 Bark beetles can work in a dynamic mutualistic fashion with fungi and mites attached to their exoskeletons, both of which feed off of trees to provide vital energy to the beetles while the beetles provide necessary organic material to the fungi and mites to survive.In this case, the relationship between the fungi and mites is functional because while both do the same job, they are optimally functional at different temperatures.Mutualist interactions can be evolutionary unstable because of the constant battle to maximize one's self-benefits.