Why cannot a population live alone by itself in nature?

Hint: A population is several all the organisms of the same group or species who live in a particular geographic area and are capable of interbreeding. Not a single population can live alone in nature because it is dependent on other populations for its various requirements and needs.

Complete answer:
There is no such habitat on earth that is inhabited just by a single species. For any species, the minimal requirement is one more species on which it can depend or feed. Even the plant species which make their own food cannot survive alone. It needs soil microbes to break down the organic matter in soil and return the inorganic nutrients to them which helps them to carry out the process of absorption. How can plants be able to manage pollination without an animal agent? It is obvious that in nature animals, plants and microbes depend on each other and cannot live in isolation. They interact in various ways to form a biological community. Many interactive linkages exist in minimal communities although all may not be readily apparent. Interspecific interactions arise from the interaction of the population of two different species that could be beneficial, detrimental, or neutral to one of these pieces or both.

Note: The interaction where both the species are benefited are called mutualism and the interaction where both the species lose is called competition. The interaction where one species is benefited and the other is neither benefited nor harmed is called commensalism. Whereas in amensalism one species is harmed and the other remains unaffected.