Answer:
Because of niche partitioning or differentiation.
Explanation:
Competition is a common ecological and evolutive process in nature. Competition might be intra- or interspecific. Competition between different species in a community or ecosystem might be due to the same resource use, or the same territory, shelter, etcetera. When a resource is useful for two or more species and limited, they compete to gain it.
The <u>principle of competitive exclusion</u> states that different species with the same requirements sharing the niche can not coexist indefinitely based on the same limited resource. <u>When two competing species coexist, this is because of niche partitioning or niche differentiation.</u>
Differentiation of effective niche is closely related to character displacement. Resource partitioning and differentiation allow both species to coexist more effectively.
In the exposed example, swallows and bats feed on insects and breed in similar habitats. However, swallows feed during the day, while bats feed during the night. Feeding at different times is an example of niche differentiation. In this way, both species can inhabit the same area and feed on the same source of food, but avoid competition.
Because if we're simultaneously moving/manipulating two different variables it can be very hard to determine why one variable is changing and why the other is changing. While this can be done with more complicated experimental designs, it usually is the case that scientists will only manipulate one variable and not two different ones.
