Tree diversity promotes functional dissimilarity and maintains functional richness despite species loss in predator assemblages

Created at: 2012-12-05

Initial title: Tree diversity promotes functional dissimilarity among species, but not overall functional richness of predator assemblages

Envisaged journal: Oecologia

Envisaged date: 2013-02-24


The effects of species loss on ecosystems depend on the functional characteristics of the species, i.e. the functional diversity, in a community. However, how functional diversity is impacted by environmental changes in natural ecosystems is only poorly understood. This particularly applies to higher trophic levels, which play a crucial role in regulating ecosystem processes and might be strongly affected by human-induced environmental changes. We analyzed how functional richness, evenness, and divergence of important generalist predators—epigeic spiders—are affected by changes in woody plant species richness, plant phylogenetic diversity, and stand age in highly diverse subtropical forests in China. Functional evenness and divergence of spiders increased with woody plant richness and stand age, whereas functional richness was not affected. Plant phylogenetic diversity had no effect on spider functional diversity. The results contrast with patterns in spider species richness, which was negatively related to plant richness in the studied forests, and suggest that functional redundancy among spiders decreased with increasing woody plant richness. Moreover, higher functional dissimilarity within spider assemblages with increasing woody plant richness indicates that the relative distribution of abundant predators in functional trait space has a strong potential to impact on ecological functions, independent of patterns in species richness or the overall available trait space. Regarding the generally hypothesized promoting effects of plant diversity on predators, our results are only supportive in the context of functional diversity (and here only for trait distributions within the overall functional trait space, and not for the size of this space), and not for patterns in species richness. Explicitly considering the functional diversity and its relationship with species richness is thus crucial for a better understanding of how predator assemblages can impact on ecosystem functions in such highly diverse, natural ecosystems.

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Andreas Schuldt Thorsten Assmann Helge Bruelheide, Prof. Walter Durka Stefan Michalski Oliver Purschke Karin Nadrowski Sabine Both Alexandra Erfmeier Martin Böhnke

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