Document: MAR-3-52-7

Scaling of resource heterogeneity and the coexistence of species.

RITCHIE, M.E.* ¹, H.OLFF ² and N.HADDAD ³

Utah State University, Logan Utah, U.S.A. ¹
Wageningen University, Wageningen, The Netherlands ²
North Carolina State University, Raleigh, North Carolina, U.S.A. ³

Abstract:
Ecologists still search for common principles that predict well-known responses of biological diversity to different factors, including the habitat structure, productivity, area, species' body size, and habitat fragmentation. Here, we show that all these patterns can arise from simple constraints on how organisms acquire resources in space. We use fractal geometry to describe how species of different size find food in patches of varying size and resource concentration. We then derive a mathematical model for the minimum similarity in size of species that share these resources. The model yields a theory of species diversity that makes a number of novel predictions about the size structure and diversity patterns of species that use similar resources, including diversity-size relationships, species-area curves, diversity vs. productivity, and the effects of habitat fragmentation on diversity. We focus here on two particular model predictions: The greater size-similarity of large species and left-skewed, rather than log-normal or right-skewed, distributions of diversity vs. size. We tested these predictions for a sap-feeding insect community with an experimental garden that manipulated the spatial distribution of grasses of different quality independently of productivity. In agreement with model predictions, we found tighter species-packing and greater species richness in plots with more aggregated distributions of grasses. Body-size patterns from extant old-field sap-feeding insect communities near our garden also support our model. These results suggest that scaling of resource use by species of different body size may explain many diversity patterns for local guilds of species that use similar resources.

Keywords: scaling, community, fractal, niche, coexistence, competition, resources, fragmentation

This abstract is being presented at: 9:15 AM in session:
Oral Session #56: Metapopulation Analysis.