PARENT SESSION
Oral Session #34: Animal Ecology: Behavior and Sociobiology.
Presiding: S. Richards
Tuesday, August 6. 8:00 AM to 11:30 AM. Grand Ballroom East, Radisson.

Patch characteristics versus spatial context: What controls large herbivore foraging?

Searle, Kate^*,1, Hobbs, Tom¹, Shipley, Lisa², Vandervelde, Thea², Wunder, Bruce¹, ¹ Colorado State University, Fort Collins, CO² Washington State University, Pullman, WA

ABSTRACT- Large mammalian herbivores interact in a reciprocal way with the spatial patterns of landscapes, responding to heterogeneity and creating it. We consider spatial patterns of forage resources as occurring in a spatial hierarchy, with smaller scales nested within larger scales. Animals can respond to this hierarchy in fundamentally different ways. In particular, it remains unclear whether the behavior observed at large patch scales is simply the molar aggregate of behaviors at fine scales, or, alternatively, if the fine scale behavior responds to context created by heterogeneity at larger scale. To test between these alternatives, we conducted an experiment to evaluate competing models predicting patch residence times of mule deer Odocoilues hemionus in a three level hierarchy. We developed alternative models predicting patch residence time as a function of internal patch characteristics and the larger spatial context. In all trials, the Marginal Value Theorem (MVT) greatly underestimated observed residence times for mule deer. The effect on patch residence time of increasing inter-patch distance was contrary to MVT predictions, with animals spending less time in patches as distance increased. The model with the greatest support in the data was a function of patch characteristics and the larger spatial context. Our results suggest that the spatial context of forage patches is an important component in the foraging decisions of mule deer but that traditional theory does not compete well against alternative models.

KEY WORDS: foraging behaviour, large herbivores, spatial scale