0:00:02 > 0:00:05living puzzle in the universe.
0:00:40 > 0:00:42..untangle their interlocking pieces
0:00:49 > 0:00:54each of Nature's Microworlds.
0:01:05 > 0:01:09Rocky Mountains of North America
0:01:25 > 0:01:28Its unique geology means that
0:01:28 > 0:01:31volcanic heat from the Earth's core comes right to the surface.
0:01:47 > 0:01:52Established in 1872, Yellowstone is the world's first national park,
0:01:57 > 0:01:59its awe-inspiring landscape,
0:01:59 > 0:02:04it's home to an array of North America's most charismatic wildlife.
0:02:11 > 0:02:14These dwell in vast forests
0:02:18 > 0:02:21Isolated by sheer mountain peaks,
0:02:21 > 0:02:26is a stage upon which scientists
0:02:26 > 0:02:29discovered surprising connections
0:02:31 > 0:02:35To fully understand the key to the rich complexity of life
0:02:35 > 0:02:39in Yellowstone today, we must look at how the presence of one animal
0:02:39 > 0:02:40can affect that of another.
0:02:42 > 0:02:44At the very top of the food chain
0:02:51 > 0:02:55to 98 wolves, in ten packs.
0:02:56 > 0:03:00the herds of large grazing mammals.
0:03:06 > 0:03:09At the other end of the spectrum
0:03:16 > 0:03:26live very independent lives.
0:03:28 > 0:03:32This was discovered after the National Parks and Wildlife Service
0:03:32 > 0:03:36launched a landmark project
0:03:39 > 0:03:45from the park for 70 years.
0:03:45 > 0:04:07They were eradicated as part of a predator control campaign
0:04:07 > 0:04:10The releases were surrounded
0:04:10 > 0:04:14Some parties claimed that wolves would unleashed devastation
0:04:14 > 0:04:18of America's rare grazing mammals.
0:04:30 > 0:04:32Soon after the reintroduction
0:04:32 > 0:04:35took a turn for the better.
0:04:42 > 0:04:45..and numbers of water birds
0:04:49 > 0:04:51This improvement in river habitat
0:04:51 > 0:04:55was down to the tireless work
0:05:02 > 0:05:06their precious reserves of water
0:05:06 > 0:05:10dry summers and remove sediments.
0:05:15 > 0:05:18The timing of the beavers' return
0:05:22 > 0:05:26between wolves and beavers?
0:05:26 > 0:05:29How are their lives interconnected?
0:05:39 > 0:05:43Before we answer these questions,
0:05:43 > 0:05:46a force to be reckoned with.
0:06:05 > 0:06:09standing 1.5 metres at the shoulder, and weighing over 300 kilos.
0:06:09 > 0:06:13only weighs about 50 kilos.
0:06:16 > 0:06:18have the advantage of numbers
0:06:29 > 0:06:33Despite the wolves' apparent advantage, the elk is in his prime.
0:06:35 > 0:06:38will not risk following him
0:06:39 > 0:06:44he makes good his escape...
0:06:44 > 0:06:45..to the disappointment of the pack.
0:06:51 > 0:06:54A wolf pack is a close family unit.
0:07:29 > 0:07:34Pack hierarchy is maintained through these ritualised play-fights.
0:07:34 > 0:07:38Rank is based on attitude rather
0:07:40 > 0:07:44And there is one other way through which they strengthen their bond.
0:07:58 > 0:08:03It maintains cohesion within the pack, even if they are separated.
0:08:03 > 0:08:07it advertises their presence,
0:08:10 > 0:08:13and letting other wolf packs
0:08:18 > 0:08:21Apart from the fact that beavers exist within wolf territory,
0:08:21 > 0:08:24they have little to do with them.
0:08:24 > 0:08:26have their numbers increased?
0:08:28 > 0:08:31at what Yellowstone was like
0:08:31 > 0:08:34before the wolves were brought back.
0:08:40 > 0:08:45Before 1995, Yellowstone's top dog
0:08:54 > 0:08:58Yellowstone had the largest coyote population in North America.
0:09:06 > 0:09:09Yellowstone's coyotes are less than half the size of the wolves
0:09:15 > 0:09:18They exist mainly on a diet
0:09:45 > 0:09:47But, during the reign of the coyote,
0:09:52 > 0:09:55Thievery is another coyote trait.
0:09:57 > 0:10:00their hard-earned winter catch
0:10:00 > 0:10:02in a burrow under deep snow.
0:10:07 > 0:10:10The coyote's excellent sense
0:10:22 > 0:10:27This fearlessness had a devastating impact on the wider ecosystem.
0:10:52 > 0:11:02But what they lack in height,
0:11:05 > 0:11:09Coyotes are not big or fast enough
0:11:15 > 0:11:21the average life expectancy of a pronghorn fawn was just 35 days.
0:11:24 > 0:11:29and the pronghorn population fell
0:11:29 > 0:11:32By the early 1990s, there was serious concern for the pronghorn.
0:11:33 > 0:11:36But all that was to change.
0:11:36 > 0:11:40coyotes were dealt a shocking blow.
0:11:57 > 0:12:00Wolves pay little attention to them.
0:12:02 > 0:12:05substantial enough to feed a pack.
0:12:09 > 0:12:14has seen pronghorn numbers increase
0:12:27 > 0:12:29to being more secretive and nervous.
0:12:29 > 0:12:32over their shoulder at every turn.
0:12:40 > 0:12:42So by, policing the coyotes,
0:12:53 > 0:12:57Were coyotes also the reason why beavers were absent in Yellowstone?
0:13:07 > 0:13:12the same material, known as a lodge.
0:13:12 > 0:13:16The lodge can only be accessed via an underwater entrance.
0:13:16 > 0:13:22Inside, safe from the attention
0:13:58 > 0:14:09relationship with the wolf?
0:14:18 > 0:14:22They will sometimes dig open beaver lodges and prey upon beavers.
0:14:26 > 0:14:29of chasing big prey like elk.
0:14:40 > 0:14:43Despite their enormous bulk, bears are surprisingly fast.
0:14:54 > 0:14:59However, bears are also quite happy to let someone else do all the work.
0:15:07 > 0:15:10all of their kill in one sitting,
0:15:10 > 0:15:15the carcass becomes an abandoned picnic just waiting to be exploited.
0:15:19 > 0:15:23only the hardest winters would bring
0:15:23 > 0:15:26the supply has not only increased
0:15:36 > 0:15:39bears are more than capable
0:15:41 > 0:15:45Fear of wolves is most definitely
0:15:56 > 0:15:59Despite strength in numbers, wolves know to respect bears -
0:15:59 > 0:16:03and powerful claws mean business.
0:16:06 > 0:16:11wolves will eat at the same table.
0:16:21 > 0:16:25an unlikely bounty to Yellowstone.
0:16:31 > 0:16:32the bear population is on the up.
0:16:34 > 0:16:38If bear predation had any impact
0:16:38 > 0:16:42we'd not expect beaver numbers to increase alongside bears'.
0:16:45 > 0:16:49to the return of the beaver.
0:17:11 > 0:17:15What other wolf relationships
0:17:15 > 0:17:17to an increase in beaver numbers?
0:17:46 > 0:17:51Bulls can weigh over 1,000 kilos.
0:17:51 > 0:17:54stand their ground against a pack.
0:17:57 > 0:18:00These giants have been roaming the plains of North America
0:18:08 > 0:18:12They can also slow their metabolism
0:18:23 > 0:18:25to reach the grass beneath.
0:18:34 > 0:18:38It's estimated that 50 million bison once lived in North America...
0:18:38 > 0:18:42before Europeans settled here.
0:18:42 > 0:18:45Overharvesting caused total numbers across the continent to crash
0:18:45 > 0:18:49to less than 2,000 in 1900.
0:18:55 > 0:18:59Now, thanks to careful management, their numbers across North America
0:19:08 > 0:19:12have anything to fear from wolves.
0:19:14 > 0:19:18But, during the summer months, it's the young that are most vulnerable.
0:19:19 > 0:19:23it's still a risky business.
0:19:28 > 0:19:30the calves from their mothers.
0:19:35 > 0:19:37But the bison are quick to react.
0:19:39 > 0:19:41A large bull joins the fray.
0:19:45 > 0:19:47Any attempt at snatching a calf
0:19:47 > 0:19:50fatal consequences for a wolf.
0:19:53 > 0:19:56they've missed their chance.
0:19:58 > 0:20:02The threat of serious injury or death is always a good deterrent.
0:20:04 > 0:20:06They must be successful soon,
0:20:06 > 0:20:09for they themselves have young to rear at this time of year.
0:20:12 > 0:20:16to be seen out in the open.
0:20:16 > 0:20:26all of their time in the den,
0:20:26 > 0:20:34they'll soon rule themselves.
0:21:04 > 0:21:09Breeding success in wolves is strongly linked to hunting success.
0:21:13 > 0:21:18If their kill rate declines, then the wolf population soon follows.
0:21:20 > 0:21:23Bison provide plenty of meat
0:21:23 > 0:21:26pushes wolves to their limits.
0:21:26 > 0:21:30Because of this, bison are not
0:21:36 > 0:21:39With bison numbers changing little in response to wolves,
0:21:42 > 0:21:45and river habitat within the park.
0:21:52 > 0:21:56But there is one prey animal that's
0:22:06 > 0:22:09Numbering tens of thousands,
0:22:09 > 0:22:11elk are the most numerous grazer
0:22:20 > 0:22:24to advertise his status to females
0:22:24 > 0:22:27and to other males in the vicinity.
0:22:28 > 0:22:31are a sign of age and status.
0:22:52 > 0:22:56But there are challengers to the throne and he must prove his worth.
0:23:00 > 0:23:04and intimidate an opponent.
0:23:15 > 0:23:19Fights may last many minutes.
0:23:24 > 0:23:27the competition is seen off...
0:23:38 > 0:23:41A large male may not eat for weeks
0:23:43 > 0:23:48And, if he's lucky, he'll mate with
0:23:48 > 0:23:52he has very little time to feed
0:23:52 > 0:24:24and regain condition before thick snow covers the lands once again.
0:24:34 > 0:24:38the elk population consists
0:24:38 > 0:24:42and elk are interdependent.
0:24:48 > 0:24:50grazed in open country without fear.
0:24:52 > 0:24:56And here lies the key to our puzzle.
0:24:56 > 0:25:01Without fear of predation by wolves,
0:25:04 > 0:25:09Especially on the river banks where everything was grazed to the ground.
0:25:12 > 0:25:14and never gained a foothold.
0:25:15 > 0:25:18strengthening the riverbanks,
0:25:21 > 0:25:25by the trampling of the herds.
0:25:27 > 0:25:30the water-holding properties of the soil are diminished.
0:25:32 > 0:25:38This in turn encourages silt to build up in fish spawning beds.
0:25:38 > 0:25:41As a whole, biodiversity decreased.
0:25:41 > 0:25:45Yellowstone was left with less habitat for birds and insects,
0:25:53 > 0:25:56The culture of fear instilled
0:25:56 > 0:25:59to their naturally flighty state.
0:26:05 > 0:26:08Instead, the herds stay on the move.
0:26:14 > 0:26:17vegetation once chewed to its roots
0:26:22 > 0:26:27Willows, aspen and cottonwood trees started to re-colonise river banks.
0:26:31 > 0:26:35for much of Yellowstone's wildlife.
0:26:48 > 0:26:52These, in turn, provide food
0:26:52 > 0:26:55which themselves provide food
0:26:58 > 0:27:09The enriched soil encourages
0:27:17 > 0:27:21This provides a much better habitat
0:27:21 > 0:27:39And fish provide an important
0:27:49 > 0:27:53a far more beneficial impact
0:28:00 > 0:28:04all levels of the food chain.
0:28:10 > 0:28:15one of Earth's great microworlds.