Which statement best defines a population in ecology?

The definition of a population in ecology is best captured by the notion of a group of individuals of the same species living in a specific geographical area at the same time. This definition emphasizes two critical aspects: the species designation, which means all the individuals belong to the same species and share genetic similarities; and the specific geographical area, which indicates that this group is localized and not scattered across different regions. This concept is fundamental to studying ecological interactions, population dynamics, and species conservation, as it allows ecologists to focus on how individuals of the same species interact with one another and their environment within the defined space.

In contrast, the other options describe different ecological concepts but do not accurately encapsulate what a population is. A group of different species living together refers to a community rather than a population. A collection of organisms that share similar roles speaks to ecological niches or guilds, and the concept of organisms reproducing at the same time pertains more to reproductive strategies or breeding populations rather than defining a population itself. Each of these alternatives lacks the specific focus on single-species groups within a defined area that is central to the definition of a population.