The list is not what is doing the exhibiting, it is the animals, so the subject of the verb is plural, hence exhibit.

You can always ask yourself: What is doing the ____? in this case, exhibiting, to figure out what the verb's subject is.

the word "that" indicates a relative clause. That clause modifies the closest prior noun. So it is the animals that exhibit a preference...

The main verb is "has been expanded" and this is what corresponds to the subject "the list"

So that we have "The list is expanding" but "animals exhibit a preference."

hi david

sorry to bug you....have sent a pm.

thx