Many species are maintained by a rain of propagules from a source population and thereby persist in a location from which they would ordinarily be excluded by competition. This is one explanation for the persistence of competitively inferior domestic species in natural environments. The purpose of our study was to estimate the effect of immigrant populations on competitively superior wild species in terms of the risks of decline - the quasiextinction risk - of the wild population and the quasiexplosion risk of the immigrant population. A simple mathematical model of escape and competition demonstrates that the risks to a wild population may be appreciable. We found that even when the species maintained by mass effects is not viable in the absence of competition and immigration, low escape rates (e.g., enough to give the invasive population a net positive growth rate) can make a wild-competing species vulnerable within 10 years. The probability that the immigrant population will exceed lower bounds increases rapidly with rates of escape and growth.

Competition Mass effect Invasiveness Coexistence Quasiextinction risk

biological invasion persistence coexistence competition (ecology) immigration species conservation