The Roles of Bats as Pollinators

Introduction

The floral biology of angiosperms is dominated by biotic pollination, especially in the tropics where up to 99 % of species in some habitats are animal-pollinated. Insects account for most of these interactions, and pollination by vertebrates is relatively uncommon. In a variety of lowland tropical forests, for example, pollination by birds and bats occurs in only 3-11 % of species. Overall, bird pollination is more common than bat pollination both locally and globally and occurs in nearly 500 genera of plants; bat pollination occurs in approximately 250 genera(Jones 2243-2255).

At least six families or subfamilies of tropical and subtropical birds are strongly adapted for nectar-feeding. By comparison, only two families of tropical bats contain flower-visitors, and morphologically specialized nectar-feeders are in the minority in both of these families.

Compared with most insects, flower-visiting birds and bats are much larger, have greater energy requirements because of their endothermic metabolism, can carry larger pollen loads, are longer-lived and may be cognitively more sophisticated. Despite the potentially greater costs to plants to attract and reward these larger pollinators, the benefits of vertebrate pollination can be substantial, especially in habitats where insect activity is limited by harsh climatic conditions. Positive aspects of vertebrate pollination include potentially more reliable visitation and the ability to carry large pollen loads considerable distances. Compared with many insects, birds and bats are excellent in promoting outcrossing, and as a result, most vertebrate-pollinated plants have hermaphroditic breeding systems; very few are dioecious.

Aim and objective

This review focuses on the evolution of bat pollination in tropical and subtropical angiosperms. This is to address two fundamental evolutionary questions: what are the causes and what are the consequences of the evolution of this pollination method? Ancillary questions include: (1) how many times during angiosperm history and in what places has bat pollination evolved? (2) What are the phylogenetic consequences of bat pollination? How many higher level taxa (genera, tribes, subfamilies, families, etc.) have evolved in association with bat pollination? And (3) by what phylogenetic routes has bat pollination evolved? How often have bat-pollinated flowers evolved from insect-, bird-, or non-volant mammal-pollinated flowers? Before examining these questions, we provide a brief overview of flower-visiting bats and the basic characteristics of bat pollination. We then examine this pollination mode from a phylogenetic and biogeographical perspective for both plants and bats. Finally, we discuss the various evolutionary routes that have resulted in bat pollination.

Flower-Visiting Bats

Only two of the 18 currently recognized families of bats contain species that are morphologically specialized for nectar-feeding. We discount the Mystacinidae, which is endemic to New Zealand and contains one genus, Mystacina, that is known to visit terrestrial flowers, as being highly evolved for flower-visiting.

Insectivory is by far the most common feeding mode in bats and is undoubtedly the ancestral feeding mode in the order Chiroptera. The two families that contain nectar-feeding bats (hereafter 'nectar bats') include Pteropodidae (Old World flying foxes and their relatives), which occurs throughout tropical and subtropical regions of ...