A keystone predator would increase niche diversity and help reduce niche competition
The correct answer is- b. It increases niche diversity.
A keystone predator is a species, which has profound impact on its ecosystem that is it can control the population and distribution of large number organisms within its habitat.
In other words, its influences the ecosystem as it increases the niche diversity.
For instance, keystone predator such as starfish feeds on the mussel Mytilus californianus and maintains the diversity of species in that communities. As other species will get proper food resources to survive.
Thus, it increases niche diversity.