Tropical forest loss and its multitrophic effects on insect herbivory

Forest loss threatens biodiversity, but its potential effects on multitrophic ecological interactions are poorly understood. Insect herbivory depends on complex bottomup (e.g., resource availability and plant antiherbivore defenses) and topdown forces (e.g., abundance of predators and herbivorous), but its determinants in humanaltered tropical landscapes are largely unknown. Using structural equation models, we assessed the direct and indirect effects of forest loss on insect herbivory in 40 landscapes (115 ha each) from two regions with contrasting landuse change trajectories in the Brazilian Atlantic rainforest. We considered landscape forest cover as an exogenous predictor and (1) forest structure, (2) abundance of predators (birds and arthropods), and (3) abundance of herbivorous arthropods as endogenous predictors of insect leaf damage. From 12 predicted pathways, 11 were significant and showed that (1) leaf damage increases with forest loss (direct effect); (2) leaf damage increases with forest loss through the simplification of vegetation structure and its associated dominance of herbivorous insects (indirect effect); and further demonstrate (3) a lack of topdown control of herbivores by predators (birds and arthropods). We conclude that forest loss favors insect herbivory by undermining the bottomup control (presumably reduced plant antiherbivore defense mechanisms) in forests dominated by fastgrowing pioneer plant species, and by improving the conditions required for herbivores proliferation.

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DOI:

https://doi.org/10.1002/ecy.1592

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