Aquatic crustaceans rely heavily on their sense of olfaction to mediate vital behaviors, such as foraging and predator avoidance. The importance of olfactory cues to the survival of aquatic crustaceans has led to the evolution of highly sensitive and elaborate olfactory organs. A plethora of research has identified the types of olfactory cues used by crustaceans during foraging, and numerous studies have demonstrated that the cues that are most abundant and easily dispersed from prey tissues elicit the strongest foraging responses. Common foraging cues for aquatic crustaceans include amino acids, nucleotides, and carbohydrates. Since each prey species or food item emits a distinct chemical signature, the finding that two sympatric species utilize different olfactory cues to forage has been suggested by previous authors to be indicative of food niche differentiation between the species (i.e., the species are attracted to different food items via the olfactory cues emitted by the food). However, few studies have demonstrated empirically that sensory divergence is an accurate measure of food niche differentiation. Furthermore, few studies have taken a comparative approach to the study of sympatric resource competitors, and thus the links between the sensory biology and the ecological niches of species remain largely unexplored. This dissertation uses a pair of ecologically similar, sympatric hermit crab species to test hypotheses regarding the links between sensory divergence and food niche differentiation. Chapter 1 provides a general introduction, and provides a background on why hermit crab species make an excellent model system for studies of sensory driven feeding behaviors. Chapter 2 identifies a subset of the olfactory cues used by the sympatric hermit crab species, and shows that the species rely on different olfactory cues to mediate their foraging behaviors. Chapter 3 compares the food niches of the two species using a combination of field experiments and laboratory analyses of collected specimens. Chapter 4 identifies a plausible mechanism of food niche differentiation between the focal species. Chapter 5 examines how the species utilize the olfactory cues released by injured conspecifics and heterospecifics to mediate cannibalistic behaviors. Chapter 6 tests the behavioral reactions of a single hermit crab species to novel food odors under different dietary treatments. The overall goal of this dissertation is to address gaps in the current literature regarding the ecological effects of sensory divergence among ecologically similar, sympatric species. The research methods used in this dissertation integrate techniques from the fields of animal behavior, ecology, and stable isotope chemistry. While understanding of the links between sensory biology and community ecology remains relatively poorly developed, the results presented in this dissertation suggest that sensory divergence may (1) be an important determinant of resource use differentiation among species in nature, and (2) contribute to the coexistence of ecologically similar, sympatric species.
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