Major Research Directions |
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My research approachI use several methods in my research including a mix of observation and field sampling, laboratory physiological analyses, laboratory and field manipulative experiments, and stochastic simulation modeling. An approach that I commonly take is to first observe natural patterns in the field. I then conduct laboratory or field physiological or experimental studies to understand the potential mechanisms behind these patterns. I then use modeling to scale these mechanisms up to population and community levels to verify that they in fact reproduce the patterns that were observed in the field. Taking this approach to mechanistically understand the factors that structure populations and communties allows me to predict and project responses of natural systems as a result of ecological changes. I have employed this research strategy, or variations on this strategy, to study several areas related to the general theme of biodiversity, defined as the variety and variability of organisms or habitats. Human activities are resulting in rapid environmental changes worldwide that alter biodiversity. Understanding the causes and consequences of changing biodiversity is therefore essential to predicting the implications of continued environmental changes. Below I briefly describe each of the main areas related to biodiversity that I am involved in.
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Mechanistically understanding the impacts of invasive species My work mechanistically explores interactions where invasive species have large impacts on native system. Understanding the underlying mechanisms behind invasive species impacts is important because invasives represent one of the main threats to biodiversity worldwide. My work has focused on two specific systems. The first is rocky intertidal habitats in New England that were invaded in the early 1800s by the European green crab and then again in 1989 by the Asian shore crab (picture on right). With the arrival of the Asian shore crab, the European green crab is being eliminated and replaced in many areas. My work has examined interactions between these species and the community impacts of each in order to understand the reason for and consequences of this species replacement. (Click here to learn more about this research.)
The other system that I have examined is the invasion of a bopyrid isopod parasite that infects the gill chamber of the burrowing mud shrimp (distended branchial chamber in picture). I first discovered this species in 2002 while conducting research on the feeding ecology of the mud shrimp. Since that time the prevalence of the parasite has increased dramatically, while its host shrimp appears to be declining. My work in this system has examined physiological impacts of the parasite on its host in order to understand patterns of host-parasite interactions and the impacts of the parasite on individual shrimp. (Click here to learn more about this research.) |
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Making population extinction more predictable My research seeks to understand the process of extinction with the goal of reducing extinction risk for endangered populations. We are currently facing the world's sixth major extinction event. However, while the threat of extinction is increasing for many species and populations, there is much about the process of extinction that we do not yet understand. This is because testing extinction theory is complicated both by logistical constraints such as the lack of replication in natural systems and by ethical constraints that eliminate the possiblity of inducing extinction in order to study the process (a general approach that is possible when studying processes other than extinction). My approach sidesteps these constraints by using laboratory bench-top populations of Daphnia, a small freshwater zooplankton that can be replicated and manipulated at the population level to easily test extinction theory. Any population can be characterized by the general population trajectory shown by the black line in the diagram to the left. A species establishes a new population that grows from small population size (region 1). Once a steady state population size is reached (K, carrying capacity shown by dotted line in graph), populations will fluctuate around this population size for some time (region 2). Finally, populations will dip below optimal size for the final time and will decline to extinction (region 3). My research has explored factors in each of these three regions that may influence extinction risk. My goal has been to improve our ability to predict extinction risk so that this risk can be reduced to the extent possible. (Click here to learn more about this research.) |
Forging a link between individual diet specialization and reproduction An NSF-funded project in my lab examines how diet choices influence individual reproductive output and thus the relative contribution of different individuals to population growth. Many species are omnivorous, consuming a broad diet that includes a mix of plant and animal foods. However, the diets of individual animals are often more specialized than the diet of the population as a whole. This individual diet specialization may have important consequences for growth and reproduction, and thus for population dynamics. This project uses several species of crabs that occur along the east coast and that fall at different regions of the omnivory continuum. |
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Using gut size as a forensic tool to determine diet My research has developed a method to determine the diet of crabs based on gut size. Determining crab diets is important because there are more than 10,500 species of crabs worldwide, each with a different diet. Further, crabs are becoming more important in many marine food webs because of the loss of large predators that previously kept crab numbers in check (for example, due to overfishing) and because of the continual movement of this highly invasive group of species into new areas. Crab guts are shaped like triangle pyramids, and gut width provides a reliable and simple means of predicting the percent herbivory of crab diets, both across species and for different members of the same species. (Click here to learn more about this research.) |
Biodiversity and ecosystem function As biodiversity changes due to the loss (extinction) or addition (invasion) of species, it is important to understand the extent to which the functioning of ecosystems is altered. My work on this topic has focused on different levels of diversity, including species diversity and intraspecific diversity (or diversity within a single species). This work encompasses both empirical and theoretical aspects, and, as with other aspects of my work, my goal is to develop a more predictive framework so that the conceptual importance of biodiversity can more usefully be implemented in management and conservation practices. (Click here to learn more about this research.) |
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Everybody eats - the role of trophic interactions in creating ecological patterns One of my longstanding interests is trophic interactions. Regardless of what else organisms do, all organisms eat. Trophic interactions therefore play a large role in ecological processes. My work with trophic interactions has ranged from merely measuring the consumption rate of individuals to determine trophic impacts of a species, to demonstrating fundamental differences in how trophic interactions control population sizes of seemingly similar consumer species, to demonstrating how adherence to concepts of foraging theory controls the spatial distribution of consumers in natural environments. I commonly incorporate aspects of trophic interactions into projects examining other questions in order to continue to advance our understanding of foraging processes and their role in ecological dynamics. (Click here to learn more about this research.) |
Multiple predator effects Multiple predator effects are a type of trait-mediated indirect effect that occur when two predator species share a common prey. My research on multiple predator effects has demonstrated several factors, including the importance of choosing the appropriate experimental design for the question of interest, the importance of trophic structure and habitat type, as well as the importance of predator and prey density. This work has largely focused on European green crabs and Asian shore crabs, and so has also provided insights into the mechanism underlying the replacement of one invasive species by another. (Click here to learn more about this research.)
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