Document: ROB-3-82-34

Rates of species accumulation of mobile organisms: An adaptive procedure for directing allocation of sampling effort.

FERNAU, R.F.* and N.H.WILLITS

University of California, Davis, CA 95616 USA 1

Abstract:
We present a new bootstrap procedure that gives an estimate of the rate of increase of species accumulation curves, and two summary statistics to provide answers to questions such as "Have I sampled enough at this site?" Because the experimental unit is the number of visits, one can answer questions like "Do I need a sixth visit, given that I have already sampled the site on five previous occasions?" One summary statistic gives the absolute number of new species. The other, the proportional increase of new species, is an estimate of the derivative of the logarithm of the species accumulation curve. When both estimates are plotted as a function of prior visits to a sampling station, the resulting curves generally decrease (reflecting diminishing returns), but by quantifying the expected additional information to be gained through further visitation, a researcher can define a threshold beyond which additional visitation to a site is unfruitful. Two dependent variables in this analysis are absolute and percent changes in observed species, which offer the investigator some options. Which of the two is more appropriate depends on the aim of the particular visit. The final stage relates the dependent variables to landscape and ecological attributes of the environment, so the investigator will know (for example) landscape correlates of stopping time, e.g."do I get more out of visits at a ridge top site, relative to a valley site?" The usefulness of these rates has many other applications for ecologists, conservation biologists, and those designing monitoring projects in dynamic ecosystems.

Keywords: rates of species accumulation curves, species richness, long term monitoring, stopping time

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This abstract is being presented at: 4:30 PM in session:
Oral Session #46: Modeling Populations and Statistical Ecology.