WILL A TALE OF TWO CATS BECOME A TALE OF ONE? CANADA LYNX AND BOBCAT DENSITY AND DYNAMIC OCCUPANCY IN A MOUNTAIN ECOSYSTEM

Sujay Singh

doi:10.7273/000007470

Climate change causes divergent range shifts for cold versus warm adapted species, potentially reshuffling biotic interactions at range peripheries. Yet, outside of coarse distributional metrics, little information exists regarding the population ecology of species along range-peripheries. Here, we use camera trap data in combination with spatially-explicit capture-recapture (‘secr’; Chapter 1) and dynamic occupancy models (Chapter 2) to examine how climate influences density and abundance (Chapter 1), and colonization-extinction dynamics (Chapter 2) of two potentially interacting species – the cold-adapted Canada lynx (‘Lynx’; Lynx canadensis) and the warm-adapted bobcat (Lynx rufus) – at a range periphery in a montane ecosystem within northcentral Washington, United States. In Chapter 1, we modeled density and abundance of lynx and bobcats during the summer of 2023 as a function of temperature and environmental gradients, and used secr models to map spatial variation in density and calculate density overlap between the two species. We also predicted future patterns of density, abundance, and density overlap using three different Shared Socioeconomic Pathway (SSP) climate change scenarios. Density was influenced primarily by temperature, with lynx density declining as a function of temperature and bobcat density increasing. Future abundances declined for lynx under all SSPs, but were stable for bobcats, with both species experiencing upward elevational shifts in density. Areas of the landscape with high lynx and low bobcat densities declined in the future, but areas with low lynx and high bobcat densities increased. Our approach, which could be applied to other species inhabiting montane systems, revealed how temperature gradients shape range edge patterns of density of cold and warm adapted mammals, with implications for future population trajectories and interactions. In Chapter 2, we utilized a long-term (2016-2024) camera trap dataset to model local colonization and extinction dynamics for lynx and bobcats in relation to changing climatic and disturbance conditions. We found that maximum summer temperature and winter snow depth are important drivers of local colonization and extinction probabilities for both species. Increasing summer temperatures reduced lynx and bobcat colonization probabilities, increased lynx extinction probabilities, and reduced bobcat extinction probabilities. Decreasing winter snow depths reduced lynx colonization probabilities and increased bobcat colonization probabilities. In the short-term, our results suggest fairly stable occupancy dynamics for both species. However, in the long-term, we suggest that the interplay of climate change with our documented colonization and extinction dynamics will result in lynx range contractions and bobcat range expansions. Thus, by utilizing a long-term camera trap dataset, we provide insights into the mechanisms driving range dynamics for cold versus warm adapted species, and our framework can be extended to other montane ecosystems to gain a process based understanding of species range shifts under changing climatic conditions.

WILL A TALE OF TWO CATS BECOME A TALE OF ONE? CANADA LYNX AND BOBCAT DENSITY AND DYNAMIC OCCUPANCY IN A MOUNTAIN ECOSYSTEM

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