Habitat-performance relationships: finding the right metric at a given spatial scale

Abstract

The field of habitat ecology has been muddled by imprecise terminology regarding what constitutes habitat, and how importance is measured through use, selection, avoidance and other bio-statistical terminology. Added to the confusion is the idea that habitat is scale-specific. Despite these conceptual difficulties, ecologists have made advances in understanding 'how habitats are important to animals', and data from animal-borne global positioning system (GPS) units have the potential to help this clarification. Here, we propose a new conceptual framework to connect habitats with measures of animal performance itself--towards assessing habitat-performance relationship (HPR). Long-term studies will be needed to estimate consequences of habitat selection for animal performance. GPS data from wildlife can provide new approaches for studying useful correlates of performance that we review. Recent examples include merging traditional resource selection studies with information about resources used at different critical life-history events (e.g. nesting, calving, migration), uncovering habitats that facilitate movement or foraging and, ultimately, comparing resources used through different life-history strategies with those resulting in death. By integrating data from GPS receivers with other animal-borne technologies and combining those data with additional life-history information, we believe understanding the drivers of HPRs will inform animal ecology and improve conservation.

Figure 1.

Correspondence among scales and metrics in HPR studies. Temporal and spatial scales positively covary so that the reference area increases from a square metre in which a food item is located at a given second to a hundred square kilometres in which a given species can be found. The metric for measuring performance should vary along this continuum of spatio-temporal dimension. At fine scales, the relevant metric will be some unit of energy gain, whereas at the very broad scale of species geographical distribution, the probability of extinction will provide the most suitable metric. The metric corresponding to Darwinian fitness can only apply at intermediate scales.