What defines the ecological role of a species in its environment?

The ecological role of a species in its environment is best defined by its niche. A niche encompasses all aspects of a species' lifestyle, including how it obtains its resources, the role it plays in its ecosystem, its interactions with other organisms, and how it responds to changes in its environment. It is essentially the "job" of the species within its community and includes its habitat, the resources it uses, and various biotic and abiotic factors that impact its survival and reproduction.

In contrast, habitat refers specifically to the physical environment where a species lives, which doesn't encompass the full scope of its interactions and roles. Evolutionary history pertains to the lineage and adaptations that a species has gone through, which might inform its niche but does not define its current ecological role. Geographical distribution indicates where a species can be found, but again does not fully capture the interactions and functional roles that characterize its niche within an ecosystem. Hence, when considering a species' ecological role, the concept of a niche provides the most comprehensive understanding.