"Abert's Squirrels have a complicated relationship with ponderosa pine trees. These squirrels mostly live in pine forests and use the trees for shelter, nesting sites, and food. Where they exploit the pines extensively, the trees produce extra terpenes—chemicals that give pines their scent—to discourage the squirrels' appetites. These trees grow more slowly than pines in areas where Abert's Squirrel is absent and the trees produce less of these chemicals. The pines vary in the amount of toxins produced, and the squirrels select trees that are less toxic. A pine growing in squirrel range may suffer reduced vitality as a consequence of having its stems and seeds eaten by squirrels, or have its growth rate reduced because it is producing more toxins. However, the squirrels provide an important benefit to the pines by distributing fungal spores (through their feces), which as mature fungi are essential to the pines' health, so the relationship is a fascinating one."

Links:
Mammal Species of the World
Click here for The American Society of Mammalogists species account