Every critter has this trait, although different versions:
Environment affinity +0,16 (+0,06/lvl);
Nature/Thunder/Fire damage absorption +20, (+5/lvl);
Thunder/Fire/Ice vulnerability +47,5% (-2,5%/lvl)
It's unknown or at least no one's revealed what the environment affinity bonus does exactly. The best guesses are that it increases a critter's combat ability in some way in certain safari zones, or that it affects elemental attacks in some way.