How species richness and total abundance constrain the distribution of abundance

1. How species richness and total abundance constrain the distribution of abundance A Weecology Production Ken Locey1, Ethan White1,2 1Dept. of Biology, Utah State University 2The Ecology Center, Utah State University Results Characteristics of the feasible set SAD feasible sets are dominated by similarly-shaped hollow-curves, revealing an a priori explanation for the ubiquitous hollow-curve. Introduction The species abundance distribution (SAD) is one of the most intensively studied distributions in ecology. The shape of the SAD is often predicted using species richness (S) and total abundance (N) as inputs. S and N constrain the shape of the SAD in ways ecologists rarely account for. There are a limited number of possible SAD shapes (the feasible set ) for any combination of N and S. Methods Contextualize empirical evenness and diversity Empirical comparisons The center of the feasible set is often highly correlated with empirical SADs (most R2 values > 75%). Empirical SADs, especially those derived from metagenomes, are often more hollow than the center of the feasible set The feasible set We used integer partitioning algorithms to find sizes of feasible sets and to generate random samples from them. Integer partitions , i.e. non-increasing sums of integers, are directly analogous to species rank-abundance distributions (RADs). pdf Evenness Distributions of wealth and abundance The central tendency The form of the RAD having the greatest overlap with other forms in a random sample of the feasible set. Conclusions Total abundance (N) and species richness (S) greatly constrain the observable variation in the form of the SAD. The general shape of the SAD can often be explained solely from these constraints. Attention to the feasible set, reveals whether empirical forms and natural variation of the SAD, as well as natural variation in observed values of evenness and diversity, are exceptional to the majority of forms that are possible, simply based on N and S. Future directions Software https://github.com/klocey/partitions https://github.com/weecology/feasiblesets Empirical comparisons 8 regional to global scale datasets comprising 9,562 communities of birds, mammals, trees, bacteria, archaea, and indoor fungi Acknowledgements We thank the numerous individuals involved in collecting/providing the data we used including the citizen scientists who collect the BBS and CBC data, USGS and CWS scientists and managers, researchers who collected/sequenced metagenomes, the MG-RAST project, the Ribosome Database Project, the Audubon Society, the U.S. Forest Service, the Missouri Botanical Garden, and Alwyn H. Gentry. We thank X. Xiao, D. McGlinn, B. Burnside, J. Kitzes, J. Parnell, James O’Dwyer and an anonymous reviewer for discussions and comments. This research was supported by a CAREER grant from the U.S. National Science Foundation to EPW (DEB-0953694) and by a research grant from Amazon Web Services to EPW and KJL.