Step 1: Understanding the Concept:
The question asks for the ecological term for the first organisms to colonize a previously uninhabited or disturbed environment. This is a concept from the study of ecological succession.
Step 3: Detailed Explanation:
Ecological succession is the process of change in the species structure of an ecological community over time.
\[\begin{array}{rl} \bullet & \text{Pioneer species are the first species to colonize barren areas. They are typically hardy, fast-growing, and have adaptations for survival in harsh conditions (e.g., lichens, mosses on bare rock).} \\ \bullet & \text{Sere(s) or Seral stages are the intermediate stages of an ecosystem advancing towards its climax community.} \\ \bullet & \text{Climax community is the final, stable, and mature stage of succession.} \\ \bullet & \text{Mesic refers to an environment with a moderate amount of moisture, not a type of species in succession.} \\ \end{array}\]
Step 4: Final Answer:
The species that first invades a bare area is referred to as a pioneer species.