Working Group on Distance Decay
Participants: Kristin Taverna, Weimin Xi
Distance decay refers to the decrease or loss of similarity between two observations as the distance between them increases. A negative relationship between distance and similarity is implicit in several ecological and evolutionary phenomena (e.g., species turnover along an environmental gradient). Variations in distance decay rates are also attributable to landscape differences (such as a resistance to movement caused by size and isolation of habitats) and species dispersal abilities (Nekola and White 1999).
Nekola and White (1999) stressed the importance of distance decay of similarity in ecological theory and biodiversity conservation. They examined the decrease in community similarity with distance using data from boreal and spruce-fir forests over a 6000km range. They found that the distance decay curves were best fit by a simple negative exponential function, and the steepness of these curves was a function of plant growth form. It was concluded that the distance decay of similarity could be caused by either a decrease in environmental similarity with distance or by limits to dispersal and niche width differences among taxa.
In his Neutral Theory, Hubble (2000) has further proposed that the distance decay of similarity in community composition under ecological drift and random dispersal is expected to be compound exponential; and the distance decay rates are also slower if the metacommunity is linked by high rates of dispersal. Neutral theory predictions provide a null model for ecologists concerned with the question of how the similarity of communities changes with distance across landscape. Using data from the North Carolina Vegetation Survey, we are interested in testing Hubble’s Neutral theory predictions by examining how distance decay rates vary among and across different community types in the Southeast. Our results can then be compared to previous studies (Nekola and White 1999, Condit et al. 2002) to explore how distance decay rates vary regionally and by species composition.
Outline of activities: On-going and Next
Other documents and information:
Hubble, S. 2001. The Unified Neutral Theory of Biodiversity and Biogeography. Princeton. Princenton University Press. Chapter 7.
Richard Condit, Nigel Pitman, Egbert G. Leigh Jr., Jérôme Chave, John Terborgh, Robin B. Foster, Percy Núñez, Salomón Aguilar, Renato Valencia, Gorky Villa, Helene C. Muller-Landau, Elizabeth Losos, and Stephen P. Hubbell. Beta-Diversity in Tropical Forest Trees, Science 2002 January 25; 295: 666-669. (in Reports)