Abstract
The high tree diversity of subtropical forests is linked to the biodiversity of other trophic levels. Disentangling the effects of tree species richness and composition, forest age, and stand structure on higher trophic levels in a forest landscape is important for understanding the factors that promote biodiversity and ecosystem functioning. Using a plot network spanning gradients of tree diversity and secondary succession in subtropical forest, we tested the effects of tree community characteristics (species richness and composition) and forest succession (stand age) on arthropod community characteristics (morphotype diversity, abundance and composition) of four arthropod functional groups. We posit that these gradients differentially affect the arthropod functional groups, which mediates the diversity, composition, and abundance of arthropods in subtropical forests. We found that herbivore richness was positively related to tree species richness. Furthermore, the composition of herbivore communities was associated with tree species composition. In contrast, detritivore richness and composition was associated with stand age instead of tree diversity. Predator and pollinator richness and abundance were not strongly related to either gradient, although positive trends with tree species richness were found for predators. The weaker effect of tree diversity on predators suggests a cascading diversity effect from trees to herbivores to predators. Our results suggest that arthropod diversity in a subtropical forest reflects the net outcome of complex interactions among variables associated with tree diversity and stand age. Despite this complexity, there are clear linkages between the overall richness and composition of tree and arthropod communities, in particular herbivores, demonstrating that these trophic levels directly impact each other.
Highlights
Plant diversity is important for maintaining ecosystem functioning and for supporting the diversity of other trophic levels (Balvanera et al, 2006; Hooper et al, 2005; Isbell et al, 2015; Siemann, Tilman, Haarstad, & Ritchie, 1998)
Disentangling the effects of tree species richness and composition, forest age, and stand structure on higher trophic levels in a forest landscape is important for understanding the factors that promote biodiversity and ecosystem functioning
Using a plot network spanning gradients of tree diversity and secondary succession in subtropical forest, we tested the effects of tree community characteristics and forest succession on arthropod community characteristics of four arthropod functional groups
Summary
Plant diversity is important for maintaining ecosystem functioning and for supporting the diversity of other trophic levels (Balvanera et al, 2006; Hooper et al, 2005; Isbell et al, 2015; Siemann, Tilman, Haarstad, & Ritchie, 1998). Fallen or standing dead plant material provides space for breeding and larval development regardless of the surrounding living tree species (Irmler, Heller, & Warning, 1996; Jacobs, Spence, & Langor, 2007; Schiegg, 2000) Combined, these variables make forests distinct from grasslands, which may alter plant–arthropod relationships. Stand age, which correlates with functional traits, environmental conditions, and the quantity of woody debris (Chen et al, 1999; Jacobs et al, 2007; Raich, 1989), may mediate arthropod diversity across the landscape more than tree species diversity These factors of stand age, heterogeneity in spatial structure and environmental conditions, may supersede the effects of tree diversity on arthropod diversity in forests. Given the host specificity of some arthropods, we hypothesized that the species compositions of tree and arthropod communities should show different associations depending on the arthropod functional group considered (as outlined above)
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