Mechanisms proposed to explain the maintenance of species diversity within ecological communities of sessile organisms include niche differentiation mediated by competitive trade-offs, frequency dependence resulting from species-specific pests, recruitment limitation due to local dispersal, and a speciationextinction dynamic equilibrium mediated by stochasticity (drift). While each of these processes, and more, have been shown to act in particular communities, much remains to be learned about their relative importance in shaping community-level patterns. We used a spatially-explicit, individual-based model to assess the effects of each of these processes on species richness, relative abundance, and spatial patterns such as the species-area curve. Our model communities had an order-of-magnitude more individuals than any previous such study, and we also developed a finite-size scaling analysis to infer the large-scale properties of these systems in order to establish the generality of our conclusions across system sizes. As expected, each mechanism can promote diversity. We found some qualitative differences in community patterns across communities in which different combinations of these mechanisms operate. Species-area curves follow a power law with short-range dispersal and a logarithmic law with global dispersal. Relativeabundance distributions are more even for systems with competitive differences and trade-offs than for those in which all species are competitively equivalent, and they are most even when frequency dependence (even if weak) is present. Overall, however, communities in which different processes operated showed surprisingly similar patterns, which suggests that the form of community-level patterns cannot in general be used to distinguish among mechanisms maintaining diversity there. Nevertheless, parameterization of models such as these from field data on the * Corresponding author. Present address: Laboratoire d'Ecologie Terrestre, Centre National de la Recherche Scientifique, UMR 5552, 13 avenue du Colonel Roche, F-31029 Toulouse cedex 4, France; e-mail: chave@cict.fr. † E-mail: helene@eno.princeton.edu. ‡ E-mail: slevin@eno.princeton.edu. strengths of the different mechanisms could yield insight into their relative roles in diversity maintenance in any given community.
Tree species in tropical rain forests exhibit a rich panoply of spatial patterns that beg ecological explanation. The analysis of tropical census data typically relies on spatial statistics, which quantify the average aggregation tendency of a species. In this article we develop a cluster-based approach that complements traditional spatial statistics in the exploration and analysis of ecological hypotheses for spatial pattern. We apply this technique to six study species within a fully mapped 50-ha forest census in peninsular Malaysia. For each species we identify the scale(s) of spatial aggregation and the corresponding tree clusters. We study the correlation between cluster locations and abiotic variables such as topography. We find that the distribution of cluster sizes exhibits equilibrium and nonequilibrium behavior depending on species life history. The distribution of tree diameters within clusters also varies according to species life history. At different spatial scales, we find evidence for both niche-based and dispersal-limited processes producing spatial pattern. Our methodology for identifying scales of aggregation and clusters is general; we discuss the method's applicability to spatial problems outside of tropical plant ecology.
The role of stochastic effects and seed dispersal limitations in maintaining the diversity of a tree community is investigated by means of a forest growth simulator called TROLL. This simulator makes it possible to investigate impacts on the spatial distribution and the extinction probability of plant species. I present the results of a two-species competition scenario. Coexistence is found to be possible for competitively dissimilar species, and the criterion for this coexistence is given analytically in the reaction-diffusion approximation. A higher frequency of tree falls implies a smaller extinction probability of least adapted species. The multispecies model is also investigated. A mathematical quantity-the persistence function-permits measurement of the ability of a species to out compete other species locally. This quantity is compared with the average time to extinction, and it is computed for the TROLL simulator. I interpret the shape of this function in light of available information on the persistence function in simple interacting particle systems. These results indicate an analogy between the dynamics of forest communities and a simple discrete and spatially explicit model, the voter model. The ecological implications of this analogy are discussed and are extended to species-rich communities.
Abstract-The system has operated in a trial mode for the past two years to assess its operational reliability. During this period two significant outages occurred. Modifications to the installation and to maintenance procedures to prevent their recurrence are described, and future plans for the operational use of the system are discussed.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2025 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.