PARENT SESSION
Poster Session #3: Herbivory.
Monday, August 6, 2001. Presentation from 10:30 AM to 12:00 PM. Exhibition Hall
26
Gain functions in small patches for a large herbivore: Evaluating evidence for competing models.
SEARLE, KATE1, HOBBS, N.1, VANDERVELDE, THEA2, SHIPLEY, LISA2, WUNDER, BRUCE 3, 1 2 3
ABSTRACT- Patterns of movements by herbivores in heterogeneous environments result from the interplay between travel among patches and residence within patches. Prevailing models predicting patch residence time depend on understanding gain functions, which portray the accumulation of food by foragers as a function of patch residence time. We developed a series of models representing gain functions for herbivores based on current understanding of mechanisms controlling their intake rate. We evaluated the strength of evidence in data for these models and for purely empirical formulations. We obtained data on cumulative dry matter intake of mule deer (Odocoileus hemionus) fawns feeding in small patches. The scale of patches was set such that animals could deplete the patch without moving their feet. We varied the composition of patches to include single plant species, multiple palatable species, and mixtures of palatable species and unpalatable ones. We held patch biomass constant while varying the geometry of plants to include many small plants or a few large ones. The shape of the gain function was influenced by patch composition and by patch geometry. Several models had support in the data, including linear, non-linear, and stepped forms. The strength of evidence in data for alternative models depended on patch characteristics. We conclude that fine scale characteristics of patches may influence large-scale movements of foraging herbivores and that a variety of models are needed to predict patch residence time.
KEY WORDS: spatial heterogeneity, foraging, herbivore, gain function