I think it would be best for you to buy the newer version. I don't think it is very different, but the format of the course requires you to read a chapter for class every week and you are tested on it through iclickers. It is your responsibility if you have the older version to make sure it is the same as the newer one. Hence, its better to buy the newer version.
Also, for the midterms he does test on textbook graphs and images, so it would be best to have the third one, since Dukas uses that to make the test.
P.s. I'm selling my Animal Behavior textbook (3rd ed with penguins on it) for $60. Email me at
[email protected] if you are interested).
Good luck in that class, its not a bad course, just that Dukas kinda makes it REALLY boring.