1. Correct, refers to the species, not a particular tiger.
2. Incorrect. (Note: "THAT tiger is my favorite animal" is correct, refers to specific tiger, as does "those tigers".)
3. Correct, refers to the generic species. It is implies that the sentence is:
"Tigers are my favorite KIND OF animal."
4. Correct, refers to the species.
5. Correct if you are referring to a specific group of tigers. It would not refer to the species as a whole.