Competitive exclusion among crayfish: effects of competition on population size (Orconectes propinquus).

Abstract

Invasion of exotic plants and animals has been consistently linked with the extinction of native species leading scientists to suspect competitive exclusion. Invasive species are controlled within their home range by predation or herbivory which has been selected for faster growing, larger and more fecund prey. When released from traditional predation pressures exotic species can experience population explosions and quickly become invasive. However, exotic crayfish have been known to both displace native species and coexist in sympatry. In order to determine if Orconectes rusticus will displace O. propinquus in northern Michigan a study was conducted in order to compare the relative fitness of similar populations of O. propinquus with and without competition from the invasive species O. rusticus. Population sizes were analyzed using mark-recapture. Due to small data sets, no relationship could be determined between the presence of O. rusticus and fitness of O. propinquus. It is possible that O. rusticus is not affecting O. propinquus and is only invasive where humans provide continuous and significant disturbance.