Interspecific competition among metapopulations with space-limited subpopulations

A model of the dynamics of a single metapopulation with space-limited subpopulations (J. Roughgarden and Y. Iwasa, 1986, Theor. Pop. Biol. 29, 235–261) is extended to include interspecific competition for space. The location and stability of steady states for the regional competition community are analyzed; a necessary condition for stable regional coexisitence of many species, and the condition for successful invasion of a new species into a region, are derived. General results are (1) the number of species that can coexist in a regional competition community is less than or equal to the number of distinct types of local habitats in the region and (2) for any pair of species coexisting in a regional community, say species-i and species-j, there is at least one place where species-i has a higher productivity relative to its larval mortality rate than species-j, and at least one place where species-j has a higher productivity relative to its larval mortality rate than species-i. A regional competition community consisting of two species competing for the space in two local habitats is analyzed using a graphical classification. If both local habitats are net “sources” of larvae for the regional populations of both species, then the qualitative results of interspecific competition on a regional scale are the same as those of the classical two-species Lotka-Volterra competition equations. If one of the local habitats is a net “sink” for larvae of one or more of the metapopulations, then additional results are possible: (1) The existence of a species may require the presence of its competitor. (2) A species which cannot invade an empty regional community may be able to invade if another species is present, and may then displace the first species leaving a regional community that again has one species. (3) A second species may invade a regional community containing one species with the end result that both become extinct.