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Research

How do spatial and temporal environmental variation both maintain and erode the composition, structure, and functioning of biological communities? 

Daphnia pulex near the water's surface. Photo: J.-F. Cart

Daphnia pulex near the water's surface. Photo: J.-F. Cart

I am particularly interested in the role of food web interactions in mediating the response of biological communities to environmental variation, and primarily focus on aquatic ecosystems. Given the ongoing and predicted future impacts of global change on environmental fluctuations, including both increased and more variable air temperatures, a predictive framework is needed to understand how such changes will impact life on Earth. Currently, the emergent properties resulting from global change simultaneously acting on multiple levels of biological organization and across various spatio-temporal scales presently preclude satisfying answers to this question.

I seek to test hypotheses that will further the development and synthesis of ecological theory as well as enhance ecological predictions associated with a warming climate and altered patterns of nutrient cycling. Below are the main themes of my research:


1) The ecology of thermal refugia: species interactions in variable environments

D. pulex (left) and D. lumholtzi (right)

D. pulex (left) and D. lumholtzi (right)

Despite predictable physiological responses that organisms exhibit in a laboratory setting in response to changes in temperature, species interactions (e.g., competition, predation, parasitism) are one reason that communities exhibit varied and seemingly unpredictable responses to changes in temperature in nature. Thus, a goal of my research program is to develop an improved framework for understanding how temperature affects species interactions and consequently the dynamics of interacting species. I have been exploring how increases in temperature may facilitate the success of non-native species by altering competitive interactions with native species and interactions with predators. Much of this research has used the exotic zooplankter Daphnia lumholtzi (Cladocera: Daphniidae) as a model organism for understanding the importance of temperature-dependent competitive interactions for community compositionhow to predict establishment success of an organism across a thermal gradient, and whether increases in temperature will benefit species resistant to predation.

From the perspective of many organisms, thermal environments are not static through time, nor are they spatially homogenous. Thus, organisms both experience variation in their surrounding environmental temperature through time, and can behaviorally thermoregulate at certain times of the day. Much of my current research addresses how this variability alters the population dynamics, food web interactions, and the structure of food webs.

Collaborators: David VasseurLauren CullerCristina Herren


2) Consequences of rare demographic events

Photo: Julie Dermansky

Photo: Julie Dermansky

One predicted consequence of global change is an increase the severity of extreme weather events, such as heat waves and heavy precipitation events. As such, understanding the effects of global change requires an understanding of how rare episodic events shape communities. As part of an ongoing collaboration, I am currently investigating the causes, magnitudes, and temporal patterns in animal mass mortality events (the rapid, catastrophic die-off of organisms).  We recently conducted the first quantitative analysis of published animal mass mortality events from across the globe. Our findings indicate that mass mortality events may be increasing in magnitude through time for certain animal taxa, and that reports of mass mortality may be increasing through time.

 

 

Collaborators: Stephanie Carlson, Adam Siepielski


3) Heating up ecological subsidies: The influence of temperature in integrating ecological subsidies into recipient ecosystems. 

Image: Karin Curtis-Hill

Image: Karin Curtis-Hill

Ecological subsidies (energy and materials that move across ecosystems) influence food web structure, key ecosystem functions, and the ability of organisms to persist in a particular habitat. However, limited information exists on the potential for temperature to alter the quality of such subsidies or the resulting response of the recipient ecosystem.

I am using leaves from terrestrial vegetation to investigate how temperature might alter ecological subsidies. Leaves are one important subsidy for aquatic ecosystems, providing both carbon and nutrients, and leaf chemistry depends on many environmental factors, including temperature and precipitation. I am currently investigating how variation in leaf chemistry due to increased temperatures will alter the detritivore-based “brown” and autotroph-based “green” lake food webs during autumn leaf drop. 

 

 

 

Collaborators: Lucas BeversdorfTrina McMahon, Andrew Mertens, Kathy Cottingham


I am additionally interested in how resource morphology can interact with other environmental variables (nutrients, the presence of other resources, temperature) to shape consumer-resource interactions. Difficult to consume organisms including the green alga Scenedesmus acutus, the cyanobacterium Gloeotrichia echinulata, and the well defended zooplankter Daphnia lumholtzi have all been focal organisms in my research. 

 
Scenedesmus acutus

Scenedesmus acutus

Gloeotricia echinulata

Gloeotricia echinulata