Niche differentiation in nectar‐collecting stingless bees: the influence of morphology, floral choice and interference competition

Abstract

Summary1. Dozens of social bee species, most of them stingless bees, occur sympatrically in the tropics. The proximate mechanisms through which they partition their resources are, apart from aggressive interactions betweenTrigonaspecies, not well studied. In the work reported here, niche differentiation at patch level was studied, using two species ofMeliponathat occur sympatrically in the Central Pacific part of Costa Rica. Foragers ofMelipona beecheiiare known to collect more concentrated nectar than doMelipona fasciataforagers, even from the same plant species. This observation raises the question of what mechanism leads to such partitioning of nectar resources? To address this question, the roles of bee morphology, floral preferences, and interference competition in partitioning of nectar sources were studied.2. It was shown experimentally that the feeding rate of both species was highest at 60% nectar concentration.Melipona fasciatapreferred 60–70% concentrations to less concentrated solutions, whereasM. beecheiiignored 20% solutions and visited the other solutions equally often. Both species preferred sucrose to glucose and fructose.Melipona beecheii,with a yellowish coloured body, preferred sunny patches, whereasM. fasciata, with a dark brown body, preferred shady patches. Interference competition between the species occurred when they visited the same sugar‐water feeder:M. fasciatawas dominant overM. beecheii.3. The nectar foraging strategies of the two species can be summarised as follows:M. beecheiiis able to visit sunlit patches, due to its lighter body colour, and is thus able to collect nectar of optimal or near optimal sugar concentration (40–65%). Individuals do not actively choose nectar with a high concentration of sugar, but the average sugar concentration in bee‐collected nectar will typically be high in sunlit patches.Melipona fasciata,on the other hand, avoids sunlit patches, but actively chooses the richest nectar in shady patches and tries to dominate such patches. Thus, niche differentiation occurs according to the radiation regime at flower patches, and interference competition will occur rarely under natural conditions. The role of similar mechanisms in other closely related stingless bees is discussed.