Human overpopulation will likely lead to more extinctions of species because

habitat destruction and resource depletion

Explanation:

As the human population is growing, more and more natural resources are required to feed them and full fill their all other requirements. But in lieu to fulfill man needs especially food,  lot of forests have been turned into cultivation land, pasture land etc. Doing this not only harm the environment but also disrupt the habitats of animal with in the forest. Habitat destruction will lead to extinction of species as they will not be able to get a surrounding appropriate for their survival. Also there can be non availability of life retaining resources like food, water etc,

Thus, Human overpopulation will likely lead to more extinctions of species because of habitat destruction and resource depletion.