PARENT SESSION
Symposium #3: The role of spatial extent in ecological pattern and process.
Sponsored by ESA Vegetation Section
Organized by: J. Nekola and H.H. Wagner.
Monday, August 6, 2001. 8:00 AM to 11:45 AM. Madison Ballroom B

Distance decay as a measurement of extent's role in community composition turnover.

Nekola, Jeffrey ¹, ¹

ABSTRACT- Distance decay is the expectation that the similarity between two observations will decrease as intersample distance (extent) increases. In both simulated and empirical data, the most linear distance decay relationships occur when distance is regressed against the log of similarity. The rate of distance decay in community composition is of particular interest as it can be influenced by environmental variation within and between habitats, spatial configuration of habitats, species niche breadth and overlap, and species dispersal ability. The variation of distance decay rates in the flora of boreal and Appalachian spruce-fir forests, and the land snail fauna of carbonate outcrops in central North America will be considered. These analyses show that distance decay rate is a dynamic variable, changing with organism size (e.g., lowest for trees and highest for herbs), dispersal ability (e.g., lowest for good dispersers like bryophytes), and degree of habitat isolation (e.g., highest on isolated habitats or peninsulas). As such, analysis of distance decay rates provide an important tool in investigating the processes underlying biogeographic pattern.

KEY WORDS: extent, community composition, distance decay, biogeography