Topic 20.4 · Core
Sustainable Resources and Endangered Species
Sustainable and renewable get used as if they mean the same thing, and for an exam answer that's a costly mix-up. A resource can be renewable in principle and still be used unsustainably, if it's removed faster than it's replaced.
What makes a resource sustainable
A sustainable resource is one that is produced or replaced at least as rapidly as it is removed, so that continued use does not make it run out. The condition that actually matters is a rate comparison — rate of replacement at least equal to rate of removal — not simply whether the resource is biological or capable of regrowing at all. Forests can be sustainable if harvested trees are replaced or allowed to regenerate quickly enough; fish stocks can be sustainable if the population reproduces quickly enough to replace the individuals removed by fishing. Both examples, worked through in full, are covered on sustainable forests and fish stocks.
Endangered and extinct are not the same word
An endangered species is one at serious risk of extinction. A species is extinct once no living individuals of it remain anywhere. A population tends to slide toward endangered when deaths or removals happen faster than successful reproduction can replace the individuals lost.
Why species become endangered or extinct
Cambridge names six routes to endangerment, and a strong answer identifies which one a scenario is actually describing rather than giving a single generic cause.
Climate change alters temperature, rainfall, food availability and habitat conditions; species unable to tolerate the new conditions, or unable to move to somewhere more suitable, decline — the underlying mechanism is covered on the enhanced greenhouse effect and climate change. Habitat destruction removes the food, shelter, breeding sites and physical conditions a species depends on, exactly as described on biodiversity and habitat destruction. Hunting removes individuals directly, and if that removal outpaces reproduction, the population shrinks. Overharvesting is the broader version of the same idea applied to any organism, plant or animal, collected or caught faster than the population can replace itself — overfishing is one specific, commonly examined case. Pollution can kill organisms outright, damage reproduction, reduce food availability or make a habitat unsuitable. Introduced speciesbrought into an ecosystem where they didn’t previously occur can compete with native species, prey on them, introduce disease, or otherwise disrupt existing feeding relationships — native populations that can’t cope with the new pressure decline as a result.
Where this leads
None of these six routes are simply background facts to memorise — each one is the starting point for a specific conservation response. Once a species is identified as endangered for one of these reasons, the methods used to protect it, monitor it and help it recover are covered next, on conserving endangered species.