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Web Ecology An open-access peer-reviewed journal
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Volume 2, issue 1
Web Ecol., 2, 57–64, 2001
© Author(s) 2001. This work is distributed under
the Creative Commons Attribution 3.0 License.
Web Ecol., 2, 57–64, 2001
© Author(s) 2001. This work is distributed under
the Creative Commons Attribution 3.0 License.

  10 Sep 2001

10 Sep 2001

Modeling population dynamics of solitary bees in relation to habitat quality

K. Ulbrich and K. Seidelmann K. Ulbrich and K. Seidelmann
  • Institute for Zoology, Univ. of Halle, Domplatz 4, 06099 Halle, Germany

Abstract. To understand associations between habitat, individual behaviour, and population development of solitary bees we developed an individual-based model. This model is based on field observations of Osmia rufa (L) (Apoideae: Megachilidae) and describes population dynamics of solitary bees. Model rules are focused on maternal investment, in particular on the female’s individual decisions about sex and size of progeny. In the present paper, we address the effect of habitat quality on population size and sex ratio. We examine how food availability and the risk of parasitism influence long-term population development. It can be shown how population properties result from individual maternal investment which is described as a functional response to fluctuations of environmental conditions. We found that habitat quality can be expressed in terms of cell construction time. This interface factor influences the rate of open cell parasitism as the risk for a brood cell to be parasitized is positively correlated with the time of its construction. Under conditions of scarce food and under resulting long provision times even low parasitism rates lead to a high extinction risk of the population, whereas in rich habitats probabilities of extinction are low even for high rates of parasitism. For a given level of food and parasitism there is an optimum time for cell construction which minimizes the extinction risk of the population. Model results demonstrate that under fluctuating environmental conditions, decreasing habitat quality leads to a decrease in population size but also to rapid shifts in sex ratio.

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