The influence of habitat and species atributes on the density and nest spacing of a stngless bee (Meliponini) in the Atlantc Rainforest

Abstract

Trigona spinipes (Fabricius, 1793) lives in perennial eusocial colonies and builds nests exposed on tree branches. The reason why this generalist habitat with exposed nests cannot nest successfully in forest habitats is intriguing. This study explores the hypothesis that this species reaches higher densites in vegetaton with open canopies and the subsidiary shading hypothesis, assuming the failure of large exposed nests in closed canopy rainforest. Comparatve field data on nest density in open canopy vegetaton (this study) and adjacent closed canopy forest (previous data) are used to test this hypothesis. At random 18 nests distributed in 40 20x200m plots in rubber groves with a density of 1.1 nests/ha, were recorded. This is a high nest density for a single species of stngless bee and correspond to 36 tmes the very low density in adjacent rainforest. The high density in the rubber groves is also associated with a regular spatal distributon of nests and it suggests territorial patrolling mechanism operatng at short distances (60 to 70m). We conclude that: (a) this species faces powerful nestng constraints in the ever green and closed canopy of rainforest, because the external structure of the nest remain wet for prolonged periods due to exposion to heavy rains and high shading; (b) the high availability of sunny sites for nestng within the deciduous and open canopy of rubber trees favours rapid nest drying and the high nest density of T. spinipes and realeasing its wide spread distributon where this agroforestry system dominates.