Bird and bat predation services in tropical forests and agroforestry landscapes.

Understanding distribution patterns and multitrophic interactions is critical for managing bat- and bird-mediated ecosystem services such as the suppression of pest and non-pest arthropods. Despite the ecological and economic importance of bats and birds in tropical forests, agroforestry systems, and agricultural systems mixed with natural forest, a systematic review of their impact is still missing. A growing number of bird and bat exclosure experiments has improved our knowledge allowing new conclusions regarding their roles in food webs and associated ecosystem services. Here, we review the distribution patterns of insectivorous birds and bats, their local and landscape drivers, and their effects on trophic cascades in tropical ecosystems. We report that for birds but not bats community composition and relative importance of functional groups changes conspicuously from forests to habitats including both agricultural areas and forests, here termed 'forest-agri' habitats, with reduced representation of insectivores in the latter. In contrast to previous theory regarding trophic cascade strength, we find that birds and bats reduce the density and biomass of arthropods in the tropics with effect sizes similar to those in temperate and boreal communities. The relative importance of birds versus bats in regulating pest abundances varies with season, geography and management. Birds and bats may even suppress tropical arthropod outbreaks, although positive effects on plant growth are not always reported. As both bats and birds are major agents of pest suppression, a better understanding of the local and landscape factors driving the variability of their impact is needed.

Bats initiate vital agroecological interactions in corn.

In agroecosystems worldwide, bats are voracious predators of crop pests and may provide services to farmers worth billions of U.S. dollars. However, such valuations make untested assumptions about the ecological effect of bats in agroecosystems. Specifically, estimates of the value of pest suppression services assume bats consume sufficient numbers of crop pests to affect impact pest reproduction and subsequent damage to crops. Corn is an essential crop for farmers, and is grown on more than 150 million hectares worldwide. Using large exclosures in corn fields, we show that bats exert sufficient pressure on crop pests to suppress larval densities and damage in this cosmopolitan crop. In addition, we show that bats suppress pest-associated fungal growth and mycotoxin in corn. We estimate the suppression of herbivory by insectivorous bats is worth more than 1 billion USD globally on this crop alone, and bats may further benefit farmers by indirectly suppressing pest-associated fungal growth and toxic compounds on corn. Bats face a variety of threats globally, but their relevance as predators of insects in ubiquitous corn-dominated landscapes underlines the economic and ecological importance of conserving biodiversity.