Non-invasive introduced species that benefit ecosystems

Fixed female cats don’t go into heat so they wouldn’t have a drive to mate but the problem is that the goal of getting enough cats fixed to even slow population growth is rarely reached without culling by euthanasia or removing cats for adoption. Also the maintaining of feeding colonies encourages dumping of more unwanted unaltered cats because they feel there is a safe place to dump them. This keeps the problem never ending with the few unaltered cats breeding to outpace the rate at which the volunteers can get the cats fixed supplemented by newly dumped cats.