Aim Tropical forests store 25% of global carbon and harbour 96% of the world's tree species, but it is not clear whether this high biodiversity matters for carbon storage. Few studies have teased apart the relative importance of forest attributes and environmental drivers for ecosystem functioning, and no such study exists for the tropics. Location Neotropics. Methods We relate aboveground biomass (AGB) to forest attributes (diversity and structure) and environmental drivers (annual rainfall and soil fertility) using data from 144,000 trees, 2050 forest plots and 59 forest sites. The sites span the complete latitudinal and climatic gradients in the lowland Neotropics, with rainfall ranging from 750 to 4350 mm year−1. Relationships were analysed within forest sites at scales of 0.1 and 1 ha and across forest sites along large‐scale environmental gradients. We used a structural equation model to test the hypothesis that species richness, forest structural attributes and environmental drivers have independent, positive effects on AGB. Results Across sites, AGB was most strongly driven by rainfall, followed by average tree stem diameter and rarefied species richness, which all had positive effects on AGB. Our indicator of soil fertility (cation exchange capacity) had a negligible effect on AGB, perhaps because we used a global soil database. Taxonomic forest attributes (i.e. species richness, rarefied richness and Shannon diversity) had the strongest relationships with AGB at small spatial scales, where an additional species can still make a difference in terms of niche complementarity, while structural forest attributes (i.e. tree density and tree size) had strong relationships with AGB at all spatial scales. Main conclusions Biodiversity has an independent, positive effect on AGB and ecosystem functioning, not only in relatively simple temperate systems but also in structurally complex hyperdiverse tropical forests. Biodiversity conservation should therefore be a key component of the UN Reducing Emissions from Deforestation and Degradation strategy.
JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Ecological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Ecological Monographs.Abstract. The North Pacific central gyre is a large, monotonous, and geologically old system. It (and other such gyres) is probably the nearest oceanic equivalent to an essentially self-regulating, climax ecosystem. We have taken a series of replicated, vertically stratified net tows for macrozooplankton and have replicated measures of a number of habitat variables.Copepods are the most numerous members of the macrozooplankton fraction of the community of the central gyre. It is likely that they are also the largest part of the biomass. There are at least 125 species regularly present and although we do not know what many of them eat, certain species can almost certainly be identified as herbivores or carnivores, and others as omnivores. We show that some species are significantly more frequent parts of each other's biotic environment than other species. These recurrent groups of species tend to occupy different depth zones. The members of the groups show strong concordance of abundance at the depth of high group coherence. Thus there is a dividing up of the water column and a clear tendency for vertical spatial structure in the copepod fauna. Within groups there is a significant constancy of dominance at the group's preferred depth over time. Thus there appears to be a large amount of species structure as well as spatial structure. A highly regulated species equilibrium is implied. There are congeners occurring within the same recurrent groups.The physical and biotic environment of each group differs with respect to both concentration (e.g., chlorophyll a) or magnitude (e.g., temperature) of habitat variables and with respect to the spatial variability of these. Our most diverse group tends to occupy a depth zone ranking high in primary productivity but does not have the greatest total environmental "richness" or greatest or least heterogeneity, and this seems contrary to what some current community theory predicts. Our evidence indicates that within groups many similar species coexist spatially and temporally.We speculate about the relative roles of competition and predation in influencing the structure we see. Aspects of modern community theory, based on competitive equilibrium, seem inadequate to explain our results. Predator regulation of structure seems a more likely explanation. However, existing information indicates a lack of sufficient specialization of what we believe to be the main predators on copepods to account for the observed constancy of copepod species structure.We suggest that a more intensive study of the role of predation is in order.
1-bstract . . Disturbance-pe~urbation, dispersal-reaction, and contemporaneous disequilibrium are Simi~a: theon~s used ~o explam the maintenance of species diversity in communities. These theories explicitly pre.dict that m patches, on certain time-space scales, there should be substantial shifts in the ?rder of s~ecies domi~ance. There is good evidence that these theories may explain species coexistence m terrestnal and manne systems of sessile organisms. We have tested this set of theories in a mobile pelagic system by examining the order of dominance of copepod species in samples separated in time a~d space, collected from "='30 min to 16 yr apart, and from hundreds of metres to thousands of k.ilometr~s ~pai_t. We cou~d not detect significant changes among the samples in rank order or in p~rcent simrlanty of spe~Ies abundance on any time scale, or on any space scale up to "='800 km, either when all 175 species or when only the 30 most abundant were considered. There was smallscale, mesoscale, seasonal, and interannual heterogeneity in physical properties during the time we ~ade ~ur measurements. Although the theories are satisfactory explanations of diversity maintenance m .sessile syst~m~, our results fail to validate them in our mobile pelagic system. Because there were episodes of significant physical variability and because of the long-term species equilibrium and constanc~ of dominance, we believe our highly diverse community to be resilient and robust, rather than fragrle_. Th~ regulatory forces are strong and almost certainly biological, rather than physical, but we cannot Identify them.
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