Answer:
The additional exposure of soil layers.
Step-by-step explanation:
Antibiotics are administered by humans, so less contact with humans won't cause an increased use of antibiotics. The prevention of invasive plant species is not a problem, nor would it be caused by improper management of free range animals. Mental Illness in animals is usually caused by being put in small enclosure or living in poor conditions, not by being allowed free range. Therefore, the answer is the additional exposure of soil layers, since excessive grazing can decimate plant and soil layers.
I hope that helped!