What are impact of excessive population growth on environment?

The American south is covered with kudzu, a Japanese plant brought there for cattle feed. Australia is covered with cactus, brought there to make living fences. Other parts of Australia are overrun by mice and rabbits, brought by accident.
www.google.com/search?tbm=isch&q=kudzu
www.google.com/search?tbm=isch&q=mice+in+australia
www.google.com/search?tbm=isch&q=rabbits+in+australia
www.google.com/search?tbm=isch&q=coral+cactus+in+australia