Answer: Species
Explanation:
If two animals can reproduce and the offspring that is produced is also fertile then it can be said that they are members of the same species.
The population of the same species live together in search of food, mate with each other to produce offspring, compete for food and compete for other resources.
It does not matters that the organism live in the same place or different, if they mate and produce a fertile offspring they belong to the same species.
