The Wolf’s Tooth

Keystone Predators, Trophic Cascades, and Biodiversity

Scientist and author Cristina Eisenberg explores the concept of “trophic cascades” and the role of top predators in regulating ecosystems. Examining both general concepts and specific issues, the book focuses on the vital connection between trophic cascades and restoring biodiversity and habitats.

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“Wolves touch the whole web of life.” Photo Credit: Terra Magazine, Oregon State University, 2008

“Wolves touch the whole web of life.”
Photo Credit: Terra Magazine, Oregon State University, 2008

Predator-prey relationships play an essential role in channeling energy flows within ecological communities. The term trophic refers to anything related to the food web, while the poetic term trophic cascades refers to the movement of energy through the community food web when predators are removed (or when they return). This dynamic resembles a waterfall and involves top-down regulation of an ecosystem, in which predators have a controlling influence on prey abundance and behavior at the next lower level, and so forth through the food web. Remove a top predator, such as the wolf, and deer grow more abundant and bold, damaging their habitat by consuming vegetation (called herbivory) unsustainably. Intensive herbivory can lead to deer literally eating themselves out of house and home, and consequently to loss of biodiversity and destabilization of ecosystems. Lacking top predators, ecosystems become capable of supporting fewer species, because the trees and shrubs that create habitat for these species have been over-browsed. With top predators in them, they contain richer and more diverse habitat, and thus can support a greater number of species such as songbirds and butterflies.

In The Wolf’s Tooth I explore the science and conservation implications of trophic cascades. To do so, I take a wide view, one in which I look at trophic cascades within the context of the web of life. I share accounts from my fieldwork that illustrate the immediacy of foundational concepts such as the ecology of fear and resource selection. Awareness of trophic cascades is essential as we address global environmental changes.


“Wolves provide food for many other species, such as this grizzly bear feeding on the carcass of an elk killed by wolves.”
Photo credit: David Moskowitz

Trophic cascades are an ecosystem’s stories writ large upon aquatic and terrestrial landscapes. Wolves and other top predators leave distinct patterns—easily observable effects, such as a flush of aspen growth or luxuriant kelp forests—in formerly impoverished systems. To those of us studying these dynamics, the landscapes in which they occur are landscapes of hope. Ecosystems speak to all of us—researchers, managers, students, and plain members of the biotic community. If we pay close attention, they will tell us what to do as we strive to heal the ecological wounds caused by human impacts and address global change.