Global effects of land use intensity on the impoverishment of insect herbivore assemblages

The modification of pristine wildlife habitats by land use is a worldwide cause of species extinction, as most native species cannot persist at high levels of human land use intensity. In this study, we gathered 90 lists of local interactions between herbivorous insects and their host plants to investigate the effects of land use intensity on the species richness and taxonomic diversity of insect herbivore assemblages. The effect of land use intensity on these insect herbivore assemblages was assessed using path analysis that controlled for differences in host plant richness, sampling effort, and the taxonomic range of plants and herbivores. We included the proportion of exotic host plant species in the path models to evaluate the extent to which the effect of land use intensity is mediated by the replacement of native with exotic host plants. Overall, we found negative effects of land use intensity on the species richness and taxonomic diversity of the insect herbivore assemblages, and these effects were mediated by an increase in the proportion of exotic host plant species. Since the effect of host plant richness was controlled for, our findings imply that the impoverishment of insect herbivore assemblages due to human land use is even greater than the loss of their host plant. A likely implication of such reduction in the species richness and taxonomic diversity of the insect herbivore assemblages is the accelerated loss of specialized plant-herbivore interactions, thus favoring interactions among generalist species and the biotic homogenization of species interactions across human-disturbed habitats.