Why species vanish when the world changes faster than they can evolve
In short: Extinction is a natural part of Earth's history, yet the speed of modern loss is alarming. When environments shift too quickly or drastically, species lose the opportunity to adapt, leading to a permanent disappearance from the biological record.
Biologically speaking, extinction occurs when a species can no longer survive or reproduce within its altered environment. Although extinction occurs naturally—since over 90 percent of all past organisms are now extinct—human actions are speeding up this process. Shifts are being triggered by elements like overfishing, hunting, disease, invasive species, climate change, and lost habitats.
Scientists distinguish between different levels of decline. A species may be 'locally extinct' or extirpated, meaning it has vanished from a specific part of its native range but persists elsewhere. For example, grizzly bears are locally extinct in California but remain in the wild in other regions. In contrast, a species is considered 'functionally extinct' when its population has dwindled to a point where the remaining members can no longer perform their essential ecological roles.
The loss of specific animals can destabilize entire ecosystems. When top predators like sharks or sea otters decline, the balance of their environments is thrown off-kilter. Even seemingly small shifts can have massive consequences; for instance, in New England, less snowy winters allow certain ticks to live longer, which subsequently contributes to the death of moose populations.
Resilience also plays a role in survival. While some species struggle, others show surprising adaptability. The American pika, a rabbit relative that prefers cold, was previously assumed to be climbing higher altitudes because of warming, yet research from the journal Arctic, Antarctic and Alpine Research in 2018 showed they remain quite hardy and inhabit warm, low-altitude areas.
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Sources
- Summary by Intellect · source: Extinction | Common ancestry and phylogeny | High school biology | Khan Academy
- Also: What is extinction? The answer is complicated.
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