Many fields of natural science suggest that organisms both respond to and also directly regulate the physical processes that structure ecosystems, in ways that have major implications for how the current loss of Earth?s biodiversity will affect our planet. A growing number of studies incorporates the influence of organisms into our understanding of biogeochemical cycles, functioning of ecosystems, and formation of habitats. Most of these studies still consider the influence of only one species at a time, ignoring the diverse array of species that might have unique impacts. The project proposed here will explicitly ask how interactions between coexisting species influence the physical process of erosion. In this project, caddisfly (Trichoptera: Hydropsychidae) diversity in experimental streams will be manipulated. Caddisflies are one of the most diverse and widespread groups of insects that live in riverbeds. They construct silken nets across pore spaces between rocks to filter feed, and previous studies have shown that nets from a single species reduce sediment motion during floods. This study will test whether multiple species of caddisfly that coexist in the same stream cause a synergistic decrease in sediment motion compared to any single species alone.

Predicting sediment transport has become increasingly important in light of land-use changes, altered flow regimes, and channel-restoration efforts, and this work will help develop a better understanding of one of the most important processes in ecology and geology. Although many researchers have shown that a single biological species can have a substantial impact on abiotic processes, few studies have mechanistically explored how multiple species of animals can synergistically regulate fundamental transport processes in streams. This approach will refine our ability to quantitatively predict erosion.

Project Report

Overview and Background As fields like ecogeomorphology and ecosystem engineering have begun to develop over the past few decades, an increasing number of case studies have illustrated that biological organisms can significantly influence the physical processes that structure ecosystems. We now have many examples showing that animals and plants can influence precipitation cycles, the forces controlling erosion, and flow regimes. Most of these studies have considered only a single, dominant organism, however, and very few studies have explicitly documented whether coexisting species in diverse communities have unique impacts. In my research, I study whether species interactions among coexisting animals that live in streams regulate how animals influence sediment stability during floods. To test whether we must explicitly account for multi-species assemblages in physical models like those that describe sediment erosion, I study caddisfly larvae in streams. Caddisflies in the family Hydropsychidae are fully aquatic as larvae. They spin silk nets in the pore spaces between rocks that they use to filter food particles out of the water. Caddisflies can be as dense as 1000s m-2 in nature, and previous studies have shown that their silk nets can bind rocks together and increase sediment stability. Caddisflies are also one of the most diverse groups of aquatic insects, and multiple species of net-spinners often live in the same stream. My preliminary work in laboratory stream flumes showed that multi-species assemblages can cause non-additive increases in sediment stability compared to species monocultures, and this non-additive increase likely results from spatial partitioning of the benthic substrate. The goals of the DDIG were to test how multiple species of caddisfly affect erosion in real streams where the organisms have access to more realistic temperature fluctuations, food sources, predators, other invertebrate competitors. Field Research Activities I conducted an experiment at the University of California’s Sierra Nevada Aquatic Research Laboratory (SNARL) near Mammoth Lakes, CA. Two common species of caddisfly, Ceratopsyche oslari and Arctopsyche californica, were collected from nearby streams and moved into replicate stream channels (Figure 1). Flow in each channel was controlled by an upstream weir, which could be opened to simulate a flood. Final settling density of the caddisflies density in the experiment varied from ~200-650 m-2, and fell within the range of densities measured in natural streams nearby. I found that caddisfly monocultures can increase the forces required to initiate grain motion by 30% over controls with no caddisflies present during a simulated flood. Polyculture treatments of both species also increased the threshold of motion by an additional 15% above the average of the monocultures, indicating that species interactions in streams with multi-species assemblages could significantly influence the effects that biological organisms have on sediment erosion. Educational Activities 1. Undergraduate training: To date, this project has included five undergraduate researchers. Four of these students have performed independent research projects. Two of these students will soon finish their undergraduate degrees, while one works for the Forest Service, one works for an ecological consulting firm, and one is in graduate school. 2. Public education & outreach: As part of the outreach component for this grant, I volunteer at the Sierra Nevada Aquatic Research Laboratory for children’s class programs. I help students (ages 10-15) sample and identify aquatic invertebrates in Convict Creek, which runs through the SNARL property. I also organize and play Macroinvertebrate Mayhem, a game of tag, with approximately five 6th grade classes that travel to SNARL on field trips. This game teaches students about the effects of environmental stressors like pollution and high temperatures on aquatic insects and fish. I also serve on UCSB’s Natural Reserve System (NRS) Advisory Committee as the graduate student representative. For this position, I participate in 4 committee meetings per year and serve as the liaison between the administration and graduate students who use the reserves for their research. I have been most active in organizing the first biennial NRS Day, which took place in February 2013 and celebrated research that takes place on UCSB’s reserves with talks given by faculty and posters given by undergraduate and graduate students.

National Science Foundation (NSF)
Division of Environmental Biology (DEB)
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Sudeep Chandra
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University of California Santa Barbara
Santa Barbara
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