One clear example of mutualism in the tundra ecosystem is the relationship between caribou and certain species of lichens.
Caribou rely heavily on lichens, particularly in the winter months when other food sources are scarce. These lichens grow on the ground and provide essential nutrients for the caribou. In return, caribou help to disperse lichen spores through their movement across the tundra, aiding in the growth and spread of these fungi. This is a classic example of mutualism because both organisms benefit from the relationship: the caribou receive sustenance, while lichens stand a better chance of expanding their habitat.