Our research group studies the ecology and conservation of freshwater ecosystems. We are especially interested in links between environmental change, species interactions, and ecosystem functioning. We frequently focus on the ecology of ‘natural enemies’, which includes parasites, predators, and invasive species. This group of organisms provides rich ecological questions that are often relevant to applied challenges in wildlife conservation, human health, and economics. Current research themes involve:

  1. Parasite ecology in freshwaters, including drivers of disease risk and the roles of parasites in community dynamics, food webs, and ecosystem processes.
  2. Causes and consequences of species invasions in wetlands, with a focus on how invasion outcomes are influenced by other forms of environmental change (e.g., nutrient inputs, habitat loss, invader interactions).
  3. Trophic interactions in freshwater streams, especially factors driving variation in the strength of species interactions and the resulting consequences for communities.
  4. Environmental change and the structure and functioning of lake ecosystems.

In studying these topics, we often combine field data with mechanistic experiments at multiple scales (e.g., laboratory, outdoor mesocosm, whole ecosystem).


Parasite Ecology – Parasitism represents the most widespread animal life-history strategy in nature. Parasites influence host traits and can regulate host population sizes, sometimes leading to significant effects on community structure and ecosystem processes. Recent projects have examined the roles of parasites in food webs and secondary production within wetlands. Ongoing work aims to determine how parasites alter nutrient cycling and primary production in streams, and in turn, how variation in nutrient stoichiometry can influence disease severity. Current project are also exploring spatial heterogeneity in disease risk and the environmental factors that shape parasite community structure in streams (e.g., forest management and biodiversity). Most of these projects have focused on trematode worms, which have complex life cycles where they infect hosts in both the aquatic and terrestrial environment.

Species Invasions in Wetlands – Invasive species have become major drivers of ecosystem change, a problem that is particularly prominent in freshwaters. Understanding the effects of invasive species, however, is complicated by numerous factors in nature, such as the occurrence of multiple invaders simultaneously and concurrent environmental changes (e.g., climate warming, pollution, habitat alteration). Much of my research involving invasive species has examined the factors that mediate interaction strengths between invaders and native community members. For example, nutrient availability, habitat complexity and community structure have important roles in moderating invasive species effects within experimental wetlands. I have also used ecosystem-level experiments to see how differences in experimental venue (e.g., laboratory enclosure, outdoor mesocosm, or natural wetland) alter experimental results. This work has focused mostly on invasive fish and bullfrogs in the western United States.

Trophic Interactions in Stream Food Webs – Quantitative measures of species interaction strengths are central to understanding food web dynamics yet most empirical food webs lack measures of interaction strengths between species. I am currently working with Mark Novak from Oregon State University on several projects in Oregon stream food webs that involve quantifying species interaction strengths in situ, and using experiments to understand factors that underly variation. This work involves stream predators (sculpin, trout, salamanders, crayfish) and their prey. We are also working to extend current approaches for measuring predator-prey interactions to host-parasite interactions in stream food webs. This work aims to assess the relative importance of predation versus parasitism in driving population dynamics of hosts, community structure, and eventually ecosystem processes including nutrient cycling and primary production.

Environmental Change in Lakes – High elevation aquatic systems are particularly vulnerable to environmental change because they integrate ecosystem responses of the surrounding landscape through the movement of water. In collaboration with researchers at the Niwot Ridge LTER in Colorado, I have been examining how alpine lakes are responding to climate change. This work has emphasized how physical, chemical and biological responses of aquatic systems can show tightly coupled responses to climate warming. Understanding and predicting how alpine systems will respond to climate change is important because they strongly affect downstream ecosystem services that humans rely on.