What If Gone

Species → Eastern Gray Squirrel

Eastern Gray Squirrel

Sciurus carolinensis

no global estimate; abundant and expanding in its native North…
Extinction risk Least Concern
Invasive speciesSeed disperserTemperate forest
Eastern Gray Squirrel (Sciurus carolinensis)
Photo: Charles J. Sharp, Wikimedia Commons (CC BY-SA 4.0)

What if it disappeared?

Impact High
Every autumn

The gray squirrel scatter-hoards a large share of its acorn harvest, a strategy where each acorn is buried separately rather than piled up — a substantial fraction of these caches are never recovered by the squirrel, which effectively plants oaks in its place, with a documented preference for red-oak-group acorns, which have longer dormancy and are therefore more worthwhile to store.

Documented
Detail

Smallwood, P.D., Steele, M.A. & Faeth, S.H. (2001). The ultimate basis of the caching preferences of rodents, and the oak-dispersal syndrome: tannins, insects, and seed germination. American Zoologist, 41(4), 840-851.

The study explains why squirrels treat red-oak and white-oak acorns differently: white oak acorns germinate almost immediately after falling, which pushes the squirrel to eat rather than store them, while red oak acorn dormancy makes them better candidates for productive forgetting.

In Britain

A field-data-driven model shows that the red squirrel's replacement by the gray squirrel isn't driven by food competition alone but chiefly by a poxvirus that the gray squirrel carries without harm: where the virus circulates alongside the gray squirrel, red squirrel decline is roughly 25 times faster than in areas where the two species coexist without the virus.

Documented
Detail

Tompkins, D.M., White, A.R. & Boots, M. (2003). Ecological replacement of native red squirrels by invasive greys driven by disease. Ecology Letters, 6(3), 189-196.

The epidemiological model combines field trapping and viral seroprevalence data to separate the effect of pure competition from that of disease, a case that has become a reference for what ecologists call "disease-mediated invasion" — the introduced species doesn't win because it's a better competitor, but because it spreads a pathogen to which it is itself resistant.

Documentation

Last verified: August 14, 2026