It depends on the ecosystem. Pollution famously caused certain moths to shift from being mostly light-coloured to mostly dark-coloured in a matter of years. The removal and reintroduction of wolves in Yellowstone caused observable changes in prey behaviour within a decade or so. Of course longer-lived species like trees take much longer to adapt, but we’re talking about birds, geckos and rodents here.
Edit: Also, most geckos, birds and rodents are r-strategists, meaning they are limited more by food than by predation.
It depends on the ecosystem. Pollution famously caused certain moths to shift from being mostly light-coloured to mostly dark-coloured in a matter of years. The removal and reintroduction of wolves in Yellowstone caused observable changes in prey behaviour within a decade or so. Of course longer-lived species like trees take much longer to adapt, but we’re talking about birds, geckos and rodents here.
Edit: Also, most geckos, birds and rodents are r-strategists, meaning they are limited more by food than by predation.
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Introduction of a new predator will disturb the ecosystem. Removal of an existing predator will also disturb the ecosystem.