The Cost of Ecosystem Change_ The Sierra Nevada Bighorn Sheep(720P_HD)

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Transcript

00:00About a half a million years ago or somewhat more sheep crossed the Bering

00:27land bridge to North America and were the progenitors of our North American sheep.

00:33And there in the last glaciation, they were separated into two populations, the doll sheep

00:41and the bighorn sheep in the southern part.

00:46The Sierra bighorn sheep is a unique subspecies, distinct from the Rocky Mountain and desert

00:52bighorns.

00:54It now clings to existence here in the Sierras, its numbers plummeting during the last century.

01:01We started out with something in the neighborhood of 17 or more herds of sheep scattered along

01:07the Sierra Nevada from Sonora Pass south.

01:11And by the 1970s, we were down to three.

01:16We started seeing very high mountain lion predation levels in the 1980s.

01:22We watched the sheep in the Sierra start avoiding winter ranges where this predation was happening.

01:28And in the late 80s, I watched as the sheep basically quit using those winter ranges and

01:34started living year-round at the tops of the mountains.

01:37And we watched the populations drop to rather low numbers.

01:42The sheep have changed the eons-old patterns of their natural history.

01:49But it could very well have to do with manipulations that modern humans have done in these ecosystems.

01:56The sheep have changed the eons-old patterns of their natural history.

02:03What has changed that brought mountain lions into the sheep's historical ranges?

02:11What is different in this ecosystem?

02:15To answer this question, we must understand what this ecosystem was like in the past.

02:23But how do we look back in time?

02:26And what do we find?

02:30Since the 1970s, archaeologist Robert Bettinger has literally dug into the human past in the

02:36White Mountains, attempting to understand the spread of culture in Western North America.

02:44From his many field studies based at the station, he has recovered evidence of what the ancient

02:49hunter-gatherers took from this environment for food and raw materials.

02:55This allows him to reconstruct the history of this ecosystem and provide biologists and ecologists

03:01a look into the past.

03:05Amidst the sagebrush steppe, Robert and a group of students explored the faint remnants of an

03:11ancient highland hunting camp and paused to reflect on how the lives of those who once

03:17lived here tell us about what this ecosystem was once like and how it has changed.

03:25It is widely perceived in the public, I think, that hunting, first of all, is the most important

03:31thing that Native Americans do.

03:34And second, when the hunting is done, that it's primarily targeted at deer.

03:38And what we really see in these villages here in the highlands is, first, that gathering's

03:44just as important, and second, that deer aren't involved at all.

03:48And the real critical prey species up here, which dominates almost to the exclusion of all

03:54other large animals in the archaeological record, is the mountain sheep.

03:59And it was so from the very beginning of the record right up until what we call the historic

04:05period, when Euro-Americans come into eastern California.

04:09So the reasonable question to ask is, what's the difference?

04:15The environment that they relied on, this alpine environment, changed from one that favored

04:20mountain sheep in the past, which was grass, to sagebrush.

04:26Look where we are, in the middle of a sagebrush meadow, which is perfectly suited to deer, ideal

04:32for deer, but absolutely unsuited to mountain sheep.

04:38So what would it look like if you came up here 250 years ago?

04:43And the answer is that it wouldn't look like what we see today at all.

04:46Instead of sagebrush, what we would see is rolling fields of grass.

04:50It wouldn't be continuous grass, it wouldn't look like Kansas, but it's bunch grasses.

04:56And it would be all over here, taller and shorter, and pretty much continuous.

05:01But what could have caused such a dramatic change?

05:05A change that saw one ecosystem of plants entirely replaced by another?

05:11Was it drastic climate change, an invasive disease, or plague of insects?

05:17It was something more devastating.

05:22In a word, it's grazing.

05:23It's grazing animals.

05:24It's cows and sheep that come up here and take the really prime pasture that the mountain

05:34sheep had depended on, the herbs, the grasses that were here.

05:38It stripped those off and caused the sagebrush to flourish in their stead and basically transformed

05:47a grassland to a sagebrush steppe.

05:51And it stretches from Owens Valley all the way east to the far rim of the Great Basin.

05:56It's a change we see everywhere in the mountain ranges of the Great Basin where the grazing by

06:03sheep removes grass, causes a replacement of bighorn sheep by deer.

06:09Mountain lions are really primarily dependent on deer.

06:12Without deer, no mountain lions.

06:15They are also a part of this introduction, deer and mountain lions together, which are making

06:21a change in the environment.

06:25With domestic livestock eating their way through the landscape, a cascade of changes has transformed

06:31this ecosystem forever.

06:34Thus we will never again see herds of bighorn dominating the mountains that for untold millennia

06:40have been their home.

06:44Their forage is gone and predators have been invited into their range.

06:50They will forever cling to existence, while we must face the task of protecting them.

07:00They will forever be able to forgive them.

07:03They will forever be able to forgive them.

07:09live a young man to protect them.

07:14If you like to make a change in the environment, you will always be able to guard them.

07:23They will never again see you.

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