Michael M. Fuller

Spatial Analysis in Community Ecology

The goal of spatial ecology is to understand the processes that govern the spatial distribution of species. Species tend to aggregate in recurring subsets of the regional pool of organisms. Sometimes there are clear geographic delineations between species groups (often caused by shared habitat preferences). But patterns of coexistence frequently vary with spatial scale and can be indistinguisable from random sorting. Many geostatistical tools are available for quantifying spatial organization. The semivariogram (figure at right) shows how correlated different locations are with increasing distance apart. In the figure, tree density is correlated up to a distance of about 70 meters, beyond which density varies randomly. The lines bracketing the points are Monte Carlo envelopes indicating the region of uncorrelated data. This figure was generated using the open-source statistical package, R.

In research with Brian Enquist (University of Arizona), I am studying the role that different processes play in the spatial association of tree species in a tropical dry forest in Costa Rica. The study plot shows substantial geographic variation in tree density and species association (see figures below).

Previous research indicates that the distribution of species is influenced by random processes, such as dispersal, as well as deterministic processes, such as habitat preferences and assymetric competition. To better understand the relative contribution of such processes, we are developing a randomization algorithm that redistributes tree species while preserving the large-scale spatial structure of the forest. An important goal of this research is to preserve the 3-dimensional organization of the forest plot when generating (simulated) random plots for comparison.

In addition to the above research, I and several members of our research group at the University of Tennessee are using spatial modeling approaches to investigate the effects of climate on the spread of invasive species. Some information on these studies can be found here.