The first thing I thought when reading the topic title was "Pokémon"!
Moontouched-Moogle said:
I presume you mean more sentient and intelligent? Some animals are supposedly smarter than humans. I think dolphins were one of them?
I don't really think anyone thinks any animal is smarter than humans. I have recently seen news articles that dolphins and elephants may be as smart as (some) (other) primates though. Anyway, I don't think there is a widely accepted theory for higher levels sentience or intelligence to really compare the different species. But even on flawed measurements like encephalization quotient [http://en.wikipedia.org/wiki/Encephalization_quotient] humans vastly outmatch any other species. Which makes sense, because I really couldn't think of any metric that would allow dolphins to outsmart us. There is no indication that their communication is anywhere near as complex as ours, or that they have extensive planning, reasoning or tool use/crafting capabilities.
Anyway, if animals suddenly achieve human-level intelligence, it depends on the animal what would happen. Physical capabilities and numbers are important factors to decide if they would be a threat to us. From the trailer I saw of The Rise of Planet of the Apes, it seems that it will be gorillas (or at least large apes). Since they are physically vastly superior to people, a group of them will pose a large initial threat, but since their numbers aren't that big, we could easily deal with them (with a couple of casualties). Maybe if the apes would be willing to negotiate we would allow them to live, but I think they'll be judged to dangerous to set free. The same would happen with most other larger animals (although some would be too weak to even try to fight us).
Very small animals will initially pose less of a threat, because they can't really harm us individually. However, because they generally have larger numbers, they might also be harder to exterminate should the need arise, and may be more capable at getting away from us. However, I think our head-start with high-level intelligence will be hard to overcome and the best any species can do is to stay out of our way.