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Why are species with small populations or limited geographic ranges often more vulnerable to extinction?
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ecology
Mourning doves (Zenaida macroura) on their nest protected within the prickly branches of a cactus in the Sonoran Desert, Arizona, U.S.
Species with small populations or limited geographic ranges are more vulnerable to extinction due to several critical ecological factors:
- Geographic Range: The size of a species' geographic range is a primary predictor of extinction risk. Species with small ranges are more easily impacted by habitat loss because their entire population may occupy a restricted area that can be destroyed entirely.1
- Genetic Diversity: Small populations are prone to losing genetic variation through random genetic drift. Without this diversity, populations lack the evolutionary flexibility to adapt to environmental changes, new diseases, or increased competition.2
- Low Dispersal and Isolation: Species with low dispersal rates cannot easily move to "rescue" declining local populations. When habitats are fragmented by development, these populations become isolated, making them unable to receive individuals from other areas that might otherwise prevent local extinction.3
- Population Density: Species with small ranges often exhibit lower local population densities, making them harder to find and more susceptible to total collapse when faced with environmental pressures.1