Global patterns in the structure and robustness of plant-herbivore networks

Abstract

My goal is to investigate global patterns in the structure of interaction networks of insect her- bivores and their host plants. Specifically, I seek to determine whether intensification of land use and the dominance of exotic host plant species influence the structure and robustness (i.e., resistance to co- extinctions) of interaction networks of insect herbivores and host plants. I also ask whether latitude has an influence on the structure and robustness of these interactions. I compiled 90 local plant-herbivore networks distributed worldwide, spanning different taxonomic groups of plants and insects and several herbivore guilds. My results showed that intensification of land use was associated with dominance of exotic plant species and can impoverish the species richness and taxonomic diversity of insect herbi- vores in the networks. Moreover, land use intensification surprisingly increases network specialization by decreasing connectance and nestedness, and increases modularity; while the increase in the propor- tion of exotic hosts had opposite effects. These changes in the network structure may be due to the pro- portionately greater loss of generalist herbivores relative to specialists. Land use intensification also de- creases the robustness of plant-herbivore networks, while the proportion of exotic host plant species increases, which is an intriguing result that contradicts previous studies. Controlling for anthropic effects that can act on the networks, my results show that plant–herbivore networks are structured inde- pendently of latitude, suggesting that the factors that influence the interactions between host plants and insect herbivores are latitudinally invariant