Answer:
E. coexistence through resource partitioning.
Explanation:
An ecosystem can be defined as the natural living habitats of both living and non-living organisms, in which they interact with one another. Essential services such as plant pollination, water purification, nutrient cycling etc that are being provided by the ecosystem are really very vital, important and useful for the sustenance of life, both for humans and enhances social welfare.
An experiment can be defined as an investigation which typically involves the process of manipulating an independent variable (the cause) in order to be able to determine or measure the dependent variable (the effect).
This ultimately implies that, an experiment can be used by scientists to show or demonstrate how a condition causes or gives rise to another i.e cause and effect, influence, behavior, etc in a sample.
In this scenario, an ornithologist (scientist that scientifically study birds) observed two species of nuthatch, in which both species forage for insects on the same trees; one of the species forages in the upper canopy while the other forages in the lower canopy. Thus, this is probably an example of coexistence through resource partitioning.
Resource partitioning refers to the situation in which different species coexisting in the same environment are able to use available resources differently without interspecific competition among them. Thus, these specifies are able to coexist while staying out of each other's path; no disturbance by one species to the other.
