Answer: on islands
Step-by-step explanation:
Founder effect can be define as a phenomena of loss of genetic variation as new population develop in an area established by very small number of individuals from a large population. It was founded by Ernst Mayr (1942). The gene pool of such individuals exhibit small number of genetic variations.
Among the options given, on islands is the correct option because it can support few individuals initially due to environmental conditions as compared to large countries, or within large populations. Small individuals can lead to the development of a large population size.