Our group studies food webs in rivers and their watersheds. We are interested in how attributes and performances of species influence their effects in food webs, and how species interactions change under different environmental regimes.
Much of our field work takes place in and around the Eel River, which flows along the North Cost of California. Six kilometers of the upper mainstem of the South Fork Eel, and entire watersheds of several of its tributaries, are protected within the Angelo Coast Range Reserve in Mendocino County, CA. The Angelo Reserve is one of the 39 large protected natural reserves dedicated to university-level research and teaching in the University of California Natural Reserve System.
In 2013, the Angelo Reserve was designated as one of nine NSF Critical Zone Observatories. We work closely with Berkeley hydrologists, geomorphologists, climate scientists, tree physiologists, and fish ecologists to link hydrologic cycles in steep forested basins of the California North Coast to water storage and release as runoff to river networks. Our lab focuses on how the timing and amount of water delivered from the watershed to channels influence conditions that affect river food webs and ecosystem linkages.
Physiology to Food Webs Down River Networks
All landscapes on Earth, even on the sea floor, are sculpted and organized by river drainage networks. Ecologists are confronting the challenge of linking these landscapes to ecology to forecast responses by both to changes in climate, land use, or biota. Addressing this challenge requires “predictive mapping”: integrating across space and time to discover:
- Where ecological regimes change
- Which spatially varying factors cause these changes
- How boundaries or gradients separating regimes will shift with altered climate, land use or biota—shrinking, expanding, or relocating the spatial domains of ecological regimes.
- how the pieces we understand at local scales add up to consequences at the basinwide, regional, or global scales of concern to society.
Ever advancing mapping, sensing, and tracing technologies make it more feasible than ever to detect factors that correlate with ecological regime changes over space. Maps that overlay ecological process rates and controls onto landscapes, in combination with field experiments that detect shifting mechanisms controlling local interactions, should help us elucidate the degree to which ecophysiology of individual species, versus more complex community interactions or ecosystem fluxes, govern ecological patterns through space and time.
Rivers exchange organisms, materials, nutrients, water, and heat with the atmosphere, their terrestrial watersheds, and longitudinally, via upstream movements of biota (“biologically mediated backflows”) and downstream movements and drift. These longitudinal exchanges can sometimes link rivers with estuaries and coastal oceans. The surface area of rivers is small relative to the area of their watersheds; terrestrial plant biomass typically dwarfs that of aquatic primary producers; and gravity pulls material down slopes. For these reasons, it is often assumed that “forests feed their rivers”. Rapid growth and excellent nutritional quality of riverine algae like diatoms, however, make them surprisingly important food sources, not only for riverine consumers, but also for emerging aquatic insects that sustain terrestrial biota like spiders, lizards, birds, and bats. We are investigating process like insect emergence and algal stranding through which “the river feeds the forest”. We have recently also recently launched studies of linkages of the river to the ocean: the potential importance of riverine algal drift for consumers in estuaries; and whether algal-mediated biogeochemistry can affect primary productivity in the coastal ocean near the river mouth.