RUI: Bottom-Up and Top-Down Influences on Processing Chain Interactions in Detritus-Based Communities

Davidson College, Davidson NC

Investigators

Abstract

Project Abstract: RUI: Bottom-Up and Top-Down Influences on Processing Chain Interactions in Detritus-Based Communities Detritus is the major food source for many communities of organisms, and detritivores provide an ecosystem service by breaking down and consuming dead organic matter. Leaf litter is the primary energy input to several of these detritus-based communities and forms the basis of a processing chain, where leaves decay over time and consumers specialize on resources in different states. Some detritivores, called processors, may facilitate other detritivores by breaking down organic matter and changing it from whole leaves to smaller particles upon which other detritivores feed. This processing chain interaction may increase the diversity of species by increasing the types of resources available for consumption. One objective of this research is to understand how processing of resources regulates community structure. Bottom-up and top-down forces may also influence resources and processing chains. Bottom-up influences, such as the amount of leaf litter, may determine whether processing chain interactions are facilitative or competitive, and how strongly they affect other consumers. Top-down forces, such as top predators, may affect individual consumers, or indirectly affect the rate of processing by adversely affecting processors. This research will determine the relative strengths of bottom-up and top-down influences on processing chain interactions in treeholes, a model detritus-based food web. Water-filled treeholes are small decomposer communities that are easily manipulated and contain processing chain interactions. Field mesocosm and natural habitat experiments will be used to determine the effects on detritivore communities and processing chains when resources, processor density, and presence of predators are systematically varied. Variables to be measured include changes in particle size distribution of leaf litter, the density and diversity of species of insects, and the diversity of microbes. The hypotheses to be tested are: 1) processing chain interactions and processors increase the diversity and abundance of resources in treeholes, which influences diversity and abundance of other detritivorous insects and microbes, 2) processors have a greater positive impact on diversity and abundance of detritivores when resources are limiting than when resources are abundant, and 3) a top generalist predator will decrease competition amongst detritivores, decreasing the impact of the processors, and affecting species richness. Understanding the relative strengths of bottom-up and top-down factors on detrital processing and processing chains will lead to a more complete understanding of how those factors affect community structure and function.