Ecologists have been studying small islands for a long time, as the populations between small islands often display remarkable diversity. The Galapagos finches, for example, represent several species of finch that all resemble a mainland finch, with various modifications. The theory remains that the population on the islands is under the influence of the founder effect. It is hypothesized that small colonies of finches were established on each island when storms would carry them far away from the coastline. Due to the small number of finches that arrived at each island, each population only had certain alleles from the parent population. Over time, the populations varied greatly, both in their size and the roles they filled within the ecosystem. Similar examples have been noted in amphibians, reptiles, and mammals. The founder effect is a well-known cause of differentiation between populations that span a great distance. This is known as the serial founder effect, if the individual populations spread over a geographic distance do not interbreed.