How wolves change rivers
How wolves change rivers
Meanwhile, the populations of other animals exploded. The entire ecosystem of the American wilderness was changed by rapidly expanding populations of large ungulates.
After decades of political wrangling with those who traditionally persecuted wolves, conservation biologists and activists who supported restoration of wolves finally prevailed: the grey wolf, Canis lupus, was finally reintroduced several areas in the northern Rocky Mountains of the United States. One of those release areas was Yellowstone National Park. Subadult wolves from several packs in Alberta’s Mackenzie Valley were captured using tranquilizer darts and released in Yellowstone in January 1995 and again in January 1996.
The presence of wolves even substantially changed ungulate behaviours. For example, the wapiti stopped munching their way through the valleys and gorges where wolves could easily ambush them. Thus, native flora was able to re-establish and re-grow, thereby increasing biodiversity by providing food and shelter to a growing variety of plants and animals.
But remarkably, the presence of wolves also changed the rivers. After reintroduction, it was noticed that riverbank erosion decreased so the rivers meandered less, the channels deepened and small pools formed. Why? The recovering vegetation stabilized the riverbanks, which in turn altered the geography of the park itself.
This phenomenon is known amongst ecologists as a «trophic cascade». In this scenario, a top-down cascade was observed when the top predator, the wolf, was exterminated from most of its natural range. Removing the top predator triggered a wide range of effects that cascaded down through the entire web of life. Although only a total of 41 wolves were reintroduced and their total population remains small, they act as ecosystem engineers by creating niches that other animal and plant species can inhabit. This lovely little video documentary shows the cascading effects that restoring wolves to Yellowstone National Park has had:
[Reading this on a mobile device? Here’s the video link.]
The narrator, George Monbiot, is an environmental activist and a writer at The Guardian. He has traveled widely and suffered a great many adventures at the hands of his fellow humans, wild animals, and a variety of microbes. He can be found on twitter @GeorgeMonbiot.
Also see; News, Information and Recovery Status Reports of grey wolves in the northern Rocky Mountains of the United States.
GrrlScientist can be found here: Maniraptora. She’s very active on twitter @GrrlScientist and sometimes lurks on social media: facebook, G+, LinkedIn, and Pinterest.
How Wolves Change Rivers
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How Wolves Change Rivers
Wolves’ effect on Yellowstone National Park
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One of the most exciting scientific findings of the past half century has been the discovery of widespread trophic cascades. A trophic cascade is an ecological process which starts at the top of the food chain and tumbles all the way down to the bottom. And the classic example is what happened in the Yellowstone National Park in the United States when wolves were reintroduced in 1995.
In some areas, the height of the trees quintupled in just six years. Bare valley sides quickly became forests of aspen and willow and cottonwood. And as soon as that happened, the birds started moving in. The number of songbirds and migratory birds started to increase greatly. The number of beavers started to increase because beavers like to eat the trees. And beavers, like wolves, are ecosystem engineers. They create niches for other species. And the dams they built in the rivers provided habitats for otters and muscrats and ducks and fish and reptiles and amphibians. The wolves killed coyotes and as a result of that, the number rabbits and mice began to rise which meant more hawks more weasels more foxes more badgers Ravens and bald eagles came down to feed on the carrion that the wolves had left. Bears fed on it, too. And their population began to rise as well partly also because there were more berries growing on the regenerating shrubs. And the bears reinforced the impact of the wolves by killing some of the calves of the deer.
But here’s where it gets really interesting. The wolves changed the behavior of the rivers. They began to meander less. There was less erosion. The channels narrowed. More pools formed. More riffle sections. All of which were great for wildlife habitats. The rivers changed in response to the wolves. And the reason was that the regenerating forests stabilized the banks so that they collapsed less often. So the rivers became more fixed in their course. Similarly, by driving the deer out of some places, and the vegetation recovering on the valley side, there was less soil erosion because the vegitation stabilized that as well.
When wolves were reintroduced to Yellowstone National Park in the United States after being absent nearly 70 years, the most remarkable «trophic cascade» occurred. What is a trophic cascade and how exactly do wolves change rivers? George Monbiot explains in this movie remix.
If you likes How Wolves Change Rivers, check out How Whales Change Climate: https://www.youtube.com/watch?v=M18HxXve3CM
One of the most exciting scientific findings of the past half century has been the discovery of widespread trophic cascades. A trophic cascade is an ecological process which starts at the top of the food chain and tumbles all the way down to the bottom. And the classic example is what happened in the Yellowstone National Park in the United States when wolves were reintroduced in 1995.
In some areas, the height of the trees quintupled in just six years. Bare valley sides quickly became forests of aspen and willow and cottonwood. And as soon as that happened, the birds started moving in. The number of songbirds and migratory birds started to increase greatly. The number of beavers started to increase because beavers like to eat the trees. And beavers, like wolves, are ecosystem engineers. They create niches for other species. And the dams they built in the rivers provided habitats for otters and muscrats and ducks and fish and reptiles and amphibians. The wolves killed coyotes and as a result of that, the number rabbits and mice began to rise which meant more hawks more weasels more foxes more badgers Ravens and bald eagles came down to feed on the carrion that the wolves had left. Bears fed on it, too. And their population began to rise as well partly also because there were more berries growing on the regenerating shrubs. And the bears reinforced the impact of the wolves by killing some of the calves of the deer.
But here’s where it gets really interesting. The wolves changed the behavior of the rivers. They began to meander less. There was less erosion. The channels narrowed. More pools formed. More riffle sections. All of which were great for wildlife habitats. The rivers changed in response to the wolves. And the reason was that the regenerating forests stabilized the banks so that they collapsed less often. So the rivers became more fixed in their course. Similarly, by driving the deer out of some places, and the vegetation recovering on the valley side, there was less soil erosion because the vegitation stabilized that as well.
When wolves were reintroduced to Yellowstone National Park in the United States after being absent nearly 70 years, the most remarkable «trophic cascade» occurred. What is a trophic cascade and how exactly do wolves change rivers? George Monbiot explains in this movie remix.
How Wolves Change Rivers
In 1926, there were no wolves remaining in Yellowstone, the species’ former native home. Between 1977 and the re-introduction in 1995, we have reliable reports of wolves being seen throughout the park. Most of them were either lone wolves or pairs, probably only transiting. Finally, in 1995, grey wolf packs were reintroduced in the Lamar Valley of Yellowstone National Park and Idaho.
Before the extermination, the wolves living within the park belonged to the subspecies Northern Rocky Mountains wolf, Canis lupus irremotus. The reintroduced species of 1995 belong to the subspecies Mackenzie Valley wolf, Canis lupus occidentalis.
The reintroduction of the wolves produced a more significant impact on the biodiversity of the Yellowstone than anticipated.
The wolves’ predation on the elk population, until then unchallenged, produced a significant increase of new-growth in various plants. Aspen and willow trees, previously grazed by the elks more or less at will, got suddenly a chance to grow. With the presence of the wolves, the elks stopped venturing into deeper, and for them dangerous, thickets where they could easily be surprised. They began to avoid areas of low visibility, which would increase the chances of wolf attacks.
The elks began avoiding open regions such as valley bottoms, open meadows, and gorges, where they would be at a disadvantage in case of an attack from a wolf pack. William J. Ripple and Robert L. Bestcha dubbed this process top-down control. In ecology, top-down control denotes that top predators regulate the lower sections of the trophic pyramid. In other words: a top predator controls the structure or population dynamics of a particular ecosystem.
With new vegetation growing and expanding came subtle changes in the waterways running through the park. That had an impact on other species as well. Various bird species came back to Yellowstone national park with the increased number of trees. The beaver, previously extinct in the region, returned to the park. Their dams across the rivers attracted otters, muskrats, and reptiles.
Probably due to the wolves keeping the coyote populations at bay, the red fox got suddenly a chance to survive because the number of rabbits and mice grew considerably. The raven, always the wolf follower, came back to the park as well, now able to feed on the leftovers of the wolves.
The wolves changed the rivers in as much as they readdressed the lost balance within the region, one we had created when we exterminated them. With a better balance between predator and prey, top meat eaters and top grazers, came the possibility for other species to thrive. With the increased vegetation growth, erosion decreased, and the river banks stabilized.
Every time we produce drastic changes in nature, we interfere deeply with the whole eco-system.
Nature is indeed a beautiful act of balance.
References and further reading
How Wolves Change Rivers
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Video quiz questions (printable)
1) An ECOLOGICAL CASCADE is
2) Wolves were re-introduced to Yellowstone in
Match the items:
| Many deer ate a lot of plants | so the vegetation (plants) was gone. |
| Deer were not hunted | so they were more and more of them. |
| There were no wolves | so nobody hunted deer. |
7) What was the first thing that the wolves did?
8) What did the wolves change?
10) The height of the trees QUINTUPLED in just 6 years.
11) There were new forests of:
Match the items:
| When there were more trees | make changes for other animals. |
| One kind of animal was able to | and that’s why the forest grew. |
| The deer didn’t eat the vegetation | it was a good time for birds to come back. |
14) The beavers build
15) Beavers’ dams provide habitat for other animals such as:
16) The wolves killed
Match the items:
| Fewer coyotes meant | food for foxes, weasels and badgers. |
| More rabbits and mice meant | how different animals depend on each other. |
| This example shows us | more rabbits and mice. |
18) Who fed on the leftovers of killed animals?
19) There were more bears because:
21) The new vegetation made river banks:
22) More vegetation caused:
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How Wolves Change Rivers
Wolves were once native to the US’ Yellowstone National Park — until hunting wiped them out. But when in 1995 the wolves returned, something interesting happened: the most remarkable “trophic cascade” occurred.
The presence of wolves substantially changed the behaviour of large grazers. Wapiti deer stopped munching their way through the valleys and gorges where wolves could easily hunt them. The vegetation was able to re-establish and re-grow, thereby increasing biodiversity by providing food and shelter to a larger variety of plants and animals.
Remarkably, the presence of wolves also changed the rivers. Riverbank erosion decreased so the rivers meandered less, the channels deepened and small pools formed. The recovering vegetation stabilised the riverbanks, which in turn changed the geography and microclimate in the park.
Have a look at this amazing video showing how one species can have a massive cascading effect on the entire ecosystem in which it lives.
What is a trophic cascade and how exactly do wolves change rivers? George Monbiot explains in this Youtube mashup.
National Geographic reports this may be one of the most important conservation concepts to come out of natural science in the last half century. Remarkable about this case study is that the same can be applied to apex predators around the world: lions in Africa, tigers in Asia. Sharks, bears, and wild dogs are all species sitting at the top of their respective food chains, creating stability amongst the species they prey on and maintaining the health of plants and animals right down the trophic ladder.