MLS3: A New Type of Multilevel Selection

In most multispecies multilevel selection (MLS) models, offspring communities are generated by random assembly of individuals in numbers reflecting sizes of parental communities releasing them (MLS1), or by differential community dispersal based on a community-level trait such as size (MLS2). In both, offspring communities colonize vacant spaces: different communities never compete for the same space. Here we propose a third MLS type (MLS3) where multispecies communities disperse (migrate) into already-occupied spaces, larger communities more frequently. Conspecific variants compete, often opposing selection for community size against fitness within species. This makes the outcome of MLS3 less apparent than MLS1 and MLS2 where such tension is absent. Our simulations show that, if community size depends strongly on reduction in the fitness of individual community members, such a reduction (comprising a sort of "inter-species altruism") will evolve. The framework we present represents a step toward conceptualizing community coalescence in the context of metacommunities.