Flower-feeding specialization in wild bee and wasp communities in seasonal neotropical habitats.

Flower visitation records were obtained for 192 species of bees and 138 species of wasps in three neotropical habitats. Four indices of feeding specialization were calculated for common species, and similar patterns were observed using each index. Variation in specialization could be attributed to several factors: the habitat and season in which species were found, the degree of sociality of species, and whether species were bees or wasps. Important differences among habitats and seasons were the number of coexisting consumer species and the species richness and phenology of resource plants. Differences in average consumer specialization among habitats and seasons may have been the result of differences in competitive pressures and to a lesser extent, differences in the flowering strategies of local plants. Eusocial bees and wasps were much more generalized in feeding than solitary species, and bees were more generalized than wasps. Bees in these neotropical communities were much less specialized than their north temperate counterparts. This pattern is reflected by the near absence of species that feed at only one or two plant species in Guanacaste, as compared to a very high frequency of these extreme specialist species in north temperate areas. Temperate zone species of bees have less "even" visitation rates to their resources than tropical bees. Consequently, temperate zone bees are more specialized in both the variety of plant species visited and the dominance of visitation to each set of resource plants. Several hypotheses are examined as possible explanations for this apparent qualitative difference in community structure between neotropical and temperate communities.