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Abstract Niche differentiation with respect to light availability as it varies across succession has often been thought to explain tree species coexistence. Demographic light‐related niches represented by growth‐survival and stature‐recruitment trade‐offs and captured by demographic groups (slow, fast, long‐lived pioneers, short‐lived breeders and intermediate) have been shown to accurately represent the biomass dynamics of secondary and old‐growth forests in central Panama in a model. However, whether the simple mechanisms of that well‐parameterized and accurate model are enough to support the long‐term coexistence of demographic groups across these trade‐offs has yet to be tested.Here, we develop a model to test whether stochastic, small‐scale gap disturbances and subsequent competition for light can support the long‐term coexistence of the observed demographic groups in the Barro Colorado Island forest dynamics plot. Specifically, to test whether the demographic differences among species promote coexistence, we compare niche simulation models, parameterized by the different demographic groups, to a variety of neutral models, where the species have the same demographic parameters.Upon exploring the estimated range of possible parameterizations of recruitment (a difficult‐to‐measure parameter), we identify several parameterizations where differences among groups along the growth‐survival and stature‐recruitment trade‐off axes facilitate long‐term coexistence. We find that gap disturbances are essential for these results, indicating that it is the differences in the subsequent competition for light through time that provide the opportunity for stabilizing niche differentiation. Additionally, the parameterizations that generate stable coexistence display successional negative density dependence and realistic within‐patch post‐disturbance forest dynamics.Synthesis. This model‐data integration exercise indicates that small‐scale disturbances and subsequent competition for light may be significant forces for stable diversity maintenance of demographic groups along the growth–survival and stature–recruitment trade‐off axes in a neotropical forest. This result, however, holds only for a subset of the empirically reasonable recruitment parameters, indicating the importance of improving the understanding of recruitment and its demographic trade‐offs for understanding demographic strategy coexistence.
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Disentangling ecologically equivalent from neutral species: The mechanisms of population regulation matter
Abstract The neutral theory of biodiversity explored the structure of a community of ecologically equivalent species. Such species are expected to display community drift dynamics analogous to neutral alleles undergoing genetic drift. While entire communities of species are not ecologically equivalent, recent field experiments have documented the existence of guilds of such neutral species embedded in real food webs.What demographic outcomes of the interactions within and between species in these guilds are expected to produce ecological drift versus coexistence remains unclear. To address this issue, and guide empirical testing, we consider models of a guild of ecologically equivalent competitors feeding on a single resource to explore when community drift should manifest.We show that community drift dynamics only emerge when the density‐dependent effects of each species on itself are identical to its density‐dependent effects on every other guild member. In contrast, if each guild member directly limits itself more than it limits the abundance of other guild members, all species in the guild are coexisting, even though they all are ecologically equivalent with respect to their interactions with species outside the guild (i.e. resources, predators, mutualists). Hence, considering only interspecific ecological differences generating density dependence, and not fully accounting for the preponderance of mechanisms causing intraspecific density dependence, will provide an incomplete picture for segregating between neutrality and coexistence. We also identify critical experiments necessary to disentangle guilds of ecologically equivalent species from those experiencing ecological drift, as well as provide an overview of ways of incorporating a mechanistic basis into studies of species coexistence and neutrality.Identifying these characteristics, and the mechanistic basis underlying community structure, is not merely an exercise in clarifying the semantics of coexistence and neutral theories, but rather reflects key differences that must exist among community members in order to determine how and why communities are structured.
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- Award ID(s):
- 1748945
- PAR ID:
- 10460747
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Journal of Animal Ecology
- Volume:
- 88
- Issue:
- 11
- ISSN:
- 0021-8790
- Page Range / eLocation ID:
- p. 1755-1765
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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