Managing invasive species to protect native biodiversity involves killing large numbers of animals, creating genuine ethical tensions between ecological welfare at population level and individual animal welfare.
Invasive species management forces a direct confrontation with the tension between individual animal welfare and ecosystem-level welfare. Individual grey squirrels, mink, and rats did not choose to colonise new habitats — they are animals with the capacity for suffering whose welfare deserves consideration even when their presence is ecologically harmful. This does not mean control is unjustified; the ecological evidence for harm from invasive species is clear, and the welfare of billions of native animals depends on healthy ecosystems. But it does mean that methods used should be as humane as possible, that non-lethal alternatives should be seriously explored, and that control programmes should be designed with welfare standards rather than pure efficiency as the governing criterion.