Nightmare Fuel: A humongous python strangles and eats their donkey. In the film, it's an anaconda which nearly constricts Fritz and Ernst to death.
Science Marches On: The exotic wildlife is thought to have come to the island by way of now-sunken land bridges. At the time of the novel's writing, continental drift wasn't even fringe science.
Values Dissonance: Humans showing up in a pristine natural habitat and promptly capturing a (baby!) elephant, a monkey, an ostrich and a bunch of other animals just does not have the same ring to it as it used to, with nearly everything going extinct and huge problems with animal trafficking.