Although anti-predator behaviors are ubiquitous in nature,
we know surprising little about the strength of non-consumptive effects in food
webs, and especially how they compare to classic trophic effects. In
collaboration, with Barbara Peckarsky and Angus McIntosh, I am testing the
impact of trophic and non-consumptive effects of trout on invertebrates and
subsequently on organic matter processing in
Using watershed-scale observational studies of streams with and without naturally reproducing trout populations, I find that leaf litter decomposition and organic matter export is lower in streams with trout. These observational findings do not appear to be the result of systematic differences in temperature, resources, or insect density between fish and fishless streams. To experimentally test non-trophic effects of predatory trout on organic matter dynamics, I used a large-scale experimental approach in which I added fish chemical cues to naturally fishless streams. A striking decrease in organic matter export and decomposition was observed in streams with the trout chemical cues added, primarily due to decreased invertebrate activity.
This research demonstrates that non-consumptive effects are transmitted through food webs and have ecosystem-level consequences similar to, or greater than, consumptive effects. From a management perspective, this work provides important information on how the stocking of trout into fishless headwater streams influences upstream ecosystem processes that also affect downstream ecosystems.
Predator-induced selection on insect flight and dispersal
Stoneflies from streams with (bottom) and without (top) fish present Stonefly larvae, Megarcys signata
are fantastically diverse and ecologically and economically important
features of life on earth. The development of aerial flight is a hallmark of
insects, and the profound effect of the phenomenon is readily apparent from
insect pests to pollinators. Predation
has been suggested as a possible selective agent in the evolution of insect
flight but has not been systematically explored. Interestingly, natural selection by
predators may select for traits that enhance aerial flight capability thereby
increasing the likelihood of dispersal to areas with lower predation risk. Stream ecosystems are particularly
appropriate systems to explore the role of predators on insect flight because
most evidence suggests the first insects and earliest flying insects were
aquatic. This research investigates
how natural selection by predatory fish, such as trout, alters traits related
to adult insect flight and dispersal.
I am using a combination of observational surveys in
Effects of Didymosphenia geminata on stream food webs and ecosystem metabolism
Didymo. Covers 75-90% of the stream bottom in late summer in the Cotton-ball sized globs of didymo on a protruding rock
I am investigating how the native but now nuisance stalked diatom, Didymosphenia geminata, affects stream ecosystem structure and function. One component of this research project explores the impacts of didymo on invertebrate community composition, growth, development time, drift behavior, and hence possible food web effects on trout populations. The second component of this research project investigates the impacts of didymo stalk production on whole-stream metabolism, specifically investigating the degree to which didymo increases the biomass of heterotrophs and ecosystem respiration thereby affecting summer dissolved oxygen levels in economically and ecologically important trout streams.