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COMPARISON OF ECOLOGICAL COMMUNITIES: THE PROBLEM OF SAMPLE REPRESENTATIVENESS
Citation:
Cao, Y., D. D. Williams, AND D P. Larsen. COMPARISON OF ECOLOGICAL COMMUNITIES: THE PROBLEM OF SAMPLE REPRESENTATIVENESS. ECOLOGICAL MONOGRAPHS. Ecological Society of America, Ithaca, NY, 72(1):41-56, (2002).
Description:
Obtaining an adequate, representative sample of ecological communities to make taxon richness (TR) or compositional comparisons among sites is a continuing challenge. Sample representativeness literally means the similarity in species composition and relative abundance between a sample and the community from which it is drawn. Because sample representativeness normally cannot be measured directly, we propose to estimate it by measuring the similarity among replicate samples randomly drawn from a community, i.e., autosimilarity. Adequate study has been conducted on (1) how well a sample actually represents the community from which it is drawn and (2) what effect variation in the level of representativeness among sites has on site-to-site comparisons. Using both field and simulated data, we show that samples of equal size (area or number of individuals) from different sites differentially represent their communities. As a result, the proportion of the true total taxon richness at a site (%TTR) achieved with a fixed sample size varies across sites. Also, site-to-site differences in observed TR change with sample size. A sample-size bias thus is introduced into site-to-site comparisons. Using the same data sets, we found that (1) samples of equal size from different sites achieved different levels of autosimilarity, with lower levels achieved in species-richer sites, indicating variation in how well samples of equal size represent their respective communities, (2) %TTR was positively and almost linearly correlated with autosimilarity, indicating that autosimilarity might be a good predictor of richness, and (3) when samples were compared at the same level of autosimilarity, similar %TTRs across different sites were achieved, i.e., the relative differences in taxon richness among sites became independent of sample size. We conclude that standardization based on autosimilarity can effectively reduce the effects of sample sizes and improve the accuracy of the community comparisons.