Derek K. Gray

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My research Interests fall into three main categories:

  1. Assessing the potential impacts of environmental change on aquatic communities

  2. Understanding the factors that influence community responses to environmental stressors

  3. Understanding the impact of dispersal and colonization processes on the distribution and abundance of plankton species

daphnia
 

Impacts of environmental change on aquatic communities

Global temperature increases have led to many physical changes in northern hemisphere lakes, including increased surface water temperatures, changes in water stratification, and earlier ice-out timing. The impacts of these ongoing changes on biota are not yet fully understood, but some possibilities include altered phenology, changing food-web relationships, altered chemical partitioning of contaminants, and the replacement of cold-water species with those adapted to higher temperatures. Rigorous scientific studies are needed to document the impacts of environmental change and to provide relevant information to natural resource managers and policy-makers.

As part of my postdoctoral work at NCEAS I am examining the effects of climate change on plankton communities in one of the world’s largest lakes: Lake Baikal, Russia. Lake Baikal is home to a unique food web that contains many endemic cold-water plankton and fish species that support a population of the world’s only freshwater seal. In collaboration with researchers from UC Santa Barbara, Michigan State University, Wellesley College, and the University of Texas, I am evaluating the likelihood that endemic plankton species will be replaced by widespread cosmopolitan species as environmental conditions change. More broadly, this collaborative research project is aimed at evaluating the potential impacts of changing plankton communities on the Lake Baikal food web as a whole.

 

Understanding the factors that influence community responses to environmental stressors

Environmental change may lead to turnover in communities as resident species are replaced by those that have physiological tolerances better suited to the altered environment. However, past studies suggest that it is difficult to predict the trajectory of community change due to the constraints imposed by ecological and evolutionary forces. To improve our ability to predict community change it is necessary to understand the ecological and evolutionary forces at play as communities respond to stressors. In other words, we need to understand why communities respond the way they do to environmental change.

Anthropogenic acidification is one of the best-studied stressors affecting aquatic ecosystems, making it an ideal case for examining the factors that influence community responses to environmental change. Industrial emissions of sulpher dioxide and nitrogen oxides caused the acidification of thousands of lakes in eastern North America and Europe. As lake water pH levels dropped in many Boreal Shield lakes, acid-sensitive zooplankton and fish species were lost. Although emissions reductions have occurred during the last three decades, aquatic communities are still in the process of recovering from this disturbance.

I have conducted extensive work with acid-damaged zooplankton communities in lakes located on the north shore of Lake Huron in Killarney Provincial Park, Ontario. As pH levels have increased in these lakes there is evidence that acid-sensitive species are attempting to recolonize. Unfortunately, community recovery has occurred at a rate much slower than expected based on documented pH increases. My work has focused on elucidating the factors that may be slowing community responses to increasing pH levels. I have used two approaches: (1) field experimentation to determine which variables impact the probability of recolonization of damaged lakes by acid-sensitive species; and (2) modeling and statistical analyses to determine the factors that drive variation in zooplankton communities across the landscape.
figure

 



The impact of dispersal and colonization processes on the distribution and abundance of plankton species
 


The composition and relative abundance of species in freshwater zooplankton communities are thought to be controlled by a combination of local and regional variables. Regional variables, such as the composition of the regional species pool and organism dispersal rates, act to determine which species gain access to individual lakes or ponds. At the local scale, community interactions, such as competition and predation, and environmental conditions, such as lake water pH or temperature, are the primary constrains on community membership. 

The relative importance of local and regional variables is hotly disputed in the literature, with some studies finding strong evidence that dispersal limitation is an important force structuring communities, and others concluding that zooplankton community composition is determined primarily by local conditions. My own work with a group of 45 lakes in Killarney Provincial Park, Ontario, strongly suggests that regional factors are important for communities in Boreal Shield lakes. Given the conflicting evidence in the literature, my future research will aim to determine the circumstances under which regional factors should be expected to play a significant role in structuring communities.



 

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