Bobbi Peckarsky

My research involves field studies of behavior, life histories and biological interactions among stream-dwelling invertebrates, predatory fish and algal resources in streams of western Colorado near the Rocky Mountain Biological Laboratory (http://www.rmbl.org).   I am interested in the mechanisms, consequences and evolution of predator-prey, consumer-resource, and competitive interactions, and how they relate to environmental disturbance as a consequence of climate change.  Recent and ongoing studies include 1) existence of alternative community states of stream grazer communities (disturbance-tolerant vs disturbance-intolerant grazers) as a consequence of the disturbance regime, 2)  the influence of trade-offs between resistance/resilience to disturbance, vulnerability of grazers to predation and nutrients on the strength of top-down interactions, 3) effects of changing environmental conditions on the prevalence of mermithid parasites and the consequences for mayfly host populations, 4) effects of upstream range expansions of novel trout and stonefly predators on mayfly mortality, behavior and life history, 5) effects of increasing extreme hydrological events and warming stream water temperatures on the synchrony of metamorphosis and oviposition, fecundity and susceptibility of mayflies to parasites and predators, 6) development of an integrative demographic model to predict the interactive effects of multiple stressors on mayflies, 7) macroinvertebrates as indicators of impacts of human activities on stream habitat quality: integrating research, education and outreach, and 8) causes and consequences of proliferation of a native, nuisance diatom (Didymosphenia geminata) on otherwise pristine stream ecosystems.

We work in high elevation streams at one of the most beautiful places in the world, the Rocky Mountain Biological Laboratory (http://www.rmbl.org), which is situated in the West Elk Mountains near Crested Butte, Colorado.   Our sites include headwater snowmelt streams and spring-fed streams that are fishless, but contain predatory aquatic insects, and lake outlet streams and lower gradient streams that contain predatory brook trout. The favorite prey of aquatic insect predators and brook trout are mayflies of the genus Baetis, who lay their eggs under rocks in many of these high elevation streams.

Our methods include sampling invertebrates, fish and algae as well as physical, chemical attributes in the field, and experiments conducted in artificial streams (mesocosms and microcosms).

Hypotheses related to ongoing studies in Rocky Mountain streams:

Alternative community states of stream grazer communities as a consequence of the disturbance regime:

• Mayfly grazers and diatoms predominate in disturbance-prone streams
• Cased-caddisfly grazers, filamentous algae and moss predominate in less disturbed streams
• Variation in the hydrological and geomorphic disturbance regime can be used to predict those alternative community states

Trade-offs between resistance/resilience to disturbance, vulnerability of grazers to predation and nutrients on the strength of top-down interactions:

• Mayflies trade-off disturbance tolerance for greater vulnerability to predation
• Cased caddisflies are protected from predation, yet vulnerable to hydrologic and geomorphic disturbance
• Behavioral trophic cascades from trout – mayfly grazers – diatoms are suppressed by nutrient limitation in high-altitude streams
• Adding nutrients reduces the strength of grazer-algal interactions

Effects of changing environmental conditions on the prevalence of mermithid parasites and the consequences for mayfly host populations:

• Warming stream temperatures can create a mismatch between the availability of mayfly hosts for the infective stages of mermithid parasites, thereby explaining spatial and temporal variation in the prevalence of parasitism
• Parasite prevalence is not recruitment-limited, but instead may be a function of post recruitment processes affecting encounter rates between parasites and hosts
• Parasitized mayflies trade-off rates of resource consumption to reduce susceptibility to predation
• Parasites suppress host risk-taking behavior and decrease consumption by predators

 Effects of upstream range expansions of novel trout and stonefly predators on mayfly mortality, behavior and life history:

• Warming temperatures may favor brown trout typical of lower elevations, thereby changing the predation regime of mayfly grazers
• Proliferation of Didymo favors a species of predatory stonefly typical of lower elevations
• Changing predation regimes can affect the mortality (consumptive effects), behavior and life history of mayfly prey (non-consumptive effects)

Increasing extreme hydrological events and warming stream water temperatures affect the synchrony of metamorphosis and oviposition, fecundity and susceptibility of mayflies to parasites and predators:

• Floods and droughts affect the availability of large rocks protruding from the stream surface used by mayflies for oviposition
• Warming temperatures accelerates mayfly development and may lead to asynchrony in the timing of metamorphosis and oviposition
• Warmer temperatures can have indirect effects on mayflies by favoring predators or parasites

Macroinvertebrates as indicators of impacts on stream habitat quality: integrating research, education and outreach:

• Educating target groups about the theory and practice of biomonitoring streams
• Assessing the impacts of disturbances on stream habitat quality
• Baseline biomonitoring of invertebrates of streams vulnerable to degradation due to human activities
• Developing a long term database of stream invertebrate communities as a basis for understanding the relative importance of natural and human-induced disturbances in explaining population and community fluctuations

Causes and consequences of proliferation of a native, nuisance diatom (Didymosphenia geminata) on otherwise pristine stream ecosystems.

• Didymo proliferation is greater under high light conditions, and is suppressed by shade
• Didymo proliferation is greater in years with early spring snowmelt, lower peak flows and higher water temperatures, which are conditions becoming more common as the climate warms in high elevation systems
• Proliferation of Didymo causes a shift from mayfly-dominated to midge dominated benthic invertebrates, which provide lower caloric food for trout, thereby resulting in lower trout growth rates