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Changes in tree community structure in defaunated forests are not driven only by dispersal limitation.

ABSTRACT: Bushmeat hunting has reduced population sizes of large frugivorous vertebrates throughout the tropics, thereby reducing the dispersal of seeds. This is believed to affect tree population dynamics, and therefore community composition, because the seed dispersal of large-seeded trees depends upon large-bodied vertebrates.We report on a long-running study of the effect of defaunation on a tropical tree community. In three censuses over 11 years, we compared sapling recruitment between a hunted and a nonhunted site, which are nearby and comparable to one another, to determine the extent to which species composition has changed through time following defaunation. We expected to find a reduced abundance of tree species that rely on large frugivores for dispersal at the hunted site and altered community structure as a consequence.Although community composition at the hunted site diverged from that at the nonhunted site, the changes were independent of dispersal syndrome, with no trend toward a decline in species that are dispersed by large, hunted vertebrates. Moreover, the loss of large-bodied dispersers did not generate the changes in tree community composition that we hypothesized. Some species presumed to rely on large-bodied frugivores for dispersal are effectively recruiting despite the absence of their dispersers.Synthesis: The presumption that forests depleted of large-bodied dispersers will experience rapid, directional compositional change is not fully supported by our results. Altered species composition in the sapling layer at the hunted site, however, indicates that defaunation may be connected with changes to the tree community, but that the nature of these changes is not unidirectional as previously assumed. It remains difficult to predict how defaunation will affect tree community composition without a deeper understanding of the driving mechanisms at play.

SUBMITTER: Hazelwood K

PROVIDER: S-EPMC7140993 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:AimThe mechanisms underlying the maintenance of biodiversity remain to be elucidated. Taxonomic diversity alone remains an unresolved issue, especially in terms of the mechanisms of species co-existence. We hypothesized that phylogenetic information could help to elucidate the mechanism of community assembly and the services and functions of ecosystems. The aim of this study was to explore the mechanisms driving floral diversity in subtropical forests and evaluate the relative effects of these mechanisms on diversity variation, by combining taxonomic and phylogenetic information.LocationWe examined 35 1-ha tree stem-mapped plots across eight national nature reserves in Guangxi Zhuang Autonomous Region, China.TaxonTrees.MethodsWe quantified the taxonomic and phylogenetic β-diversity between each pair of plots using the (abundance-based) Rao's quadratic entropy and the (incidence-based) Sørensen dissimilarity indices. Using a null model approach, we compared the observed β-diversity with the expected diversity at random and calculated the standard effect size of the observed β-diversity deviation. Furthermore, we used distance-based redundancy analysis (dbRDA) to partition the variations in taxonomic and phylogenetic observed β-diversity and β-deviation into four parts to assess the environmental and spatial effects.ResultsThe taxonomic β-deviation was related to and higher than the phylogenetic β-deviation (r = .74). This indicated that the species turnover between pairwise plots was mainly the turnover of closely related species. Higher taxonomic and phylogenetic β-deviation were mainly concentrated in the pairwise karst and nonkarst forest plots, indicating that the species in karst forests and nonkarst forests were predominantly from distantly related clades. A large proportions of the variation in taxonomic and phylogenetic β-deviation were explained by the joint effect of environmental and spatial variables, while the contribution of environmental variables was greater than that of spatial variables, probably owing to the influence of the sampling scale dependence, integrality of sampling size and species pool, and the unique climatic and geomorphic characteristics.Main conclusionsOur study highlights the importance of phylogeny in biodiversity research. The incorporation of taxonomic and phylogenetic information provides a perspective to explore potential underlying mechanisms that have shaped species assemblages and phylogenetic patterns in biodiversity hotspots.

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Changes in tree community structure in defaunated forests are not driven only by dispersal limitation.

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