Cullers beware - killing 'pest' animals can increase their abundance
Christopher Johnson
8th May 2015 - reproduced from:
A study of feral cats in Tasmania shows that culling them to reduce their impact on native wildlife had a paradoxical effect - their population went up! If you can't take 'pest' animals out faster than they can reproduce and move in from nearby areas, writes Christopher Johnson, you're better off not bothering at all.
What went wrong?
What seems to have happened in these cases is that young animals quickly moved in from surrounding areas to replace dominant adults removed in the cull. Most of these young animals would normally have died. The sudden increase in their survival allowed abundance to overshoot pre-cull levels.
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The more general problem is that removing some animals from a population creates more space and food for those that are left, and can disrupt social controls on breeding. Survival, reproduction and immigration all increase as a result, and the population quickly rebounds.
For culling to produce a lasting reduction in abundance, it is essential not just to accomplish the relatively easy task of removing animals from a high-density population. We also need to be able to continue removing animals at rates that equal or exceed the capacity for increase of a population with improved survival and reproduction.
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