From steps to home range formation: species‐specific movement upscaling among sympatric ungulates

Tablado, Z., Revilla, E., Dubray, D., Saïd, S., Maillard, D., & Loison, A. (2015). From steps to home range formation: species‐specific movement upscaling among sympatric ungulates. Functional Ecology 30, 1384–1396.

Space use and movement patterns depend on a combination of external factors (i.e. environment) and internal factors. The interaction between these two drivers means that different animals – whether these be individuals, populations or species – will differ in their responses to the same or similar environmental factors. In addition, the differences between animals may depend on the spatial and/or temporal scale of investigation. In this paper, Tablado et al. ask how the spatial and temporal scale of investigation affects differences in movement patterns (displacement and home range size) between animals with different foraging strategies (grazers, browsers and mixed feeders). Other studies have successfully scaled up from space use to home ranges and incorporated multiple spatial and temporal scales, but this study adds to those previous studies by investigating interspecific differences in these scaling parameters.

To answer this question, the authors used GPS tracking of three ungulate species in the French Alps. These three species have different feeding strategies, leading the authors to hypothesize that, in comparison to grazers and mixed feeders, browsers, which eat forbs and fruits, would move more at small scales because of their search strategy, but would move less at larger scales because they are less social and thus do not need to cover as large an area to satisfy the resource needs of the entire population. Using GLMMs that tested the effect of temporal resolution and feeding strategy on two space-use variables (net displacement and range area), they were able to at least partially confirm these hypotheses. Their models both showed a significant interaction between species and time, where all species increased their movement with temporal scale but differences between the species increased with time. Specifically, the increase in displacement over time was smallest for the browsing species, consistent with the hypothesis that their solitary behavior allows more consistent space use across time. The authors also find that each species group responds differently to some environmental variables (e.g. risk) independent of scale, and that there are differences between groups that appear at one scale but not others (e.g grazers and mixed feeders increased their movements in forested areas and browsers decreased their movements in these same areas, but only at small scales).

Unlike most other models and methods we have discussed in this course, this study used a statistical approach to study a phenomenon, rather than building a mechanistic model. By using this data-based approach, the authors highlight the real-life need to consider multiple mechanisms when scaling up models, even when using a mechanistic approach. Their results show that these effects of scale may differ depending on the species or group being investigated, meaning that a single mechanism or function will not necessarily scale up all models appropriately.