What is an example of a population in an ecosystem?

A population in an ecosystem is defined as a group of organisms of the same species that live in a particular area and can interbreed. In this case, a group of the same species of rabbits in a field exemplifies a population, as it consists solely of rabbits in a defined area that share common genetic traits and can reproduce with one another.

This definition is crucial because it emphasizes the importance of the same species coexisting in a specific location, which is fundamental to the concept of a population. The other choices do not fit this definition appropriately. For example, all the trees in a forest represent multiple species, and a single oak tree is just an individual organism rather than a group. All birds within a city encompass various species, not a single one, therefore not constituting a population by the standard definition.