US Geological Survey


Date of this Version



Journal of Animal Ecology 2015, 84, 647–651


Published 2015. This article is a U. S. Government work and is in the public domain in the USA


In ‘Trophic cascades from wolves to grizzly bears in Yellowstone’, Ripple et al. (2014) hypothesize that a wolf (Canis lupus)-caused trophic cascade has resulted in increased consumption of fruit by grizzly bears (Ursus arctos) in Yellowstone National Park (YNP). The authors proposed that in the absence of wolves, competition between grizzly bears and elk (Cervus elaphus) for berryproducing shrubs, along with high elk numbers, resulted in decreased fruit availability to grizzly bears. They further hypothesized that post-wolf reintroduction (with a subsequently reduced elk population), there would be an increase in the establishment of berry-producing shrubs and fruit availability to grizzly bears and an increase in the percentage of fruit in grizzly bear diets (Ripple et al. 2014). However, for a variety of reasons, the comparisons Ripple et al. (2014) used to demonstrate increased fruit availability and consumption by grizzly bears post-wolf reintroduction are flawed and tenuous at best. Importantly, a more parsimonious hypothesis, not sufficiently considered by Ripple et al. (2014), exists and is better supported by currently available data I review here.