Recovery of a marine keystone predator transforms terrestrial predator–prey dynamics

Abstract

Sea otters ( Enhydra lutris ) and wolves ( Canis lupus ) are two apex predators with strong and cascading effects on ecosystem structure and function. After decades of recovery from near extirpation, their ranges now overlap, allowing sea otters and wolves to interact for the first time in the scientific record. We intensively studied wolves during 2015 to 2021 in an island system colonized by sea otters in the 2000s and by wolves in 2013. After wolf colonization, we quantified shifts in foraging behavior with DNA metabarcoding of 689 wolf scats and stable isotope analyses, both revealing a dietary switch from Sitka black-tailed deer ( Odocoileus hemionus ), the terrestrial in situ primary prey, to sea otters. Here we show an unexpected result of the reintroduction and restoration of sea otters, which became an abundant marine subsidy for wolves following population recovery. The availability of sea otters allowed wolves to persist and continue to reproduce, subsequently nearly eliminating deer. Genotypes from 390 wolf scats and telemetry data from 13 wolves confirmed island fidelity constituting one of the highest known wolf population densities and upending standardly accepted wolf density predictions based on ungulate abundance. Whereas marine subsidies in other systems are generally derived from lower trophic levels, here an apex nearshore predator became a key prey species and linked nearshore and terrestrial food webs in a recently deglaciated and rapidly changing ecosystem. These results underscore that species restoration may serve as an unanticipated nutrient pathway for recipient ecosystems even resulting in cross-boundary subsidy cascades.

Loss of sea turtle eggs drives the collapse of an insular reptile community

“…For instance, the conservation of wolves in Yellowstone National Park led to the recovery of willow trees and the return of beavers, which in turn drastically affected stream ecosystems (35). On island systems, such as in the case of the sea otter-wolf relationship (7), the consequences can be severe and drive the relatively small local populations to near extinction, as seen in our study. Therefore, management actions that are meant to conserve a specific species need to be carefully assessed to determine how interactions with other species will be affected (37).…”

“…In the case of Orchid Island, numerous species were affected due to their general susceptibility to the top snake predators. These top-down effects operating through the interaction between marine subsidies and generalist predators may be more widespread in nature than is generally appreciated [e.g., (6)(7)(8)11)]. For instance, a recent study showed that the proliferation of wolves because of previously unavailable marine prey (sea otters) drove the extinction of terrestrial ungulates on an island (7).…”

“…These top-down effects operating through the interaction between marine subsidies and generalist predators may be more widespread in nature than is generally appreciated [e.g., (6)(7)(8)11)]. For instance, a recent study showed that the proliferation of wolves because of previously unavailable marine prey (sea otters) drove the extinction of terrestrial ungulates on an island (7). Our case illustrates that the marine subsidy-generalist predator interaction can significantly affect not just single prey species but can actually destabilize an entire community through the trophic network.…”

Wolves turn into sea wolves by feeding primarily on sea otters

“…Predator-prey interactions on Coronation Island (above) and Pleasant Island (below); from Roffler et al (2023) [1]; CC BY-NC-ND 4.0.…”

Coevolution with artificial intelligence: are we at the start of a new era for academic publishing?

“…It is observed that a wolf population would die of starvation when their primary prey -often ungulates -disappeared. However, for the wolves on Pleasant Island of Alaska, when "running out" of deer, they switched to feeding on sea otters instead (Roffler et al, 2023). This change in primary diet and hunting strategy basically turned these apex predators into "sea wolves", driven by fundamental survival desire (Le, 2023).…”