9th International Deer Biology Congress

AUTHORS: Stephen L. Webb, Noble Research Institute, LLC

ABSTRACT: Resource selection modeling has strong applications in conservation because resource selection is a fundamental ecological process shaping movement and distribution [1], and offers spatially explicit guidance for targeted management. As animals move across the landscape, they must make trade-offs associated with resource selection to meet needs of survival and reproduction, and for minimizing risk [2]. Fitness is influenced by resource-related decisions by individuals where each resource choice has costs and benefits associated with it. Therefore, individual variation (also referred to as heterogeneity) warrants further investigation in resource selection modeling and how it structures demographic performance such as survival.

Studies of Rocky Mountain elk (Cervus elaphus) and white-tailed deer (Odocoileus virginianus) will be presented to highlight the conceptual framework to study individual variation in resource selection and its applications for modeling demographic outcomes and functional responses, and improving conservation and management. The general approach included estimating resource selection functions (RSFs) and estimating Cox proportional hazards models to quantify risk of mortality as a function of covariates depicting landscape-level features. Spatial models of occurrence and risk are combined to provide a spatially-explicit assessment of the relationship between habitat and demographic performance, wherein low-performance habitat (e.g., sink habitat) was defined as high probability of occurrence coupled with high risk of mortality, and high-performance habitat (e.g., source habitat) was high probability of occurrence coupled with low risk of mortality. For white-tailed deer, fully random effects models are used to estimate conditional (i.e., representing an individual) and marginal (i.e., representing the population-level response) coefficient estimates from RSFs to study behavioral strategies that may influence survival or encounter probability of mates during rut.

Variability in the occurrence of elk was driven by selection for specific resource features as well as responses to human activity. Risk of mortality in elk was a function of human modification of the landscape with little variation explained by resource features. Proximity to industrial (i.e., oil and gas) development was associated with increased risk of mortality whereas proximity to residences and agricultural structures was associated with decreased risk. Individual-level results revealed added complexity – risk of mortality was associated with a consistent pattern of occurrence relative to industrial development, yet the association between risk and occurrence relative to structures (e.g., houses, barns, buildings) was highly variable and likely a function of disparate land-use practices [3]. Using individual elk RSF coefficients (i.e., conditional responses) revealed functional responses for human disturbance and security cover. Elk selected randomly for disturbed areas when level of disturbance was low, but elk showed stronger avoidance as disturbance increased. Elk also used greater security cover relative to its availability especially when exposed to human disturbance [4]. Results from white-tailed deer are forthcoming based on data from [5] and [6].

Prioritizing management based on occurrence without a connection to a demographic outcome risks poor performance because occurrence alone can be a misleading indicator of fitness. Therefore, management may be most effective when individual variation is considered and linked to demographic outcomes.