Climate change has the potential to greatly affect biodiversity and there is convincing evidence that most taxonomic groups are already responding to the recent climate warming. Even though the impacts of climate change on biodiversity are felt across a wide range of ecosystems, the severity and sometimes the direction of these impacts are likely to differ across space because factors other than climate will influence how biodiversity responds to climate change. For example, composition and configuration of land cover may play significant roles in the relative vulnerabilities of biodiversity to changing climate. However, despite some initial investigations, empirical evidence for the influence of land cover is lacking because studies that integrate both land cover and climate are rare. The overarching goal of my dissertation was to assess the relative roles of climate change and land cover in the observed changes in avian biodiversity. Specifically, I was interested in the influences of land-cover composition and configuration on relative vulnerabilities of different avian groups to climate change and spatial scales at which such influences are relevant. Chapter 1 focuses on testing the utility of the spatially-varying coefficients (SVC) model to quantify the influence of non-stationarity on relationships between temporal community change in avian assemblages and environmental covariates. Chapter 2 investigates bioclimatic relationships of grassland and forest breeding birds across varying gradients of grassland and forest habitat. Chapter 3 investigates the relationship between temporal changes in avian assemblages and the interaction of climate change and land-cover fragmentation. Chapter 4 explores scale-dependence of temporal changes in avian communities and investigates relevant environmental drivers of the community change at different spatial scales. The collective works in these chapters contribute four primary conclusions for better understanding of the implications of the interaction of land use and climate change to avian diversity. First, relationships between changes in biodiversity and environmental factors are often spatially non-stationary, i.e., the relationship between a response variable and the predictor covariates varies across the spatial extent of the study. Second, the amount of suitable land cover can significantly alter species responses to climate change, but this effect of land cover depends on the type of habitat. Third, impacts of climate change on ecological communities are more pronounced in regions of unfragmented landscapes than in locations with fragmented habitats. Fourth, temporal changes in community composition are scale-dependent and so are the mechanisms driving these changes. Specifically, climate change operates at smaller spatial scales than landscape fragmentation. The implications of these findings suggest that current conservation strategies may be insufficient to protect biodiversity in the face of climate change. Existing biodiversity conservation generally focuses on conserving large regions with undisturbed and contiguous habitats that generally support high species diversity. My results suggest that ecological communities of such habitats will undergo the most drastic compositional changes as a result of climate change. Thus, it is critical that the existing conservation strategies are placed in the context of climate change. My work suggests that successful biodiversity conservation needs to consider both the individual species' vulnerabilities to climate change based on their habitat association or life-history strategies and relative vulnerabilities of entire communities based on the landscape in which these communities persist.
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