Thirty Years of Forest Census at Barro Colorado and the Importance of Immigration in Maintaining Diversity

Richard Condit,Stephen P Hubbell,Ryan A Chisholm,Lee A Newsom

doi:10.1371/journal.pone.0049826

Richard Condit, Stephen P Hubbell + Show 2 more

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https://doi.org/10.1371/journal.pone.0049826

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Abstract

The neutral theory of community ecology can predict diversity and abundances of tropical trees, but only under the assumption of steady input of new species into the community. Without input, diversity of a neutral community collapses, so the theory's predictions are not relevant unless novel species evolve or immigrate. We derive analytically the species input needed to maintain a target tree diversity, and find that a rate close to per recruit would maintain the observed diversity of 291 species in the Barro Colorado 50-ha tree plot in Panama. We then measured the rate empirically by comparing species present in one complete enumeration of the plot to those present five years later. Over six census intervals, the observed rate of input was to species per recruit, suggesting that there is adequate immigration of novel species to maintain diversity. Species interactions, niche partitioning, or density-dependence, while they may be present, do not appear to enhance tree species richness at Barro Colorado.

Highlights

The crucial assertion of the neutral theory of community ecology is that diversity can be maintained in the absence of species differences as long as there is steady input of new species via speciation or immigration [1,2]
Various models produce predictions of species abundance distributions as they depend on dispersal, and these have been tested against real forests [6,7,8,9], but the theory [1] includes a quantitative prediction of diversity as a function of speciation [10]
Barro Colorado over 30 years, and the observed rate was consistent through time and a quantitative match to the theoretical rate needed to maintain diversity

Summary

Introduction

The crucial assertion of the neutral theory of community ecology is that diversity can be maintained in the absence of species differences as long as there is steady input of new species via speciation or immigration [1,2]. Various models produce predictions of species abundance distributions as they depend on dispersal, and these have been tested against real forests [6,7,8,9], but the theory [1] includes a quantitative prediction of diversity as a function of speciation [10]. In the absence of novel species input, the neutral theory is irrelevant, and stabilizing mechanisms such as niche differentiation among species or competitive interactions must maintain diversity [11,12].

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