Foraging strategies of generalist and specialist Old World nectar bats in response to temporally variable floral resources

Abstract

© 2017 The Association for Tropical Biology and Conservation Foraging theory predicts that generalist foragers should switch resources more readily, while specialist foragers should remain constant to preferred food resources. Plant-pollinator interactions provide a convenient system to test such predictions because floral resources are often temporally patchy, thus requiring long-lived pollinators to switch resources seasonally. Furthermore, flowering phenologies range from ‘steady-state’ (low-rewarding but highly reliable) to ‘big-bang’ (high-rewarding but ephemeral) plant species. We assessed how nectarivorous Old World bats respond to this temporally variable floral environment by examining their diets throughout the year. Over 15 months of fieldwork in southern Thailand, we simultaneously: (1) recorded the flowering phenologies of six bat-pollinated plant taxa; and (2) assessed the diets of seven common flower-visiting bat species. As predicted, the generalist nectarivore (Eonycteris spelaea) frequently switched diets and utilized both big-bang and steady-state resources, while the specialist nectarivores (Macroglossus minimus and M. sobrinus) foraged on one or two steady-state plant species year-round. Our results suggest that larger and faster bat species are able to fly longer distances in search of big-bang resources, while smaller bat species rely on highly predictable food resources. This study supports the theory that generalist foragers have flexible diets, while specialist species restrict foraging to preferred floral resources even when other floral resources are more abundant. Moreover, these findings demonstrate how plant flowering phenology and pollinator diet breadth can shape the frequency and constancy of pollinator visits; we further discuss how such interactions can influence the potential extent of gene flow within a patchy floral environment.