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)

Nature+, Thunder- : Air, Bird, Hornet, Moth, DragonWyrmBeholder

Thunder+, Fire- : Ground, Gorilla, Lizard, Mammoth, Mantis, Owlbear, Raptor, Spider, WolfCerberusLionSteed, Tortoise

Fire+, Ice- : Water, Crustacean, Fish, Walrus, Crocodile, Calamari, Toad, Hydra

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.

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