Oral Session #95: Trophic Structure.
Presiding: D. Wise
Thursday, August 8. 1:00 PM to 3:45 PM. Palo Verde Room, Radisson.

Biological mechanisms responsible for the network structure of food webs.

Martinez, Neo*,1, Williams, Richard1, 1 Romberg Tiburon Center, Tiburon, CA

ABSTRACT- Food-web patterns and models have emerged that enable ecologists to successfully predict the detailed trophic structure of many, if not all, aquatic and terrestrial ecosystems. However, the biological basis of this success has yet to be fully described. We will present statistical and computational analyses that demonstrate how energetic, physiological, ecological, and evolutionary mechanisms provide the basis for the success of food web patterns and models. More specifically, the constant connectance pattern illustrates how then number of trophic links between species increases as the square of the number of species. This pattern appears to be due to physiological mechanisms associated with body sizes and evolutionary mechanisms associated with the Red Queen hypothesis. Furthermore, the niche model illustrates how simple rules concerning the trophic niche partitioning of a one-dimensional community niche space faithfully reproduces food webs almost indistinguishable from the largest and most highly resolved empirical food webs in the literature. This model appears to be based in ecologically contingent mechanisms affecting the number and trophic generality of species found in a habitat, energetic mechanisms associated with the direction of energy flowing from plants to higher trophic levels, and evolutionary mechanisms associated with phylogenetic constraint that limits species to possess generally contiguous trophic niches. These mechanisms are general enough to be applicable to virtually all habitats studied by ecologists and therefore may help form a theoretical foundation for the science of ecology.

KEY WORDS: predictive theory, trophic stucture, ecological complexity, functional diversity