What is one effect of immigration on a population living in an ecosystem

When a new species immigrates into an ecosystem, the competition for limited resources within the ecosystem increases. The new species tries to fit in the ecosystem by entering into the existing food chains and there by destabilizes the system by feeding on either the producers or the primary consumers. The new species may also cause harm to essential components of the ecosystem, thus it can be harmful as well.

of those who start drinking before they're 15 will develop alcohol dependence