Species range boundaries are the result of abiotic tolerances, biotic interactions, and organismal movement capabilities. It is commonly thought that these ranges are determined by climate at regional spatial scales and biotic interactions at local scales. However, there are multiple cases where biotic interactions have been shown to have effects on species distributions at regional geographical extents. My research attempts to delineate which environmental (biotic and abiotic) variables are important in determining Eastern box turtle (Terrapene carolina carolina) occurrence at multiple spatial scales. Eastern box turtles are listed as Vulnerable by the IUCN because of their rapid decline and because the causes of their decline have not ceased and are not reversible. Predation is thought to be a cause for their decline in areas where other factors have previously stressed their populations and where predator densities are unusually high.
I have collected fine scale box turtle and box turtle predator density data at over 30 sites on Long Island, NY. I have analyzed these data with density-based Bayesian n-mixture models to find which variables determine occurrence on a fine spatial scale. I then used species distribution models to determine which variables affect species ranges at regional spatial scales.
Results/Conclusions
Preliminary analyses have been conducted at local and regional spatial scales. Preliminary results have suggested that human factors like road density and landscape features like percent forested area are important for local box turtle occurrence while climate variables remain the only variables that matter at regional spatial scales. Interestingly, the distance to the nearest roads and percent forest are the most important variables in models conducted at regional spatial scales when climatic covariates are not included.
This research provides new insight into how species ranges should be modelled by exploring the spatial scales at which biotic and abiotic variables matter the most. By exploring how predation affects box turtles at multiple spatial scales we will be able to make more informative model predictions to aid in conservation efforts for this species.