In ecology and evolution, the small population idea suggests that smaller populations have less genetic diversity, which leads to less variety in traits and makes it harder for them to adapt. However, this has been challenged in recent years, with evidence that other factors might also play a role in shaping variation in traits. There haven’t been many large-scale studies, especially in aquatic environments.
Using the global spread of brown trout as a case study, a large team of researchers, some of them from the Fish Futures team, looked at variation in traits across different populations and found that neither the size of the original population nor how long the fish had been introduced affected the variety in their traits. Instead, this variation seemed to be more influenced by local conditions specific to each population, rather than the region as a whole. This suggests that phenotypic variation depends more on local factors and selection than on population size.