Removing subordinate species in a biodiversity experiment to mimic observational field studies

Background:Positive effects of plant species richness on community biomass in biodiversity experiments are often stronger than those from observational field studies.This may be because experiments are initiated with randomly assembled species compositions whereas field communities have experienced filtering.Methods:We compared aboveground biomass production of randomly assembled communities of 2–16 species(controls)with experimentally filtered communities from which subordinate species were removed,resulting in removal communities of 1–8 species.Results:Removal communities had(1)12.6%higher biomass than control communities from which they were derived,that is,with double species richness and(2)32.0%higher biomass than control communities of equal richness.These differences were maintained along the richness gradient.The increased productivity of removal communities was paralleled by increased species evenness and complementarity.Conclusions:Result(1)indicates that subordinate species can reduce community biomass production,suggesting a possible explanation for why the most diverse field communities sometimes do not have the highest productivity.Result(2)suggests that if a community of S species has been derived by filtering from a pool of 2S randomly chosen species it is more productive than a community derived from a pool of S randomly chosen species without filtering.

Latitudinal and elevational patterns of phylogenetic structure in forest communities in China’s mountains

The phylogenetic structure incorporates both ecological and evolutionary processes to explain assembly of a local community.The "phylogenetic niche conservatism"(PNC) hypothesis suggests that distributions of species along environmental gradients reflect both ancestral traits and ecological fitness of individual species. The temperature is generally regarded to change in similar ways along both latitudinal and elevational gradients but with different historical contingence. Therefore, comparing the latitudinal and elevational patterns of phylogenetic structure of communities is of help to depict the effects of ecological and evolutionary processes in shaping the community assembly. In this study, we explored the latitudinal, elevational and climatic patterns of phylogenetic structure of 569 angiosperm tree communities from 38 mountains across China. We found a larger mean abundance-weighted net relatedness index(NRI) than the presence/absence-based NRI;and the NRI decreased when the species pool downscaled from the full pool to county-level pool. The mean family age and phylogenetic species evenness decreased with latitude, and increased with temperature of the coldest month and precipitation;whilst NRI increased with latitude, and decreased with mean temperature of the coldest month. In most mountains, NRI, mean family age and phylogenetic species evenness showed non-significant trends along the elevational gradient. Our results support the main predictions of PNC for the latitudinal gradient, i.e., species tend to be more phylogenetically related to each other and clades are younger in temperate environments,compared to those in tropical environments. We suggested that independent species pools and abundance should be incorporated in analysis to fully represent the phylogenetic structure of communities.