Islands host unique ecosystems and species due to the large impact of the "big four" processes—mutation, gene flow, genetic drift, and natural selection. When a population is isolated on an island, it can undergo speciation, where new species arise due to genetic divergence over time. This isolation limits gene flow from mainland populations, allowing distinct traits to emerge.
However, the isolation that fosters unique adaptations can also make island species more vulnerable. Islands often have limited resources and space, leading to intense competition among species. The lack of natural predators can make island species less prepared for new threats. When predators or diseases are introduced by human activities, island species, having evolved in isolation, may lack the defences needed to combat these new challenges. This makes them more susceptible to predation and diseases from outside their ecosystem.