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

Abstract

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.Abstract in Thai is available with online material.

Small Pteropodid Bats are Important Pollinators of Durian in Terengganu, Malaysia

“…are highly reliable food sources for bat species to forage at as compared to Durio spp. which showed the big-bang flowering strategy (Stewart & Dudash, 2018), in which plants flower massively only for a few days in a year (Gentry, 1974). The same finding was also reported by Thavry et al (2017), in which pollen grains of Sonneratia spp.…”

“…Musa spp. are steady-state plants (Stewart & Dudash, 2018), which bear a few flowers every day for several months (Heithaus et al, 1975), hence providing enough food resources for bats over extended periods. Sonneratia spp.…”

“…were not reported in our study for all bat species. During the peak flowering events of bigbang plants, pteropodid bats were found to switch their diets and utilise both the bigbang and steady-state plants (Bumrungsri et al, 2013;Stewart & Dudash, 2018;Thavry et al, 2017). The six unidentified pollen Mohamed (2014) in the mangroves of Setiu, Terengganu.…”

What shapes the trophic niche of European plethodontid salamanders?

“…However, species trophic niche is generally characterised by a certain degree of intrinsic plasticity, allowing diet shifts when competition occurs, but also to cope with temporal and local variability of the available resources [ 8 , 14 ]. Indeed, beside the intrinsic characteristics of individuals, the realised trophic niche is strongly related to the ability to persist in an environment where food resources vary in space and time [ 15 ], and thus to the capacity to obtain from different subsets of resources the complex combination of elements needed to fulfil physiological and metabolic requirements [ 16 – 18 ]. In wide-ranging species, it is likely that populations forage in environments differing in terms of resource availability and trophic networks [ 16 , 19 ].…”

The Critical Importance of Old World Fruit Bats for Healthy Ecosystems and Economies

“…For this reason, leaf consumption is considered to be more widespread than reported; because of its relatively high protein content, the "juice" of the leaves is the only part swallowed by the bats (Kunz and Diaz, 1995;Nelson et al, 2000b). Also, some pteropodid genera such as Cynopterus, Megaerops, and Pteropus have been recognised as being frugi-nectarivorous (Stewart et al, 2014;Aziz et al, 2017b;Stewart and Dudash, 2018); in one 28-month study, the most frequently occurring food item in Pteropus rufus faeces was Agave sisalana pollen, and many faecal samples were pure Agave pollen (Long and Racey, 2007). Further studies on frugivorous bats, employing a more holistic combination of methods over longer time periods, may reveal more diverse diets than currently recognised.…”