prey Density

...................

86

Competition-Predation

88

Habitat Selection

..................................

92

C O N C L U S I O N S ............................................

94

SUMMARY

..............................................

96

APPENDIX

..............................................

100

LITERATURE CITED

......................................

v

112

LIST OF TABLES

page
1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

_i
Average monthly discharge rates (m3 *s ) for the St.
Marys River, Michigan during Janurary, 1982
through September, 1983.
.
.
.
.
.

6

Key to dominant species of emergent vegetation and
composition of mixed stands of emergent vegetation in
the west littoral zone of lower Lake Nicolet, St. Marys
River shown in Figure 3.
.
.
.
.
.

9

Area of emergent vegetation and open water occupying
the west littoral zone of lower Lake Nicolet, St.
Marys River.
.
.
.
.
.
.
.

11

Summary of physical and chemical parameters measured
monthly in the west upper littoral zone of lower Lake
Nicolet, St. Marys River during 1982 and 1983.
.

27

Area (m2) of emergent macrophytes and other
predominant cover types in the study area during
May, June, and July 1983.
.
.
.
.
.

29

Descriptive statistics for eggs carried by female
Lestes disjunctus disjunctus collected in the study
area during 1982 and 1 9 8 3 . . . . . .

30

Descriptive statistics for Lestes disjunctus
disjunctus eggs hatched from Sparganium eurycarpum
leaves collected in the study area in September, 1982
and dead vegetation collected in April, 1983.
.

31

Head width measurements from Lestes disjunctus
disjunctus nymphs used in population estimates for
the study area and from nymphs reared in the
laboratory.
.
.
.
.
.
.
.
.

34

.

-2

.

Mean density (no'm ) of Lestes disjunctus
disjunctus nymphs collected from four cover types
in 1982.
.
.
.
.
.
.
.
.
.
-2

.

.

Mean density (no'm ) of Lestes disjunctus
disjunctus nymphs collected from two cover types in
the study area during 1983.
.
.
.
.
.

vi

35

36

Estimated stage-frequency data for total Lestes
disjunctus disjunctus nymphs within the 4.03 hectare
study area in the St. Marys River during 14 May
through 13 July, 1983.
.
.
.
.
.
.

37

Number of Lestes disjunctus disjunctus exuvia
collected from stands of high and medium density
Sparganium eurycarpum within the study area in 1983.

39

Estimated total number of Lestes disjunctus disjunctus
in the study area entering each of twelve life stages
in 1983.
.
.
.
.
.
.
.
.
.

42

Life table parameters for female Lestes disjunctus
disjunctus in the study area during 1983.

43

Summary of mortality factors for female Lestes
disjunctus disjunctus in the study area during 1983.

44

Instantaneous growth rates of Lestes disjunctus
disjunctus, Aeshna canadensis, Enallagma hageni,
Buenoa spp. and Umbra limi m competition experiment
pools.
.
.
.
.
.
.
.
.
.

77

Comparison of estimated number of Lestes disjunctus
disjunctus in competition pools from sampling on the
final day of experiments with the actual number
recovered.
.
.
.
.
.
.
.
.

77

Density of macroinvertebrates as mean number over
1 m 2 of substrate in Sparganium eurycarpum beds
located in a littoral zone of the St. Marys River.

100

Annual production estimates for Lestes disjunctus
disjunctus from the St. Marys River, Michigan.

107

Production statistics for common macroinvertebrates of
a Sparganium eurycarpum bed in the St. Marys River,
Michigan.
.
.
.
.
.
.
.
.

108

Total number of prey in guts of Lestes disjunctus
disjunctus nymphs collected from a Sparganium
eurycarpum bed in the St. Marys River, Michigan.

109

Density of zooplankton as mean number/liter in a
Sparganium eurycarpum bed located in a littoral zone
of the St. Marys River.
.
.
.
.
.

110

vii

LIST OF FIGURES

Map of the St. Marys River, Michigan and Ontario

5

Weekly range in water level at the center of the
study area in 1982 and 1983.

7

Distribution of aquatic macrophytes in the west
littoral zone of lower Lake Nicolet, St. Marys River,
including the study area.
.
.
.
.
.

10

Modified Gerking sampler.

19

.

.

.

.

.

Average daily water temperature in the study area
during 1982 and 1983 .
.
.
.
.
.
.

28

Lestes disjunctus disjunctus egg hatching rate in
relation to water temperature.
.
.
.
.

32

Frequency distribution of Lestes disjunctus
disjunctus head width measurements.

33

Estimated adult male and female Lestes disjunctus
disjunctus population in the study area during 1983.

40

Length-dry weight relationship for Lestes disjunctus
disjunctus nymphs from the St. Marys River.
Curve
fitted by regression.
.
.
.
.
.
.

67

Growth of Lestes disjunctus disjunctus at 16 and 20°C
in low prey microcosms. Data are plotted as means
and standard errors with a line fitted by regression.

68

Growth of Lestes disjunctus disjunctus at 16 and 20°C
in medium prey microcosms. Data are plotted as means
and standard errors with a line fitted by regression.

69

Growth of Lestes disjunctus disjunctus at 16 and 20°C
in high prey microcosms. Data are plotted as means
and standard errors with a line fitted by regression.

70

Specific growth rate of Lestes disjunctus disjunctus
at 16 and 20°C as a function of prey level. Curve
fitted by specific growth equation.

72

viii

page
14.
15.
16.

17.

18.

19.
20.

Survival of Lestes disjunctus disjunctus in high,
medium, and low prey microcosms at 16°C.
.

.

73

Survival of Lestes disjunctus disjunctus in high,
medium, and low prey microcosms at 20°C.
.

.

74

Average daily water temperature recorded in
experimental pools during competition-predation
experiments.
.
.
.
.
.
.
.
.

76

Growth of Lestes disjunctus disjunctus in the contol
pool and in pools with Aeshna canadensis, Enallagma
haqeni, Buenoa spp. or Umbra limi .
.
.
.

77

Survival of Lestes disjunctus disjunctus in the
control pool and in pools with Umbra limi, or
Aeshna canadensis. .
.
.
.
.
.
.

78

Survival of Lestes disjunctus disjunctus in pools
with Buenoa spp. or Enallagma hageni.
.
.

79

Average number of Lestes disjunctus disjunctus
nymphs in three cover areas and three cover densities
with and without Lepomis macrochirus present.
.

81

21.

Survival of Lestes disjunctus disjunctus nymphs from
the field population, the control competition-predation
pool, and the 20°C high prey density treatment.
.
83

22.

Comparison of Lestes disjunctus disjunctus nymphal
growth in the field with predicted growth.
.
.

ix

85

1

CHAPTER ONE

Demographics and Life History of the Damselfly
Lestes disjunctus disjunctus
in the St. Marys River, Michigan.

2

INTRODUCTION

Odonata
are

often

large

inhabiting

numerically

proportion

Crowder

and

predaceous

of

Cooper
habits

fresh-water
abundant

the

environments

and represent

a relatively

invertebrate

1982).
of,

littoral

This

nymphs

biomass

abundance,

has

(Benke

along with

stimulated

interest

qualitative life history and behavioral studies,
analyses of diets (Corbet 1962, 1980).
focused
in

on

either the potential

littoral

interactions

systems
as

or

possible

the
in

as well as

More recent work has

functional

inter-odonate
factors

1976;

role of Odonata
or

regulating

odonate-fish
populations

(Benke 1978; Johnson and Crowley 1980; Johnson et al. 1985).
However, few studies have attempted to quantitatively examine
population dynamics of Odonata (Lawton 1970; Benke and Benke
1975).

Demographic

are rare.

analysis

of aquatic

insect populations

The only study of Odonata to quantify survival in

all life stages is Ubukata (1981).
During the past few decades, ecological research has been
increasingly

directed

toward

quantitative

approaches.

However, basic life history information is often lacking for
these studies (Rosenberg 1975).

Corbet (1954) recognized two

basic types of life histories for Odonata:

"spring species"

that spend the winter in final instar diapause,
synchronously

in spring or "summer species"

then emerge

that spend the

3

winter in early instars and emerge asynchronously throughout
the summer.

It is now recognized that a wide range of life

history types exist between these two extremes
Jenner

1971).

disjunctus
stage

Previous

Selys

in

indicate

diapause,

studies
it

hatches

of

spends
in

present

The

early

developmental pattern

during

separate

seasons

Lestes

disjunctus

the winter in the egg
spring,

relatively synchronously in mid-summer
1974a).

(Paulson and

and

emerges

(Sawchyn and Gillott

of discrete life stages

and

relatively

and rapid development makes L. d. disjunctus

synchronous

an attractive

species for the study of odonate demographics.
This chapter presents results of a demographic analysis
of a natural population of L. d. disjunctus using life table
techniques.

Ancillary

observational,

which relate to interpretation of population

or

life

studies,

history

data,

phenomena

other predators

habitat

been

quantitative

included.

and

Related

presented in chapter two, examine the influence on

nymphs of water temperature,
with

have

both

selection

as well
as

prey density, and interactions
as

the

possible

population size of L. d. disjunctus.

influence
mechanisms

of

fish on

regulating

4

AREA OF STUDY

The

St.

Marys

River originates at Whitefish Bay,

Superior and flows southeast 113 km to Lake Huron
The drainage basin,
is

comprised

bedrock

of

Ordovician
the

west

of

lacustrine

origin

in

2,367 km2 ,

sediments
the east

overlying
grading

to

shale and Silurian age Niagaran Dolomite in

(Dorr

and

undeveloped

in

north.

twin

The

and

Precambrian
age

(Figure 1).

which encompasses anarea of

till

Lake

the

Eschman
south

cities

1970).

and

of

The basin

moderately

Sault

Ste.

is

developed

Marie,

largely
in the

Ontario

and

Michigan with a combined population of approximately 100,000
constitute

the

single

population

center

within

Between the twin cities of Sault Ste. Marie,

the basin.
a portion

of the river is diverted through a system of navigation locks
and power canals with the remainder flowing over an extensive
rapids.

Below the St. Marys Rapids the river is divided into

several channels

and broad expanses by a series of islands.
_ i

Average gradient throughout the river system is 6.0 cm*km

,

however, most of this drop in elevation (6.0 m) occurs at the
rapids

and

controlled

navigation
at

the

lock

rapids

complex.

and

River

navigation

discharge

lock

complex

is
by

compensating structures.
1960
1983).

through

1980

Annual discharge during the period
_i
averaged 2,202 m 3 ‘s
(Quinn and Kelly

Average monthly discharge during the period of study
_i
ranged from 1,229 to 2,979 m 3 's
(Table 1).

5

ST. MARYS RIVER
ONTARIO

Lak^l
Nicoletl V K

v

MICHIGAN

irummond'

Lake Huron
10 kilometers

Figure 1.

Map of the St. Marys River, Michigan and Ontario

6

Table 1.

Lake
discharge,

Average monthly discharge rates (m3 's~ ) for the
St.Marys River, Michigan during January, 1982
through September, 1983 (NOAA, GLRL unpub.).
month

1982

1983

January
February
March
April
May
June
July
August
September
October
November
December

1,229
1,286
1,286
1,305
1,730
2,101
2,078
2,387
2,398
2,534
2,837
1,382

2,291
2,314
2,452
2,424
2,922
2,951
2,911
2,979
2,398

Nicolet
with

receives

the

into Lake George

approximately

remainder

(McNabb et al.

flowing

65%

around

1983).

of

Sugar

this
Island

Lake Nicolet has a

surface area of 3,958 ha, water depth averages approximately
3 m except in the navigation channel, which is maintained at
a minimum

8.6

m

depth by

dredging.

Water

retention time

within the Lake Nicolet basin was determined to be only 21.6
hours by McNabb and colleagues (1983).

Where the shoreline

is protected from wind and water currents, extensive emergent
wetlands (Cowardin et al. 1979) have developed.
A

site within

the

emergent wetlands

on the west side

of Lake Nicolet in the St. Marys River, approximately 18.5 km
south of Sault Ste. Marie, Michigan, was selected as the area
of study.
30"

W.

Map coordinates were 49° 2 0 1 19" N and 84°
The

study

site

encompassed

an

area

of

4.03

131
ha

7

extending from the shore to a depth of approximately 1.0 m.
However,
discharge

water
and

depth

varied

meteorologic

during

both

conditions

years,

varied

as

river

(Figure

2).

The predominant aquatic macrophyte within the study area
was bur
Both

bur

reed,
reed

Sparganium
and

eurycarpum

hardstem

bulrush,

(Table 2,
Scirpus

Figure

3).

acutus, form

extensive beds along the west shore of Lake Nicolet.

Type

and location of emergent macrophytes present in the area are
shown

in

presented

Figure
in

Table

consisted mostly
spp.

3,

of

with
3.

estimates

Submersed

Potomogeton

of

the

macrophytes

area

occupied

in the

gramineus, and

area

Ranunculus

8

1883

Water depth

(cm)

1982

11

j

ii it i i i i f r i i ii i

F M A M J

J A S O N D J F M A M J

i

i j i

j

AS

Month
Figure 2.

Weekly range in water level at the center of the
study area in 1982 and 1983.

9

Table 2.

Key to species of mixed stands of emergent
vegetation in the west littoral zone of lower Lake
Nicolet, St. Marys River shown in Figure 3.
(Adapted from McNabb et al. unpub.).

Map
Designation

Species Combinations

A

Scirpus acutus
Eleocharis smallii

B

Scirpus acutus
Sparganium eurycarpum

C

Sparganium eurycarpum
Typha latifolia

D

Sparganium eurycarpum
Phragmites australis

E

Sparganium eurycarpum
Scirpus acutus and/or
Eleocharis smallii

G

Sparcfanium eurycarpum
Grammaceae

H

Scirpus americanus
Scirpus acutus and/or
Eleocharis smallii

I

Sparganium chlorocarpum

J

Other(s)

10

study

S cirp us acu tu s - high d e n s ity

E le o c h a ris s m a llii

S c irpus ac u tu s - medium d en sity

P h ra g m lte s a u s tr a lis

S cirpus acu tus - low d en sity

Typha la tlfo lia

Sp arganium euryc arp u m

Figure 3.

area

nrai

M ixe d s ta n d - high d e n s ity

Distribution of aquatic macrophytes in the west
littoral zone of lower Lake Nicolet, St. Marys
River, including the study area. (McNabb et al.
unpub.).

...

i«•«

IZ
s

ooo
o® •

oc o

ooo
ooo
ooo
00~ o^bVtW

000
OO 9 0
°$ J& !
o ^

°°oo^o

OOOOOVJ&OO

o o o o o \ o o o o o o o o o fio
O OO OOOOO,A oooolo
o o o o o o o o o o o o^o o o o o
oo —
o o o o o o >T*\ o o o

m

m

M ix e d s ta n d - m edium d e n s ity
M ixe d s ta n d - lo w d e n s ity
O p e n in g s

@

oo

•••

see

5

M u s k ra t house

150

_l

11

Table 3.

Area of emergent vegetation and open water
occupying the west littoral zone of lower Lake
Nicolet, St. Marys River.
(McNabb et al. unpub.).

Vegetation Type
Scirpus acutus

Density
High
Medium
Low

Area
(hectares)

Percent
Total

6.67
5.31
3.97

15
11
9

Sparganium eurycarpum

-

12.59

28

Eleocharis smallii

-

1.37

3

Typha latifolia

-

0.85

2

Mixed stand (A)

High
Medium
Low

3.66
0.76
0.57

8
2
1

Mixed stand (B)

High
Medium

1.77
0.39

4
< 1

High
Medium
Low

0.74
0.75
0.75

2
2
2

5.16

11

Other mixed stands
(C-J)

Open water

-

12

MATERIALS AND METHODS

Physical-Chemical Measurements
Water quality parameters
stands

of bur

reed

at

Dissolved oxygen was
of

the

Winkler

were

the north

measured

titration,

measured monthly within
edge

of

the

study

area.

using the azide modification

alkalinity

using methyl

orange

titration, turbidity using a Hach model 2100 turbidimeter, pH
using a combination electrode,
by

acid

digestion,

and

phosphorus colorimetry after

nitrogen

by

the

Kjeldahl

method.

Methods used are described fully in Standard Methods for the
Examination of Water and Wastewater (APHA 1980).
Water

temperature

was

monitored

during 1982

and

1983

using a Ryan model 600 recording thermometer, located at the
center

of the

study

weekly

and average

area.

tapes were

changed

daily water temperature calculated from

temperatures

recorded

2400

From

hours.

Thermograph

at 0400,

January

0800,

through

1200,

1600,

February,

ice

2000,

and

extended

through the water column and 10 to 20 cm into the sediment.
An effort to record ice temperature during this period was
made,

but periodic thawing and refreezing made retrieval of

the recording thermometer without damage difficult.

13

Area of Cover
Sampling

during

1982

suggested

that nymphs

of

Lestes

disjunctus disjunctus inhabited two types of cover within the
study area.
emergent
floated
nymphs

These included beds of bur reed and mats of dead

macrophytes
on

the

from

surface.

the previous

years

To

population

quantify

growth which
size

of

in the study area, the aerial extent of each habitat

was determined.
Area

(m2 ) of dead matted vegetation was determined by

measuring the width of the mat at 10 m intervals along shore.
For mats not associated with the shoreline both length and
width was measured at intervals short enough to define mat
shape, usually 5 to 10 m.
Dead

matted

dynamic habitat.

vegetation

unexpectedly

However,

and

some

storms

concentrating
served

to

bordering

the

floated

remainder

intertwine
the

toward

stems

shoreline.

mats

while

shore where wave

action

forming

During

the

a

single

course

of

this

vegetation

became

quite

rapid

in

floating dead vegetation remainded by July.
take

a

offshore,

mat began to decay and sink to the bottom.

to

be

rising water levels

this

necessary

to

Initially mats of vegetation were scattered

throughout the littoral zone.
spring

proved

measurements

of

the

June

thick
the

mat

summer

Decay of
and

little

It was therefore

dead vegetation mat

cover each time population samples were collected.
The area (m2 ) of bur reed beds within the study area was
determined using polar planimetry of habitat maps drawn from

14

low

altitude

during

photographs

1983

suggested

taken

in

1982.

neither

the

Ground
extent

truthing
nor

the

configuration of bur reed beds had changed appreciably since
1982.

Population Sampling
Egg Stage
Population size of the egg stage was estimated using two
separate techniques.
fecundity

of

The

first method involved determining

adult females,

then combining these data with

adult population estimates to obtain an estimate of the total
number

of

eggs

technique

oviposited

in

for estimating egg

the

study

area.

The

second

population size also provided

information on egg mortality.
Method 1: Adult females to be used for ovarian analysis
were collected weekly using an aerial net,
collecting

jar

laboratory.

containing

Total

length

chloroform,
and

color

sacrificed in a

and returned to

the

of

was

each

female

recorded on a numbered envelope, the individual placed in the
envelope,

and frozen until ovaries could be examined.

When

examining

ovaries,

dish

containing water,

a

eggs

was

placed

a

petri

and

Abdominal contents were then removed,

separated from other tissue,

which

in

the abdomen severed from the thorax,

the sternum removed.
ovaries

female

and teased apart.

All

could be discerned under a stereozoom binocular

microscope were counted.
Odonata have a panoistic type ovary in which successive

15

batches of eggs may mature following an oviposition episode.
However,
to

it is unlikely that a female will live long enough

oviposit

Therefore,

her

full

compliment

of

eggs

(Corbet

1962).

total egg counts provide an estimate of potential

fecundity rather than an estimate of realized fecundity.
derive

estimates

oviposited,

of

fecundity

the

a method suggested by Corbet

employed.

In this method,

ages

subtracted

are

or

from

the

number

recognized:

post-reproductive.

eggs

p. 27) was

of

found

in

Three age classes of

pre-reproductive,

Age was

eggs

The difference is then used as

an estimate of total eggs oviposited.
were

(1962,

of

the number of eggs at successive

pre-reproductive individuals.

adults

number

To

determined

reproductive,

using

color

and

changes

associated with aging (Corbet 1962).
Method 2: This method involved collecting and hatching
eggs

following

oviposition.

Lestes

disjunctus

disjunctus

oviposits endophytically in emergent macrophyte tissue 10 to
20 cm above the water surface.

In September 1982, following

the completion of oviposition, 0.25 m 2 plots of bur reed were
collected
plant,
to

from

the

study

area.

The

upper portion of the

extending to 20 cm below the water surface was taken

insure

collection

of

all

eggs.

Five

samples

were

collected from each of 4 strata including; the shoreline and
25, 50, and 75 m offshore.
Plant

stems

collected were returned to the laboratory

and refrigerated at 1°C for 100 days to insure completion of
egg diapause.

When removed from the refrigerator, stems were

16

placed

in aquaria

containing

was controlled at 20°C,
a 150

|j sieve,

tepid tap water.

Temperature

aquaria water filtered daily through

and newly hatched nymphs recorded.

Nymphs

capable of orienting their body so as to stand and capable of
movement were classified as alive.

The weighted mean number

of nymphs hatching per unit area was then multiplied by the
area

(m2 ) of

viable

egg

bur

reed

population

within
size

in

the

study

September

area

to

estimate

(see nymph

stage

methods for discussion of weighted mean).
In

April

1983,

ten

0.25

m2

samples

of

dead

matted

vegetation from the previous years growth were collected from
the study area.

At this time,

not emerged from the sediment.

stems of live macrophytes had
Stems of dead vegetation were

not refrigerated, but placed in aquaria containing tepid tap
water and incubated at 20°C.
and

Methods to determine the number

condition of nymphs hatching were identical to September

collections.

The mean number of nymphs hatching from April

samples was multiplied by the area of matted vegetation (m2 )
to estimate egg population size at that time.
in

egg

population

size

between

September

The difference
and

April

was

assumed to be overwintering mortality in the egg stage.
Percent of nymphs hatching per day was calculated from
stems collected in April and incubated at 16 and 20°C.

These

data in combination with data published for hatching rates of
L. d. disjunctus incubated at 12 and 15°C (Sawchyn and Church
1973) were used to develop a regression equation which would
predict

hatching

rate

as

a

function

of temperature.

The

17

intercept

of

the

regression

line

was

interpreted

as

the

threshold temperature for L. d. disjunctus.

Nymph Stage
Sampling for nymphs was initiated when cumulative degree
days

recorded

determined
were

in

the

in the

collected

field

neared

laboratory.

from

egg

development

Beginning on May 1,

times

samples

the dead vegetation mats every 2 days

until nymphs were found.

Following the appearence of nymphs,

a more rigorous sampling scheme was initiated.
The

dynamic

behavior
effort

of

in

nature

nymphs,

of

each

prevented

proportion

to

the

strata,
the

area

combined with

allocation
of

each

of

the

sampling

strata.

Early

instar nymphs occur exclusively in the dead matted vegetation
from which they hatch and remain in this strata for several
weeks.

As

disperse,

aquatic

with

macrophytes

many

Because of this,

moving

begin

to

the

to

develop,

dense

bur

nymphs

reed

beds.

initial sampling effort was limited to the

dead vegetation strata and later expanded to include the bur
reed strata.
Sampling
intervals,
instars

in both

with

field,

of the
a

conducted

exceptions,

until

at

3

to

nymphs

4 day
reached

Sampling was then conducted weekly.

On

a minimum of 12 samples was collected from each

strata sampled.
a map

several

IX and X.

each date,

strata was

Sample locations were selected randomly from
study

series

area gridded into 1 m 2 units.

of poles

with

surveyors

flags

was

In the
placed

18

along

a grid

of

50 m

intervals

to

aid in locating sample

sites.
Sampling
using

a

within

modified

sampler

the

bur

Gerking

consisted

of

a

reed

sampler

plexiglass

strata was

accomplished

(Mittelbach
box

with

1980).

This

sliding doors

attached to the bottom and a 150 |j plankton net attached to
the

top

were

(Figure

sharpened

4).
to

The

inner edges of the sliding doors

pinch

off

plant

stems

when

closed.

However, thick fibrous stems of bur reed could not be severed
easily and a knife was used for this purpose.
In collecting a sample the operator walked slowly toward
the

sample

location holding the sampler above the emergent

vegetation

with

the

doors

in

the open

position.

Upon

arriving at the desired location, the samper was lowered over
the emergent stems and pushed gently through the water column
to

the

sediment

forcefully

as

collector,

and

possible,

sampler was then
upward.

surface.

a

knife

The
the
used

doors were then
sampler
to

closed

rotated

sever

plant

lifted from thewater with

toward
stems.

as
the
The

the doors facing

Macrophytes were removed from the sampler and placed

in an 18 L pail and the remaining contents of the sampler
rinsed into the plankton net collecting jar.
The Gerking sampler proved ineffective in sampling the
dead floating vegetation because leaves and stems of bur reed
and bulrush had become
Pushing
possible.

the

Gerking

intertwined so as to form a matrix.
sampler

through

these

mats

was

not

Consequently this strata was sampled using a 0.3 m

25 cm

,
Ficpire 4.

Modified

sample r *

20

diameter plankton net of 70 |j mesh attached to a circular net
frame on a wooden handle.
In collecting a sample,

the cod end of the plankton net

and the handle were held in one hand so as to close the net
mouth.

The net was

about

1 m,

mat.

Excess

trimmed

and

lowered

to

the bottom, pushed forward

lifted quickly from the bottom through the

stems

hanging

using

scissors.

collection was

identical

beyond

the

Treatment
to

the

of

net

diameter

samples

were

following

treatment of Gerking

type

samples.
Following

collection,

samples

were

returned

laboratory and nymphs sorted while still alive.
usually completed within 24 hours of collection.
nymphs,
baking

to

the

Sorting was
In sorting

a small amount of sample water was placed in a pyrex
dish

and

examined over

a light table.

The

volume

examined at any one time was adjusted so that the bottom of
the dish remained visible.
sections of 20 to 25 cm,
and

examined

for

Plant stems were cut into short
floated in tap water in the dish,

nymphs.

Number

of

nymphs

collected was

converted to number *m ”2 .
When sampling
associated variance

s

=

s2 =

n iW i

two

strata,

was

a weighted average

calculated

its

(Sokal and Rohlf 1969):

+ N 2w2/Wl + w 2

X 2x +

and

x 22/(n1-l)(n2-l)

21

where N = weighted average,
wl ‘*2 = wei9hting
area)

factor

= number in strata 1 or 2,

(proportion of the total

sampling

for strata 1 or 2, and s 2 = variance of N.
Nymphs

using

sorted

a

Taxonomy

from samples were identifiedto species

stereozoom binocular

followed

caudel lamella,

Walker

microscope,

(1953).

Total

(10

length,

-

70X).

excluding

and head width were recorded for 20 or more

nymphs for each sampling date.

Exuvia
Number

of

counting exuvia

nymphs

molting

to

adults

in the study area.

were

estimated by

Exuvia were counted in

two sub-strata within bur reed strata; 1) the outer edges of
plant beds

consisting of medium cover and 2) the center of

plant beds which consisted of heavy cover.

Ten plots

(1.0

m 2 ) were established in each strata and exuvia collected from
plant

stems

anticipated.

weekly or

more

frequently,

if

rain

was

A weighted average number of nymphs molting'm"2

was calculated from these data and multiplied by the area of
bur reed to estimate nymphs molting in the study area.

Adult Stage
Population estimates for adults were made using mark and
recapture techniques.
d.

disjunctus

waters

edge

Following emergence, tenneral adult L.

flew to the treeline,
and

remained

there

for

70 to 100 m from the
several

days

before

22

returning

to

individuals

the

had

water.

Marking

returned

to

the

was

not

study

initiated until

area.

This

insured

that individuals had hardened and minimized mortality due to
handling.
Marking was
felt tip marker.

accomplished using a red colored "Sharpie"
Marks

consisted of a series of dots

dashes applied to one or both wings.

and

This code was changed

daily and allowed the collector in the field to distinguish
the

date

an

individual

had

been marked.

Both marking and

recapturing were conducted daily between 0800 and 0930 hours
by walking a prescribed area within the study area.
date the number of each sex marked was recorded,

On each

as well as

those recaptured and the date of release of recaptures.
Adult population estimates were calculated from mark and
recapture

data

using

a

modification

of

the

Peterson

population estimate (Begon 1979):
A
N± = [ M ^ ^

+ l)/(m. +1)]

A
where

=

the

estimated

population

size

on

day

i;

n^

+ 1 = the number of individuals caught on day i + 1; m^ + 1 =
the
M^

number
= the

of marked individuals caught on day i + 1; and
number

of marks

at

risk on day

i consisting

of

individuals marked from day i-6 to day i-1 (the total number
of marked individuals considered for population estimates).
M^ was used in place of r^ (number marked on day i) of the

23

normal Peterson estimate.
A

standard

error

of

the

population

estimate

was

calculated from:
A
------------------------SEn = V M 2i (n+l)(n-m)/(M+l)2 (m+2)
To

test

survival,
on 20,
for

the

influence

of

handling

40 individuals were collected,

and

marking

on

a wing mark placed

and 20 individuals neither marked nor handled except

netting.

Both marked

released within a screen

and

unmarked individuals were then

tent and survival monitored.

Prey

provided daily were predominantly mosquitoes.

Data Analyses
Age Specific Life Table
Construction

of

information

on

through

particular

a

the

an

age specific

total

number

stage

or

of

life

table

individuals

instar.

requires
that pass

Field

sampling

provides information on the number of individuals observed on
each sampling occasion only, which is a function of the total
number entering a stage and the probability of surviving to
be sampled.

Because of this the total number of individuals

entering

stage

a

techniques.

must

be

estimated

using

statistical

A method developed by Richards and Waloff (1954)

was used to estimate stage recruitment.

This method assumes

a single pulse of recruitment and consists of plotting the
regression

of

decreasing

numbers

with

time

after

peak

abundance.

This regression line is then extended back to the

time when the stage was first found (t^) and the population

24

corresponding to time t^ is the number of individuals alive
just before the stage is seen for the first time (Southwood
1978).
Stage
life

recruitment

table

to

interpretation,
1,000

data were

further

then used to

describe

the

data.

construct
For

ease

a
of

stage recruitment data were initially set at

individuals.

The

life

table

then

contained

the

following columns (Deevey 1947):

x

The pivotal age (egg, instar, or adult)

1

A

The number surviving at the beginning of a
stage

d

A

The number dying during the age interval x,
i1* - w

q

T

The proportion dying during the interval x to x+1

A

The total number of age units beyond the age x or
the life remaining to those at age x which is
given by:
T
where

x
L

= L , + L - +
xl
x2

L

xw

= number alive between age x and x + 1

and w = the last stage
e

The expectation of life at age x which is given by:
e = T /I
x
x7 x

25

m

The

average number of eggs oviposited per female.

Population Rate of Increase
The net reproductive rate (RQ ) was calculated from
survival

(1 ) and
X

age

R0 =

specific

data

from

during

and

1983

population

rate

(m ) data where:
X

n xmK

Additionally,
1982

fertility

of

natural conditions.

adult

and egg population estimates

enabled

increase

the

(A)

for

calculation

of

the population

the
under

With non-overlapping generations, A can

be shown to be comparable to the intrinsic rate of increase
(r) for populations with overlapping generations
1978):

Nt = V

rt = ^ 0
ert =
er = \
r = In A

With non-overlapping generations A

t

= Rq .

(Southwood

26

RESULTS
Physical-Chemical Measurements
River water at this location was soft and low in both total
phosphorus

and

total

nitrogen.

Dissolved

oxygen

levels

_ i

decline to around 8 m g ‘L
90%

saturation

fluctuated

by mid-summer, but remained above

during

only

all

moderately

seasons.
during

the

Turbidity
open

water

and

pH

period

(Table 4).
Water temperature began to rise in April with the period of
initial warming to 10°C being rapid (8 to 9 days) during both
years.

Following

this

initial

warming

period

water

temperatures

fluctuated,

(Figure 5).

Water temperature began to decline by August in

both

years.

but rose steadily through mid-July

Maximum

average

daily

water

temperatures

recorded in 1982 and 1983 were 22.3 and 26.9°C, respectively.

Area of Cover
Floating mats of dead vegetation provided the only cover
in the study area until aquatic macrophytes began to develop
in early June,

1983

(Table 5).

mats was 7,769 m 2 at ice out.
(-22.7%)

The area of dead vegetation
This was reduced to 6,008 m 2

in late April when rising water levels caused mats

to float above the substrate and stems to which they had been
anchored,

allowing

some

to

drift

offshore.

This

cover

27

Table 4.

Summary of physical and chemical parameters
measured monthly in the west littoral zone of
lower Lake Nicolet, St. Marys River during 1982
and 1983.
D.O.
pH
Aik.
(mg/L) (s.u.) (mg/L)

Turb.
(NTU)

Total P Total N
(mg/L)
(mg/L)

1982
11.8
9.9
9.4
8.0
9.2
9.1
11.1

May
June
July
August
September
October
November

8.20
7.24
7.86
7.57
7.42
7.63
7.50

n.d.
n.d.
n.d.
n.d.
n.d.
37.5
40.0

5.37
1.85
2.49
2.70
3.18
2.83
3.52

n.d.
.008
.009
.017
.082
.114
n.d.

n.d.
.066
.332
.228
.681
.710
n.d.

n.d.
3.45
2.68
2.30
2.37
2.69
3.10
3.50

n.d.
n.d
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.

n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.

1983
April
May
June
July
August
September
October
November

10.9
10.5
8.3
7.8
7.7
7.9
9.2
10.2

7.89
8.06
8.14
7.53
7.48
7.59
7.86
n.d.

41.0
39.4
38.2
39.1
39.2
39.2
39.0
n.d.

n.d. = no data
remained somewhat stable until mid June, when the dead stems
began to decay.
the

end

of

Stem decay was rapid from 13 June through

sampling,

resulting in near total loss of dead

vegetation cover by 13 July 1983.
Both bur
water

surface

emergent
reed

reed and hardstem bulrush leaves reached the
the

aquatic

(Table

5).

first week of June.

macrophyte within the
Distribution

of

The most
study

bur

reed

abundant

area was
was

bur

nearly

continuous at the north edge of the study area and fragmented
by pockets of open water elsewhere (Figure 3).

25
0

1983

20

Temperature

(C )

h

15
Ki

00

f4

10
0

1982

Tte*

5

0

w m m

f
A

nr
M

r
J

i
J

i
A

T
S

O

Month

Figure 5.

Average daily water temperature in the study area
during 1982 and 1983.

N

T
0

29

Table 5.

Area (m2 ) of emergent macrophytes and other
predominant cover types in the study area
during May, June, and July 1983.
Sparganium Scirpus
eurycarpum acutus

Date
May 14
17
20
24
27
June 2
9
13
17
22
26
29
July 6
13

15,192
15,192
21,200
21,200
21,200
21,200
21,200
21,200

Mixed
Dead Veg.
vegetation
Mats

5,787
5,787
5,787
5,787
5,787
5,787
5,787
5,787

Open
Water
37,192
37,192
37,192
37,192
37,192
37,192
5,802
5,802
5,802
7,562
8,202
8,362
8,582
8,766

6,008
6,008
6,008
6,008
6,008
6,008
6,008
6,008
3,140
1,380
740
580
360
176

4,403
4,403
4,403
4,403
4,430
4,403
4,403
4,403

Demographics
Egg Stage
Ovaries collected from 47 adult females in 1982 and 65
collected

in

fecundity.
among years

1983

were

Differences
were

Whitney U-test

examined

to

determine

potential

in the number of eggs per age group

non-significant

P > 0.05,

in all comparisons

Table 6).

(Mann-

While pre-reproductive

adults in 1982 averaged 25.7% more eggs per female than those
collected in 1983, differences were largely the result of one
single

individual

associated

with

bearing
means

were

219

eggs.

relatively

Standard
low,

errors

excepting

30

Table 6.

Descriptive statistics for eggs carried by female
Lestes disjunctus disjunctus collected in the study
area during 1982 and 1983.
1983

1982
age

n

Immature
Pre-reproductive
Reproductive
Post-reproductive
A (Pre - Post)

21
9
10
7

X

S.E.

n

105.5
47.0
32.0
73.5

23.8
6.5
6.5

15
20
20
10

S.E.

X

83.9
47.0
38.7
45.2

5.2
3.5
4.3

pre-reproductive adults in 1982, suggesting little variation
in eggs per female by age class.
The weighted mean from areas 25, 50,

and 75 m offshore

in September 1982 and the mean number of eggs hatching from
dead

vegetation

(Table 7).
the

collected

in

April

1983

were

determined

No eggs hatched from bur reed stems collected in

shoreline

observations

sub-strata

confirmed

during

that

September,

females

1982.

Later

did not oviposit along

shore and data from the shoreline samples were subsequently
omitted in calculating weighted mean number of eggs hatching
from

bur

reed.

Data were

variable

during both years

with

_2

ranges

of

0

to

1,344

eggs'm

m

1982

and

22

to

1,199

_2

eggs'm

in

significant

1983.
for

Differences
both

egg

among-seasons

comparisons (Mann-Whitney U-test
Egg hatching rate,

in

density
and

were

among

non­

strata

P > 0.05).

as percent of eggs hatching per day,

was positively correlated with water temperature (Figure 6).

31

Table 7.

Descriptive statistics for Lestes disjunctus
disjunctus eggs hatched from Sparganium eurycarpum
leaves collected in the study area m September,
1982 and dead vegetation collected in April, 1983.
September, 1982
n

April, 1983

15

x Alive
S.E.
% Dead

10

183.5
90.3
6.0

343.2
131.0
3.4

A linear regression of hatching rate against incubation water
temperature gives an equation of:

% eggs hatching/day = -1.63 + 0.38(T), r2 = 0.95

The regression line intercepted the X-axis at 4.3°C which
was interpreted as the threshold temperature.

Nymph Stage
Ten instars were determined using measurements of head
widths from nymphs collected in the field and nymphs of known
instar

reared

in

the

laboratory.

Separation of

instars

4

through 10 was possible utilizing a frequency distribution of
head

width

However,
and

3

nymphs

measurements

from

slight differences
necessitated
for

separation

the

the

field

data

(Figure

7).

in head widths of instars 1, 2,

measurement

(Table

8).

of

laboratory-reared

Variation

of head width

% Hatching/Day

6

4

2

5

10

15

20

Incubation Temperature (C)

Fioure 6.

Lestes disjunctus disjunctus egg hatching rate as
a function of water temperature.

33

% of total

10

5

0

Head width (mm)

Figure 7

Frequency distribution of Lestes disjunctus
disjunctus head width measurements.

34

Table 8.

Head width measurements from Lestes disjunctus
disjunctus nymphs from the study area and from
nymphs reared in the laboratory.
Field Data

Instar
I
II
III
IV
V
VI
VII
VIII
IX
X

Laboratory Data

x

S.E.

n

0.37
0.51
0.61
0.90
1.24
1.54
2.02
2.54
3.07
3.60

0.01
0.01
0.01
0.01
0.02
0.02
0.04
0.01
0.01
0.02

28
25
38
26
23
22
17
14
21
26

|
|
|
|
|
|
|
|
|
|

x

S.E.

n

0.34
0.43
0.64
0.87
1.30
1.55
2.04
2.57
2.94
n.d.

0.00
0.00
0.02
0.01
0.00
0.05
0.08
0.06
0.03

5
5
7
8
2
4
8
4
6

measurements within instars increased with increasing instar
but was low for both field and laboratory data.
In

1982,

estimates

was

conducted

including; bur
vegetation,
shore.

preliminary sampling
on 4

for

dates in

nymph
4

density

cover

types,

reed, hardstem bulrush,floating mats

and

mixed-species

Cover present

was

emergent

similar

to

of dead

macrophytes

along

that present in 1983

except that vegetation mats were distributed throughout the
area

rather

analyzed

by

than

located

collection

Whitney U-test

(Table

hardstem bulrush were
0.05).
0.05).

All

other

date
9).

only

along

shore.

and cover type using
Differences

significant

comparisons

on

were

11

among bur

Data

were

a Mannreed

and 18 June

non-significant

and
(P <

(P

>

35

Table 9.

Mean density (no'm ) of Lestes disjunctus
disjunctus nymphs collected from four cover types
in 1982.
Date
18 June

11 June
Plant Cover
Type

n

S . eurycarpum
S . acutus
Veg. Mats
Mixed Vegetation

In 1983,
exclusively
June,

22.9
0.0
24.6
12.5

10
10
10
10

nymphs

within

n

X

were

the

10
10
10
10

first

dead

on

25 June
n

X

25.0
2.1
27.7
14.6

10
10
10
10

14 May.

vegetation

X

18.7
0.0
21.6
8.3

They occurred

strata

through

before a portion emigrated to the bur reed.

13

Density

within the dead vegetation strata increased rapidly following
initial

hatching,

with

the

seasonal

occurring on 20 May (Table 10).
declined slowly
Single

sample

-2

maxima

(105.8'm

)

Density within this strata

through 17 June, then declined more rapidly.
density

estimates

ranged

from

0 to 4 3 1 ‘m

_2

Nymphs were first collected from the bur reed strata on
17 June.

Dip

netting,

numbers of nymphs
vegetation mats.

the

week before this,

produced low

in bur reed stands 1 - 2 m from the dead
However, no nymphs could be located beyond

this 1 - 2 m border and it was assumed that emigration from
the dead vegetation mats had yet to begin.
within
Density
began,

the
in

bur
this

reed

strata was

strata

increased

initially

Density of nymphs
low

(Table

slightly until

10).

emergence

while continuing to decrease in the dead vegetation.

36

Table 10.

_2

Mean density (no'm
) of Lestes disjunctus
disjunctus nymphs collected from two cover types
m the study area during 1983.
Dead Vegetation

Date
May

14
17
20
24
27
2
9
13
17
22
26
29
6
13

June

July

n

x

6
12
12
12
12
18
18
18
16
16
12
12
12
12

12.8
87.4
105.8
105.4
95.1
80.6
77.2
72.0
77.1
37.4
24.9
12.0
5.2
5.2

Sparganium eurycarpum

S.E.

n

6.2
21.3
24.1
21.3
23.8
24.1
28.7
21.0
21.0
9.9
7.1
6.0
2.7
2.7

x

S.E.

0.0
0.0
15.5
20.7
22.2
22.3
8.7
0.0

12
12
12
12
12
12
12
12

0.0
0.0
5.8
7.1
6.9
6.0
3.9
0.0

Differences in density of nymphs among strata were tested b]
date

using

numbers
June

a

Mann-Whitney

of nymphs were

(P <

0.05).

U-test.

Significantly

lowei

found in the bur reed strata on 17

Differences

among strata on later dates

were non-significant (P > 0.05).
Estimates

of total population size by instar or stage

frequency data
was

composed

were

determined

entirely

of

first

(Table 11).
instars

on

The population
14

and 17 May.

Instars II and III entered the population on 20 May followed
by instar IV on 2 June.

Development after 2 June was more

rapid due to increasing water temperatures.

Length of time

specific instars were present in samples ranged from 15 days
(instar VIII)

to 20 days

(instars

IV and V), with the mean

Table

11.

Date

Day

May 14
17
20
24
27
June 2
9
13
17
22
25
29
July 6
13

1
4
7
11
14
19
26
30
34
39
43
46
53
60

Estimated stage-frequency data for total Lestes disjunctus disjunctus nymphs
within the 4.03 hectare study area in the St. Marys River during 14 May
through 13 July, 1983.

I

II

III

IV

V

VI

VII

VIII

IX

X

116962
219929
579748 193250 193250
289235 481296 192519
173704 260558 434262
39607 66249 323885 301801
33843 167802 436425 66980
197285 328809 131524
110050 349918 168854 31631
73656 97864 196241 122586 24723
40438 112246 157244 134993 22745 22251
26516 17357 52552 105013 122941 69909
7076
7076 50090 121782
348
1043

38

being 18.5 days.
date

are

Low numbers collected on the final sampling

probably

the

result

of

emergence

having

begun

between 6 and 13 July.

Exuvia
Exuvia
stands

were

of

collected

emergent

bur

from

reed

high

stems

and
(Table

medium

density

12).

Ranges

associated with means for heavy and medium bur reed were 0-5
-2

and 0-3'm

respectively.

No exuvia were found in 2 of 10

quadrats from heavy cover and in 4 of 10 quadrats from medium
cover.

Although mean density of exuvia in heavy cover was

roughly

twice

that of medium cover,

among the strata were non-significant

differences in density
(Mann-Whitney U-test,

P > 0.05).

Adult Stage
A

total

of 292

sampling in 1982.
marked

(100)

population
females

23

were

marked

during preliminary

Because of relatively low numbers of males

and recaptured (5%) data were not adequate for

estimates

marked

estimates

adults

of

males.

in 1982 was

9.9%.

Recapture

rate

for

192

Weighted mean population

for the periods 11 through 16 July and 17 through

July were 23,871

(SE = 7,826)

and 19,694

(SE = 7,522),

respectively.
In 1983 adult L.

d. disjunctus were first observed in

the study area on 11 July.
several days earlier.

However, emergence may have begun

A total of 696 adults were marked in

39

.

Table 12.

.

.

-2

.

Number Lestes disjunctus disjunctus exuvia'm
collected from stands of high and medium density
Sparganium eurycarpum within the study area in

Plant cover

n

High Density

10

2.10

0.55

Medium Density

10

0.90

0.31

1983,
188

433

females

(18.6%)

and 263 males.

bore

marks,

Of 1,012 females captured

while

64

captured, were marked individuals.
were 5.6 days

for females

S.E.

X

of

570

males

(11.2%)

Average ages at recapture

(range 1 - 2 5 )

and 6.1 days (1 -

24) for males.
Estimates of female population size in 1983 ranged from
10,516

on

17

population

July

size

to

732

on

generally

4 August

decreased

(Figure
with

8).

time

as

Adult
most

emergence was completed in the first week.

An increase

estimated

July

likely

population

the

result

size

of

during

windy

26

to

conditions

relative to the total number observed.
noted for both sexes.
1983

ranged

Males

were

from
less

6,552

28

reducing

was

most

recapture

This second peak was

Estimates of male population size in
on

abundant

17
than

July to 1,053
females

in

on

the

1 August.
study

through 3 August, but slightly more common thereafter.
also appeared to be more active,
quantified.

in

area
Males

although movements were not

(10

)

10-1

Number of Adults

female

male

July
Figure 8.

31

1

August

Estimated adult male and female Lestes disjunctus
disjunctus population in the study area during
1983.

12

41

Emigration from the study area was measured in a 625 m 2
area adjoining the study area on 19 and 30 July 1983.
July,

2 marked males

unmarked

along with 34

females were captured.

and 3 of

34

unmarked males

On 19
and 43

On 30 July,

3 of 31 males

females were marked individuals

(9.6 and 8.8%

respectively).
Average age at death for adults held in a screened tent
was 7.3 days (range 2 - 20), while marked adults averaged 5.6
days at death (range 1 - 18).

Differences in mortality among

marked and unmarked adults were non-significant (Kolmogorov Smirnov

test,

(0.250)

was

P

only

>

0.10).

However,

slightly

less than

the

observed

D

value

the critical value of

0.265 at 20 df,P < .10 suggesting some minimal influence from
marking.

Life Table
Estimates of total numbers of L.

d.

disjunctus

in the

study area passing through each of 12 life stages during 1983
were

calculated

(Table 13).

Egg stage estimates are taken

from the product of estimated adult females present in 1982
and

the

oviposit.

average
This

number
estimate

of

eggs

they

were

is slightly less

estimated

(17.7%)

to

than the

estimate derived from eggs hatched per unit area and area of
bur reed present in September,
larger
3.0%.

figure would

reduce

1982 (3,890,200).

Use of the

adult survival by approximately

42

Table 13.

Estimated total number of Lestes disjunctus
disjunctus in the study area entering each of
twelve life stages in 1983.

Female

Stage
egg
I
II
III
IV
V
VI
VII
VIII
IX
X
adult

128,400
81,000
66,800
18,500

Male

Total

118,500
74,700
61,700
16,800

3,202,000
730,800
723,800
713,700
616,600
475,100
419,800
330,600
246,900
155,700
128,500
35,800

Sex ratio for instars VIII through X was determined to
be 1.08:1.0 female to male.

From the egg through instar VII

a sex ratio of 1:1 was assumed.
Of 1,000 female eggs oviposited in 1982, an estimated 12
(1.2%)

survived

to

the

adult

stage

in

1983

(Table

14).

Mortality was greatest in the egg stage when viewed in terms
of numbers

dying

(d ).

However,

q

A

X

(proportion dying)

equally large in instar X (Table 14).

was

Other mortality rates

(q ) tended to increase with increasing instars, with several
exceptions.
first

These

collected on

exceptions

were

9 June before

at

instar

V which was

emegration from the dead

vegetation strata began and instar IX.
Mortality within the egg stage could be partitioned into
three

factors:

overwintering

mortality,

mortality

due

to

43

Table 14.

X

Life table parameters for female Lestes
disjunctus disjunctus in the study area during
1983.

dx

X.

egg
1
2
3
4
5
6
7
8
9
10
adult

1000
228
226
223
193
148
131
103
80
51
42
12

<*x

772
2
3
30
45
17
28
23
29
9
30
12

.772
.009
.013
.134
.233
.115
.214
.223
.362
.176
.714
1.000

Tx

ex

1,937.0
1,323.0
1,096.0
871.5
663.5
493.0
353.5
236.5
145.0
79.5
33.0
6.0

1.94
5.80
4.85
3.91
3.44
3.33
2.70
2.30
1.81
1.56
0.79
0.50

mx

45.2

(0.012)(45.2) = 0.542

R0 =

loss of vegetation containing eggs, and mortality at hatching
(Table
the

15).

egg

The greatest source of explained mortality at

stage

containing

eggs.

difference

in

nearly

as

(18.9%)
Egg

was

due

mortality

to

loss

from

as

from

vegetation

overwintering

September 1982 and April 1983
high

of

vegetation

(the

estimates) was
loss,

while

mortality at hatching was relatively low.
Net

reproductive effort calculated

suggests

that only

slightly more than half the eggs this cohort began with will
be replaced.

Population rate of increase (X), based on net

reproductive rate was -0.612.
Evaluation of the influence of mortality factors on net
reproductive

effort

was

possible

from

calculation

of

44

Table 15.

Summary of mortality factors for female Lestes
disjunctus disjunctus in the study area during
1983.

Nymph

Egg
Over­
winter

dx
% Apparent
Mortality
% Indispensable
Mortality

Veg.
Loss

Hatch- Egg
Total
ing
1000

228

12

6

772

216

12
12.0

167

189

16.7

18.9

6.0

77.2

94.7

0.9

1.0

0.0

4.1

27.0

3.00

2.36

log (Population size)

indispensible mortality

Adult

(Table 15).

1.08

This is the percentage

of the population that would have survived to the adult stage
had the mortality identified not occurred (Southwood 1978).
Of

the

mortality

overwintering

factors

would

have

quantified,
resulted

vegetation
in

net

and

reproductive

effort increases to 0.994 and 0.949 respectively.
mortality had a negligible effect on R q .

loss

Hatching

45

DISCUSSION

Life History
In the St. Marys River Lestes disjunctus disjunctus is
univoltine.
the

It passes the winter in the egg stage, hatches

following

early

July.

previously

spring,
This

and

life

reported

completes nymphal

cycle

for

among

similar

d_^ disjunctus

(Sawchyn and Gillott 1974a)
1981).

is

development by
to

life

cycles

from Saskatchewan

and Alberta (Baker and Clifford

Overwintering in the egg stage is apparently common
Lestidae

in north temperate climates,

other Odonata (Corbet 1962).

but rare among

In western Canada, L_^ congener

also overwinters in the egg stage (Sawchyn and Gillott 1974b).
Of three species of Lestidae coexisting in a North Carolina
pond,

two

(L.

d.

australis

and

Archilestes

grandis

)

overwintered in the egg stage, while L^ vigilax overwintered
as early instars.
Eggs within stems of Sparqanium eurycarpum collected in
September

and

refrigerated

successfully hatched.
in

100

days

at

1.0°C

were

However, S_^ eurycarpum stems collected

September but not refrigerated failed to produce nymphs

suggesting

a

temperature-controlled

diapause.

These

observations are consistent with those of Ingram (1976) where
L. d. australis eggs collected shortly after oviposition also
failed

to

hatch

but

do

not

demonstrate

diapause

since

46

diapause is set in the preceeding stage (adult in the present
case).
egg

Sawchyn

development

and Church

(1973)

studied

in a a population

dL_ disjunctus

from Saskatchewan.

Eggs

oviposited in July developed to near the point of hatching by
late August, then entered diapause.

Diapause development was

initially controlled by temperature and later by photoperiod.
Post-diapause development was also controlled by temperature
and photoperiod,

but

been

Sawchyn

wetted.

could

not

take

place unless eggs had

and Gillott

(1974a)

found

that

post-diapause development could take place at 0.0 °C and egg
hatching

could

temperatures

occur

would

near 4.5

result

in

an

°C

although

St.

Marys River,

4.3

°C,

low

extended hatching period.

The estimated threshold temperature for
the

such

d. disjunctus from

is very near the minimum egg

hatching temperature reported by Sawchyn and Gillott (1974a).

May

Nymphs

first hatched from eggs in the study area on 14

1983.

Hatching

appeared

to

be

at

least

moderately

synchronized as maximum densities of first instar nymphs were
collected on 18

May.

Degree of hatching synchrony has not

been investigated previously.
stage,
in

diapause in the

egg

combined with the rapid warming of water temperature

shallow

suggest

However,

littoral

that

zones

synchrony

of

in north
egg

temperate

hatching

may

areas,
be

a

would

general

phenomenon among Lestidae.
Nymphs of L. d. disjunctus developed rapidly through 10
instars in less than 60 days following hatching.
developmental

rates

have been

Comparable

reported for other temperate

47

zone Lestidae including:
and Gillott

1974a;

australis, L.

Baker and Clifford 1981),

vigilax,

(Ingrain 1976),

L. d. disjunctus in Canada (Sawchyn

and

A^

grandis

rectangularis

disjunctus

in North

in Pennsylvania

Carolina,
(Gower and

Kormondy 1963), and L^ sponsa in England (Corbet 1962).
The flight period of L
River

is well

within

1

the

disjunctus from the St. Marys

range

species in Canada (Walker 1953).

of

time

reported

Adults of L

1

for

the

disjunctus

have been observed as early as 24 June in British Columbia
and as late as 16 October in Saskatchewan (Walker 1953).

In

the present study L_^ d^ disjunctus began emergence on 10 July
1983 and adults were last seen on 1 September.
emerged

during

emergence.

the

This

first

is

two

consistant

weeks
with

Most adults

following
well

initial

synchronized

emergence of L^ d^ disjunctus reported from Saskatchewan by
Sawchyn and Gillott (1974a).
was

A similar pattern of emergence

noted in Saskatchewan for

Gillott 1974a) and L^ congener
In North Carolina
vigilax, and A^

Ingram

grandis

unguiculatus

(Sawchyn and Gillott 1974b).

(1976)
all

(Sawchyn and

had

found L^ d^ australis, L.
a more extended emergence

period.
Most Lestidae exhibit a preference for a vegetation type
to

oviposit

available

in

(Corbet

typically well
1963;

Bick

although

and

a variety of plant species may be

1962).

Oviposition

above the water surface
Hornuff

1966).

In

sites

are

also

(Gower and Kormondy
Saskatchewan,

L^_

d.

disjunctus, L. unguiculatus, and L_^ dryas all oviposited in

48

green stems of Scirpus (Sawchyn and Gillott 1974a) while L.
congener

oviposited

Gillott

1974b).

reported

to

(Ingram

1976)

Lestes

disjunctus

and

only

australis

in Eleocharis

In Indiana

americanus

(Sawchyn and
has

been

oviposit primarily in Juncus in North Carolina

Bick 1961).

Hornuff

only in dry Scirpus stems

in Sparganium spp.

St.

oviposited

exclusively

in

eurycarpum.

Ovipositing in green stems may provide moisture
for

species
alone
plants

for

amount

could

studies

of

stems

development

(1974a).

However,

cover

noted that

oviposition

provide

sites

report

vegetation

L_;_ d^
of

as

disjunctus
Sparganium

suggested

by

selectivity of plant

oviposition would not be necessary if moisture

determined

oviposition

River

green

pre-diapause

Sawchyn and Gillott

Marys

(Bick and

the

necessary

In

(Bick and

eurinus oviposited in Sparganium

and L_^ unguiculatus

1966).

in Indiana

moisture.

are

also

that

is

nymphs

selected
provided

favoring

d^_ disjunctus
and

sites

Erickson

since
It
on
for

many

is
the

possible
basis

nymphs.

heavy cover.

of

that

of

the

Previous

Walker

inhabits areas rich

(1984)

species

(1953)

in aquatic

found nymphs among Glyceria

and Carex in a pond nearly filled with aquatic vegetation.
In the St. Marys River in July 1983, the surface area of S .
eurycarpum in a 1 meter plot in 0.5 m of water was over 7.5
m 2, three times the surface area provided by Scirpus acutus
(2.5 m 2 ), the other common emergent macrophyte in the study
area (Knoecklein pers. comm.).

Dense emergent vegetation may

49

be selected as oviposition sites to insure adequate cover for
survival of offspring as well as providing moisture for eggs.
Nymphs experience high mortality in the presence of fish and
seek or are restricted to cover (Chapter Two).

Demographics
Studies of aquatic insect populations have generally not
attempted

to

gather

the

demographic analysis.

kinds

Instead,

of

data

required

researchers have

for

focused on

either the aquatic stages (Lawton 1970; Macan 1974; Benke and
Benke 1975; Benke 1978) or aerial stages (Parr 1973; Garrison
1978;
The

Garrison and Hafernik 1981) and only rarely on both.
only

published

complete

survivorship

amurensis,
1981).

a

dragonfly

from

egg

1.20%.

While

greater

than

species

with

(1981)
the

univoltine.
with

mechanisms

such

a

was

study

to

overall survival

for this

to be

of L.

stage was

d.

disjunctus

reported,

it

is

contributing

much

overall

life

cycles

substantially

to

0.17

to

disjunctus

estimated

d.

disparate

aernea
(Ubukata

adult stage

in

a

cycle

L.

Similarity

construct

Cordulia

life

survival

adult

of

for

six year

through

the

survival
Ubukata

sufficient

estimated

egg

through

set

curve

In the present

from the

being

species

Ubukata

0.20%.

data

is

to be

slightly

shorter

lived,

survival

among

may

indicate

mortality

are

intrinsic rather than environmental or that survivorship is
more closely related to life history than seasonality.

50

A complete survivorship curve provides a summary of the
proportion

of

a

cohort

occuring

in

influence

life

shape

the curve.Animals

of

remarkably
varients
type

specific

surviving
stages

history

similar

through

or

age

time.

Mortality

classes

which may

characteristics are revealed by the
from

in having

Drosophila

to

man

are

survivorship curves which are

of the diagonal or intermediate between type I and

II

curves

(Deevey

1947;

Hutchinson

1978).

In

summarizing the available data for agricultural insect pests
Price

(1975)

catagories

found

based

species

could

be

separated

into two

on the shape of survivorship curves.

His

type A species suffered 70% or greater mortality through midlarval
less

stages,

mortality

survivorship

while type B species experienced only 40% or
through

curve

the

for

L.

same developmental

stages.

d.

intermediate

disjunctus

was

between type A and B, but skewed toward the type B.
mortality
85%.

This

at the mid
apparent

nymphal
anomaly

stage
arises

was

also

from

the

The

However,

approximately
comparison

of

cohort life table data with time specific life table data.
Price1s survivorship curves are plotted with instars on the
x-axis and so are equivalent to time specific life table data
whereas

in

the present

study cohort

life

table

for

L.

d.

disjunctus was developed.
Mortality in the egg stage was attributed to either loss
of

vegetation,

overwintering,

or

difficulty

at

hatching.

Mortality attributed to loss of vegetation was estimated to
be the greatest single source of mortality in the egg stage,

51

although mortality
Since

few

from overwintering was nearly as great.

studies of odonate populations have examined the

egg stage and those studies dealt with ponds, comparable data
from large open ecosystems are not available. This source of
mortality was
with

related

prevailing

to high water

winds

and

levels

commercial

ship

passes within 700 m of the study site.
Great Lakes are variable.

in

combination

traffic

which

Water levels in the

Average discharge in the St. Marys
_1

River during May has ranged from 1,331 to 3,443 m 3 's

since

control structures were constructed in 1922 (Quinn and Kelly
1983).

When water

broken off

at

portion

the

of

the

levels
ice

stem

are high

line

still

in spring,

plant stems

are free to float up
attached to roots

or

from the
rhizomes.

Strong offshore winds during these periods of high water may
serve

to push

floating stems offshore.

Water displaced by

passage of commercial vessels also generates water currents
in littoral areas (Duffy et al. 1984) and may serve to export
floating

stems

attributed

to

to

offshore

hatching

areas.

difficulties

The
is

6.0%

mortality

comparable

to

egg

mortality reported for L. d. disjunctus by Sawchyn and Church
(1973).

These

authors

found that egg mortality was related

to temperature below freezing and varied from 6.0% at 0°C to
100% at -20.0 to -22.0°C.

They found eggs deposited in stems

located where snow collected experienced lower mortality than
eggs

deposited

this

was

in

attributed

stems

which

to the

did

not

collect

insulating properties

snow
of

and

snow.

Survival of Enallagma boreale nymphs frozen into ice in the

52

St.

Marys

River

was

also

partially

insulating properties of snow
portion

of

egg

mortality

to

the

(Duffy and Liston 1985).

The

attributed

attributed

to

freezing

in

the

present study is well within the range reported by Sawchyn
and Church (1973).
Survival

of

L.

period was 5.3%.

disjunctus

during

the

entire

nymphal

This survival rate is similar to survival

rates reported for Ladona deplanata (0.5-7.9%), Epitheca spp.
(7.0-8.9%),

and

(Benke

Benke

and

Celithemis
1975).

fasciata
Lawton

Pyrrhosoma nymphula varied
cohorts.

Macan

(1964)

(3.2-14.6%)

(1970)

in Georgia

found

survival

of

from 0.5 to 30.0 or 40.0% among

reported 50.0% survival in Enallagma

cyathigerum , considerably higher than survival of Pyrrhosoma
nymphula from the same pond.
Sources

of

determined.

mortality

Dietary

canadensis, Libellula
(Notophthanlmus
bullhead

in

analysis
spp.

stages

of

predators

(Anisoptera ),

viridescens

(Ictalurus

nymphal

juvenile

not

(Aeshna

red-spotted

viridescens),

nebulosus),

were

juvenile

bluegill

newt
brown

(Lepomis

macrochirus), and juvenile rock bass (Ambloplites rupestris))
from the study area revealed low numbers of damselfly nymphs
with

none

being

unpublished).

identified

as

Lestidae

(Day

1983;

Duffy

In other areas of the St. Marys River, Odonata

occurred in 62.5% of stomachs
115 mm (Green 1980).
fish he examined,

his

from juvenile rock bass 76 -

While Green (1980) found no Lestidae in
fish were collected from beaches

and

areas of low cover where Lestidae would probably not occur.

53

Relatively low numbers of this size rock bass were found in
the study area, however, low numbers of a vertebrate predator
such

as

this

population.
may have

could

inflict

Other predators

preyed on nymphs

americanus, and Belostoma

heavy mortality

on an

odonate

common in the study area which

include Ranatra spp.,
spp.

Lethocerus

Each of these invertebrate

predators occurs in heavy vegetation, which would place them
in proximity to L. d. disjunctus nymphs.
Studies
been

of

limited

adult

to

odonate

pond

populations

environments

(Corbet

have

apparently

1980).

Maximum

numbers of adults associated with ponds typically range from
less than 100 to over 1,000
1973,

(Corbet 1952;

Moore 1964; Parr

1976; Van Noordwijk 1978; Garrison 1978; Garrison and

Hafernik 1981; Ubukata 1981).

Maximum population size for L.

d. disjunctus in 1983 was approximately an order of magnitude
greater than has previously reported.
present study were
studies

and

somewhat.
recapture

lower than rates often reported for pond

probably
Garrison

73%

of

overestimated
and

dragonflies

he

Hafernik

Ischnura

seepage in California.
22

Recapture rates in the

population
(1981)

gemina

marked

estimates

were

able

around

a

to

small

Ubukata (1981) recaptured 50% of the

marked

and

Garrison

damselflies

he marked.

In

addition,

the

study

area

was

detected

Emmigration

from

the

study

overestimates of population size.

in

area

(1978)

23%

of

some emigration
the current
would also

the
from

study.

result

in

54

The

number

of

eggs

carried

by

among species.

Endophytic species,

plant

in

tissues,

species

which

lay

endophytically.

general
eggs

lay

eggs

Most

Zygoptera,

varies

widely

which place eggs inside

fewer

in water.

Among

Odonata

than

exophytic

Zygoptera

Calyopteryx

oviposit

maculata

may

lay from 1,267 to 1,810 eggs over a 4 to 14 day period and
from 525 to 750 per day

(Waage 1978).

Sawchyn and Gillott

(1974a) found that L. d. disjunctus in Saskatchewan laid only
6

eggs

per

females

episode.

examined

and

They

suggested

probable fecundity value.
limited,

found

45
the

and

112

latter

eggs

in two

number

Their total egg counts,

is in close agreement with egg counts

was

a

although

for females

from the St. Marys River.
Net

reproductive

effort

calculated

from

data

on

potential fecundity and adult population size was 0.542 (A. =
-0.612)

indicating

the

present

cohort

would

replace

only

slightly more than half of the eggs from which it arose.

Had

eggs not been lost from the population with vegetation that
was carried offshore prior to egg hatching, net reproductive
effort would

have

been

0.994

(A = -0.006)

and the present

cohort would have been capable of replacing itself or nearly
so.

Since seasonal flows in the St. Marys River appear to be

stochastic with periods between high water years ranging from
2

to

14

years

since

1900

(Quinn

and

Kelly

1983)

it

is

unlikely that L. d. disjunctus has evolved to compensate for
this source of mortality.

55

CHAPTER TWO

The Influence of Environmental and Biological Factors
on Growth, Survival and Habitat Selection in
Lestes disjunctus disjunctus

56

INTRODUCTION

Odonata

are

freshwater

common

lentic

predatory

littoral

aquatic

zones

insects

and,

in

of

favorable

environments, often coexist in diverse assemblages comprising
a

relatively

large

proportion

of

the

biomass where they occur (Corbet 1962,
1975;

Crowder

and Cooper

1982;

total

invertebrate

1980; Benke and Benke

Crowley

and

Johnson

1982).

These factors, along with the relatively long odonate nymphal
period have prompted considerable interest in the mechanisms
which influence growth,
among

species

Since

the

(Lawton

pond

and

survival,
et

al.

lake

and facilitate coexistance

1980;

littoral

Johnson

et

al.

environments

1985).

in

which

odonates attain greatest density and diversity are physically
and

biologically

complex,

it

seems

plausible

that

both

physical factors and interactions with other predators would
influence growth and survival (Benke 1978; Crowder and Cooper
1982; Wetzel 1983).
The
fluctuate

thermal
on both

fluctuations
This

regimes

in

a diel

air

heterogeneous

of north temperate
and

annual

temperature
thermal

cycle

(Ward

environment

and

littoral zones
in response
Stanford

enables

a

to

1982).
greater

array of species to inhabit littoral zones than inhabit more
thermally stable environments, by providing a wider range of
temperatures

(Sweeney and Vannote 1978;

Vannote and Sweeney

57

1980).

In

zones,

aquatic

growth

increasing
1982).

and

water

Water

potential

insects

development

temperature

temperature

prey

typically

and

prey

is

inhabiting

positively

(Mackay

related

to

1979;

Merritt et

al.

the

physiology

of

influences
capture

littoral

rates

as

well

as

the

physiology of the odonate (Bottrell et al. 1976; Cresens et
al.

1982;

consists

Erickson

primarily

1984).

The

diet

of microcrustacea

of

odonate

nymphs

and chironomid

larvae

which appear to be a high quality food resource (Vijverberg
and

Frank

common

1976).

Furthermore,

at water temperatures

these

favorable

prey

are

typically

for odonate growth,

suggesting that food limitation under natural conditions is
unlikely (Bottrell et al. 1976).

However,

interactions with

other odonates, other predaceous insects, or fish may depress
prey capture rates, influencing growth and survival.
Lestes

disjunctus

disjunctus

inhabits permanent ponds,

marshy bays, and slow weedy streams throughout Canada and the
northern
River,

United
Michigan

develops

rapidly,

Experiments

States

(Walker

L.

disjunctus

d.

with

reported

1953).

emergence
here

In

the

hatches
occurring

were

in

St.

Marys

spring

and

in early July.

conducted

to

elucidate

mechanisms influencing growth and survival of L. d disjunctus
and to aid in the understanding of demographic data reported
in

Chapter

one.

experiments:

Three

questions

were

posed

in designing

1) what is the influence of water temperature

and prey density on growth and survival of nymphs?

2) what

influence

on

do

naturally

coexisting

predators

have

the

58

growth and survival
do

fish have

hypotheses
would

were

be

temperatures,
predator

on

habitat
that

higher

levels.

selection

increased

positively

hypothesis was that
nymphs

of L. d. disjunctus?

growth

correlated

prey

For

and

the

densities,
fish

-

3) what influence

survival?
and

with
and

survival

rates

higher

water

lower

habitat

A priori

coexisting

experiment,the

fish would restrict the distribution of

to heavy cover and increase nymph mortalitiy rates.

59

MATERIALS AND METHODS

Water Temperature-Prey Density
The influence

of water temperature and prey density on

growth and survival

of L.

d.

under controlled conditions.
were

obtained

from

eggs

disjunctus nymphs was studied
Nymphs used for the experiment

collected

in

hatched at treatment temperatures.

the

study

area

and

Hatching was completed on

23 May, the experiment begun on 24 May, and continued through
26 July 1983.
An experimental design consisting of rearing nymphs in
low,
20 °C

medium,
was

or high prey density microcosms at both 16 or

employed

microcosoms

were

temperature

throughout
employed

combination.

at

the

experiment.

each

prey

Low,

Duplicate

level

and

water

and

high

prey

medium,

densities were defined as 0.5, 1.0, and 2.0 times the density
of

prey

microcosms
microcosms

in

the

field

were
was

study

area

replenished.

allowed

to

at

Thus,

vary

during

the

time

prey
the

prey

density
course

of

in
in
the

experiment while tracking prey resources in the environment.
Microcosms
commercial
filtered

bus

used
trays

through

a

were

30

x

filled with
149|j

sieve.

controlled by floating microcosms

45

x

10cm

5 liters
Water

deep

plastic

of river water
temperature

was

in a "Living Stream" used

60

as a water bath.
and/or

second

nymphs'm

-2

instars.

This

.

level
.

.

and

of

microcosm

river

water

water

using plastic pails
149p

sieve.

140

the field.

oligocheates, and chironomid
completely

exchanged

filtered river water at 3 day intervals.
liters

equaled

replenished with natural prey from the study

(149 600|j microcrustacea,

larvae)

stocking

, similar to peak densities recorded m

Prey were
area

Each microcosm was stocked with 20 first

The

was

collected

with

Every 3 days,

from

the

study

70

area

and concentrated to 10 liters through a

60

liters

change

microcosm water.

passed

through

a 600p

mixed,

and 1.0,

0.5,

of

filtered water

was

used

to

The 10 liters containing prey was
sieve to remove large invertebrates,

and 0.25 liters added to high, medium,

and low prey microcosms respectively.
Survival

was

monitored

weekly by counting

all

nymphs

remaining in microcosms.

Growth, determined by measuring the

length

each prey density

of

10

treatment,

nymphs

was

in

also monitored weekly.

and

temperature

Length measurements,

excluding caudal lamella, were recorded to the nearest 0.1 mm
under

a

stereozoom

ocular micrometer.

binocular

microscope

When measuring nymphs,

equipped

with

an

small individuals

were transferred from microcosms to petri dishes containing
water

using

transferred

a

"turkey

using

an

baster",

aquarium net.

stressed by this procedure.

larger

individuals

Nymphs

did

not

were
appear

Length data was later converted

to dry weight using a length-dry weight regression equation
developed

for

L.

d.

disjunctus.

Toward

the

end

of

the

61

experiment,

fewer than 10 nymphs remained in some treatments.

Specific growth rate was determined at each water temperature
and prey level using the equation (Sweeney and Schnack 1977):
gr = (£nwt2 - £nwt l )/T
where lr\ = natural logarithm; GR = instantaneous growth rate;
W = dry mass; and T = time interval.
each

temperature

was

then

Specific growth rate at

expressed

as

a function of prey

density using the Michaelis-Menten equation:
“ =
where

(j is

+ p>

specific

growth

rate;

Mmax

= maximum

growth rate; P = prey density level; and

specific

= prey density at

0.5 u
Mmax
Growth response and survival among water temperature and
prey

density

treatments

was

also

tested

using

separate

two-way ANOVA of final dry mass and of average mortality/day.
This

provided

a

statistical

measure

of

significance

in

differences observed.

Competition - Predation
The
L.

d.

influence of competition on growth and survival of
disjunctus

was

studied

by

rearing

nymphs

in

the

presence of other predators with which it naturally occurs.
These other predators were collected from the study area and
included Enallaqma
and Umbra limi.

hageni, Aeshna

canadensis, Buenoa

spp.,

Aeshna canadensis, Buenoa spp.,and U. limi

hatch in spring at about the same time as L. d. disjunctus .
Enallaqma hageni overwinter as nymphs in mid-instar.

62

Competition experiments were conducted in 1.0m diameter
plastic

wading pools

pool was

each having

an area of 0.78m2 .

Each

filled with 100 liters of filtered river water and

covered with

a mat

of

dead Sparganium eurycarpum stems to

simulate conditions in the study area where nymphs hatch and
co-occur with the potential competitors used.

Stems had been

dried prior to adding them to pools to eliminate hatching of
either

L.

d.

disjunctus or other animals and contaminating

experiments.
conditions
with

100

Stocking

observed
L.

d.

rates

in the

.

.

disjunctus

were

field.
nymphs

chosen

All pools
(= 128’m

-2

).

to

reflect

were

stocked

Four pools

weredesignated as treatment pools with pool one receiving 10
E. hageni; pool two,

15 A. canadensis; pool three, 15 Buenoa

spp.; pool four, 20 U. limi; and pool five, the control pool,
receiving no additional stocking.
Each week 20% of pool water was exchanged with filtered
river water and prey coollected from 40 liters of river water
were

added

communities

to

each

developed

appeared similar.

pool.
in

Algal

pools

and

within

microinvertebrate
two

weeks

and

all

Water temperature was measured and pools

examined for possible invading animals daily.
Growth
weekly.
nymphs
mass

as

and

survival

nymphs

in pools

was

measured

Growth was determined by measuring the length of 10
from each
in

the

pool,

then converting

length data to dry

temperature-prey experiment.

estimated by sampling,
natural

of

conditions

and

Survival

was

since pools were designed to simulate
cover

added prevented

counting

all

63

nymphs
sweep

present.
samples

aquaria net.

Weekly

in
A

sampling

each pool
single

consisted

using

sweep

of

triplicate

a 15cm wide

sample

rectangular

represented

600cm2 or

7.6% of the pool area and was collected by placing the net in
the center of the pool and pushing it to the outer edge. At
the

termination

of

experiments

regular

sampling

was

conducted, then pools drained and all nymphs couted to assess
the efficiency of sampling.
Data for growth and survival were analyzed using one-way
ANOVA.

Growth was measured as final dry mass

and survival

as average mortality per day.

Habitat Selection
Field
disjunctus

observations
nymphs

quantify

the

survival,

an

exposed to

is

suggested

limited

influence

of

areas

fish

experiment was

three

to

distribution

on

designed

cover densities

of

L.

d.

of heavy cover.

habitat

To

selection

and

in which nymphs were

first without,

then with

fish.
Habitat
liter

selection experiments

fiberglass

aquarium

were

measuring

70

fitted with an under gravel filter.
substrate
achieve
third

was

three

added

cover levels.

(1,165cm2 )

included 2 clumps
provide

heavy

and

and

of

the

aquatic

conducted in a 100
x

50

x

30cm

deep

Washed sand and gravel
macrophytes

planted

to

Each cover level occupied one
aquarium.

of Carex

spp.

medium

cover

Macrophytes

and 2 Ranunculus
respectively.

planted
spp.

Low

to

cover

64

consisted of floating dead Scirpus spp. stems which covered
less

than

half

of the

low

cover

surface

area.

Following

planting, the aquarium was allowed to equilibrate for 1 week.
At the end of the week,
were

introduced

and

20

late instar

allowed

to

(VI - VIII)

acclimate

3

days

nymphs
before

experiments were initiated.
Following

the

acclimation

period habitat

nymphs

was

recorded for 5 consecutive days.

during

the

experiment

included

the number

selection by
Data recorded

and position

of

nymphs in each of the three cover areas at dawn, mid-day, and
dusk.

Positions recorded included the aquarium bottom, side,

and on plants.

After 5 days, three bluegill sunfish (Lepomis

macrochirus) 48 to 60 mm total length were introduced and the
5

day

experiment

repeated.

Data

were

analized

using

a

three-level nested ANOVA.

Field Data
Growth under natural conditions was investigated for a
population of L. d disjunctus inhabiting the St. Marys River.
Nymphs were collected weekly for the purpose of obtaining dry
weight data from which a length-weight relationship could be
determined.

Following

collection,

nymphs

were

returned

to

the laboratory and held in aquaria containing filtered water
for

24

length,

hours

to

insure

passage

excluding caudal lamellae,

of

fecal

pellets.

Total

was then recorded to the

nearest 0.1mm under a binocular microscope equipped with an
ocular micrometer.

Length was recorded and nymphs placed in

65

pre-weighed pans, oven dried at 60°C for 48 hours, moved to a
dessicator containing CaS04 until cooled, then weighed to
the

nearest

recorded

O.lmg

were

using

used

to

a

Mettler

calculate

M1500
a

balance.

regression

to

Data

equation

relating dry weight to length.
A detailed demographic study of L. d. disjunctus in the
St.

Marys

measurements
and

conducted

for

all instars

distributional

methods
O ne.

River

data.

and discussion of

A

during
as well
complete

results

is

1983

provided

length

as survival estimates
description of
presented

field

in Chapter

66

RESULTS

Length-Dry Weight
A

length-dry

measurements

of

weight

179

relationship

nymphs

(Figure

was

9).

developed
Lengths

from

measured

ranged from 2.2 to 21.1mm, while dry weight ranged from 0.1
to 12.6mg.

Dry weight was related to length for individual

nymphs by the exponential regression equation:
£flW = £n0.12 + 0.22(L), r 2 = 0.97
where

= natural logarithm; W = mg dry weight;

and L = mm

length excluding caudal lamellae.

Water Temperature-Prey Density
Growth of nymphs

as determined by final dry weight was

significantly greater at 20°C than at 16°C [F,.. .. = 31.88, P
IJ-/^ ;
< .005]. Nymphs in 20°C treatments averaged 4.55, 5.43, and
5.20mg after 64 days

for low,

respectively while nymphs
2.11,

medium,

and high prey levels

in 16°C treatments averaged 1.18,

and 2.05mg for the same prey levels

and 12).

(Figures 10, 11,

Average final dry weight of nymphs at 20°C was 199%

greater than final dry weight at 16°C over all prey levels.
No significant difference was found in growth among prey
levels

[F^4 ,37)

2 .34, P > .05].

Growth at the medium prey

level was greatest for both temperature treatments
10,

11,

and

12).

Evidence

of

physical

attack

(Figures
was

also

67

weight (mg.)

5-

4-

Dry

3-

2-

1

-

T

5

T

10

I

15

Length (m m )

Figure

9.

Length-dry weight relationship for Lestes
disjunctus disjunctus nymphs from the St.
Marys River. Curve fitted by regression.

20

5-

high

Dry

weight (mg.)

68

2

-

low

10

20

30

40

50

60

Days

Figure 10.

Growth of Lestes disjunctus disjunctus at 16 and
20°C in low prey microcosms. Data are plotted
as means and standard errors with a line fitted
by regression.

69

7

(mg)

5

weight

6

4

Dry

high

3
2
low

1

10

20

30

40

50

60

Days

Figure 11.

Growth of Lestes disjunctus disjunctus at 16
and 20°C in medium prey microcosoms. Data are
plotted as means and standard errors with a
line fitted by regression.

70

7

6

O)

5

E
sz

4

O)
o
£
>%
i-

high

3

o

2
low

1

10

20

30

40

50

60

Days

Figure 12.

Growth of Lestes disjunctus disjunctus at 16 and
20°C in high prey microcosms. Data are plotted
as means and standard errors with a line fitted
by regression.

71

greatest

at

missing

medium

lamellae

prey

on

levels.

live nymphs

This

evidence

and partially

included

canabalized

dead individuals.
Instantaneous
day)

growth rates

at 20°C averaged .055,

(equivalent to % growth per

.060, and .065 for low, medium,

and high prey levels while instantaneous growth rates at 16°C
were

.030,

.037,

and

.039

for

the

same

prey

levels.

Regressing (prey level/ instant- aneous growth rate) against
instantaneous growth rate yielded a half saturation (K ) prey
P
value of 0.179 and maximum specific growth rate (u
) of
max
0.70

for

20°C

(r2

specific growth rate
0.39

respectively

calculated

from

=

.94).

Half

(Hmav)
values
iUaX

(r2 =
these

.67).
data

saturation

and

for 16°C were

Prey

specific

produce

curves

maximum

0.161 and

growth

rates

nearing

an

asymptote at the high prey level for both temperatures where
they bracket average specific growth (0.061) of nymphs in the
field (Figure 13).
Nymphs in high prey microcosms had significantly greater
survival than nymphs in either medium or low prey microcosms
[ANOVA,

F^2

= 19.85,

P < .005].

Overall survival after

64 days was greater at 16°C than at 20°C (Figures 14 and 15).
However,

differences

among temperature

significant [ANOVA, F ^

= 2.81,

treatments

P > .05].

were not

72

07 1
20 C

rate

06 -

growth

05 -

04

Specific

16 C

.03

oo

02

5

1

2

Prey level (x field)
Figure

13.

Specific growth rate of Lestes disjunctus
disjunctus at 16 and 20°C as a function of
prey level. Curves fitted by specific growth
equation.

73

% Survival

1 0 0 -I

60 H

20 H

20

40

60

Time (days)

Figure 14.

Survival of Lestes disjunctus disjunctus in
high, medium, and low prey microcosms at
16°C.

74

% Survival

1 0 0 -I

60 H

20 H

20

40

60

Time (days)

Figure 15.

Survival of Lestes disjunctus disjunctus in
high, medium, and low prey microcosms at 20°C.

75

Competition-Predation
Competition experiments were terminated following day 51
as

emergence

of

L.

d.

disjunctus

prior to day 58 sampling.
with

littoral

(Figures

zone

5 and

Water temperature in pools varied

temperatures

16).

from several pools began

No

but

were

significant

slightly

differences

warmer

in growth

among control or treatment pools could be detected after 51
days

[ANOVA,

F^4 2 8 j

Instantaneous
0.052

to

=

0.97,

growth rates

0.070

while

P

>

.25]

(Figure

17).

for L. d. disjunctus ranged from

instantaneous

growth rates

for other

predators ranged from 0.026 to 0.101 (Table 16).
Pool samples underestimated nymph density in most cases
(Table 17).

Differences among estimated and actual density

were significant

(X2v4 = 12.58,

P < 0.05).

Survival of L.

d. disjunctus

was influenced by the of presence A.canadensis

and

E

probabley

hageni

(Figures

18

and 19).

Survival was

significantly lower in the A. canadensis treatment pool than
in

other

pools

Differences

in

significant.
mortality
however,

survival

Nymphs

during
E.

tF (4 io)

in

the

hageni

=

9 -65/

among
E.

hageni

initial

began

to

two
emerge

<

-005,

other
pools

pools

test].

were

experienced

weeks

of

from pools

disjunctus

SNK

from

not
high

experiments,
during the

third week

releasing L.

predation.

Survivorship curves for all other treatments were

similar.

d.

all

F

competition or

76

25-1

Temperature

(C)

20-

15-

10-

10

20

30

40

50

Days

Figure 16.

Average daily water temperature recorded in
experimental pools during competition
experiments.

77

Table

16.

Instantaneous growth rates of Lestes disjunctus
disjunctus , other invertebrate, and a vetebrate
predator m competition-experiment pools.

L.

Competitor
Wi

Wf

GR

Days

Control
A. canadensis
E . hageni
U. limi
Buenoa spp.

Table 17.

d.
Wf

Wi

disjunctus
GR

Days

.31

4.87

.054

51

.4

12.2

.101

44

.26

5.58

.070

44

2.0
.9

5.2
2.9

.042
.023

22
51

.31
.32

5.13
4.56

.056
.052

51
51

.4

1.5

.026

51

.27

5.78

.060

51

Comparison of estimated number of Lestes
disjunctus
disjunctus
in
competition-predation
pools from sampling on the final day of
experiments with the actual number recovered.

Number/m2
Treatment
Control
A. canadensis
E. hageni
Buenoa spp.
U. limi

Estimated

Actual

33
0
11
22
28

23
4
13
28
38

7
E. h.

(mg.)

6

weight

u. I.

Dry

a)

1

10

20

30

40

Days
Figure 17.

Growth of Lestes disjunctus disjunctus in the
control pool and in pools with A. canadensis,
E- hageni, Buenoa spp., or U. limi pools.

50

79

100 H

% survival

75-

50 -

25

A. c.

10

20

30

40

50

Days

Figure 18.

Survival of Lestes disjunctus disjunctus in
the control pool and m pools with Umbra limi>
or Aeshna canadensis.

60

100 i

% survival

75 -

50 -

25 B. s p p .

E. h .

10

20

30

40

50

Days

Figure 19.

Survival of Lestes disjunctus disjunctus in the
Buenoa spp. and Enallagma haqeni treatment pools.

81

Habitat Selection
The

presence

survival

of

and habitat

fish

had

an

selection of

influence
L.

d.

on

both

disjunctus

the

nymphs

(Figure 20). Average number of nymphs per observation period
in the absence of fish (18.7) was significantly greater than
after

(11.0)

fish had been introduced [ F ^ 4) =

p <

.001].
Nymphs in aquaria without fish occurred in cover density
types and areas within cover equally excepting dead stems in
low cover

(Figure

20).

Nymphs

in

the

fish treatment also

selected cover types approximately equally,

however,

in the

presence of fish, nymphs were much more abundant on plants in
all

cover

stems).
cover

densities(low

Differences

and

least

in

in

cover

density

distribution

plants

were

were

greatest

dead

in

the high cover area and differences

low
in

nymph density among cover types were significant [F^12 162) =
21.67, P < .001).

Field-Laboratory Comparisons
Survival of nymphs reared at 20°C and high prey density,
and

nymphs

in

experiments
field.

the

was

control

compared

pool
with

from

competition-predation

survival

of

nymphs

in

the

Survival of nymphs in the control pool after 51 days

was 18.0% and was similar to the 18.6% survival observed in
the field population at day 53
at

20°C

and

high

prey

density

(Figure 21).
exhibited

Nymphs reared
higher

survival

rates than in either the control pool or field (Figure 21).

82

Cover density

Ave. no. nym phs/area

low

medium

ippp

liim

bottom
fish
Figure 20.

D

side

plants
no fish H!

Average number of Lestes disjunctus disjunctus
nymphs in three cover areas and three cover
densities with and without Lepomis macrochirus
present.

100

0

20

C-high prey

75

% survival

50

fie ld

25
control

10

20

30

40

50

60

Days
Figure 21.

Survival of Lestes disjunctus disjunctus nymphs
from the field population, the control
competition-predation pool, and the 20°C high
prey density treatment.

84

To test the accuracy of the prey specific growth model
growth

of

nymphs

temperature
field.

data

in
and

the

field

compared

was

with

predicted

using

growth observed

field
in

the

Predicted growth approximates observed growth in the

field through day 36 and begins to diverge at day 43 (Figure
22).

Growth

greater

than

in the

field between

predicted

(Figure

day 43
22).

and 51 was much
However,

water

temperatures in the field were also greater than the highest
treatment temperature during this period.

85

7

6

Dry weight (mg.)

5

4

3

predicted

observed

10

20

30

40

50

Days

Figure 22.

Comparison of Lestes disjunctus disjunctus
nymphal growth m the field with predicted
growth.

86

DISCUSSION

Water Temperature-Prey Density
Nymphal

growth

in

L.

d.

disjunctus

was

significantly

influenced by water temperature but not prey density in the
water

temperature-prey

density

experiments.

Under

natural

conditions, water temperature may influence nymphal growth by
influencing both prey

turnover

rates

(Hall 1964;

Threlkeld

1980) and predator functional response (Cresens et al. 1982),
as

well

as

the

bioenergetics

of

nymphs.

Thus

a

clear

distinction between temperature and prey density effects is
tenuous.
food

Temperature also influences

conversion

processes
1981).

efficiency,

(Vannote
For

and

example,

enzyme

Sweeney

food assimilation and

kinetics,

1980;

respiration

in

and

Sweeney
L.

endocrine

and

d.

Vannote

disjunctus

nymphs fluctuates on a diel basis in response to diel changes
in water temperature and dissolved oxygen tension (Erickson
1984).
Growth
specific
in

the

of

nymphs

growth model
field until

predicted
closely

from

the

prey

density

approximated observed

growth

field water temperature increased above

the highest test temperature.

Since the greatest proportion

of

this

growth

temperature
predict

took
it

growth

place
is

not

in the

during

certain
field

the

period

of

warmer

model would

water

accurately

even though predictability

is

87

quite good at lower water temperatures.
A

positive

relationship

between

increasing

water

temperature and growth rates of aquatic insects from natural
populations
1979;

has

been

Johannsson

experiments

have

demonstrated

1980;
also

Merrit
shown

et

that

numerous
al.

times

1982).

growth

(Mackay

Controlled

rates

of

aquatic

insects generally increase with increasing water temperature
(Heiman
1979).

and

Knight

1975;

Sweeney

1978;

Ward

and

Cummins

However, for cold adapted species increased growth is

often correlated with decreasing water temperature

(Grafius

and Anderson 1979).
While controlled experiments are of value in elucidating
mechanisms

such as the relationship between temperature and

growth the use of constant temperatures has been criticized
as not refelecting the heterogeneous thermal environment of
many

aquatic

authors

insects

argue

(Vannote

that

diel

and

Sweeney

thermal

1980).

These

fluctuations

may

significantly influence the growth and development of aquatic
insects

(Vannote

developmental

and

rates

Sweeney
from

1980;

constant

Sweeney 1984).
and

fluctuating

temperature experiments have been reported,

Similar
water

though (Humpesch

1982).
The

influence

of

food

quantity

and

quality

on

development of aquatic insects is neither as well documented
nor understood as the effects of temperature.
the present

study

indicate

Results from

that prey density significantly

influenced survival of nymphs of L.d. disjunctus while water

88

temperature did not.
as previous

These results were somewhat surprising

studies of Zygoptera suggest nymphs can survive

long periods

without

food

and that a very narrow range of

prey densities may separate 0 and 100% survival
a l . 1980).

(Lawton et

Other investigators have suggested food quantity

or prey abundance is rarely limiting under natural conditions
(Benke

1978;

Vannote and Sweeney 1980;

Vodopich and Cowell

1984).
Under
shown

to

be

chironomid
Cummins

experimental
limiting

conditions,
to

growth

larvae Paratendipes

1979).

generations

Ward

of this

food

and

and

chironomid per

however

(1979)
year

normally univoltine in Augusta Creek,

has

development

albimanus

Cummins

quality

been

of

the

(Ward and

produced

from

two

a population

Michigan by providing

high quality food in summer when food present in the creek is
of

low

quality.

Variation

microcrustacean prey commonly
nymphs

in

food

quality

consumed by L.

and many other predaceous

aquatic

d.

insects

among

disjunctus
does

not

appear to be great enough to significantly influence growth
and

development

Frank

1976).

treatments

(Cummins

The

in

the

and Wychuck

greater
present

mortality
study

1971;

Vijverberg

observed

may

have

and

at low prey

resulted

from

cannibalism (Gallepp 1974).

Competition-Predation
Nymphs
experiments

of

L.

d.

experienced

disjunctus

in

significantly

competition-predation
greater

mortality

in

89

the presence of A. canadensis nymphs than they did in either
the

control

or

comparisons

of

significant.
data

treatment pools.

mortality

However,

which,

while

suggestive.
pool

other

First,

combined

statistically

results

pools

was

significant,

are

from

the

A.

canadensis

pool

larger odonates may prey on the smaller

L. d. disjunctus nymphs.

intraspecific

among

other

several patterns did emerge from the
not

with

inversely

growth

of the

initial high mortality in the E. hageni

suggests that these

was

or

None

Second,

proportional

competition

for

growth of L. d. disjunctus
to

survival

food

resources

indicating

may

influence

growth.
Comparison

of

population,

the

microcosom

also

nymphal

control pool,
suggest

survival

among

the

field

and 20°C high prey treatment

intraspecific

competition,

as

survival in the control pool was nearly identical to that in
the

field.

Survival in both the control pool and the field

were roughly 30% lower than in the 20°C high prey treatment
during a comparable time period and roughly 20% lower than
when

the

temperature

experiments

were terminated.

This 20

to 30% difference may reflect the magnitude of intraspecific
interaction on survival.
Dietary
five

analysis

dominant

littoral

zone

support

to

regulating

have

odonates
of the
the

odonate

been

conducted

inhabiting

St.

Marys

hypothesis

of

populations

the

River.

for

study

four

of the

site

in

These studies

inter-odonate
as

well

as

the
lend

predation
influencing

90

survival in the competition pools.
of

the

diet

of

A.

canadensis

disjunctus populations

consist

most vulnerable to predation

Zygoptera comprised 1.7%

during
of

spring

early

when

instar

(Day 1983).

L.

d.

individuals

However,

odonates

were not found in the diet of the anisopteran Libelulla spp.
nor in the diet of the zygopterans Enallagma boreale or L. d.
disjunctus

(Day

cannibalism

(Fox 1975)

shown

to

1983;

influence

1978).

Benke

unpublished).

in natural

estimated

only

6.8%

South Carolina pond would be

predation

rates

that

of

the

populations
consumption

of

was

an

(Benke
of

larger odonates

one
in a

sufficient to account for the

mortality observed for smaller species.
odonate

Low

or inter-odonate predation have been

survival

(1978)

odonate per day by

Duffy

extreme

He suggested inter-

form

of

interference

competition.
More

recent

inhabiting

a

interactions

studies

of

Tennessee

and

a

diverse

lake

competition.

have
Field

odonate

community

addressed
studies

over

species
a three

year period indicated interspecific competition was of little
importance in obtaining food resources
1982).

Rather,

determined
reduce

Crowley and Johnson

interactions

and

interactions.

(1982) believed habitat

seasonal

Enclosure

(Crowley and Johnson

segregation

experiments

acted

with

to

both

damselflies and dragonflies from this same community have also
failed

to

demonstrate

(Johnson et al. 1985).
interference

exploitation

(resource)

competition

However, these authors have suggested

competition

in

the

form

of

inter-odonate

91

predation

as

a

mechanism

regulating

populations

of

the

influenced

by

dominant species in this community.
The

contention

that

growth

is

intra-specific interactions is based on the observed inverse
relationship

between

interactions

were

inhibiting

growth

also

access

to

and

survival.

suggested

food

as

resources

Intra-specific

more

important

than

in

inter-specific

interactions by Crowley and Johnson (1982).

The probability

of nymphs locating and remaining in a favorable feeding site
should

be

inversely

related

to

population

series of behavioral experiments,
demonstrated
disjunctus

that

nymphs

locate

and

of

Baker

(1980,

Coenagrion

defend

density.

1981a,b) has

resolutum

favorable

In a

and

feeding

L.

sites.

Success in defending a feeding site is apparently related to
size.

In

populations

individuals

were

individuals,

however,

of

capable

similar
of

sized

repulsing

nymphs

smaller

slightly

larger

small nymphs could not defend feeding

sites from much larger nymphs (Baker 1980, 1981a).
Both mortality
fitness.

For

and growth

most

related

to

1984).

Furthermore,

of

female

aquatic

survival

such

as

size

are ultimately reflected in

insects,

(Sweeney

fecundity

and Vannote

is

linearly

1981;

net reproductive effort is the product

and young produced and for semelparous

insects

is

Sweeney

a measure

of

fitness

species

(Mitchell

1981).

This relationship of mortality and growth has apparently not
been quantified in aquatic insects but has been for bluegill
by Werner

and

his

colleagues

who

illustrate

how

decreased

growth can equal higher mortality (Werner et al. 1983).

92

Habitat Selection
Bluegill sunfish clearly influence both the distribution
and

survival

of L. d.

conditions.

disjunctus nymphs under experimental

In the absence of fish, nymphs were relatively

uniformly distributed both among and within (on macrophytes,
sediments,
Following
either

and

aquaria

the

sides)

introduction

selected

or

of

the

three

cover

bluegills,

were restricted

densities.

surviving

nymphs

to macrophytes.

These

results are in general agreement with previous investigations
of fish-invertebrate interactions reported for littoral zones
which suggest fish exert a major influence on invertebrates
in this habitat (Hall et a l . 1970; Crowder and Cooper 1982).
These laboratory results also corroborate field studies which
found

L.

d.

disjunctus

nymphs

restricted

to dense

cover

provided by Sparganium eurycarpum.
The
refugia

importance
for

larger

increasingly
several
One

hatching

in

sites

disjunctus

in

aquatic

littoral

better

examples

species

of

from
the

documented.
a

long

tarn,

St.

Marys

in

zone invertebrates
Macan

providing

is becoming

(1977)

provides

term study of Hodson’s Tarn.

Lestes

toMyr iophyl lum

the

macrophytes

sponsa,

spp.

disperses

much

River moves to S.

like

L.

from
d.

eurycarpum.

Following the introduction of brown trout (Salmo trutta) to
this tarn L.
of

the

sponsa dissappeared, returning only after most

fish

had

been removed.

Two

other

species

of

Coenagrionidae declined in density following the introduction
of brown trout,

then were drastically reduced in number when

93

macrophyte

cover

was

lost

(Macan

1977).

Changes

in

vegetation density and the presence or absence of fish often
result

in

shifts,

composition,

but

not
in

only
the

in odonate
entire

density

invertebrate

or

species

community

(Crowder and Cooper 1982; Morin 1984; Gilinsky 1984).
This study consisted of several experiments intended to
describe

mechanisms

influencing

growth,

survival,

and

habitat selection of L. d. disjunctus in the St. Marys River.
Results from this and other studies emphasize the importance
of

lentic

littoral

zones

as

invertebrates as well as fishes.

valuable

habitats

for

Littoral zones have a more

heterogeneous diel and annual thermal regime which favors the
growth and development of a wider array of species (Ward and
Stanford
also

1982;

more

profundal

(Crowder

physically
or

complexity

Sweeney

limnetic

creates

and

Cooper

a

1984).
complex
zones.

Littoral
and
This

zone

patchy

habitats
than

increased

and reduces

predator

either

structural

greater amount of microhabitat
1982)

are

types

efficiency

thereby stabilizing predator-prey interactions (Crowley 1978;
Anderson 1984; Cook and Stearns 1984).

94

CONCLUSIONS

Quantitative
aquatic
of

insects

life

aspects

were

natural

In
used

this
to

population

Laboratory

the

life

histories

of

many

are lacking or available for only portions

cycles.

techniques

of

studies

study

age

investigate

of
of

Lestes

specific

life

table

the demographics
disjunctus

mechanisms

of

a

disjunctus.

influencing

population

biology were integrated with the field investigation.
Both

absolute

(q ) were
X

greatest

found
single

mortality

to

be

(d )

greatest

identifiable

and
in

source

relative

the

egg

mortality

stage.

of mortality

in

The
eggs

was related to vegetation loss resulting from Lake Superior
level management and commercial navigation which influenced
river

water

level

and

current

patterns.

However,

mortality from overwintering was nearly as high.

egg

Mortality

from vegetation loss was sufficient to reduce the population
rate

of

increase

-0.612.

Population

physiological
highly

irregular

magnitude

roughly

nature

of

the egg

to potentially

greater

neutral

adjustments

or behavioral,

mortality to both

with

from

or

zero

to vegetation

are
this

loss,

to

either

improbable because of the
event.

and nymphal

regulate

growth

Other
stages,

population

sources
while

growth,

of

of a
occur

regularity and are more likely offset through

physiological or behavioral population adjustments.

95

Laboratory studies provided insight into the mechanisms
regulating natural
temperature
survival.

and

populations

prey

However,

density

of L. d.
clearly

disjunctus.

influence

Water

growth

and

interactions among water temperature and

prey (food) levels make separation of the influence each has
on growth or survival problematic.
demonstrated
(bluegill)
nymphs.

that

invertebrate

and

Laboratory studies also
vertebrate

predators

influence both survival and habitat selection by

SUMMARY

The population ecology of Lestes disjunctus disjunctus,
a

common

zygopteran

temperate
1983

North

using

studies
St.

carried

Marys

prey

out

and

and

margins

investigated

in

north

during 1982

and laboratory

studies.

and

Field

in the Lake Nicolet basin of the

the

influence

coexisting

survival of nymphs.

lake

Michigan. Laboratory

examine

density,

was

field

River,
to

ponds

America,

integrated

were

conducted

of

of

studies

water

predators

were

temperature,

on

growth

and

Additional laboratory studies examined

the influence of fish on survival of and habitat selection
by nymphs.
The

St.

Superior.

Marys

Average

study

ranged

basin

receives

time

within

water

from

shorelines

is

monthly
1,229

about

the

quality

River

- 2,979

during

extensive

is

single

discharge

65% of

basin

the

short (<

one

such

Nicolet.

eurycarpum.
emergent

The

littoral

study

the period

of

The Lake Nicolet

24

hr)

seasons.

emergent

from Lake

flow and water retention
promoting high
Along

wetlands

characterized by well developed beds
Sparganium

during

m 3/sec.

this

all

outflow

are

protected
present,

of Scirpus acutus and

site

was

located within

zone on the west shore of Lake

97

In

the

St.

exclusively

in

Marys

green

July and August.
female was
Eggs

L.

d.

disjunctus

of

S.

stems/leaves

eurycarpum

estimated to be 73.5 in 1982 and 45.2

with

in

summer

apparently

termination

of

entered

diapause

in

temperature and possibly moisture related.
September
not

oviposits

and

refrigerated

refrigerated

positively

during

The average number of eggs oviposited per

oviposited

autumn

River

failed

related

to

diapause
spring

hatch.

water

Egg

in

being

Eggs collected in

successfully hatched

to

in 1983.

while

hatching

temperature

and

eggs

rate

was

could

be

described by the regression equation:
% hatching/day = -1.63 + 0.38(T), r2 = 0.95.
The threshold temperature was determined to be 4.3°C.
Nymphs

were

first

Development through
18.5 days/instar.
following
were

the

10

collected

nymphal

on

14

in

1983.

instars was rapid averaging

Emergence began on 10 July, 1983, 58 days

appearance

of

first

instar

restricted

in

distribution

to

areas

consisted

of

either

of

dead

which

May

mats

nymphs.

Nymphs

of dense

cover,

vegetation

or

S.

_2

eurycarpum.

Maximum density of nymphs'm

was 105.8.

Adults emerged from the St. Marys River in early July.
Densities

of adults emerging from heavy and medium density

beds of S. eurycarpum averaged 2.1 and 0.9'm
The
tree

tenneral
line

period

period

100-200

the still

emergent wetland.

m

-2

respectively.

following hatching was spent along the
in

from the waters

sexually

immature

edge.

adults

After

returned

to

Average life of adults was 6.0 days.

this
the

98

Estimated

population

sizes

of

selected

stages

in the

4.03 ha study area were as follows: eggs 3,202,000; instar I
730,800;

instar X 128,500;

and adults 35,800.

Mortality in

the egg stage was partitioned into that occuring from loss
of

vegetation,

unexplained.

overwintering,

hatching

Overall survival

difficulty,

and

from egg to adult female was

1 .2%.
The net reproductive effort for L. d. disjunctus in the
study

area was

1982

and

1983

0.542.
was

Population rate of increase between

-0.612.

Mortality

attributed to vegetation loss,

in

the

egg

stage

a stochastic event, was great

enough to explain the negative rate of population increase.
In the

laboratory,

significantly
treatments.
growth

of

predators.

nymphs

greater

in 20°C treatments

growth

Prey

density

nymphs

nor

Maximum

prey

did
did

than
not

the

specific

nymphs

significantly
presence
growth

of

rates

achieved
in

influence
coexisting
at 16

20°C were 0.39 and 0.70 percent per day respectively.
predicted
nymphs

from
in

specific

the

growth

field

through

underestimating growth in the
predict

growth

in

later

rates

field.

stages

may

16°C

Growth

approximated that
day

36,

and

of

thereafter

Failure to accurately
have

been

related

to

warmer water temperatures in the field.
Survival of nymphs was significantly influenced by prey
density

but

temperature.

was

not

significantly

Survival was

also

presence of another odonate,

influenced

by

water

significantly lower in the

Aeshna canadensis, than in the

99

presence

of

other

Survival

of

nymphs

coexisting
in

the

predators

field

and

or

a

control

control.
pool

from

competition-predation experiments were similar and 20 - 30%
lower

than

difference

in
is

interactions.

20°C

- high

potentially

prey density
the

influence

treatments.
of

This

intraspecific

APPENDIX

Table 18.

Density of macroinvertebrates as mean number over 1 m 2 of substrate in
Sparqanium eurycarpum beds located in a littoral zone of the St. Marys River.
Date
Taxa

6-3

6-9

6-17

6-22

COELENTERATA
Hydrazoa
Hydroida
Hydra americana

64

128

117

14

PLATYHELMINTHES
Turbellaria
Tricladida
Dugesia spp.

16

64

53

3504
576
96
144

1456
128
48

3912
259

ANNELIDA
Oligocheata
Haplotaxida
Naididae
Stylaria fossularis
Ve^dovskyella comata
Nais communis
N. barbata
N. simplex
Pristina
longiseta longiseta
Chaetoqaster limnae
Stevens oniana
trivandana
Tubificidae
Peloscolex ferox

4-19

5-5

333

5-13

256

5-21

576

5-27

48
32
160

352

6-29

7-6

35

336

5670
14
21

4361
455
28

2485
343
301

63
53

105

63

280

555

7
1153

7
371

728
154

21
14

196

Table 18. (cont'd.).
Date
Taxa
Hirudinea
Rhynchobde H i dae
Glossiphoniidae
Batracobdella
michiganiensis
Glossophonia
complanata
Helobdella fusca
H. michiganiensis
H. stagnalis
Pharyngobde11 i dae
Erpobdellidae
Erpobdella punctata
ARTHROPODA
Crustacea
Isopoda
Asellidae
Asellus intermedia
Amphipoda
Talitridae
Hyalella azteca
ARACHNIDA
Acarina
Hydracarina

4-19

5-5

5-13

5-21

5-27

6-3

6-9

6-17

6-22

6-29

7-6

11
8
16
32

256
21

7
7
35

441

11

16

432

928

270

196

21

14

80

32

336

64

32

300

427

119

357

32

256

208

320

176

230

147

28

271

Table 18.

(cont'd.).
Date
Taxa

4-19

Insecta
Collembola
Ephemeroptera
Baetidae
Callibaetis spp.
Cloen spp.
Baetiscidae
Baetisca spp.
Caenidae
Caenis spp.
Odonata
Zygoptera
Coenagrionidae
Enallagma boreale
E . hageni
Lestidae
Lestes
disjunctus disjunctus
Anisoptera
Aeshnidae
Aeshna canadensis
Libellulidae
Libelulla spp.
Sympetrum
rubicundilum

5-5

5-13

5-21

5-27

24

16

160

6-3

6-9

6-17

6-22

6-29

7-6

14

14
8

48
8

56
32
13

800

16

53
11
106

11

64
16
95

544

16
28

725

168

392

343

16

7
7

630

33

81

47

51

30

17

16

28

18

14

11

14

18

16

7

Table 18.

(cont'd.).
Date
Taxa

Hemiptera
Corixidae
Siqara alternata
Notonectidae
Bueno a spp.
Hebridae
Hebrus spp.
Merragata spp.
Mesovelndae
Mesovelia spp.
Veliidae
Microvelia spp.
Trichoptera
Hydroptilidae
Ochrotrichia spp.
Oxyethira spp.
Leptocendae
Ceraclea spp.
Mystacides spp.
Oecetis spp.
Trianodes spp.
Limnephi1idae
Grammotaulus spp.
Nemotaulus spp.
Phryganeidae
Phryganea spp.
Polycentropodidae
Polycentropus spp.
Lepidoptera
Acentropus spp.

4-19

5-5

5-13

5-21

5-27

6-3

6-9

8
16

16

32

6-17

6-22

6-29

7-6

21

28

35

7

7

21

14

7
21
268

140

7

112

28

21

77

7

84
7
125

48

16

200

77

21

84

84

96

112

75

7

14

28

32
16

7

127

32

48

192

14

14

32
16
16

99

7
35
7

63

Table

18.

(cont'd.).
Date

104

Taxa

4-19

Coleoptera
Chrysomelida (adult)
Donacia spp.
Dytiscidae
Hydrovatus spp.
Haliplidae
Haliplus spp. (larvae)
(adult)
Hymenoptera
Diptera
Ceratopogonidae
Alludomyia needhami
Bezzia varicolor
Culicoides spp.
Palpomyia prunescens
Chironomidae
Ablabesmia spp.
Labrundinia spp.
Larsia sppT
Dicrotendipes spp.
Endochironomus spp.
Enfeldia spp.
Glyptotendipes spp.
Lauterborniellia spp.
Microtendipes spp.
Parachironomus spp
Paratanytarsus spp.
Polypedilum spp.
178

5-5

5-13
.-13

5-21

5-27

6-3

6-9

6-17

6-22

6-29

7-6

119

91

84

77

16
21
16
16

11
11
7

125

368
128
128
32

48
48

384
48
48

341
64
64
21

32
32
7

84
133
133

42
42

1295

833
134
134

35
777
1463
504

35
63

280

32
16
333
125

704
704

16
240
240

96
160
160
48
48

320
32
720
720
96
96

8
48

80
480
480
16
16
384

371
371

107
315
315
126
126

21

120
80

48
96

48
16

48
208

240
176

7

208
384

96
464

7
43

56
77
7

21
539

Table 18.

(cont'd.).
Date
Taxa

4-19

Chironomidae (cont1d .)
Phaenospectra spp.
Psectrocladius spp.
Pseudochironomus spp.
Stichtochironoinus spp.
Tanytarsus spp.
Corynoneura spp.
357
Cncotopus spp.
178
Heterotnssocladius spp.
Orthocladius spp.
Culxcidae
Aedes intrudens
Dixidae
Dixa spp.
Empididae
Sciomyzidae
Sepedon fuscipenis
Stratiomyidae
Stratiomys spp.
Tipulidae
Erioptera spp.

5-5

5-13

5-21

125

320

32

5-27

6-3

6-9

6-17

6-22

1000

7
1414

64

84

144

144
64

64

592

288
32
64
16

35
77
35

112
406

6-29

7-6

666
21

672

21
28

32
21
16

7

32
7
16
11
16

231

Table 18.

(completed).
Date
Taxa

4-19

5-5

MOLLUSCA
Gastropoda
Basommatophora
Ancylidae
Ferrisia paralella
Lymnaeidae
Pseudosuccinus columella
Physidae
Physa qyrina gyrina
P. Integra
P. jennessi skinneri
Planorbidae
Helisoma anceps anceps
H. corpulentum
vermilion
Gyraulus parvus
G. deflectus
Promenetus
exacuous exacuous
Planorbula armiger
Pelecypoda
Eulame11ibranchia
Sphaeriidae
Sphaerium securis
TOTAL

713

5-13

8

5-21

5-27

6-3

48

16

80

6-9

6-17

6-22

7

16

6-29

7-6

14

11
242

70

105

98

14
11
7

7

14

14

35
14
14

25

14

42

35

16
8
16

16

128

16

64
16

16

16
1418

2135

1680

16

2160 10080

32
16

7104 10245 12108

175
7

21

182

8402 24043

Table 19.

Annual production estimates for Lestes disjunctus disjunctus
St. Marys River.
Shore Habitat

Date

N
(no/m2 )

May 14

12.8

AN

W
(mg)

87.4

20

105.8

24

105.4

27

95.1

June 2

80.6

77.1
37.4

-3.77

0.21

0.08

0.21

2.16

0.23

3.26

0.26

0.88

0.35

1.79

0.46

-2.35

0.63

24.81

15.5
1.09

6.8

18.63

0

5.75

0

13.6

Total annual production (mg/m2 )
= 58.63
Weighted mean annual production = 134.72 mg/m2

8.7
0.1

1.34

-2.14

5.51

74.94

9.97

86.74

9.09

8.7

7.44

-3.25

1.93

22.3
2.74

0.63
0.74

-1.6

27.69

4.05

5.2

0.51
-5.2

20.7

1.43

12.0

5.2

0.21

0.74
25.4

13

-14.55

0.51
39.7

July 6

0.19

0.41
-5.1

29

W(AN)

0.28
5.2

22

W

0.24
3.4

17

W
(mg)

0.21
14.5

72.0

AN

0.21
10.3

13

N
(no/m2 )

0.21
0.4

77.2

W(AN)

0.20
-18.4

9

Sparganium eurycarpum

0.19
-74.6

17

W

from the St.

10.84
=

156.29

108

Table 20.

Production statistics for common macroinvertebrates
Sparganium eurycarpum beds in the St. Marys River,
Michigan.

Taxon
Ephemeroptera
Caenis spp.
Trichoptera
Ceraclea spp.
Trianodes spp.
Polycentropus spp.
Grammotaulus spp.

Uncorrected
N
B
P
DT
(no/m2 )(mg/m2 ) (mg/m2 )
CPI

273

71.3

50.5

6

303.2

4.25

57
4
25
46

11.3
8.8
29.9
81.3

5.7
6.3
16.2
33.5

5
6
5
6

28.5
37.8
80.8
201.0

2.52
4.28
2.70
2.47

32.9
2.1
176.0
38.8

5
3
5
4

164.5
6.3
879.9
155.4

5.14
2.33
4.06
2.89

Chironomidae
Larsia spp.
370
Paratanytarsus spp.
141
1187
Polypedilum spp.
Psectrocladius spp. 328
Amphipoda
Hyalella azteca

Annual
P
Annual
(mg/m2)
P/B

32.0
2.7
216.5
53.8

1059

756.9

749.8

3

2249.7

2.97

187

76.3

76.4

5

381.9

5.01

Oligocheata
Stylaria fossularis 2004

523.0

340.8

6

2044.7

3.91

Isopoda
Asellus intermedia

109

Table 21.

Total number of prey in guts of Lestes disjunctus
disjunctus collected from Sparganium eurycarpum beds
in the St. Marys River, Michigan.
June

May
Taxon

13

CLADOCERA
Acroperus spp.
Alona spp.
Bosmina spp.
Camptocerus spp.
Chydorus spp.
Chydoridae
Eurycercus spp.
Graptoleberis spp.
Macrothrix spp.
Pleuroxus spp.
Polyphemus spp.
Sida spp.
Simocephalus spp.
Unidentified
Cladocera

21

2
1

July

27

3

9

22

29

6

1

3

2

21
5

22

2
5

1
10
1

1
13
7
1

7
74
21
4
2

15
1
5
1
121
50
9

39
8
6

1

2

COPEPODA
Macrocyclops spp.
Cyclopoida
copepodids
Harpactacoida
Copepoda nauplia

2

7

16

3

4

5

ROTIFERA
Keratella spp.

12
1

4

OSTRACODA

2

6
1

2

1

16
4

2

5
1

6

39
1

9
1

9
1

110
8
12
7

1
2
3
1
2

3

6

1

5
1
2
2
1
1
17

2

*

6
7
0 .9

3

2

2

1

1
2
7

14

14
11
1.3

33
18
1.8

64
6
11
10
261
93
20
2
1
4
2
15
3

3

1

CHIRONOMIDAE
Corynoneura spp.
Dicrotendipes spp.
Labrundinia spp.
Larsia spp.
Polypedilum spp.
Pseudochironomus spp
Tanytarsus spp.
Unidentified
Chironomidae
1
Total Prey
Total Nymphs
Ave. Prey/Gut

6

Sub
Total

1

3

33
15
2.2

51 191 246
15
14
15
3.4 13.6 16.4

1
1
3

5
106
9
11.7

680
104
6.5

Table 22.

Density of zooplankton as mean number/liter in Sparganium eurycarpum beds
located in a littoral zone of the St. Marys River.
Date
Taxa

4-19

ARTHROPODA
Crustacea
Cladocera
Acroperus harpae
Alona guttata
A. exigua
A. mtermidia
A. guadrangularis
A. rectangularis
Alonella acutirostris
Bosmina~longirostris
Camfftocerus rectirostris
Cenodaphnia megalops
C. guadrancrula
Chydorus <^ibbosus
C. sphaencus
3
Daphnia spp.
Eurycercus lamellatus
Graptoleberis testudinella
Ilyocryptus spinifer
Lathonura rectirostris
Macrothrix rosea
Ophryoxus gracilis
Pleuroxus denticulatus
P . procurvus
P. truncatum
P. uncinatus
Polyphemus pediculus
Sida crystallma
Simocephalus serrulatus

5

5-13

5-21

5-27

6-3

6-9

6-17

6-22

6-29

7-6

1

3

17
4

24

34
20

70
38

33

65
11

45
19

74

5
11
4

25
21
30
11
12

7

15

2

4
38
16

2

1
5

1
3

24

18

122

1
1

40
1

77

43

1
7

2

114

285

2

1
7
1

90
1
13

98

114

3
98

4

18
11

53
3

14
6

33

14

88
3
21

6
2

3
22
20

47

7
7
16
1

2
3

7
1

33
2
7
1
16

7
53

16

7
14

7
56

Table 22.

(completed).
Date
Taxa

4-19

Copepoda
Macrocyclops albidis
Cyclopoida copepodida
Cyclopoida nauplia
Harpactacoida
Ostracoda
Total

3

5-5

5-13

1
1
1

27
24
7
2

5

159

5-21

5-27

6-3

6-9

6-17

6-22

6-29

7-6

3
16
5

1
1

1

34

27
53
40
7
66

66
81
30
12
25

9
44
20
4
2

11
100
28
11
19

10
51
5
7
17

10
46
1
6
34

128

191

672

502

266

620

406

468

112

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