Can environmental degradation be used as a justification for the culling of an invasive alien species? We have a lot of feral foxes in Australia which decimate the local wildlife. Foxes are not native to Australia but where introduced by humans. Local wildlife is not adapted to these predators and are an easy prey for foxes. What is the Buddhist view on killing an invasive alien species destroying the local environmental life cycle?
This is a complex question to which there is no right answer.  

Karma is created by our intention.  The intention with which we engage in an action.  You can look at your intention.  Are you engaging in it for your own convenience or a well considered belief that it will ease suffering?  

Do you know enough to make a decision about the situation?  Will the suffering of foxes you kill be less than the suffering of the native animals?  Do you know that the environment should be restored or is that just your own attachment to how things should be?

When I consider situations like this and the questions that arise it becomes clear the world we live in is messy and there are situations for which there is not a right answer.  Purity within samsara is not possible.  What I can do is work to purify negative karma, accumulate good karma, and develop wisdom.

Ultimately, killing is killing and most of us have ignorance of self-grasping.  Killing invasive foxes with self-grasping ignorance creates its own karma.  Very strong conviction that it was the best course of action would be required before I took on such karma.