I tend to rule 0 a lot of the stuff like this I consider deffecient. I would give animals the vision benefits of what I consider their real world equivalents to have. All predator species that hunt at night get low light vision. All prey species would probably get a bonus to their spot checks against people sneaking into their area, but a minus for anything that might require a sharp eye. Most snakes would suffer pretty nasty penalties to spot checks, but if something is hidden, or invisible near them, they might have a slight advantage.