Population Dynamics of Male Euglossine Bees in Amazonian Forest Fragments

Abstract

At sites near Manaus, Amazonas, Brazil we measured the impact of forest fragmentation on populations of male euglossine bees. The visitation rates of 15 species of male euglossine bees to three chemical attractants were determined for continuous forest; isolated 1, 10, and 100 ha forest fragments; and a cleared area. For most species, visitation rate declined with fragment size, even though openings separating fragments and continuous forest tended to be narrow (as little as 100 m). Preand post-isolation comparisons for individual fragments exhibited the same trend. Bee species attracted to scents in the clearing differed from those of the forest indicating there was little potential for forest pollination by these clearing species. These results are discussed with respect to the impact of forest fragmentation on plant species richness and the design of natural and commercial forest reserves. EUGLOSSINE BEES ARE KNOWN TO BE important pollinators of neotropical orchids and other plant families (Williams & Dodson 1972, Braga 1976). The greatest species richness occurs in forest habitats, but species are present in open habitats (Zucchi et al. 1969). Strong fliers, euglossines range over large areas (Janzen 1971, Ackerman et al. 1982) and have diverse home range structures (Janzen 1981). Male euglossine bees use chemicals from orchid fragrances, probably as building blocks for pheromones that attract females (Kimsey 1980, Williams & Whitten 1983). Commercially available chemicals can be used to attract male euglossine bees, thus making it possible to measure precisely the relative population densities of the numerous species that occur in a given locality and that are attracted to chemical baits. Therefore, male euglossine bees are ideally suited to study population dynamics in forest fragments. In this study, we used three chemical scents to quantify relative population densities of male euglossine bees in continuous forest and forest fragments of different sizes. Methyl salicylate and cineole are known to attract a wide variety of euglossine species (Williams & Dodson 1972) and along with vanillin were chemicals that had been used in studies in Brazil (Braga 1976). Based on pre-fragmentation data collected in 1982 and 1983, the population of male euglossine bees was homogeneous in the continuous forest. In 1983 following fragmentation of the forest, the male euglossine bee populations were monitored in I Received 20 June 1985, revision accepted 27 November 1985. 176 BIOTROPICA 19(2): 176-179 1987 relation to habitat size and were found to be lower in small forest fragments.