The Impact of Ants and Vertebrate Predators on Arthropods and Plants: A Meta-Analysis

The trophic interactions between plants, insect herbivores and their predators are complex and prone to trophic cascades. Theory predicts that predators increase plant biomass by feeding on herbivores. However, it remains unclear whether different types of predators regulate herbivores to the same degree, and how intraguild predation impacts these trophic interactions. Specifically, we lack a more comprehensive view of the effects of various groups of predators on a global scale. Here we report a meta-analysis of 486 experiments gathered from 157 publications reporting the effect of insectivorous vertebrates (birds and bats) and ants on richness and abundances of all arthropods; predatory (spiders, ants, others) and herbivorous (chewers and others) arthropods; and on plant damage. Generally, the absence of vertebrate predators led to the increase of predatory arthropods by 18%, herbivorous arthropods by 75%, and plant damage by 47%. In contrast, after the removal of ants, the increase in the abundances of other predatory arthropods did not compensate for the missing ants, herbivore arthropods increased their abundances by 53%, and plant damage increased by 146%. Ant exclosure effects were more pronounced at lower elevations and latitudes, whereas vertebrate exclosure did not show any clear geographical patterns. Furthermore, exclusion effects remained robust across various plant growth forms and habitat types, with neither precipitation nor NDVI significantly influencing most observed outcomes. We found vertebrate insectivores to be the more dominant predators of arthropods, but we detected that the strength of their trophic cascades was weakened by intraguild predation. On the other hand, we found that although ants were relatively less dominant as predators, and their influence was detectable only in the most productive sites, the effect of the trophic cascades they caused on plants was stronger than that of vertebrate insectivores.