Squirrels of the World

Ecology, Behavior, and Conservation 19

squirrels can cause tree damage, depredate crops, gnaw elec-
trical and telephone wires, burrow beneath human struc-
tures, pilfer seeds, and serve as vectors for disease, their
signifi cance in forest and grassland ecosystems undoubt-
edly outweighs their potential costs. Squirrels perform con-
siderable ecosystem services—such as seed planting and
dispersal, pollination, and fungal spore dispersal—and they
may serve as indicator species for the health of some
ecosystems.
Some squirrels are seen as keystone species, due to their
disproportionate infl uence on their ecosystems, often be-
cause of their role as ecosystem engineers that structurally
change the environment. Examples include marmots (Mar-
mota), prairie dogs (Cynomys), and some ground squirrels
that create burrows and maintain shortgrass habitats that
are used by many other species. Red squirrels (Tamia s c iur u s
hudsonicus) and Douglas’s squirrels (T. douglasii) form large
piles of conifer-cone debris and cache newly harvested
cones within these middens, and many animals use the re-
sulting structures and food concentrations.
Squirrels also form a signifi cant prey base for a multitude
of other species. Subsistence and sport hunting of squirrels,
as well as trapping for pelts, occur in many areas, ranging
from the use of Callosciurus for food in Southeast Asia to the
millions of pelts of Sciurus and Marmota harvested annually
throughout Eurasia. Additionally, squirrel byproducts are
collected for their potential medicinal value, such as the
droppings of Tr o g o p t e r u s (in China) and Eupetaurus (in Paki-
stan and India), and the oils of Marmota in Asia.
Squirrels serve as models for human functions, patholo-
gies, and diseases: Funambulus (for metabolism and repro-
duction), Sciurus niger (for metabolic disorders), S. carolinen-
sis (for the lens and color vision in the human eye), Marmota
monax (for the hepatitis virus and related carcinomas, and
for atherosclerosis), and Ictidomys tridecemlineatus (for cho-
lesterol-induced pathology and atherosclerosis). Moreover,
numerous species provide examples for environmental edu-
cation. In some countries, encouraging recreational obser-
vations of squirrels has also generated a lucrative industry
(examples of some consumer products are nest boxes and
squirrel feeders) and that, along with the legal pet trade, pro-
vides a substantial economic impact. As a result, squirrels
can produce signifi cant fi nancial benefi ts.
Meanwhile, in terms of conservation, most major ecosys-
tems have been fragmented t hrough huma n act ivit ies during
the last 200 years. In particular, the forested and grassland
ecosystems inhabited by the squirrels have undergone ex-
cess levels of loss and fragmentation, with worldwide defor-
estation rates of 0.33 percent per year^ and grassland system
reductions at a rate of 0.08 percent per year—a combined
habitat loss of over 4 percent each decade at the current rates.

Habitat fragmentation has important consequences for the

biotic components of ecosystems, often changing genetic

variation, population densities, home range size, reproduc-

tive performance, and biodiversity. The consequences of

habitat loss and fragmentation can be profound.

Awareness of the conservation status of squirrels thus

takes on great importance when viewed in the context of

the ecological signifi cance of the taxa. We know that the

major threats to their persistence are habitat loss and frag-

mentation, overexploitation and persecution, and invasive

species. When we assess the level of imperilment of squir-

rels using the IUCN Red List database, we see that most spe-

cies are considered to be of least concern with respect to

their conservation status. This presents a positive outlook

for the conservation of squirrels. However, about one in fi ve

species is either of elevated conservation risk or so poorly

known that an assessment cannot be rendered.

The state of our knowledge of the population trends for

the members of the Sciuridae is of additional concern. Ac-

cording to the IUCN, more than 60 percent of the species are

either decreasing (~ 25%) or the trend is unknown (~ 35%);

only just over 35 percent of the species are considered to be

stable or increasing. Clearly there is much work to be done

toward the conservation of squirrels.

Critically Endangered

Endangered

Vulnerable

Near Threatened

Least Concern

Data Deficient

Increasing

Stable

Decreasing

Unknown

IUCN level of imperilment for all species of the Sciuridae.

IUCN assessment of the population trends for all species of

the Sciuridae.