ECOLOGICAL ROLE OF WOLVES
Over millennia wolves have evolved as family-based social units that are tightly bonded and reliant upon each other for survival.
A wolf pack, or family unit, lives in a highly organized manner and together they operate as a keystone species to maintain important ecological interactions. The beneficial ecological functions of wolves are invaluable and irreplaceable.
Wolves are carnivores which sit at the top of the food chain (i.e. as an apex consumer), although they drive ecological interactions at various levels of complex food web. In North America grey wolf diet is dominated by large and medium sized wild ungulates (6). Apex consumers help maintain important ecological processes which benefit biological diversity and ecosystem resiliency (1,2,3,4,7,8,9,11). The direct and indirect effects of wolves cascade through several trophic levels, as shown in the image below from Status and Ecological Effects of the World's Largest Carnivores.
Apex Predator: These are predators with no natural predators of their own. They reside at the top of the food chain. The removal of apex predators, usually caused by humans, can radically affect an ecosystem.
Ungulate: a hoofed animal, e.g. moose, deer, elk, caribou.
Conceptual diagram showing direct (solid lines) and indirect (dashed lines) effects of gray wolf reintroduction into the Greater Yellowstone ecosystem.
This is a simplified diagram, and not all species and trophic interactions are shown.
IMAGE REFERENCE: (8)
Scientific Figure on ResearchGate.
The complex interactions driven in a top-down manner by wolves and other top consumers have landscape-level effects as seen in this image from Trophic Downgrading of Planet Earth (11). Researchers on Isle Royale, in Banff and Yellowstone National Parks, and elsewhere, have helped us understand how wolves help aid the growth and diversity of trees and vegetation, and thus many other organisms too. Aquatic ecosystems are similarly regulated and enriched by apex consumers (11).
Landscape-level effects of trophic cascades from four terrestrial ecosystems. (A) Upland habitat of islands with (right) and without (left) Arctic foxes in the Aleutian archipelago. Foxes drive terrestrial ecosystems from grasslands to tundra by limiting seabirds and thereby reducing nutrient inputs from sea to land (47). (B) Venezuelan forests on small islands of Lago Guri (left: jaguar, cougar, and harpy eagles absent) and mainland forest (right, predators present). A diverse herbivore guild erupted with the loss of predators from the island, thereby reducing plant recruitment and survival (68). (C) Riparian habitat near the confluence of Soda Butte Creek with the Lamar River (Yellowstone National Park) illustrating the stature of willow plants during suppression (left, 1997) from long-term elk browsing and their release from elk browsing (right, 2001) after wolf reintroductions of 1995 and 1996 (25). (D) Decline of woody vegetation in Serengeti after eradication of rinderpest (by early 1960s) and the recovery of native ungulates (by middle 1980s). Left, 1986; right, 2003 (69).
IMAGE REFERENCE: (11)
Trophic Downgrading of Planet Earth- Article.
Scientific Figure on ResearchGate.
Scientific studies carried out in Banff and Yellowstone National Parks showed that when wolf numbers were low or absent ungulate density increased and adversely affected the growth of aspen and willow species in riparian areas (3,4,7,9). The reduction in plant biomass resulted in a reduction of active beaver lodges, which in turn negatively affected songbird abundance and diversity. These are some indirect effects that wolves exert on ecosystems.
Where wolf populations have been extirpated or exploited in North America, a cascade effect is observed in which small mammals, fish, insects, birds, amphibians, ungulates, tree species and vegetation all suffer. Yellowstone provides a great example of how the impoverished ecosystem was dramatically re-invigorated when wolves were returned into their native area. Researchers documented changes to the entire Yellowstone ecosystem since wolves began enriching the landscape through a return of their presence in significant numbers in 1995/96 (6). Within a decade, wolves had helped restore much of Yellowstone’s ecology to its former vibrant self.
IMAGE REFERENCE: National Geographic Magazine March 2010 ed. “Wolf Wars”.
Another way that wolves help maintain biodiversity is by providing feeding opportunities for other animals with the leftovers from a wolf kill. A distinctive and important trophic contribution of wolves is their consistent provision of carrion (4,9). In this way, carrion production by wolves may supplement or support many other animals in the wildlife community that scavenge, including bears, wolverines, coyotes, cougars, lynx, bobcats, martens, ravens, eagles, foxes, magpies, jays, beetles….the list goes on.
Ecological studies have shown that loss of a keystone species is more apt to cause a series of linked extinction events, resulting in a degraded ecosystem where biological diversity suffers. The combined role of the wolf pack as an umbrella species and keystone species merits added protection for wolves.
Keystone species: One whose influence on its community or ecosystem is disproportionately large relative to its abundance. When a keystone species is removed, the entire ecosystem can collapse.
Wolves and disease control
Another incredibly important natural service provided by wolves is helping to control the spread and outbreak of diseases. When wolves and other carnivores kill and eat sick animals they are providing a valuable line of defense against disease transmission. For example, ultra-lethal Chronic Wasting Disease (CWD), a fatal neurological disease that effects members of the deer family, is a major conservation concern expanding across North America. Saskatchewan recently reported a record number of confirmed cases of CWD. By directly removing diseased animals from the landscape, which are more vulnerable and easier to hunt, wolves help to limit and control the spread of diseases that affect the animals they consume. Wolves and other animals that scavenge help to rid and limit contagions by consuming ungulate carcasses when animals have succumbed to disease. In addition, the mere presence of wolves on a landscape causes large ungulates to behave differently, moving these animals around the landscape rather than allowing them to cluster in areas for prolonged periods, which in turn helps mitigate the contraction and spread of contagious diseases.
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