What If Gone

Species → Gray Wolf

Gray Wolf

Canis lupus

225,000 individuals
Extinction risk Least Concern
Apex predatorTrophic cascadeTemperate forestReintroduction
Gray Wolf (Canis lupus)
Photo: Mas3cf, Wikimedia Commons (CC BY-SA 4.0)

What if it disappeared?

Impact High
2 years

Without wolves, elk and bison are noticeably less vigilant — a behavioral effect that reversed within the very first years after reintroduction.

Documented
Detail

Laundré, J.W., Hernández, L. et Altendorf, K.B. (2001). Wolves, elk, and bison: reestablishing the "landscape of fear" in Yellowstone National Park, U.S.A. Canadian Journal of Zoology, 79(8), 1401–1409.

Within the first two years after wolf reintroduction (winter 1995–1996), female elk and bison showed significantly higher vigilance in areas at risk of predation than in wolf-free areas. This is what the authors call the "landscape of fear": the predator's presence changes prey behavior even before direct predation changes their numbers.

15 years

Without wolves to maintain that vigilance, willows, aspens, and alders stayed too heavily browsed to regain height; since reintroduction, these woody species have been regaining height in several parts of the park — a documented but uneven effect, not a park-wide one.

Documented
Detail

Ripple, W.J. et Beschta, R.L. (2012). Trophic cascades in Yellowstone: The first 15 years after wolf reintroduction. Biological Conservation, 145(1), 205–213.

Lighter elk browsing allowed woody species to regain height and cover in part of the park — a real but non-uniform effect across the territory. The authors also note an increase in beaver and bison populations over the same period, plausibly linked to the resurgence of available woody plants and herbaceous forage.

Several decades

If the resurgence of willows and aspens holds, it could in turn favor beaver expansion and, by extension, the restoration of riparian wetlands.

Extrapolated
Detail

Extrapolation à partir de Ripple & Beschta (2012), qui documente séparément le regain de végétation ligneuse et l'augmentation des populations de castor sur la même période, sans mesurer le lien de cause à effet entre les deux comme un tout.

Beavers depend on willow and aspen wood to build their dams; a sustained expansion of this wood could therefore favor beaver expansion, whose dam-building activity in turn restores riparian wetlands (see the beaver entry). Each link in this chain is documented separately; the full chain has never been tracked as a single phenomenon.

What's missing to confirm it: No study measures whether beaver expansion in Yellowstone actually translates, park-wide, into detectable wetland restoration — this is a logical extrapolation from two separately documented effects, not a third, measured effect.

A century and beyond

No study tracks this cascade over so long a horizon: the reintroduction itself is only three decades old.

Insufficient

Documentation

Last verified: August 6, 2026

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