Persistence of the sexes in metapopulations under intense asymmetric competition

1. When the two sexes compete so intensively that one of them may be consistently excluded from patches of habitat, how can they coexist in the population as a whole? 2. To address this question, we constructed a population model capable of simulating the dynamics of sex-specific life-history stages within frequently disturbed patches and across a multipatch system strongly influenced by extinction and colonization (metapopulation). 3. We parameterized the model based on the dioecious bryophyte Marchantia inflexa, attempting to capture sufficient biological realism for the results to be quantitatively comparable with natural patterns. 4. In nature, M. inflexa spreads by tissue extension and dispersal of asexual propagules within patches or sexual spores between patches. Females have faster tissue expansion and males greater production of asexual propagules. Some patches and even entire populations lose males or, more rarely, females. 5. In the model, males were often eliminated by competition from individual patches, but both sexes almost always persisted in the metapopulation (as in nature), with females typically predominating. Male advantage during patch filling and spores produced and dispersed where males (the fugitive sex) had not yet been eliminated kept both sexes in the model system. 6. Similar mechanisms may maintain both sexes in other systems, particularly small, highly disturbed populations where life-history traits and mortality differ between the sexes.