Here is a non-comprehensive guide of strengths, weaknesses of the traits from the base game, along with a few combo ideas. If you see anything to add or correct, feel free to post.
Each trait has a universal downside: it takes up a slot that can’t therefore be occupied by another trait (stronger defence = weaker feeding / vice versa).
Each defensive trait has a situational downside: it also works against my own predators (in case my predators are unable/unwilling to attack an opponent’s species).
+ negates Warning Call, which is a powerful defensive trait
− when there are no Warning Calls
Combo: Warning Call on my own species (to guarantee a reserve of food, if needed)
+ can’t be eradicated by non-Intelligent predators / more efficient with a low population (or a species that can fill up quite fast)
− less efficient on high pop counts
Combo: Long Neck, Fat Tissue, Intelligence
+ gives access to another source of food, esp. when plants get scarce / attacks opponents’ populations
− very situational and requires the right environment. If there are no valid targets, extinction is certain
Combo: Fat Tissue, Cooperation, other Scavengers
+ both a defensive and an offensive trait. The more Climbing cards I have, the fewer my opponents are likely to draw to get past mine
− both a defensive and an offensive trait (can therefore appeal to opponents)
+ low-food environments (quick-feed advantage), if combo with Carnivore
− little helpful in high-food environments
Combo: Foraging, Long Neck, Intelligence, Cooperation
+ impassable if enough population and non-Intelligent predators
− each attack suffered makes this less efficient; once the predator has more population, entirely inefficient. In low-food environments, high population is hard to maintain.
Combo: traits that help maintain high population (esp. Intelligence)
+ in high-food env. / used on high-pop, high-BS carnivores, can be a killer
− in low-food env.
Combo: Carnivore / replace it with another Fat Tissue (score the food on it and shoot again)
+ payed off at the first trigger; in high-food env.
− in low-food env.
Combo: Defensive Herding, Pack Hunting, other Fertiles + put high food into the Hole
+ in low-food env. (quick-feed advantage)
− if enough plants for all / useless with Carnivore
Combo: Long neck, Cooperation, Intelligence
+ low-BS predators (esp. early game)
− inefficient once the predator has got fat enough (or Pack Hunting)
+ an always applicable defense
− will never prevent an attack
Combo: more dissuasive with low BS, Hard Shell
+ if I keep cards in hand, I am (carnivore: nearly) sure to feed
Combo: Carnivore, Foraging, Cooperation, Burrowing
+ in low-food env. / always guarantees 1 plant
− in high-food env. / useless with Carnivore
Combo: Burrowing, Foraging, Cooperation
+ if preys have too high BS (esp. higher than 5)
− does not help go round most defenses
+ if there are several attacks per round (esp. high player count)
− if there are too few attacks per round
Combo: other Carnivore species (to guarantee that attacks happen), Cooperation
+ impassable if conditions are met and predators are not Intelligent
− can become useless if the species to the right (a prey of choice for your opponents) goes extinct
Combo: Cooperation (the protectee maintains its protector)
+ protects 2 species (no other trait does that good)
− negated by Ambush; does not protect the species with Warning Call and takes up a slot that could help it survive
Combo: any other environment-suitable defensive trait