I just had an other idea:
You have 2 populations, for example ants bringing food to their anthills.
The mutationrate at the best anthill is food_anthill (high) (so they won't mutate that easiely)
(i use food_anthill instead of an high value because at the beginning they have to mutate more)
and at the other:
abs(food_anthill-food_anthillenemy)
so the ants will change their behaviour if they are doing something wrong.
What do you think?