Neutrality without incoherence: a response to Clark.

In an earlier paper [1], we found that equations based on the neutral theory of biodiversity enjoyed considerable success in predicting the relaxation times for avifaunal extinctions on isolated habitats. We suggested that the neutral theory of biodiversity might turn out to be a useful tool in conservation biology. However, Clark [2] maintains that our study ‘does not need UNTB, neither does it support it’. In addition, he argues that the ‘UNTB should not be a part of conservation planning’ although ‘simple models should always be considered’. We would like to stress that neutral theory is itself a simple model, and should not be excluded from being used simply. We agree with Clark that there is nothing in our analysis to show that ‘the species that went extinct fast were the same as those that did not’ or that ‘these species occupy the same niche or have the same fitness’. However, this is not the only logic that sets the neutral theory apart. The stochastic elements of neutral theory, which lead to the random-walk type population dynamics, are crucial to the theoretical results and applications that emerge. 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. Of course, other models might also fit the data well, such as a model based on symmetric competition, for example. An empirical regression equation for the avifauna extinction data [1] predicts those data better than does the