When and where will I find my next meal?: Quantifying the Effects of Spatiotemporal Forage Predictability on Ungulate Movement Behaviors in Two Disparate Systems

Abstract

Environmental predictability is increasingly accepted as an overarching driver of animal movement strategies, via its role in the evolution of cognitive abilities that allow species to exploit the spatiotemporal variability of their environments. Recent research has furthered our understanding of how predictability not only underlies animal movement tactics, but also directs movement decisions as a source of information relevant to behaviors such as site fidelity and home-range establishment. Although research has examined the relationship between predictability and movement strategies at the species level, the mediating influence of environmental context is rarely considered. In addition, research has mainly focused on the relationships between predictability and large-scale movement behaviors, and much less is known about environmental predictability in regard to animal movement over finer scales. We address these knowledge gaps by examining how environmental predictability of a mule deer seasonal home ranges relates to average daily movement in two populations inhabiting disparate ecoregions in Utah, USA. We employ two separate metrics of predictability, representing spatial and temporal constancy of Normalized Difference Vegetation Index (NDVI) values, and explored how home range area and forage abundance modulated the relationships between constancy and daily relocation distance. We found that spatial constancy of an individual’s home range significantly impacted daily relocation distance during the summer and had significant interactions with home range area and forage availability. Interestingly, individuals inhabiting spatially predictable home ranges moved more when in a seasonally limiting environment, and less in a non-limiting environment, and forage availability within a spatially predictable home range functioned to reduce the directional impacts of predictability. Temporal constancy was a significant predictor of daily movement in non-limiting seasonal environments, resulting in shorter daily movements in temporally predictable home range areas. Finally, I found a significant interaction between spatial and temporal constancy, which resulted in shorter daily movement of individuals inhabiting home ranges that were spatially and temporally predictable. Together, our results demonstrate the use of environmental predictability in practical foraging decisions that enable animals in these populations to meet nutritional and life-history requirements and support the need to consider environmental context when studying environmental predictability and animal movement. Understanding how habitat quality and predictability impact daily movements and energy expenditure of ungulates at a population level aids our ability to predict how shifts in vegetation dynamics will impact individual fitness, population demographics, and ecosystem functioning.