Predicting local and non-local effects of resources on animal space use using a mechanistic step-selection model

Background/Question/Methods

Predicting space use patterns of animals from their interactions with the environment is fundamental for understanding the effect of habitat changes on ecosystem functioning.  Recent attempts to address this problem have sought to unify resource selection analysis, where animal space use is derived from available habitat quality, and mechanistic movement models, which link the detailed movement processes of an animal with its emergent utilization distribution.  Such models bias the animal's movement towards patches that are easily available and resource-rich, and result in the predicted probability density at a given position being a function of the habitat quality at that position.  However, in reality, the probability that an animal will use a patch of the terrain tends to be a function of the resource quality in both that patch and the surrounding habitat.  We propose a mechanistic model where this non-local effect of resources naturally emerges from the local movement processes, by taking into account the relative utility of both the habitat where the animal currently resides and that of where it is moving.  We explain statistical techniques to parametrize the model from location data.  We test the model by fitting it to caribou (Rangifer tarandus) GPS data.

Results/Conclusions

Steady-state animal probability distributions arising from the model have complex patterns that cannot be expressed simply as a function of the local quality of the habitat.  In particular, large areas of good habitat are used more intensively than smaller patches of equal quality habitat: a real aspect of animal space use that is missing from previous mechanistic resource-selection models.  Comparisons of the model with the caribou data show strong positive correlations between the model's predicted space use and the actual caribou positions.