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SCALETOOL IntroductionDriversBiodiversityPolicies and managementConnectivity and protected areas
From species traits to dispersal distances Simulation of genetic data Population Viability Sex-biased dispersal Biodiversity scaling Perspectives for landscape scale management Conservation strategies at appropriate spatial scales
 

Sex-biased dispersal

Individuals of the same species do not necessarily disperse identically. Dispersal rather depends on the mating system with the non-territorial sex dispersing. Therefore, knowledge on sex-biased dispersal is essential for conservation management.
Dispersal, defined as an unidirectional movement between natal and breeding site, is crucial for (meta)population persistence and creates gene flow. This gene flow is a key process in the evolution and dynamics of populations. Sex-biased dispersal, i.e. dispersal biased toward one sex, may occur as a consequence of divergent evolutionary interests between sexes. In anisogamous species, females produce large, energetically rich gametes, while males produce small, highly mobile gametes. In general, males produce many more gametes than females and try to fertilise as many females as possible. In contrast, females generally have a limited number of chosen partners. Male fitness is thus largely determined by mating duration while female fitness results from the number and/or the quality of her eggs. Such asymmetry leads to different sex roles, with conflicting optimal fitness strategies concerning reproduction, the so-called sexual conflict. Sexual conflict can induce male-male competition (e.g. for sexual partner access), female-female competition (e.g. for feeding or egg-laying habitat patches) and male-female competition (antagonistic co-evolution). Both these intra- and inter-sex competitions may have strong consequences on which sex tends to disperse more frequently to reach new territories, new social groups and there with new mating partners.

Our literature review yielded data on 214 species. The analysis of this data set showed that species with polygamous males (i.e. polygynous or promiscuous mating systems) and territorial females tended to show male-biased dispersal whereas species with territorial males and performing parental care tended to show female-biased dispersal. Further, the presence of sexual size dimorphism was positively related to the degree of male biased dispersal demonstrating that species where males were bigger than females showed a greater degree of male-biased dispersal.

Differential sex-biased tendencies have relevance for understanding how dispersal and population structure interact. Therefore, knowledge on sex-biased dispersal is essential to develop and assess potential solutions for problems involving habitat management and landscape planning. Our results suggest that mating systems are key factors in determining the direction of sex-biased dispersal. Therefore, different conservation strategies might need to be adopted for different species groups to allow a natural (sex-biased) exchange between different populations and for maintaining persistent metapopulations.


Dispersal processes in a landscape context. At each step, the males and females might make a different decision, might be selected for, or are having different success rates, to mention a few.

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