They live in the same habitat and niche. They forage and eat the same type of food. They mate and produce fertile offspring. They are similar in appearance and color.
I am hesitating between 4 options to answer the following question, which option should I choose?
Question: Which factor determines if two individuals are members of the same species?
Possibilities:
- They live in the same habitat and niche.
- They forage and eat the same type of food.
- They mate and produce fertile offspring.
- They are similar in appearance and color.

They mate and produce fertile offspring.