Species-specific foraging strategies of the syntopical and synchronous bees Panurgus calcaratus (Scopoli, 1763) and Dasypoda hirtipes (Fabricius, 1793) (Hymenoptera: Apidae).

Abstract

Two ground-nesting, oligolectic bee species, Panurgus calcaratus (Scopoli, 1763) and Dasypoda hirtipes (Fabricius, 1793), which are syntopical and synchronous, were studied in the Wahner Heide Nature Reserve (Rhineland, Germany). To study mechanisms of ecological separation or niche differentiation the species-specific seasonal and diurnal rhythms and the foraging strategies were examined. In addition to provisioning behaviour, their oligolecty was examined by analysing pollen samples from females after flower-visiting and by observations of the bees on their pollen sources. Both species exclusively visit yellow, photonastic liguliflorous Asteraceae as pollen sources, prefer to construct their nests on sandy soils with poor vegetation and are active from the beginning of July until the end of August. Analysed samples show pollen grains belonging to yellow liguliflorous Asteraceae only and there was no specialisation within the oligolecty on certain plant species. Collection of pollen is limited by the photonastic flowers of the pollen sources, and the bee activity is mainly influenced by climatic factors like light intensity, cloudcover, and air-temperature. The diurnal activity period of Dasypoda hirtipes is much longer and this species is active at lower temperatures. The specific diurnal and seasonal behaviour and activity rhythm of the two bee species are discussed with regard to body size and coloration, the ability of heat absorption and reflection, risk of overheating, and ecto- and heterothermal effects to heat budgets. Each species follows its own foraging strategy which is mainly influenced and limited by ultimate factors as the bees` physiology under the given abiotic conditions. Neither nesting sites nor pollen and nectar resources are limited and consequently there is no evidence for competition between both species.

Keywords

Interspecific competition, oligolecty, optimal foraging strategies, photonasty, resource partitioning, separation mechanisms.