Explain in your own words the founder effect

The founder effect is the reduction in genetic variation that results when a small subset of a large population is used to establish a new colony. The new population may be very different from the original population, both in terms of its genotypes and phenotypes.

Example:

The founder effect is a case of genetic drift caused by a small population with limited numbers of individuals breaking away from a parent population. The occurrence of retinitis pigmentosa in the British colony on the Tristan da Cunha islands is an example of the founder effect

true, generally referred to as invasive species given that they have no natural predators in new environment