Woody plant phylogenetic diversity mediates bottom–up control of arthropod biomass in species-rich forests

Abstract

Global change is predicted to cause non-random species loss in plant communities, with consequences for ecosystem functioning. However, beyond the simple effects of plant species richness, little is known about how plant diversity and its loss influence higher trophic levels, which are crucial to the functioning of many species-rich ecosystems. We analyzed to what extent woody plant phylogenetic diversity and species richness contribute to explaining the biomass and abundance of herbivorous and predatory arthropods in a species-rich forest in subtropical China. The biomass and abundance of leaf-chewing herbivores, and the biomass dispersion of herbivores within plots, increased with woody plant phylogenetic diversity. Woody plant species richness had much weaker effects on arthropods, but interacted with plant phylogenetic diversity to negatively affect the ratio of predator to herbivore biomass. Overall, our results point to a strong bottom-up control of functionally important herbivores mediated particularly by plant phylogenetic diversity, but do not support the general expectation that top-down predator effects increase with plant diversity. The observed effects appear to be driven primarily by increasing resource diversity rather than diversity-dependent primary productivity, as the latter did not affect arthropods. The strong effects of plant phylogenetic diversity and the overall weaker effects of plant species richness show that the diversity-dependence of ecosystem processes and interactions across trophic levels can depend fundamentally on non-random species associations. This has important implications for the regulation of ecosystem functions via trophic interaction pathways and for the way species loss may impact these pathways in species-rich forests. Global change is predicted to cause non-random species loss in plant communities, with 23 consequences for ecosystem functioning. However, beyond the simple effects of plant species 24 richness, little is known about how plant diversity and its loss influence higher trophic levels, 25 which are crucial to the functioning of many species-rich ecosystems. We analyzed to what 26 extent woody plant phylogenetic diversity and species richness contribute to explaining the 27 biomass and abundance of herbivorous and predatory arthropods in a species-rich forest in 28 subtropical China. The biomass and abundance of leaf-chewing herbivores, and the biomass 29 dispersion of herbivores within plots, increased with woody plant phylogenetic diversity. 30Woody plant species richness had much weaker effects on arthropods, but interacted with 31 plant phylogenetic diversity to negatively affect the ratio of predator to herbivore biomass. 32Overall, our results point to a strong bottom-up control of functionally important herbivores 33 mediated particularly by plant phylogenetic diversity, but do not support the general 34 expectation that top-down predator effects increase with plant diversity. The observed effects 35 appear to be driven primarily by increa...

Belowground top-down and aboveground bottom-up effects structure multitrophic community relationships in a biodiverse forest

“…Our results conform with previous findings on diversity relationships among individual taxa in our study system as well as in others 9, 16, 34 . These findings emphasize the important role of plant communities in directly structuring community patterns not only of herbivores, but also of predators and parasitoids 35 , in the aboveground forest compartment.…”

“…The comparatively weak connections across trophic levels in the richness and diversity analyses (especially between plants and herbivores) deviate from the findings of a similarly comprehensive study 12 , which, however, was conducted in a much less complex, experimental grassland system and did not differentiate among groups of herbivores or predators. On the other hand, our results are consistent with those of previous studies on individual trophic groups in our study system, which found that many effects of woody plant species richness or diversity acted on higher trophic level abundance rather than on richness or diversity patterns 34, 53, 54 . Moreover, species richness relationships among plants, arthropods, and microorganisms in our studied forests were found to be highly non-linear across spatial scales 39 .…”

“…Epigeic spiders, centipedes, epigeic ants, weevils, isopods and diplopods were sampled with pitfall traps (4 traps per plot from March to September 2009 53 ). Beating of understory trees and shrubs was used to sample Lepidopteran larvae, arboreal spiders, and ants (25 plant individuals per plot on three sampling dates in 2011 and 2012 34 ). Cavity-nesting predatory wasps and the associated parasitic wasps were sampled with reed-filled trap nests (2 traps per plot from September 2011 to October 2012 63 ).…”

“…In mature forests, the influence of bottom-up effects of the producer level on higher trophic levels might therefore predominate over potential top-down effects of consumers on trees. Many studies have reported strong bottom-up, tree-controlled impacts on the diversity or composition of individual groups of organisms at higher trophic levels, both belowground 20, 33 and aboveground 34, 35 . However, whether bottom-up control predominates when it comes to the structuring of community associations across the multiple groups of organisms at multiple trophic levels in biodiverse forests remains poorly explored.…”

Early positive effects of tree species richness on herbivory in a large‐scale forest biodiversity experiment influence tree growth

“…Many grasshoppers have a relatively broad host plant spectrum (Bernays & Chapman ), and the same probably applies to dominant caterpillars in our study region (see Schuldt et al . ,b). Increases in the abundance (e.g.…”