Ecological Influences of Ecological Influences of Canis Canis lupus arctos lupus arctos and and Canis lupus Canis lupus of Yellowstone National Parkof Yellowstone National Park

Joanna Denninghoff

Winter Ecology – Spring 2005

Mountain Research Station – University of Colorado, Boulder

PurposePurpose

How have the varying habitats and How have the varying habitats and ecosystems between arctic wolves ecosystems between arctic wolves and the gray wolves of Yellowstone and the gray wolves of Yellowstone been affected by wolf predation? been affected by wolf predation?

How do the different ecosystems How do the different ecosystems affect these wolf populations as well affect these wolf populations as well as ungulates and scavengers as ungulates and scavengers throughout the separate latitudes?throughout the separate latitudes?

IntroductionIntroduction The extreme differences between the habitats The extreme differences between the habitats

of arctic wolves (above 67* lat.) and the gray of arctic wolves (above 67* lat.) and the gray wolves of Yellowstone allowed for the wolves of Yellowstone allowed for the opportunity to research the differences of opportunity to research the differences of wolves’ behavioral differences and wolves’ behavioral differences and environmental effects caused by their environmental effects caused by their differing habitats and resource availabilities. differing habitats and resource availabilities.

Although these two species of wolves may Although these two species of wolves may seem somewhat abstract to one another, the seem somewhat abstract to one another, the genetic diversity between them is very genetic diversity between them is very insubstantial. The arctic wolf is just one of the insubstantial. The arctic wolf is just one of the subspecies of the gray wolf, subspecies of the gray wolf, Canis lupus Canis lupus (Marquard-Petersen, 1998).(Marquard-Petersen, 1998). Because of this, Because of this, the differences between the wolves can be the differences between the wolves can be considered to be due to their varying considered to be due to their varying environments and the ecological pressures environments and the ecological pressures each faces.each faces.

Gray Wolves of YellowstoneGray Wolves of Yellowstone Re-introduced in 1995 and 1996 with about Re-introduced in 1995 and 1996 with about

31 wolves; now at around 177 wolves.31 wolves; now at around 177 wolves. Re-introduction gave way to major changes Re-introduction gave way to major changes

in ungulate populations as well as in ungulate populations as well as scavengers’ populations and behavior scavengers’ populations and behavior (Wilmers, 2004).(Wilmers, 2004).

Prior to re-introduction, carrion availability Prior to re-introduction, carrion availability was due to hunters kills and end-of-winter was due to hunters kills and end-of-winter die-offs (resulting in overwhelming amounts die-offs (resulting in overwhelming amounts of carcasses—wasted) (Wilmers, 2004)of carcasses—wasted) (Wilmers, 2004)

Wolves provided for constant and dispersed Wolves provided for constant and dispersed sources of carrion for scavengers (coyotes, sources of carrion for scavengers (coyotes, ravens, magpies…beetles, vegetation).ravens, magpies…beetles, vegetation).

Gray Wolf BehaviorGray Wolf Behavior Wolves preferably feed on young, weak, sick, Wolves preferably feed on young, weak, sick,

or older prey (the more vulnerable), so as to or older prey (the more vulnerable), so as to gain food with the least amount of energy gain food with the least amount of energy loss. (Wilmers, 2004; Ripple, et. al., 2003)loss. (Wilmers, 2004; Ripple, et. al., 2003)

Wolves do not hibernate and hunt in packs Wolves do not hibernate and hunt in packs year-round. In lower elevations (food is year-round. In lower elevations (food is more abundant) wolves will not guard or more abundant) wolves will not guard or defend their kills after they are finished defend their kills after they are finished gorging, leaving scavengers to take their fill.gorging, leaving scavengers to take their fill.

As a result of the reintroduction of wolves, As a result of the reintroduction of wolves, both scavenger health and, indirectly, both scavenger health and, indirectly, potential prey (ie: elk) health has increased potential prey (ie: elk) health has increased (Wilmers, 2004).(Wilmers, 2004).

Benefits due to the Re-Benefits due to the Re-introduction of Wolvesintroduction of Wolves The re-introduced gray wolves has proven The re-introduced gray wolves has proven

(despite conflicting opinions of hunters) to be (despite conflicting opinions of hunters) to be beneficial to the entire ecosystem of YNP.beneficial to the entire ecosystem of YNP.

Wolves have had a positive effect on both the Wolves have had a positive effect on both the fitness and population sizes of certain ungulates, fitness and population sizes of certain ungulates, which allows more available food sources for which allows more available food sources for foraging ungulates during winter Wilmers, foraging ungulates during winter Wilmers, 2004).2004).

Ravens, along with myriad scavengers are able Ravens, along with myriad scavengers are able to feed throughout winter, thus remain in better to feed throughout winter, thus remain in better health than before wolves.health than before wolves.

With the continuous hunting of wolves, there are With the continuous hunting of wolves, there are much less wasted resources (Wilmers, 2004).much less wasted resources (Wilmers, 2004).

Yellowstone ConclusionsYellowstone Conclusions Thus, it appears to be obvious that wolves prove to Thus, it appears to be obvious that wolves prove to

be extremely beneficial to environments populated be extremely beneficial to environments populated with unchecked ungulates especially during winter with unchecked ungulates especially during winter months.months.

Overpopulation of foraging ungulates caused Overpopulation of foraging ungulates caused crashes in years prior to wolf re-introduction. The crashes in years prior to wolf re-introduction. The only check on browse species in winter, before was only check on browse species in winter, before was snow depth, winter severity and hunting (Wilmers, snow depth, winter severity and hunting (Wilmers, 2004).2004).

Although other predators exist in these areas: Although other predators exist in these areas: coyotes, bears and cougars—they had no coyotes, bears and cougars—they had no documented effects on winter patterns of elk documented effects on winter patterns of elk populations and herbivory (Ripple, et. al., 2003).populations and herbivory (Ripple, et. al., 2003).

After re-introduction, elk started foraging at sites After re-introduction, elk started foraging at sites that allowed for earlier detection and successful that allowed for earlier detection and successful chance for escape.chance for escape.

Yellowstone ConclusionsYellowstone Conclusions Had not wolves been absent from Had not wolves been absent from YNP for decades, the observed dataYNP for decades, the observed dataprovided insight into the importance provided insight into the importance of such a key predator. Re-of such a key predator. Re-introduction of wolves decreased the introduction of wolves decreased the overpopulation of ungulates, thusoverpopulation of ungulates, thus increasing available herbivory for increasing available herbivory for foragers, which in turn led to andforagers, which in turn led to and increase in such populations as beaversincrease in such populations as beavers and avian species that rely on un-and avian species that rely on un-browsed herbivory in later months, browsed herbivory in later months, and also and increase in many faunal species (Ripple, and also and increase in many faunal species (Ripple,

et. al., 2003). All of these interactions in this et. al., 2003). All of these interactions in this ecosystem are greatly a result of the presence of ecosystem are greatly a result of the presence of wolves. wolves.

Artic Wolves: IntroductionArtic Wolves: Introduction Arctic wolves have significant differences from gray Arctic wolves have significant differences from gray

wolves despite their genetic similarities. wolves despite their genetic similarities. Unfortunately, arctic wolves have not been under Unfortunately, arctic wolves have not been under intensive studies (Mech, 2000).intensive studies (Mech, 2000).

These observations used methods of direct These observations used methods of direct observation of kills and examination of kill sites. observation of kills and examination of kill sites. Also, feces samples were often used to determine Also, feces samples were often used to determine the diets of these wolves (Marquard-Petersen, the diets of these wolves (Marquard-Petersen, 1998).1998).

In contrast to the accessible, protected, and highly In contrast to the accessible, protected, and highly observed wolves of YNP, arctic wolves have not observed wolves of YNP, arctic wolves have not been under intense observation, possibly because been under intense observation, possibly because their ranges are so remote. Most data in the past their ranges are so remote. Most data in the past has come from hunters, Inuits, and such (Mech, has come from hunters, Inuits, and such (Mech, 2000).2000).

Adaptations and BehaviorAdaptations and Behavior Arctic wolves live in the regions above 67* latitude. This Arctic wolves live in the regions above 67* latitude. This

environment/land is covered in ice and snow all year environment/land is covered in ice and snow all year round except for a couple months in mid summer round except for a couple months in mid summer (Marquard-Petersen, 1998).(Marquard-Petersen, 1998).

This “summer” period is very influential on ungulate prey This “summer” period is very influential on ungulate prey densities, which in turn may affect wolf populations.densities, which in turn may affect wolf populations.

Arctic wolves have adapted well to their harsh Arctic wolves have adapted well to their harsh environments: they are covered in long, thick fur to keep environments: they are covered in long, thick fur to keep warm in temperatures as low as -70* F. They also warm in temperatures as low as -70* F. They also minimize heat loss by having more rounded ears, shorter minimize heat loss by having more rounded ears, shorter muzzles, shorter legs, smaller/stockier stature and have muzzles, shorter legs, smaller/stockier stature and have fur between the pads of their feet (Unknown, 2005).fur between the pads of their feet (Unknown, 2005).

These wolves do have similarities to their cousins such as These wolves do have similarities to their cousins such as living, hunting in packs, living in a social hierarchy and living, hunting in packs, living in a social hierarchy and hold territories (Mech, 2000). hold territories (Mech, 2000).

HabitatHabitat The habitat of arctic wolves is extremely The habitat of arctic wolves is extremely

different from their southern counterparts. different from their southern counterparts. They live in harsh winter environments They live in harsh winter environments almost year-round (~3 months of almost year-round (~3 months of “summer”). “summer”).

Prey consists of muskoxen, lemmings, arctic Prey consists of muskoxen, lemmings, arctic hares, and arctic foxes. Wolves are rarely hares, and arctic foxes. Wolves are rarely killed from conspecific aggression (probably killed from conspecific aggression (probably due to the low density of arctic wolves) due to the low density of arctic wolves) (Marquard-Petersen, 1998).(Marquard-Petersen, 1998).

Wolves tend to occur where muskoxen are Wolves tend to occur where muskoxen are common. In areas where muskoxen density common. In areas where muskoxen density is low, there were fewer observations of is low, there were fewer observations of wolves (Marquard-Petersen, 1998).wolves (Marquard-Petersen, 1998).

Denning BehaviorDenning Behavior Because of higher latitudinal locations, females Because of higher latitudinal locations, females

birth 2-3 pups in late May, early June. This birth 2-3 pups in late May, early June. This contrast southern relatives in that the southerners contrast southern relatives in that the southerners birth about one month earlier to about 5-6 pups. birth about one month earlier to about 5-6 pups. The lower number of pups may be due to scarcity The lower number of pups may be due to scarcity of prey in the arctic (Gray, 1993).of prey in the arctic (Gray, 1993).

Because of permafrost, arctic wolves must den in Because of permafrost, arctic wolves must den in rock outcroppings, caves, or shallow depressions, rock outcroppings, caves, or shallow depressions, in contrast to wolves of Yellowstone who are able in contrast to wolves of Yellowstone who are able to dig dens (Gray, 1993).to dig dens (Gray, 1993).

With arctic wolves the observed time of extensive With arctic wolves the observed time of extensive travel of pups with the pack was much earlier travel of pups with the pack was much earlier than most southern wolves. Also, pups used kill than most southern wolves. Also, pups used kill sites as temporary rendezvous sites after the sites as temporary rendezvous sites after the pack has begun traveling which provides not only pack has begun traveling which provides not only a place to meet but allows pups to rest, feed a place to meet but allows pups to rest, feed explore and gain experience while adults continue explore and gain experience while adults continue hunting (Gray, 1993).hunting (Gray, 1993).

Arctic Wolves’ Hunting Arctic Wolves’ Hunting BehaviorBehavior In the Arctic, densities of mammals are much In the Arctic, densities of mammals are much

lower than those of mammals inhabiting lower lower than those of mammals inhabiting lower latitudes (this also reflects in smaller litter size, latitudes (this also reflects in smaller litter size, probably due to lack of an abundance of probably due to lack of an abundance of resources), so population and productivity resources), so population and productivity declines are more serious (Ripple, et al, 2003).declines are more serious (Ripple, et al, 2003).

Because of low animal densities, prey densities, Because of low animal densities, prey densities, naturally, are also low in the arctic because naturally, are also low in the arctic because there is a scarcity of grazing plants which there is a scarcity of grazing plants which requires animals to roam large areas (Marquard-requires animals to roam large areas (Marquard-Petersen, 1998).Petersen, 1998).

This requires arctic wolves to have territories of This requires arctic wolves to have territories of well over 1,000 sq. mi.—well over 1,000 sq. mi.—wellwell over the ranges of over the ranges of their southern counterparts.their southern counterparts.

Hunting ContinuedHunting Continued Although capturing larger prey requires increased Although capturing larger prey requires increased

effort relative to small animals, more food is effort relative to small animals, more food is secured with larger kills (feeding a pack for secured with larger kills (feeding a pack for around 6 days) (Marquard-Petersen, 1998).around 6 days) (Marquard-Petersen, 1998).

However, arctic wolves will respond if large prey However, arctic wolves will respond if large prey becomes unavailable; then relying more on small becomes unavailable; then relying more on small mammals for food (Marquard-Petersen, 1998).mammals for food (Marquard-Petersen, 1998).

In contrast to the Yellowstone wolves, arctic In contrast to the Yellowstone wolves, arctic wolves will prey on anything and eat the entire wolves will prey on anything and eat the entire carcass (including fur, bones, skull…) (Mech, carcass (including fur, bones, skull…) (Mech, 2000).2000).

In this environment, it is the wolves, rather than In this environment, it is the wolves, rather than the scavengers, that are most benefited (or the scavengers, that are most benefited (or harmed) by ungulate populations and predation.harmed) by ungulate populations and predation.

Environmental InfluencesEnvironmental Influences Arctic wolf populations and productivity are easily Arctic wolf populations and productivity are easily

affected by ungulate populations (because of low animal affected by ungulate populations (because of low animal densities) (Marquard-Petersen, 1998; Mech, 2000).densities) (Marquard-Petersen, 1998; Mech, 2000).

These lower densities can cause much more detrimental These lower densities can cause much more detrimental and serious affects if populations become even less and serious affects if populations become even less dense, which, then effects the wolves (Marquard-dense, which, then effects the wolves (Marquard-Petersen, 1998).Petersen, 1998).

Early onset of winter might cause adverse demographic Early onset of winter might cause adverse demographic effects in arctic herbivores by shortening their summer effects in arctic herbivores by shortening their summer replenishment period; which on average is only about 3 replenishment period; which on average is only about 3 months (Ripple, et. al., 2003; Mech, 2000).months (Ripple, et. al., 2003; Mech, 2000).

If winter sets in during August, ungulates will go into If winter sets in during August, ungulates will go into winter without enough energy reserves causing winter without enough energy reserves causing starvation of the ungulates, and thus, in turn, the wolves starvation of the ungulates, and thus, in turn, the wolves (Marquard-Petersen, 1998).(Marquard-Petersen, 1998).

Discussion/ConclusionDiscussion/Conclusion Arctic wolves are Arctic wolves are influenced by their influenced by their environmentenvironment and have been for the time they and have been for the time they have existed in such harsh terrain. A decline in have existed in such harsh terrain. A decline in arctic prey can severely damage arctic wolf arctic prey can severely damage arctic wolf populations (since mammalian densities of all populations (since mammalian densities of all inhabitants are at such low densities already).inhabitants are at such low densities already).

Gray wolves of Yellowstone, however, have Gray wolves of Yellowstone, however, have greatly greatly influenced their environment, influenced their environment, rather rather than being influenced so much than being influenced so much byby the the environment.environment.

The reintroduction of wolves in Yellowstone The reintroduction of wolves in Yellowstone National Park has had great, advantageous National Park has had great, advantageous impacts on the ecology of and around the park. impacts on the ecology of and around the park. The environmental affects on these wolves The environmental affects on these wolves plays a much less important/determining role plays a much less important/determining role on their behaviors and such (thus far), in on their behaviors and such (thus far), in contrast to the arctic wolves of the north.contrast to the arctic wolves of the north.

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