The missing link: from island extinction to Neutral Theory (a reply to Halley and Iwasa)

Abstract

Halley and Iwasa and I agree that simple models can be valuable [1xNeutral theory as a predictor of avifaunal extinctions after habitat loss. Halley, J.M. and Iwasa, Y. Proc. Natl. Acad. Sci. U.S.A. 2011; 108: 2316–2321CrossRef | PubMed | Scopus (28)See all References, 2xThe coherence problem with the unified neutral theory of biodiversity. Clark, J.S. Trends Ecol. Evol. 2012; 27: 198–202Abstract | Full Text | Full Text PDF | PubMed | Scopus (28)See all References]. Their fine study shows that a model can ignore factors contributing to extinction (habitat, dispersal, life history, physiology, exotic enemies, human activity) and still describe species losses from islands or patches of different size. Their letter [3xNeutrality without incoherence: a response to Clark. Halley, J.M. and Iwasa, Y. Trends Ecol. Evol. 2012; 27: 363Abstract | Full Text | Full Text PDF | PubMed | Scopus (5)See all References][3] acknowledges our shared agreement on the utility of simple models. We part company on what this has to do with the Unified Neutral Theory of Biodiversity.Given the issues I raised in [2xThe coherence problem with the unified neutral theory of biodiversity. Clark, J.S. Trends Ecol. Evol. 2012; 27: 198–202Abstract | Full Text | Full Text PDF | PubMed | Scopus (28)See all References, 4xBeyond neutral science. Clark, J.S. Trends Ecol. Evol. 2009; 24: 8–15Abstract | Full Text | Full Text PDF | PubMed | Scopus (70)See all References], which they objected to in [1xNeutral theory as a predictor of avifaunal extinctions after habitat loss. Halley, J.M. and Iwasa, Y. Proc. Natl. Acad. Sci. U.S.A. 2011; 108: 2316–2321CrossRef | PubMed | Scopus (28)See all References][1], in the Cell Press Discussion on neutral theory (http://news.cell.com/discussions/trends-in-ecology-and-evolution/ecological-neutral-theory-useful-model-or-statement-of-ignorance) and again in their letter, I would expect clarification on how their study supports the Unified Neutral Theory of Biodiversity. In both [2xThe coherence problem with the unified neutral theory of biodiversity. Clark, J.S. Trends Ecol. Evol. 2012; 27: 198–202Abstract | Full Text | Full Text PDF | PubMed | Scopus (28)See all References][2] and [4xBeyond neutral science. Clark, J.S. Trends Ecol. Evol. 2009; 24: 8–15Abstract | Full Text | Full Text PDF | PubMed | Scopus (70)See all References][4] I addressed the many definitions, including that species are functionally equivalent, that all have the same fitness or that all have the same probability of recruitment success. I addressed the belief that the Unified Neutral Theory of Biodiversity is a null model for niche differences or that it represents an alternative to niche or fitness differences. I demonstrated why neutral models do not assume that all individuals obey the same rules of engagement, and why they do not predict that coexistence occurs in the absence of niches. This list of motivations, assumptions, and interpretations may not be exhaustive, but it is close.The statement in the letter by Halley and Iwasa most relevant to Neutral Theory does not respond to the question of how their study supports it:It is not necessary to buy into any interpretation of the niche (or the stronger claims of unification) to apply these mechanisms and get useful results that fit the data well.Halley and Iwasa seem to be saying that it does not matter what niches are. One of the few persistent claims about Neutral Theory has been that it is an alternative to niche theory. Since Neutral Theory does not address niches or lack thereof [5xResolving the biodiversity debate. Clark, J.S. et al. Ecol. Lett. 2007; 10: 647–662CrossRef | PubMed | Scopus (98)See all References][5], proponents now simply avoid saying what a niche is. So how does a study such as [3xNeutrality without incoherence: a response to Clark. Halley, J.M. and Iwasa, Y. Trends Ecol. Evol. 2012; 27: 363Abstract | Full Text | Full Text PDF | PubMed | Scopus (5)See all References][3] support it? What definition of Neutral Theory does it support?My paper that Halley and Iwasa object to in their letter [2xThe coherence problem with the unified neutral theory of biodiversity. Clark, J.S. Trends Ecol. Evol. 2012; 27: 198–202Abstract | Full Text | Full Text PDF | PubMed | Scopus (28)See all References][2] focuses on the need to move beyond claims that the Unified Neutral Theory is being criticized for reliance on simple models. From introductory statistics courses onward we learn to construct simple models and penalize large ones. Nobody wants a complex model when a simple one will suffice. There is no debate about this. The criticism of Neutral Theory concerns vague and shifting definitions and misinterpretation of models.The Unified Neutral Theory finally appears to be no more than a defense of simple models. If proponents now acknowledge that it has nothing to say about niche differences [6xThe case for ecological neutral theory. Rosindell, J. et al. Trends Ecol. Evol. 2012; 27: 203–208Abstract | Full Text | Full Text PDF | PubMed | Scopus (56)See all References][6], the Unified Theory defaults to a statement that simple models can be useful, apparently the point of [3xNeutrality without incoherence: a response to Clark. Halley, J.M. and Iwasa, Y. Trends Ecol. Evol. 2012; 27: 363Abstract | Full Text | Full Text PDF | PubMed | Scopus (5)See all References][3]. All ecologists – including those who do not count themselves as theorists – should be concerned when such basic modeling principles are taken as a unified theory for our discipline.