18 Ecology, Behavior, and Conservation
how scatter-hoarding squirrels contribute to forest regen-
eration. That they do this is undeniable. How, when, and
the precise mechanisms by which they scatter-hoard are
still largely unanswered. However, research to date pro-
vides good evidence that squirrels are critical agents of seed
dispersal for at least nine genera of hardwood trees (Aescu-
lus, Carya, Castanea, Castanopsis, Corylus, Fagus, Juglans, Litho-
carpus, and Quercus) and two species of conifer (Pinus ko-
raiensis and P. jeff reyi).
Dispersal of Fungi
Squirrels frequently supplement their diets with a variety of
fungi. When these fungi include hypogeous, endorhyzal
species, squirrels insert themselves into a three-way mutu-
alism that is often crucial for forest function and regenera-
tion. Endorhyzal fungi are closely associated with the roots
of many tree species: the tree provides critical metabolic by-
products for fungal growth, whereas the fungi sequester
vital nutrients from the soil that are essential for tree
growth. The fungi clearly cannot live without the tree, and
the tree’s growth is greatly inhibited without its association
with the fungi. However, these fungi fruit underground,
and their spores appear to be solely dependent on animals
(primarily rodents) for their dispersal. Rodents, especially
squirrels, feast on these truffl es when other foods are not
available or when critical nutrients (e.g., calcium) are
needed. The fungal spores are then readily dispersed in the
rodents’ feces. The most thoroughly studied relationship is
that of the sciurids of the Pacifi c Northwest in the USA and
the moist, temperate, conifer forests in which they reside.
The northern fl ying squirrel (Glaucomys sabrinus), in particu-
lar, is a truffl e specialist and, as a consequence, an essential
contributor to forest function. A similar relationship has
been suggested for the southeastern fox squirrel (Sciurus ni-
ger niger) in the longleaf pine forests of the southeastern
coastal plain of the USA. Although this relationship be-
tween squirrels, fungi, and trees has only been explored in
a few systems, it is likely to exist in numerous forests
throughout the world.
Ecosystem Services and Conservation
The closely knit relationships between squirrels and plants
demonstrate the substantial ecosystem services they pro-
vide. A myriad of values are ascribed to squirrels. While
A Himalayan striped squirrel (Tamiops mcclellandii, foreground) and Finlayson’s squirrels (Callosciurus finlaysonii) at a market in
Thailand. Photo courtesy Israel Didham.