"It is notorious that each species is adapted to the climate of its own home"

"… Species in a state of nature are limited in their ranges by the competition of other organic beings quite as much, or more than, by adaptation to particular climates"

    Charles Darwin, The Origin of Species

These two lines, from the same page of Darwin's most important work, demonstrate the uncertainty that has surrounded, and still surrounds, our understanding of the factors that limit the geographic ranges of species.  Indeed, the question of what determines the distribution of species is an enduring issue in ecology.  The answers to questions regarding the determinants of species distributions are important to understanding the origin of geographic patterns of biological diversity and planning for biodiversity conservation as human activities reduce available habitat, decrease opportunities for successful dispersal, and alter climate to a degree that is physiologically significant.

Species Distributions

My research interests focus on the patterns of species distributions and the factors that influence these patterns.  I am interested in addressing these questions at multiple scales, from global and continental scales down to the scale of a sample plot in an ecological field study. I am especially interested in how we can use information on species distributions and the factors that affect them to understand the potential impacts of global change on population, species and biotic communities. My collaborators and I currently use a variety of approaches to the creation of statistical models to study these patterns and develop explanatory hypotheses that can account for variation in species distributions.  These approaches include, or have included, ordinary linear regression, statistical ordination, and species distribution models.  I have incorporated bootstrapping of datasets and model construction to better understand the uncertainty that accompanies the performance of statistical models of species distributions.

The Niche and Community Ecology

I find that the idea of the ecological niche is a powerful unifying concept, bringing together ecology, evolution, biogeography, and physiology.  Much of my current work focuses on aspects of the niche of species.  With collaborators, I have been successful in using the niche concept to structure models of the ecological relationships between species and their environments, and doing this with both plants and animals. Since my initial efforts to model tree species distributions during the Holocene (see Pearman et al 2008, Ecology Letters), I have become increasingly interested in how the niche changes over time.  Some of this change can, in some cases, be associated with evolutionary processes, as when patterns of niche variation area associated with the evolutionary distances among species in a phylogeny.

The increasing availability of both phylogenetic information and data on the distribution of species provides just one motivation for combining evolutionary and ecological information in synthetic analysis.  I have become increasingly interested in working with molecular systematists and phylogenetic trees to understand how ecological niches change over long time spans.  Along with several collaborators, I hope to contribute to development of the use of phylogenetic analyses of niches to understand how species may also display trends toward rapid niche evolution.  This understanding may contribute to predicting impacts of climate change.  Rapid niche evolution may be the only alternative to extinction in species that have limited powers of dispersal or for which dispersal opportunities are limited by anthropogenic habitat destruction.