| Abstrakt: |
The state of biotic communities inhabiting different water bodies is analyzed aiming to determination of conditions facilitating development of biological invasions. Mass-balance and dynamic models are used to reveal the factors ensuring the invasion of zebra mussel, Dreissena polymorpha, in Naroch Lakes (Byelorussia), and smelt, Osmerus eperlanus, in Lake Syamozero (Karelia). The results obtained indicate that for invasions leading to trophic chain lengthening, the main factor of successful invasion is the availability of resources that are not utilized by aboriginal species. Highest chances for successful invasion belong to invading species feeding on those trophic groups which contribute to the most extent to forming of 'excess' (i.e., available for the invader) production. It is shown that establishment of an alien species in a native community appears to be possible only when total amount of such 'excess' production is higher then some threshold value. Under conditions of spatio-temporal environmental heterogeneity, the timing factor, which determines the exact moment of an alien species intrusion, becomes important as well. |
