Final answer:
Reptiles often become apex predators on islands due to the absence of larger mammalian predators, their ability to thrive in isolated environments, and the lack of competition. Introduced species by humans can further tip the balance in favor of reptiles by outcompeting or preying on non-native species. Over time, isolated reptile populations may evolve further defenses in the absence of natural predators.
Step-by-step explanation:
Reptiles often become apex predators on islands due to a combination of factors. They are generally carnivores, and in the absence of larger predators, they can dominate the top of the food chain. Many reptiles possess adaptations that allow them to thrive in isolated environments, like efficient water conservation and the ability to eat a variety of prey.
Moreover, islands usually lack the diversity of larger ecosystems found on continental land masses, which means there are often fewer large mammalian predators to compete with reptiles. This allows large reptiles to fill the niche of apex predator more easily. Reptilian dominance can be further consolidated when introduced species, like cats and dogs, prey upon or outcompete non-native prey species, leading to declines in local biodiversity and disturbing the ecological balance. For instance, on the Galápagos Islands, the marine iguanas have become threatened due to non-native predators brought in by humans.
Island ecosystems are also subject to extinction threats from introduced species, such as the brown tree snake on Guam, which caused the extinction of several bird and reptile species. As islands contain a disproportionate number of endemic species and thus a unique biodiversity, the loss of a top predator like a reptile can have cascading effects on the entire ecosystem.
If reptile populations are undisturbed, they may evolve additional defense mechanisms over time, such as camouflaged coloration, sharp spines, or toxins, especially if new predators are introduced. Islands that have no natural predators for certain reptile species provide an environment where these reptiles can more easily become dominant and avoid competition that would normally challenge them on the mainland.