Abstract
Intraspecific cleptoparasitism represents a facultative strategy advantageous for reducing time and energy costs. However, only a few studies about nesting dynamics have described intraspecific cleptoparasitic behaviour in obligate solitary bees. We focused on nesting dynamics with the characterisation of nest owner replacements and frequency of true usurpation in four aggregating species belonging to different phylogenetic lineages--Andrena vaga (Andrenidae), Anthophora plumipes (Apidae), Colletes cunicularius (Colletidae), and Osmia rufa (Megachilidae). Our study, based on the regular observation of individually marked females, shows that nest owner replacement affects 10-45% of nests across all of the studied species and years. However, 39-90% of these nests had been abandoned before owner change and thus true nest usurpations represent only a part of observed nest replacement cases. Females tend to abandon their nests regularly and found new ones when they live long enough, which is in accordance with risk-spreading strategy. We suggest that the original facultative strategy of observed solitary bees during nest founding is not cleptoparasitism per se but rather reuse of any pre-existing nest (similar to "entering" strategy in apoid wasps). This is supported by gradual increase of nests founded by "entering" during the season with an increase in the number of available nests. Although the frequent reuse of conspecific nests results in frequent contact between solitary females, and rarely, in the short-term coexistence of two females in one nest, we detected unexpectedly low level of conflict in these neighbourhood societies. We suggest that nesting dynamics with regular nest switching and reusing reduces long-term and costly intraspecific aggression, a key factor for the origin and evolution of sociality.