Effects of land-use intensification on nectar resources, bird assemblages and bird-flower interaction networks in the Western Ghats, India

Abstract

1.Agricultural expansion is a major driver of tropical forest loss globally, making it critical to determine factors that maintain key plant-animal interactions, such as nectarivory, in human-dominated landscapes. In the Paleotropics, which is experiencing rapid expansion of tree crop plantations, few studies have compared floral and nectar-feeding bird communities, their interactions, and network organisation along a tree crop intensification gradient. In a cashew agriculture-forest matrix of the northern Western Ghats of India, we compared forests, cashew agroforests, and cashew monocultures to assess, 1) the abundance, diversity, and composition of flowers and nectar-feeding birds, 2) diversity of bird-flower interactions, and 3) network organisation. Floral abundance declined most sharply in monocultures, followed by agroforests. The abundance and diversity of nectar-feeding birds peaked in agroforests. Forests had the highest floral diversity and bird-flower interactions. Nectivore community composition differed across land-use types, with agroforests harbouring both forest specialists and open-habitat species typically found in monocultures. We found that sunbirds dominated plant-flower interactions across land-use types. After rarefaction (to control for differences in network size), agroforests and monocultures showed higher connectance, specialisation, and modularity than the forest network. Our results suggest that plantations that retain native trees (agroforests) can partially offset the alterations caused in floral resource availability and nectar-feeding bird communities by cashew cultivation. Planting bird-pollinated native tree species along orchard edges can make cashew farming more suitable for nectar-feeding birds, and has the potential to benefit cashew production by attracting avian pollinators.