My research uses observational and experimental methods to understand how large-scale environmental drivers, spatial heterogeneity and evolutionary history influence community assembly and recruitment dynamics in lotic systems. Additionally, I investigate how interactions between river geomorphology, fluvial dynamics and species life-history influence the structure and dynamics of metazoan food webs. In particular, I am interested in empirically evaluating theoretical predictions of ecosystem structure and function. Lotic ecosystems are among the most threatened on a global scale due to anthropogenic impacts on natural fluvial processes. A greater understanding of the ecological dynamics of lotic systems under natural flow regimes is vital for restoration strategies to be successful, and to predict impacts of large-scale environmental drivers such as global climate change.
Identification of constraints on river restoration and enhancement
Systematic anthropogenic alteration of rivers during the last century has significantly impacted the ecological integrity of these systems. Reductions in species diversity, and abundance of charismatic taxa associated with fluvial modification have triggered restoration efforts designed to enhance ecological function in degraded systems. During the early part of this decade, a 1.4 km reach of the Merced River, California, was restored using a combination of mechanical shaping and substrate addition to provide spawning and rearing habitat for Chinook salmon. As part of an interdisciplinary effort to determine factors limiting the success of restoration, I am using observational and experimental methods to identify abiotic and biotic bottlenecks for Chinook production at different life stages. Additionally, I am investigating how restoration efforts affect the structure and dynamics of the Merced River fish assemblage. Species that have evolved divergent life history strategies rely on different environmental conditions for recruitment and restoration strategies that focus on one or a few species may have unintended impacts on other native taxa. Collaborators: Brad Cardinale, Hunter Lenihan, Mike Healey, Tom Dunne.
Food web architecture in a species rich river-floodplain ecosystem
The use of stable isotopes to investigate food web structure and dynamics has become increasingly prevalent in ecology. Isotopes provide several advantages over traditional stomach contents analysis including: providing a measure of material that is actually assimilated, integration of diet over relatively long time periods, and facilitating calculation of a continuous trophic position for consumers. Isotopic methodologies are well suited for food web studies in species rich aquatic systems where omnivory is prevalent and obtaining sufficient sample sizes for stomach contents analysis is difficult. Using isotopic samples from over 100 fish and invertebrate species from the Cinaruco River, Venezuela, we are modeling pathways of carbon flow within metazoan food webs in the main river channel and floodplain lakes. Samples collected during different seasons (wet vs. dry) will be used to examine how flood pulses influence sources of primary production supporting consumer taxa. Additionally, isotope-based niche metrics will be used to test predictions regarding the expansion and contraction of species’ niche width based on resource availability as mediated by seasonal changes in water level. Collaborators: Kirk Winemiller and Craig Layman.