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Functional volumes, niche packing and species richness: biogeographic legacies in the Congo Basin.

ABSTRACT: Understanding the determinants of species coexistence in complex and species-rich communities is a fundamental goal of ecology. Patterns of species coexistence depend on how biotic interactions and environmental filtering act over ecological and evolutionary time scales. Climatic fluctuations in lowland rainforests of the Congo Basin led to the number of vertebrate species being significantly lower in central compared with northern ecoregions of the Basin. We used null models to assess whether climatic variations affected the community assembly of shrews. A consistent limit to functional similarity of species was not related to species richness. Rather, species richness is constrained by environmental factors, and these constraints are stronger in the central lowland forests of the Congo Basin. By constraining species geographic distributions, historical effects of rainforest refugia arising from climatic fluctuations may affect contemporary species composition of local shrew communities. The Congo River represents a vicariance event that led to allopatric speciation of shrews and continues to represent a barrier to dispersal. Ultimately, the historical effects of this barrier have led to differences in the functional volume of shrew communities in northern and central ecoregions. We suggest that the analyses of community assembly can be used to identify Holocene refugia in the Congo Basin.

SUBMITTER: Van de Perre F

PROVIDER: S-EPMC7137932 | biostudies-literature | 2020 Mar

REPOSITORIES: biostudies-literature

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Functional volumes, niche packing and species richness: biogeographic legacies in the Congo Basin.

Van de Perre Frederik F Willig Michael R MR Presley Steven J SJ Mukinzi Itoka Jean-Claude IJ Gambalemoke Mbalitini Sylvestre MS Leirs Herwig H Verheyen Erik E

Royal Society open science 20200304 3

Understanding the determinants of species coexistence in complex and species-rich communities is a fundamental goal of ecology. Patterns of species coexistence depend on how biotic interactions and environmental filtering act over ecological and evolutionary time scales. Climatic fluctuations in lowland rainforests of the Congo Basin led to the number of vertebrate species being significantly lower in central compared with northern ecoregions of the Basin. We used null models to assess whether c ...[more]

PMID: 32269793

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Project description:BackgroundXylogenesis is synchronous among trees in regions with a distinct growing season, leading to a forest-wide time lag between growth and carbon uptake. In contrast, little is known about interspecific or even intraspecific variability of xylogenesis in tropical forests. Yet an understanding of xylogenesis patterns is key to successfully combine bottom-up (e.g., from permanent forest inventory plots) and top-down (e.g., from eddy covariance flux towers) carbon flux estimates.MethodsHere, we monitor xylogenesis development of 18 trees belonging to 6 abundant species during 8 weeks at the onset of the rainy season from March to April 2022 in a semideciduous rainforest in the Yangambi reserve (central Democratic Republic of the Congo). For each tree, the weekly cambial state (dormant or active) was determined by epifluorescence microscopy.ResultsWe find interspecific variability in the cambial phenology, with two species showing predominant cambial dormancy and two species showing predominant cambial activity during the monitoring period. We also find intraspecific variability in two species where individuals either display cambial dormancy or cambial activity. All trees kept > 60% of their leaves throughout the dry season and the monitoring period, suggesting a weak relationship between the phenology of the cambial and foliar. Our results suggest that individual trees in Yangambi asynchronously activate their cambial growth throughout the year, regardless of leaf phenology or seasonal rainfall.ConclusionThese results are consistent with global analysis of gross primary productivity estimates from eddy covariance flux towers, showing that tropical biomes lack a synchronous dormant period. However, a longer-term monitoring experiment, including more species, is necessary to confirm this for the Congo Basin. As Yangambi is equipped with facilities for microscopic wood analysis, a network of inventory plots and a flux tower, further research in this site will reveal how xylogenesis patterns drive annual variability in carbon fluxes and how ground-based and top-down measurements can be combined for robust upscaling analysis of Congo basin carbon budgets.

Project description:It has often been suggested that the productivity of an ecosystem affects the number of species that it can support. Despite decades of study, the nature, extent, and underlying mechanisms of this relationship are unclear. One suggested mechanism is the "more individuals" hypothesis (MIH). This proposes that productivity controls the number of individuals in the ecosystem, and that more individuals can be divided into a greater number of species before their population size is sufficiently small for each to be at substantial risk of extinction. Here, we test this hypothesis using REvoSim: an individual-based eco-evolutionary system that simulates the evolution and speciation of populations over geological time, allowing phenomena occurring over timescales that cannot be easily observed in the real world to be evaluated. The individual-based nature of this system allows us to remove assumptions about the nature of speciation and extinction that previous models have had to make. Many of the predictions of the MIH are supported in our simulations: Rare species are more likely to undergo extinction than common species, and species richness scales with productivity. However, we also find support for relationships that contradict the predictions of the strict MIH: species population size scales with productivity, and species extinction risk is better predicted by relative than absolute species population size, apparently due to increased competition when total community abundance is higher. Furthermore, we show that the scaling of species richness with productivity depends upon the ability of species to partition niche space. Consequently, we suggest that the MIH is applicable only to ecosystems in which niche partitioning has not been halted by species saturation. Some hypotheses regarding patterns of biodiversity implicitly or explicitly overlook niche theory in favor of neutral explanations, as has historically been the case with the MIH. Our simulations demonstrate that niche theory exerts a control on the applicability of the MIH and thus needs to be accounted for in macroecology.

Dataset Information

Functional volumes, niche packing and species richness: biogeographic legacies in the Congo Basin.

Publications

Functional volumes, niche packing and species richness: biogeographic legacies in the Congo Basin.

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