Editing Greater Yellowstone Ecosystem (section)

===Fauna===
{{See also|Category: Fauna of the Rocky Mountains}}{{More citations needed section|date=April 2024}}
Anecdotal information on [[grizzly bear]] abundance dates to the mid-19th century, and administrators have made informal population estimates for more than 70 years. From these sources, ecologists know the species was common in Greater Yellowstone when [[Europe]]ans arrived and that the population was not isolated before the 1930s, but is now. Researchers do not know if bears were more or less common than now.

A 1959-1970 bear study suggested a grizzly bear population size of about 176, later revised to about 229.{{r|ecosystem}} Later estimates have ranged as low as 136 and as high as 540; the most recent is a minimum estimate of 236,{{r|ecosystem}} but biologists think there may be as many as 1,000 bears in the ecosystem.<ref name="DM 2024-01-06">{{Cite news |last=Koshmrl |first=Mike |date=2024-01-06 |title=Montana to start trucking grizzlies into Yellowstone region to improve delisting prospects |url=https://dailymontanan.com/2024/01/06/montana-to-start-trucking-grizzlies-into-yellowstone-region-to-improve-delisting-prospects/ |access-date=2024-01-31 |work=Daily Montanan |language=en-US}}</ref> Although the Greater Yellowstone population is relatively close to recovery goals, the plan's definition of recovery is controversial. Thus, even though the population may be stable or possibly increasing in the short term, in the longer term, continued [[habitat loss]], climate change, and increasing [[human]] activities may well reverse the trend.{{cn|date=January 2024}}

[[Yellowstone cutthroat trout]] (''Oncorhynchus clarki bouvieri'') have suffered considerable declines since European settlement, but recently began flourishing in some areas. Especially in [[Yellowstone Lake]] itself, long-term records indicate an almost remarkable restoration of robust populations from only three decades ago when the numbers of this [[fish]] were depleted because of excessive harvest. Its current recovery, though a significant management achievement, does not begin to restore the species' historical abundance. Also, they declined because of invasive lake trout. An aggressive lake trout removal program has caused the cutthroats to rebound.

Early accounts of [[pronghorn]] (''Antilocapra americana'') in Greater Yellowstone described [[herd]]s of hundreds seen ranging through most major [[valley|river valley]]s. These populations were decimated by 1900, and declines continued among remaining herds. On the park's northern range, pronghorn declined from 500 to 700 in the 1930s to about 122 in 1968. By 1992 the herd had increased to 536.

====Gray Wolf reintroduction====
{{main|History of wolves in Yellowstone}}
The park is a commonly cited example of [[apex predator]]s affecting an ecosystem through a [[trophic cascade]].<ref>{{Cite news |last=Weston |first=Phoebe |date=2022-06-23 |title='People may be overselling the myth': should we bring back the wolf? |url=https://www.theguardian.com/environment/2022/jun/23/rebalancing-act-bringing-back-wolf-fix-broken-ecosystem-aoe |access-date=2022-06-24 |work=The Guardian |language=en}}</ref> After the reintroduction of the [[gray wolf]] in 1995, researchers noticed drastic changes occurring. [[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 and aspens to grow, creating habitat for [[North American beaver|beaver]],<ref name=LOE032015>{{cite news|title=Beyond the Headlines|url=http://loe.org/shows/segments.html?programID=15-P13-00012&segmentID=5|access-date=March 22, 2015|work=Living on Earth|date=March 20, 2015}}</ref> [[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]] population. The bears, emerging from hibernation, chose to scavenge off wolf kills to gain needed energy and fatten up after fasting for months. Dozens of other species have been documented scavenging from wolf kills.<ref>{{Cite journal|last1=Smith|first1=Douglas W.|last2=Peterson|first2=Rolf O.|last3=Houston|first3=Douglas B.|date=2003-04-01|title=Yellowstone after Wolves|url=https://doi.org/10.1641/0006-3568(2003)053[0330:YAW]2.0.CO;2|journal=BioScience|volume=53|issue=4|pages=330–340|doi=10.1641/0006-3568(2003)053[0330:YAW]2.0.CO;2|s2cid=56277360 |issn=0006-3568|url-access=subscription}}</ref>