Although our tools are more advanced, in many ways the science of biodiversity is not much farther along than medicine was in the Middle Ages. We are still at the stage, as it were, of cutting open bodies to find out what organs are inside.
–Stephen P. Hubbell, 2001.
Niche evolution, ecological limits, and the macroecology of land plant biodiversity
There are more than 400,000 species of plants on Earth, and they form the foundation of all terrestrial ecosystems, from tropical rainforests, to prairies, to arctic tundras. But why are there so many plant species, and why do ecosystems differ so strikingly in the diversity and characteristics of their plants? These seemingly simple questions have intrigued biologists for a long time, but the need to predict how ecosystems will respond to human-caused climate change has given them a new urgency. Centuries of biological exploration and surveys by thousands of researchers have yielded a wealth of data on the geography, ecology, and evolutionary relationships of plant species, yet scientists have only begun to bring these data together to understand the fundamental ecological and evolutionary processes that shape plant biodiversity in relation to changing climates. Taking a computational “ecoinformatics” approach to these questions, we are collaborating with Dana Royer from Wesleyan University, Brian Enquist from the University of Arizona, and international collaborators from the Botanical Ecology and Information Network (BIEN). Supported by a National Science Foundation grant, we are investigating the fundamental ecological and evolutionary processes that generate continental-scale variation in plant biodiversity. The diversity and structure of vegetation is strongly correlated with climate, and plant photosynthesis plays a critical role in regulating carbon dioxide in the atmosphere, so understanding how plants have responded to climatic variation in the distant past is one of the keys to anticipating future responses to climate change.
This research project leverages the BIEN database, the largest botanical dataset in existence, with information on the distribution, ecology, and evolutionary history nearly 100,000 plant species in North and South America. Combining computational advances in biodiversity informatics, phylogenetic analysis, and multivariate niche modeling, we will test whether the colonization of novel environments is limited by niche evolution, and whether less physiologically favorable environments actually impose hard ecological limits on the number of plant species they can support. The unprecedented scale of this approach will require both the modification of existing analytical methods and the development of new statistical tools. The project will also develop undergraduate curricula to train the next generation of researchers in the unique skills necessary to work with such large-scale data.
Metabolic scaling and the functional and physiological ecology of organisms and ecosystems
Metabolism is “the fire of life.” Organisms take in material resources from their environment and transform it metabolically to fuel all living processes, including growth, maintenance, foraging, defense, and reproduction. Thus, the rate of metabolism provides a fundamental index of how fast an organism lives. Principally, we are interested in the problem of metabolic scaling; that is, how the rate of metabolism changes with the size of the organism. Across over 20 orders of magnitude in size, spanning creatures as different as bacteria and blue whales, metabolic scaling often takes on a consistent mathematical form known as an allometric power law. Moreover, an inter-related set of mathematical regularities link these scaling properties of individual organisms to the functioning of whole ecosystems. In particular, for plant communities, the distribution of plant sizes, and in particular the size of the larges individual plants, may be an important determinant of ecosystem function and primary productivity.
Another part of this project was an NSF-supported collaboration among faculty from Kenyon’s departments of biology (Chris Gillen and Harry Itagaki) and mathematics (Brad Hartlaub and Judy Holdener). To understand how organism morphology influences metabolic scaling, we used larvae of the tobacco hawkmoth, Manduca sexta, as an experimental system. Manduca is an ideal experimental platform for the study of metabolic scaling, because the larvae grow approximately 10,000-fold in mass in less than three weeks, without large changes in ecology or behavior. The ability to address metabolic scaling in an experimental setting provides a unique opportunity to test recent theories proposed to explain the origin of metabolic scaling, including those focused on the importance of fractal-like exchange surfaces and resource distribution networks inside organisms.
Elevational and latitudinal gradients in the taxonomic, phylogenetic, and functional diversity of forests
Forests occupy vast tracts of land from the humid tropics to the high arctic, and their activities influence the very composition of the air we breathe. But forests are not interchangeable; they vary enormously in stature, in species composition, and in diversity. Lowland tropical forests can contain hundreds of tree species in a single locale, while vast tracts of the taiga are dominated by less than a handful of species. These gradients in biodiversity, the changes in the richness and abundance of species from place to place, are one of the keys to understanding both the origin of Earth’s diverse biosphere and to predicting how it will respond to future changes. In this project, which is a collaboration with Brian Enquist and Brad Boyle at the University of Arizona, Nate Swenson at the University of Maryland, and many others, we conducted a series of forest surveys along elevational gradients at latitudes ranging from central Colorado to Costa Rica. The goal of our analysis is to understand how the functional and phylogenetic dimensions of biodiversity change along elevational gradients, and whether the responses are similar between tropical and temperate ecosystems. The NSF supported this project via a Research Opportunity Award.
Forest community structure, primary produtivity, and carbon sequestration in a mosaic landscape
In their trunks, roots, and soils, the forests of the world sequester an enormous amount of carbon, effectively removing CO2 from the atmosphere. This process, known as primary productivity, is a critically important negative feedback to climate change, and forest management is one of the primary mitigation strategies that we have available. In the eastern United States, many rural areas are complex mosaic landscapes of agricultural lands, tree plantations, successional forests, and more mature woodlots that have never been cut. In this project, which is central to my Ecology Lab course at Kenyon College, we focus on quantifying the carbon budget of three forest stands at the Brown Family Environmental Center, including a successional old field dominated by sycamore (Platanus occidentalis), a white pine (Pinus strobus) plantation, and a mature, mixed-species stand that includes white oaks (Quercus alba) that have likely been standing for well over a century. Using extensive field measurements of tree growth, leaf production, and soil respiration, we ask how the structural and compositional differences between the stands affect their rates of primary productivity and their capacity for carbon sequestration. Data from this project, through Kenyon’s Office of Green Initiatives, also informs Kenyon’s effort to move towards Carbon Neutrality.