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.