Empirical Evaluation of Neutral Theory

Abstract

We describe a general framework for testing neutral theory. We summarize similarities and differences between ten different versions of neutral theory. Two central predictions of neutral theory are that species abundance distributions will follow a zero-sum multinomial distribution and that community composition will change over space due to dispersal limitation. We review all published empirical tests of neutral theory. With the exception of one type of test, all tests fail to support neutral theory. We identify and perform several new tests. Specifically, we develop a set of best practices for testing the fit of the zero-sum multinomial (ZSM) vs. a lognormal null hypothesis and apply this to a data set, concluding that the lognormal outperforms neutral theory on robust tests. We explore whether a priori parameterization of neutral theory is possible, and we conclude that it is not. We show that non-curve-fitting predictions readily derived from neutral theory are easily falsifiable. In toto, there is a current overwhelming weight of evidence against neutral theory. We suggest some next steps for neutral theory.

Predicting community structure in snakes on Eastern Nearctic islands using ecological neutral theory and phylogenetic methods

“…Equilibrium is an important part of UNTB, and the probable lack of equilibrium has been used to criticize UNTB or show that predictions are inconsistent given time and other factors [22,73]. However, we point out that many community studies are consistent with UNTB and that although equilibrium may not have been demonstrated in all cases, it is likely that some relaxation of this constraint and the zero-sum assumption is permitted [74,75] or is unnecessary to predict SAD [76,77].…”

The "neutral" community structure of planktonic herbivores, tintinnid ciliates of the microzooplankton, across the SE Tropical Pacific Ocean

“…The neutral model, due largely to its assumption of ecological equivalency among species within a community, has generated a great deal of controversy (for recent examples see Holyoak and Loreau, 2006;McGill et al, 2006;Alonso et al, 2006). There are differences of ecological significance between tintinnid species, for example LOD is related to the size of prey most efficiently grazed.…”

Quantifying the effects of seed arrival and environmental conditions on tropical seedling community structure

“…Similarly, just as selection nonrandomly alters the relative abundance of alleles, ecological filtering may fall more strongly upon individuals of some species than upon others, thus driving a community toward niche assembly. Accordingly, communities subject to intense predation or disturbance regimes appear resistant to stochasticity in community structure, and are well fitted by nicheassembly models (McGill 2003;McGill et al 2006;Chase 2007). On the other hand, communities subject to relatively benign environments and moderate rates of predation and disturbance appear more sensitive to stochasticity, and are well fitted by models of dispersal assembly (Fukami 2004).…”