Document: RAP-3-51-18

The abundant center pattern of species' distributions: Dimension matters.

SAGARIN, R.D.* and S.D.GAINES

University of California, Santa Barbara, CA 93106, USA ¹

Abstract:
A long and widely held belief in biogeography is that a species' abundance should be greatest at the center of its range and decline in abundance toward the edges, which have uniformly low abundance. Many biogeography texts have described this "abundant center" distribution and it has even been called a "general rule" of biogeography. This distributional pattern has been taken as a given condition in discussions of higher order ecological theories including species' responses to climate change, population dynamics, the designation of habitat reserves, pest outbreaks, and genetic population structure. Yet there have been surprisingly few empirical studies aimed at illustrating this pattern in nature, and fewer still which conclude that the pattern exists. We review these studies and find that many are biased towards finding the abundant center pattern because they fail to appreciate the problems in presenting a two-dimensional pattern (abundance across a range area) in one-dimensional space (abundance vs. distance from the center or edge). We propose that marine intertidal species along the western coast of North America represent an ideal system for examining the abundant center distribution as their ranges can essentially be defined in one-dimensional space. We present results of population surveys of several intertidal invertebrate and plant species conducted over the entire range of the species. These surveys show that an abundant center pattern is not a universal feature of intertidal species' abundance distributions and that the primary signal is of extreme site-to-site variation in abundance. The results suggest that broad generalizations need to be tested before they are applied blindly to management situations.

Keywords: biogeography, generalizations in ecology, abundance distributions, intertidal populations

This abstract is being presented at: 9:45 AM in session:
Oral Session #56: Metapopulation Analysis.