Over 80% of the carbon fixed in photosynthesis in the tropical canopy falls as litter where it is decomposed in the “brown” food web of microbes, microbivores, and their predators. The taxa in these webs may represent 60% of the forest’s invertebrates and their abundance can vary 100-fold at small spatial scales. Yet, despite its importance in releasing carbon into the atmosphere, recycling ecosystem nutrients, and sustaining much of the forest’s biodiversity, we are profoundly ignorant of the factors shaping abundance in these webs. Like the green forest canopy above it, the tropical litter represents one of the last ecological frontiers on the planet.

A basic goal of ecology is to understand the processes that generate the vast variation in abundance and biomass among taxa in time and space. Food webs summarize the flow of elements and energy in ecological systems. One basic type of web groups taxa into trophic levels based on shared prey and predators. A significant and attainable goal for Ecology is to predict the biomass across these trophic levels in time and space. Our current NSF is exploring the processes that regulate abundance and decomposition in the Brown Food Web (BFW) of a Panama rainforest.

The primary objective is to understand why virtually every rate and population parameter of major taxa varies at least 100-fold as one moves from one m2-plot to the next. Patchiness is a basic property of assemblages; the small size of these players, combined with the importance of BFW in cycling nutrients, makes this a model system.

Toward this end we are integrating three theories in ecology: OFAN, which predicts trophic structure along productivity gradients, Ecological Stoichiometry, which predicts the nature of resource limitation, and Defense theory, which predicts patterns of allocation to defense in differing environments. 

We are using these theories to explore the dynamics of tropical litter food webs in the Republic of Panama’s Barro Colorado National Monument (BCNM). Most of what we know about the structure and function of food webs comes from plant-based, or “green” webs. 

We are integrating three theories (below). Trophic theory proposes that the balance of resource and predator limitation varies with the amount of resources available at the base of the web; ecological stoichiometry proposes that resources limiting biomass reflect the balance of chemical elements allocated to growth and defense relative to their availability; defense theory posits that the optimal allocation between growth and defense is determined by the intensity of predation and the time it takes for the prey to reach reproductive age.