Research Interests

The general goal of my research activities is to understand the consequences of environmental dynamics for ecosystem processes and natural communities at various temporal and spatial scales. I address my questions in aquatic systems with a special emphasis on planktonic organisms, as they are the foundation of energy input and transfer in aquatic food webs. My research is motivated by this issue and is organized around four primary theses:

I use a multi-disciplinary approach, combining descriptive field studies, experimental research (field and laboratory), and historical data with statistical modeling to relate external variations on ecosystem dynamics and species responses.

Ecosystem Responses to Environmental Change

A major goal of my research is to understand how natural variation and human alteration of the environment impacts ecosystem processes and dynamics. My research in this field spans from human impacts on alpine zooplankton diversity, the response of ecosystems to changing nutrient inputs, the effect of UV radiation on life history, to the impact of climate change on various lake processes.

To address this issue I am using field observations and long-term datasets to extract ecosystem responses to environmental (including climate) variation over an extended time period. I investigate how climate change affects phenologies of important physical and biological processes, trophic interactions between phytoplankton and zooplankton, and population dynamics of zooplankton species with a complex life cycle. I also focus on how phytoplankton species diversity, organization, and species community composition are impacted by altered physical processes linked to climate change.

Food-Web Dynamics

I use experiments and observational studies to address questions aimed at understanding mechanisms that regulate zooplankton populations, such as food resources and predation. In the past I studied pelagic food web configurations of high-mountain lakes and currently I seek to understand how phytoplankton food quality effects zooplankton (copepod) reproduction. I am also interested in the effects of marine-derived nutrients on freshwater ecosystem production. Particularly, whether bear predation on salmon affects growth of salmon scavengers, such as caddis flies. In this context I use stable isotope techniques to understand changes in energy-flow pathways and fatty acids to characterize phytoplankton food quality.

In another project I focus on the dynamics and identity of picophytoplankton in oligotrophic lakes using flow cytometry and molecular work.

Behavioral and Evolutionary Ecology

My interest is in the ecological and evolutionary relationships between an organismís behavior, life history, and population dynamics with the abiotic and biotic environment. My research emphasizes the occurrence and adaptive significance of behavioral patterns in zooplankton as well as life-history responses to environmental stressors. My approach is to examine these questions through coordinated experimental work and field observations. I use mainly Daphnia as a model organism, but also include other zooplankton species. I also focus on the ability of organisms to adapt to altered environmental conditions linked to climate change.

Modeling

I use a combination of population, statistical, and simulation modeling approaches to investigate the spatial and temporal dynamics of aquatic ecosystems. I concentrate mainly on historical datasets to investigate climatic effects on important physical and biological lake processes using time-series analysis and dynamic linear modeling (a Bayesian time-series technique). In other projects I use mathematical models (spectral analysis like Wavelet and Fourier transform) in combination with a novel age/stage structured simulation model to examine population dynamics of a copepod species over an extended time span, and multivariate analysis to characterize temporal reorganizations of ecological communities.