Apex Predator - Ecological Role

Ecological Role

See also Mesopredator release hypothesis

Apex predators affect prey species' population dynamics. Where two competing species are in an ecologically unstable relationship, apex predators tend to create stability if they prey upon both. Inter-predator relationships are also affected by apex status. Non-native fish, for example, have been known to devastate formerly dominant predators. One lake manipulation study found that when the non-native smallmouth bass was removed, lake trout, the suppressed native apex predator, diversified its prey selection and increased its trophic level.

Effects on wider ecosystem characteristics, such as plant ecology, have been debated, but there is evidence of a significant impact by apex predators: introduced arctic foxes, for example, have been shown to turn subarctic islands from grassland into tundra through predation on seabirds. Such wide-ranging effects on lower levels of an ecosystem are termed trophic cascades. The removal of top-level predators, often, recently, through human agency, can radically cause (or disrupt) trophic cascades. A commonly cited example of apex predators affecting an ecosystem is Yellowstone National Park. After the reintroduction of the gray wolf in 1995, researchers noticed drastic changes occurring in the Greater Yellowstone Ecosystem. Elk, the primary prey of the gray wolf, became less abundant and changed their behavior, freeing riparian zones from constant grazing. The respite allowed willows, aspens, and cottonwoods to grow, creating habitat for beaver, moose, and scores of other species. In addition to the effects on prey species, the gray wolf's presence also affected the park's grizzly bear, a vulnerable species. The bears, emerging from hibernation, chose to scavenge off wolf kills after fasting for months. They can also eat wolf kills in autumn to prepare for hibernation. As grizzly bears give birth during hibernation, a greater food supply may improve the mother’s nutrition and increase the number of cubs. Dozens of other species, including eagles, ravens, magpies, coyotes, and black bears, have been documented scavenging from wolf kills. Keystone species are apex predators within functional groups, a concept first described by zoologist Robert Paine to explain the relationship between Pisaster ochraceus, a species of starfish, and Mytilus californianus, a species of mussel.

• The saltwater crocodile is the largest living reptile and is the dominant predator throughout its range.

• The Tiger is the second largest non-aquatic mammalian predator in the world, behind the Polar bear. Pictured is the Siberian tiger, the largest subspecies of tiger and of the cat family, all of which are consummate predators irrespective of size.

• A killer whale observes a Weddell seal on an ice floe near Rothera Station, along the Antarctic Peninsula. Killer whales are known to sometimes kill other whales while hunting in packs, earning them the title "Wolves of the Sea", and even killing the Great White Shark one-on-one as prey.

• Large dogs may be well behaved around humans -- but part of the good behavior of these recent descendants of wolves includes using all of the usual lethal characteristics of wild carnivores in collaboration with a creature (Man, a Great Ape and not a true carnivore) clever and intelligent enough to fashion and use tools even deadlier than the claws and fangs of larger carnivores. These two creatures are the top of the food chain in much of their shared world.

• The whale shark, the world's largest shark and fish, has small prey only as large as small fish but is not itself prey even if it has a well-deserved reputation as a "gentle giant".

• Death comes swiftly and without warning for small vertebrates on the ground, on a tree branch, in the sky, or on or just below the waterline (like the salmon that this eagle just caught) that the bald eagle sees with its superb vision from a safe and distant perch, pierces with its talons, and removes swiftly to eat.