The role of bats in pollination networks is influenced by landscape structure

Abstract

Nectarivorous bats are essential to the functioning to both agricultural and natural ecosystems in the tropics, yet these pollinator communities are declining as a result of habitat loss and hunting. Temporal variation and habitat changes lead to both roost and floral resource loss, which is the major driver of bat pollination decline. This study aims to determine how the bat pollination networks in mixed-fruit orchards are affected by flowering seasons and different land-use types. We estimated the abundance of nectarivorous and frugivorous bats using video observations to determine floral visitation rates from 18 mixed-fruit orchards in Southern Thailand. Pollination networks were then created based on network level indices (number of interactions and specialisation) and species level indices (strength−dependence of plant on each bat, and generalised degree−the number of interactions per species divided by the number of possible interacting partners) for each bat group at each orchard. We found that specialisation in low season networks was higher than those from peak season. Nectarivorous bats showed higher levels of normalised degree, and strength than frugivorous bats. The normalised degree of frugivorous bats, but not nectarivorous bats increased with the proportion of urban area within 30 km radius. The strength of bats was positively correlated with the proportion of plantations within a 2 km radius. Our results show that both bat guilds are strongly integrated into pollination networks where they occur and provide evidence that increasing the area of plantation and urban alters the degree of generalization of pollinators which can significantly impact pollination success of plants.