Time to extinction in relation to mating system and type of density regulation in populations with two sexes
Bernt-Erik Sæther, Institute for Biology, Norwegian University of Science and Technology, Realfagsbygget, N-7491 Trondheim, Norway. Fax: +4773591309; E-mail: Bernt-Erik.Sather@bio.ntnu.no
- 1Population viability models usually consider only the female segment of the population. However, random variation in sex ratio as well as the mating system may also affect variation in fitness among females. Here we develop population models incorporating demographic stochasticity in both sexes. Furthermore, we consider the effects on the estimated time to extinction and whether density regulation acts only on females or on total population size.
- 2We applied these models to two populations of polygynous great reed warblers Acrocephalus arundinaceus L. with differences in population trends to investigate the importance of considering sex in population viability models.
- 3Demographic stochasticity was larger in a polygynous than in a monogamous mating system.
- 4The estimated time to extinction was considerably shorter for a monogamous than for a polygynous mating system, particularly if density regulation acted only on females than rather on the total population.
- 5This study demonstrates that structure of mating system must be included when making population viability analysis based on counts of total population sizes. It is especially important to model the specific effects of density regulation on the two sexes.