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High population variability and source-sink dynamics in a solitary bee species

  • Markus Franzén
  • Sven Nilsson
Publishing year: 2013
Language: English
Pages: 1400-1408
Publication/Series: Ecology
Volume: 94
Issue: 6
Document type: Journal article
Publisher: Ecological Society of America

Abstract english

Although solitary bees are considered to play key roles in ecosystem functions, surprisingly few studies have explored their population dynamics. We investigated the population dynamics of a rare, declining, solitary bee (Andrena humilis) in a landscape of 80 km 2 in southern Sweden from 2003 to 2011. Only one population was persistent throughout all years studied; most likely this population supplied the surrounding landscape with 11 smaller, temporary local populations. Despite stable pollen availability, the size of the persistent population fluctuated dramatically in a two-year cycle over the nine years, with 490-1230 nests in odd-numbered years and 21-48 nests in even-numbered years. These fluctuations were not significantly related to climatic variables or pollen availability. Nineteen colonization and 14 extinction events were recorded. Occupancy decreased with distance from the persistent population and increased with increasing resource (pollen) availability. There were significant positive correlations between the size of the persistent population and patch occupancy and colonization. Colonizations were generally more common in patches closer to the persistent population, whereas extinctions were independent of distance from the persistent population. Our results highlight the complex population dynamics that exist for this solitary bee species, which could be due to source-sink dynamics, a prolonged diapause, or can represent a bet-hedging strategy to avoid natural enemies and survive in small habitat patches. If large fluctuations in solitary bee populations prove to be widespread, it will have important implications for interpreting ecological relationships, bee conservation, and pollination.


  • Ecology
  • Andrena humilis
  • apiformes
  • bee conservation
  • bet-hedging strategy
  • colonization
  • diapause
  • extinction
  • metapopulation
  • population dynamics


  • ISSN: 0012-9658
Sven G. Nilsson
E-mail: sven [dot] nilsson [at] biol [dot] lu [dot] se

Professor emeritus




Research group

Biodiversity and Conservation Science