Answer:
It can be best explained with the help of Gause's law of competitive exclusion.
It states that no two species can coexist stably which compete for exact same resources.
In such conditions, the species which is inferior to other in terms of adaptations either extinct or evolve towards a different ecological niche.
For example, Galapagos island finches evolved with different shapes and sizes of beaks as an adaptation towards limited resources available such as different types of seeds or food.