Research

Research in the Tewksbury lab spans disciplines, but the majority of our work focuses on the ecology, conservation, and evolution of species, populations and communities. For a one-page overview of current research Josh and his group are working on, click here .

Evolution and ecology: The Mystery of Toxic Fruit

Many of the most intricate and fundamental interactions between plants and their herbivores, pathogens, and pollinators are mediated by plant secondary metabolites--compounds with no physiological (primary) function in the plants that produce them. Many plants produce these metabolites in ripe fruit, but their importance in mediating interactions between plants and seed dispersers, seed predators, and fruit pathogens is largely unexplored. Given the tremendous influence of secondary metabolites on plant-herbivore interactions, consideration of their role in seed dispersal may be critical for developing general theories of dispersal ecology and plant-animal interactions. This is one focus of my lab.

The current view of fruit-frugivore interactions generally fails to acknowledge the diverse array of frugivores-microbes, fungi, invertebrates and vertebrates-and hence simplifies the complex selection pressures on fruits and the secondary metabolites within them. We are attempting to take a broad view of frugivory, including tests with all of these frugivores.

Why chilies are hot: an integrative exploration of secondary metabolite function in ripe fruit: I am working in collaboration with Dr. Doug Levey (University of Florida), using chilies and capsaicin (the chemical responsible for the chili's fiery taste) as a model system to address the function of secondary metabolites in ripe fruit, and to examine selection on secondary metabolite production in the field. We take a broad approach, asking "Why be hot?" from the perspective of the plant. The project explores a long-standing evolutionary paradox: Why do so many plants place compounds in ripe fruit that are apparently toxic to fruit-eating animals? I am in the process of testing six non-exclusive hypotheses for the role of secondary metabolites in ripe fruit. The work entails laboratory trials with captive frugivores and field studies using wild chili species that are widely separated geographically and phylogenetically. One species occurs in Bolivia, where 17 species in the genus overlap. The other occurs in southern Arizona, at the northern tip of the natural range for the chilies. To learn more about this project, click below.

MORE INFO.

People: Josh Tewksbury, David Haak, Noelle Machnicki, Doug Levey (co-PI)

Conservation and Ecology: Landscape Connections

Landscapes, corridors, and the persistence of plant populations

This is a collaborative research program run by the Corridor Research Group. We are examing the importance of wildlife corridors to mitigate the effects of landscape fragmentation by linking patches of habitat. To do this, we have created the largest set of experimental landscapes designed explicitly to examine the impacts of connectivity, and our investigations span a wide range of species and interactions in an effort to determine the impacts of landscape corridors on individuals, populations, and communities. All of this work takes place in a restoration context: our landscapes are in one of the most diverse and endagered communities in North America, long-leaf pine savannah.

Much of the research in these landscapes focuses on how patch connectivity affects plant-animal interactions and how changes in these interactions affect plant fitness, population persistence, and community assembly in fragmented landscapes. We compare rates of herbivory, pollination, fruit set, and seed dispersal between experimentally isolated and connected habitat patches to determine the relative effects of habitat isolation on these processes, and we do this work in experimentally planted species of restoration concern. This work has led to a more comprehensive understanding of the role of landscape connectivity in maintaining mutualisms between plants and animals, and the role of these mutualisms in maintaining species diversity

For more information on this project, follow the More Info link below, or click here for a list of publications associated with this research.

MORE INFO

People: Josh Tewksbury, Doug Levey, Nick Haddad, Ellen Damschen

Please E-mail Josh for additional information and research opportunities within this program.

Ecology and Conservation: The Fate of Silent Forests

Understanding the consequences complete bird loss on tropical ecosystem function

Birds in forests eat insects and fruit, and move seeds throughout the forest (seed dispersal), but how important are these actions for forest structure? The research addresses this question on the island of Guam (where birds are absent because the non-native brown tree snake has eliminated them) and the nearby islands of Rota, Tinian and Saipan (with native birds remaining). The research uses experiments and observations to determine the importance of birds for seed dispersal and pest control (i.e. reduction of plant eating insects) for ten common tree species that vary in characteristics like seed size, manner in which seeds are dispersed, and growth rate.

The research addresses basic ecological questions, including whether seed dispersal is important for tree species diversity and whether birds control forest insect populations. If birds are critical to the functioning of a healthy forest, then the current global decline in birds may lead to the breakdown of forests worldwide. This research is additionally important because insects are the largest pests to working forests, which provide billions of dollars to the global economy each year. Thus, the results from this work will inform management from local to global scales. Finally, several educational programs will target local Pacific Islander high school and college students.

People: Haldre Rogers (PhD student), Josh Tewksbury

Conservation, Ecology and Evolution: Climate Change, Thermal Physiology and Latitude

The impacts of climate warming in the tropics are often predicted to be small relative to those in temperate regions because the rate of climate warming in the tropics is lower than at higher latitudes. Yet these predictions are based only on the magnitude of climate change may be misleading.

Our research in this area starts with the basic assumption that the impacts of climate warming on organisms depend not only on the magnitude of the environmental temperature shift but also on an organism’s behavior, morphology, physiology, and ecology. We have begun addressing these problems by focusing first on the direct impacts of warming on the performance and fitness of ectothersms, using data from a wide range of experiments that track organismal performance as a function of temperature. By collecting these data from insects, frogs, lizards, and turtles from around the world, we are able to test basic assumptions about how climate relates to physiology, and how physiology predicts the sensitivity of organisms to changing climate. Our work (and work by others) suggests that the negative effects of climate change should be greatest on animals that are physiologically specialized with respect to temperature and have limited acclimation capacity. Further, species living in warm climates are likely to suffer disproportionately from small increases in temperature, which are likely to decrease performance. Finally, species that live in aseasonal environments are particularly vulnerable to increases in temperature, because changes in behavior and phenology are much less likely to provide relief from rising temperatures. All of these traits appear to be more common in tropical ectotherms, suggesting that even a moderate amount of warming in the tropics may cause severe declines in many tropical ectotherms.

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People: Josh Tewksbury, Curtis Deutsch, Kimberly Sheldon, David Haak, Ray Huey, Cameron Ghalambor, Paul Martin.

To download our most recent paper on this, click here.

Evolution, Ecology and Conservation: Diversity Gradients

Understanding global gradients in species diversity

The latitudinal gradient in taxonomic richness is one of the oldest and broadest patterns in nature. Moving from either pole towards the equator, taxonomic diversity increases across plants, vertebrates, and invertebrates, within oceans, in freshwater, and on land, and across the majority of continents and oceans. The pattern is at least 270 million years old, and recurs after decimation by mass extinction events. Despite the robustness of the latitudinal gradient in diversity, we still do not understand why it occurs.

In our lab, we take diverse approaches to examining the causes of latitudinal variation in species richness. At one end, the gradient is caused by abiotic factors that covary with latitude, which has led the lab to work with global climate data sets for both recent periods and the past 18,000 years. On a proximate level, variation in species richness is caused by variation in speciation and/or extinction. To examine these proximate factors we study population divergence of birds in both field settings, and by amassing a global data set of biogeographical information on all 9,800 species of birds. Our goal is to test hypotheses put forth to explain latitudinal variation in species richness by generating large, composite data sets of publicly available information, and coupling this with field, lab, and aviary experiments that test ideas that no available data address.

This work has led us in a variety of directions, from ongoing tests of mechanisms leading to elevational gradients in species turnover across latitude to studies linking latitudinal gradients in physiology to impacts of climate change. Click this link for more information on this research.

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People: Kimberly Sheldon (Graduate Student), Paul Martin (former grad. student and collaborator), Josh Tewksbury

Natural History

Towards a quantitative natural history

One of the largest factors limiting rapid advances in conservation, ecology, and to a lesser extent, evolutionary biology, is a lack of academic focus on the collection, organization, and dissemination of quantitative natural history information. My lab is involved with several projects aimed at creating structures and incentives for the collection archiving and integration of natural history information.

One such initiative, in partnership with the Yanayacu Natural History Reseach Group seeks to quantify the Natural History and nesting biology of Ecuador's Mainland Avifauna - to see video clips and progress to date, click here.

People: Robert Dobs (program director), Paul Martin (PhD student) (lab / field coordinator), Josh Tewksbury

Please E-mail Rob or Josh for additional information and research opportunities within this program.

For more about the location, visit the Yanayacu Biological Station.

Avian Ecology

My research interests in avian ecology focus on the processes limiting breeding success in bird communities. On one level, I am interested in identifying and testing predictive relationships between landscape structure and nest predation, brood parasitism, and the population health of bird communities. A second interest involves modeling the demographic effects of predation and parasitism across different avian life-histories. Recently I have been examining trade-offs in behavior and life-history faced by birds contending with the duel selection pressures of nest predation and brood parasitism, with a particular interest in identifying opportunities for and constraints on anti-parasite adaptation.

I am currently working on two collaborative projects focusing on landscape ecology, as well as ongoing projects focusing on avian behavior and evolution. Landscape projects include an examination of the effects of fragmentation and cattle grazing on breeding bird communities across riparian systems in five western states, and an expansion of previous work examining effects of landscape change on nest predation and brood parasitism in riparian bird communities in two western river systems.

Through my research in avian ecology, I have had the opportunity to collaborate with many fine scientists and institutions. A few of my principal collaborators include Thomas Martin, Sallie Hejl, Point Reyes Bird Observatory, David Dobkin, Shannon and Lindy Garner, Vicki Saab, Amy Cilimburg, Michael Kuehn, Wajid Jenkins, and Todd Musci.

People: Josh Tewksbury

Please E-mail Josh for additional information and research opportunities within this program.