The causes and consequences of between-stream variation in aquatic macroinvertebrate communities in stream networks

I analyzed stream invertebrate community data and conducted experiments using leaf decomposition and the production of fine particulate organic matter (FPOM) by stream detritivores as a model system. My research addresses three questions: (1) How do biotic, abiotic, and random processes affect stream insect communities within and between streams? (2) How do shredding invertebrates affect the production and export of FPOM? (3) How does the spatial arrangement of shredding invertebrates across headwater streams within a watershed affect FPOM availability in downstream reaches?;I analyze changes in aquatic invertebrate communities within and among streams in watersheds in eastern Pennsylvania between 1970 and 1997. I found that the organization of the communities was strongly affected by abiotic factors including water chemistry, temperature and dissolved oxygen. The stream communities were also affected by distance to other stream reaches by interspecific interactions.;I looked at the physical factors structuring the invertebrate communities in Upper Peninsula of Michigan streams. I manipulated shredder species richness feeding on leaf litter in mesocosms modeled after Upper Peninsula of Michigan streams and measured the quantity and quality of FPOM produced by their feeding. Both the richness and specific identity of the shredding macroinvertebrates had a strong influence on the production of FPOM.;I manipulated the spatial arrangement of shredders between two locations within an artificial stream environment and measured the FPOM exported downstream. I found that the spatial arrangement of shredding invertebrates in an artificial stream had a significant impact on FPOM export when shredders were eating senesced leaves, but not green leaves. These results are one of the first times that a link between spatial arrangement of species and an ecosystem process, here FPOM production, has been experimentally demonstrated.;My dissertation shows that the environment, interspecific interactions, and dispersal limitation concurrently act to affect the distribution of species across tributaries within a stream network. Evidence from my experimental manipulations suggests that changes in the spatial distribution of shredder species within a network could impact the leaf decomposition rates within each stream reach, thereby affecting the FPOM received by downstream ecosystems.