Foraging Behaviour of Solitary Bees: Implications for Outcrossing of a Neotropical Forest Tree Species

Abstract

Most flowering plants of neotropical forests display adaptations for animal pollination (see references cited by Frankie, Baker & Opler (1974a) and by Frankie (1975, 1976)), but, since little information is available on the foraging behaviour of the animals involved, there has been considerable speculation as to whether widely spaced, conspecific plants in these forests are selfor cross-pollinated (Corner 1954; Baker 1959; Fedorov 1966; Ashton 1969; Bawa 1974). Bees constitute one of the major groups of visitors to a large proportion of tree species occurring in certain lowland forests (Janzen 1967; Frankie 1975). The potential for interplant movement of bees in Central America has been emphasized by Janzen (1971, 1974), who found that certain euglossine bees in Lowland Wet forests may forage over distances of several kilometres. Janzen has also suggested that members of other bee genera (e.g. Bombus, Centris, Ptiloglossa and Xylocopa) may forage over similar distances. Experimental studies on the nature of breeding systems of tree species in a Costa Rican Dry forest indicate that of the tested species (many of which are bee-pollinated), most have obligate outbreeding systems (Bawa 1974). Bawa's findings strongly imply that bees and other anthophilous animals effect pollination through inter-plant movement. However, patterns of pollinator foraging behaviour in relation to breeding systems have yet to be experimentally investigated for any neotropical plant species. In this paper experimental data are presented on the breeding system of a papilionaceous tree, Andira inermis (Swartz) H.B.K., and on the movements of its pollinators. Early experiments (detailed below) showed that A. inermis is self-incompatible. The flowers show clear adaptation for pollination by bees. The specific questions asked in this study were as follows. (i) What kinds of bees visit Andira flowers and what are their patterns of inter-tree movements ?