What is a niche and how can two species coexist by occupying different ecological niches?

• A. A niche is the physical space a species occupies; coexistence occurs when species share the same space but use different resources.
• B. A niche is the set of resources and conditions a species needs to survive; by specializing in different foods, habitats, or times, species can reduce competition and coexist.
• C. A niche is the genetic makeup of a species; coexistence occurs when they share identical niches.
• D. A niche is the number of offspring produced; coexistence occurs when both have high reproduction.

Answer: (B)

The idea being tested is that a niche is the set of resources and conditions an organism needs to survive and reproduce, and that two species can coexist by using different parts of that niche. A niche isn’t just where an organism lives; it includes what it eats, where it forages, when it’s active, and the environmental conditions it tolerates. When two species specialize in different foods, habitats, or times of activity, they reduce direct competition because each is filling a different role in the ecosystem. This resource partitioning lets them share the same general area without one driving the other to extinction. For example, two bird species in the same tree might feed on different insect prey or forage at different heights or times, allowing both to persist. So the best description is that a niche encompasses the resources and conditions needed to survive, and coexistence arises when species differentiate in what they use of that niche. The other ideas fall short because they reduce the niche to only space, or to genetics, or to reproduction count, none of which fully capture how niche use supports coexistence.