0:00:01 > 0:00:06Our planet is the greatest living puzzle in the universe.
0:00:06 > 0:00:08A collection of worlds within worlds,
0:00:08 > 0:00:13each one a self-contained ecosystem bursting with life.
0:00:17 > 0:00:19But how do they work?
0:00:20 > 0:00:26The intricate web of relationships and the influence of natural forces
0:00:26 > 0:00:32makes each microworld complex and unique.
0:00:33 > 0:00:37So to discover their secrets, we need to explore them one by one.
0:00:39 > 0:00:42Untangle their interlocking pieces
0:00:42 > 0:00:46and ultimately reveal the vital piece,
0:00:46 > 0:00:48the key to life itself,
0:00:48 > 0:00:54hidden deep within each of nature's microworlds.
0:01:03 > 0:01:08The Amazon. The largest rainforest on Earth.
0:01:10 > 0:01:13Feeding the mightiest river in the world.
0:01:19 > 0:01:24It drains over 40% of South America
0:01:24 > 0:01:29and holds a fifth of the entire world's river water.
0:01:31 > 0:01:35Up to 12 metres of rain falls in parts of the Amazon every year.
0:01:39 > 0:01:45But what makes the Amazon even more incredible is the life within it.
0:01:48 > 0:01:53For sheer diversity of species, it's unparalleled.
0:01:53 > 0:01:58It is estimated to be home to up to 3 million species.
0:01:58 > 0:02:04Over 500 kinds of mammal, 30% of the world's bird species,
0:02:04 > 0:02:10and its plants produce 20% of the world's oxygen.
0:02:12 > 0:02:16The Amazon River even holds more kinds of fish
0:02:16 > 0:02:18than the whole of the Atlantic Ocean.
0:02:21 > 0:02:26A complex ecosystem with infinite connections and relationships,
0:02:26 > 0:02:31but as we shall discover, as in all our microworlds
0:02:31 > 0:02:36there is one piece that this entire system relies on to survive.
0:02:41 > 0:02:46And without it, the rainforest would look like this.
0:02:47 > 0:02:50Areas that have been slashed and burned for agriculture
0:02:50 > 0:02:56fail rapidly, and before long the land cannot even support crops.
0:02:56 > 0:02:59All our microworlds rely on nutrients,
0:02:59 > 0:03:02they are the building blocks of life.
0:03:02 > 0:03:05Phosphorous, potassium and calcium,
0:03:05 > 0:03:09vital elements that plants need to grow.
0:03:09 > 0:03:13But these nutrients are not a stable part of any ecosystem.
0:03:13 > 0:03:17Here they are either locked up and unobtainable in living tissue
0:03:17 > 0:03:21or washed out by the incessant rain.
0:03:23 > 0:03:25And it's so poor in available nutrients
0:03:25 > 0:03:30that scientists refer to the Amazon as a wet desert.
0:03:39 > 0:03:43The endless rain affects the trees, plants and soils
0:03:43 > 0:03:48and are constantly washing the building blocks of life away.
0:03:48 > 0:03:51Life here is actually surprisingly hard.
0:03:53 > 0:03:56So how in such a nutrient-poor microworld,
0:03:56 > 0:03:59is there so much diversity and life?
0:04:02 > 0:04:07The answer is that in nature, adversity leads to adaptation.
0:04:12 > 0:04:16Animals and plants have carved out incredible niches
0:04:16 > 0:04:17and formed vital relationships,
0:04:17 > 0:04:21not just to survive, but to thrive here.
0:04:21 > 0:04:27But is there one that holds the key to all this success?
0:04:33 > 0:04:37Understanding the Amazon, the most complex ecosystem on Earth,
0:04:37 > 0:04:41is one of the greatest challenges that ecologists have ever faced.
0:04:44 > 0:04:47Our only chance is by unpicking its web of connections
0:04:47 > 0:04:50until we can hopefully discover how the Amazon is able to support
0:04:50 > 0:04:54such diversity on such slim pickings.
0:04:57 > 0:05:00The Amazon is so massive and so intricate
0:05:00 > 0:05:03that we are really going to have to delve deep
0:05:03 > 0:05:07and get under this microworld's skin to search for the pivotal piece.
0:05:12 > 0:05:15So in our investigation we need to start small
0:05:15 > 0:05:18and focus on the details first.
0:05:24 > 0:05:29Like all microworlds, the Amazon is a showcase of natural selection.
0:05:29 > 0:05:34The inhabitants have evolved over time to exploit every niche,
0:05:34 > 0:05:38every opportunity that exists within its world.
0:05:41 > 0:05:43But what makes the Amazon special
0:05:43 > 0:05:46is the vast number of relationships that have developed.
0:05:49 > 0:05:54Particularly compelling is the interaction between flowers
0:05:54 > 0:05:58and one of the most beautiful groups of birds on the planet.
0:05:58 > 0:06:01Hummingbirds.
0:06:04 > 0:06:07Like bees, they are attracted to flowers
0:06:07 > 0:06:10for their energy-rich nectar.
0:06:12 > 0:06:16But in a world where every nutrient has to be locked up safely,
0:06:16 > 0:06:19the flowers can't give their valuable resources away
0:06:19 > 0:06:22unless they get something in return.
0:06:26 > 0:06:29The plants need to be pollinated.
0:06:29 > 0:06:34So as the birds feed, they get their heads sprinkled with pollen.
0:06:36 > 0:06:40But this only works if the hummingbird delivers the pollen
0:06:40 > 0:06:43to another flower of the same species.
0:06:43 > 0:06:46And that's the clever bit.
0:06:46 > 0:06:51Over thousands of years, the flowers and the birds have evolved together,
0:06:51 > 0:06:55so that only the species of bird with the right-shaped beak
0:06:55 > 0:06:59can get nectar from their species of flower.
0:07:00 > 0:07:02The birds are guaranteed food
0:07:02 > 0:07:06and the plant guarantees it gets pollinated.
0:07:11 > 0:07:14Relationships like this are born out of necessity
0:07:14 > 0:07:17but they might not hold the key to how this world works.
0:07:23 > 0:07:26The pivotal piece in many microworlds is a constant,
0:07:26 > 0:07:28something that doesn't change much
0:07:28 > 0:07:30so the rest of the world can keep up.
0:07:30 > 0:07:34So to find the key in this complicated world,
0:07:34 > 0:07:38first we need to find this constant.
0:07:39 > 0:07:43And there is one thing you can rely on in a rainforest -
0:07:43 > 0:07:44rain.
0:07:50 > 0:07:53Massive quantities of rain fall on the Amazon.
0:07:53 > 0:07:58An average downpour can dump two-and-a-half centimetres of water on the forest every hour.
0:08:02 > 0:08:08This rain usually comes from water evaporated from the sea.
0:08:08 > 0:08:14However, the Amazon is so immense, it literally makes its own rain.
0:08:14 > 0:08:1770% of the rain that falls
0:08:17 > 0:08:21has evaporated from the trees themselves.
0:08:23 > 0:08:26And this constant rain has had a direct effect
0:08:26 > 0:08:30on the shapes of things in the forest.
0:08:32 > 0:08:35Plants have developed leaves with gutters and spouts
0:08:35 > 0:08:37to get rid of as much water as possible
0:08:37 > 0:08:40because a leaf that doesn't dry off will end up rotting alive.
0:08:44 > 0:08:46Life can't survive without water,
0:08:46 > 0:08:49so the rain is an essential part of this system,
0:08:49 > 0:08:52but as we've seen, all the good it does
0:08:52 > 0:08:56is balanced by the damage it causes,
0:08:56 > 0:09:00literally washing away the rainforest itself.
0:09:04 > 0:09:08So if the rain's effect is to carry the forest away,
0:09:08 > 0:09:11what happens to it after this?
0:09:13 > 0:09:16Well, it ends up being transported
0:09:16 > 0:09:20by the most obvious force in our microworld, the Amazon River.
0:09:32 > 0:09:34It is a huge destructive force.
0:09:37 > 0:09:41Each year it removes an enormous one billion tons of sediment and mud
0:09:41 > 0:09:45from the forest basin on its march to the sea.
0:09:47 > 0:09:52During the course of this programme, it will have dumped the equivalent
0:09:52 > 0:09:56of 150,000 Olympic-sized swimming pools into the ocean.
0:10:00 > 0:10:04But the river is not as constant as you might think.
0:10:04 > 0:10:07It is so powerful that it scours deep channels
0:10:07 > 0:10:10barging its way through the forest,
0:10:10 > 0:10:15constantly changing course on its way to the Atlantic.
0:10:15 > 0:10:21But as destructive as it seems, it also creates opportunities for life.
0:10:23 > 0:10:26As the river loops through the forest,
0:10:26 > 0:10:28these meanders become very curved
0:10:28 > 0:10:33until eventually the neck of the meander touches the opposite side,
0:10:33 > 0:10:38cutting off a big loop from the main river.
0:10:40 > 0:10:43In creating these pools, known as oxbow lakes,
0:10:43 > 0:10:47the river creates a slightly different habitat to be exploited.
0:10:51 > 0:10:54These isolated bodies of water are the ideal space
0:10:54 > 0:10:57for one of the river's top predators,
0:10:57 > 0:10:59the two metre long giant otter.
0:11:02 > 0:11:05The lakes are full of fish and the waters are calm so the otters
0:11:05 > 0:11:10use them to rear their young away from the powerful main river.
0:11:11 > 0:11:15So in a microworld where every available space is to be exploited,
0:11:15 > 0:11:18the otters have turned this dead end feature of the river
0:11:18 > 0:11:20to their advantage.
0:11:23 > 0:11:27The river is actually a dynamic element in this environment.
0:11:27 > 0:11:30It's not the key to its existence,
0:11:30 > 0:11:33but its destructive nature does open up
0:11:33 > 0:11:35a lot of opportunities to life.
0:11:38 > 0:11:41Some of the sediment the river picks up gets dumped again,
0:11:41 > 0:11:44forming large banks.
0:11:47 > 0:11:51The minute space becomes available, something is there to exploit it.
0:11:51 > 0:11:57Thousands of giant river turtles use these banks to make their nests.
0:12:01 > 0:12:05So many come here that each wave digs up the nests laid moments before
0:12:05 > 0:12:11and in a world short on nutrients this bounty is not missed for long.
0:12:13 > 0:12:16At every turn, another opportunity is created
0:12:16 > 0:12:22and the black vultures are ready to jump in and make the most of it.
0:12:22 > 0:12:24Like their sea-dwelling cousins,
0:12:24 > 0:12:28these turtles have a strategy that involves producing so many eggs
0:12:28 > 0:12:31that they can afford to lose some casualties along the way.
0:12:34 > 0:12:35But in this ever-changing world,
0:12:35 > 0:12:40the turtles might have to look for a new nesting site next year.
0:12:43 > 0:12:46So the river is dependent on the rains,
0:12:46 > 0:12:49both are prominent players in the Amazon's ecosystem
0:12:49 > 0:12:53but they both play a role in removing the most vital piece
0:12:53 > 0:12:55of this puzzle, the nutrients.
0:12:57 > 0:13:00So how does the forest keep hold of enough of the good stuff
0:13:00 > 0:13:03to stay alive?
0:13:08 > 0:13:13In the Amazon, 99% of the nutrients are locked up in living tissues,
0:13:13 > 0:13:18so when any of this becomes available it's pounced upon.
0:13:18 > 0:13:21Nothing goes to waste -
0:13:21 > 0:13:27trees, leaves, dung and dead bodies are recycled almost immediately.
0:13:32 > 0:13:35The recycling team are an ungainly rabble of floor dwellers
0:13:35 > 0:13:40that lurk and skulk in the dark, damp recesses of the forest.
0:13:42 > 0:13:45Like this giant metre-long earthworm.
0:13:45 > 0:13:51They methodically race against the rains to reclaim as many nutrients as possible.
0:13:57 > 0:14:00Even so, commodities are scarce.
0:14:00 > 0:14:04Phosphorus, potassium and calcium, essential elements for life
0:14:04 > 0:14:10are hard to find, and because of the rain can be gone in a heartbeat.
0:14:12 > 0:14:15But the recycling teams are good,
0:14:15 > 0:14:20so good that sometimes things get recycled before they're even dead.
0:14:24 > 0:14:28Spores of the cordyceps fungus float through the air
0:14:28 > 0:14:32and find their way inside an insect host.
0:14:32 > 0:14:35The fungus attacks them from inside their bodies,
0:14:35 > 0:14:39killing them and consuming them from within.
0:14:41 > 0:14:43The fruiting body then erupts out of the dead insect
0:14:43 > 0:14:47and releases its spores to float through the air
0:14:47 > 0:14:50and infect other unfortunate individuals.
0:14:52 > 0:14:54But even here, there is a dark interdependency.
0:14:54 > 0:14:57Each strain of cordyceps fungus
0:14:57 > 0:15:01only infects its own particular species of insect.
0:15:11 > 0:15:13These recyclers play a vital role,
0:15:13 > 0:15:18keeping what little nutrients there are moving around the ecosystem.
0:15:18 > 0:15:21But this is certainly not enough
0:15:21 > 0:15:25to have created this forest of giants in the first place.
0:15:29 > 0:15:32So where would the trees normally get their nutrients from?
0:15:36 > 0:15:39Here trees can grow to over 50 metres tall.
0:15:39 > 0:15:45There is enough light and water in the Amazon to fuel rapid growth.
0:15:48 > 0:15:52But it is not enough. These giants like everything here
0:15:52 > 0:15:55need those nutrients to grow to these incredible sizes.
0:15:58 > 0:16:01Trees usually get all the nutrients they need from the soil,
0:16:01 > 0:16:04but what is different in this microworld
0:16:04 > 0:16:08is that these are some of the poorest soils on the planet.
0:16:10 > 0:16:14Only 1% of the nutrients in this ecosystem are found in the soil,
0:16:14 > 0:16:17compared to 50% in temperate forests
0:16:17 > 0:16:22so the Amazon trees are really up against it.
0:16:24 > 0:16:28Only the top 50 cm has any nutritional value,
0:16:28 > 0:16:33below this there is only clay that is no use to plants.
0:16:37 > 0:16:40So in response, the trees send their roots not down,
0:16:40 > 0:16:44but out through as much of the fertile top soil as they can.
0:16:47 > 0:16:51The only problem with this is that it makes them pretty unstable.
0:16:57 > 0:17:01One way around this is to create huge buttress roots that help stabilise them.
0:17:04 > 0:17:07And they need a good foundation because they are competing with
0:17:07 > 0:17:11the other trees for the other vital resource here - sunlight.
0:17:13 > 0:17:16The trees are so successful in exploiting sunlight
0:17:16 > 0:17:19that the forest floor is in constant shade.
0:17:19 > 0:17:22Only 2% of sunlight penetrates this canopy.
0:17:24 > 0:17:27So how does a young plant that's just starting out
0:17:27 > 0:17:29get established here?
0:17:33 > 0:17:37Cheese plant seedlings have a strange solution to this problem.
0:17:40 > 0:17:44Instead of heading for light, they search for darkness.
0:17:46 > 0:17:52The shadows created by a buttress root of a big tree.
0:17:58 > 0:18:02Once there and using the tree for support,
0:18:02 > 0:18:05they can race upwards towards the light.
0:18:10 > 0:18:14The cheese plant pours its energy resources into thin and rapid growth
0:18:14 > 0:18:20rather than strong stems, and leans on the tree for a helping hand.
0:18:20 > 0:18:24This gives it an advantage in a world where nutrients are limited.
0:18:31 > 0:18:35Other plants don't even bother to start at the bottom.
0:18:37 > 0:18:41Bromeliads grow high up in the branches of trees
0:18:41 > 0:18:44and so start life closer to the light.
0:18:50 > 0:18:53They have ponds in their centres
0:18:53 > 0:18:55that fill with up to eight litres of rain water,
0:18:55 > 0:19:01offering a water source 30 metres above the ground.
0:19:07 > 0:19:12And where there are ponds, there are usually frogs.
0:19:12 > 0:19:15One of the most poisonous creatures on earth
0:19:15 > 0:19:20relies upon the bromeliads for their rooftop pools.
0:19:20 > 0:19:23This poison arrow frog carries its tadpole,
0:19:23 > 0:19:29hatched from an egg laid on a leaf, to a pool in a bromeliad heart.
0:19:30 > 0:19:36Here the tadpole has its own private pool, tended by its parents.
0:19:36 > 0:19:39So the frogs rely on the bromeliad for a home
0:19:39 > 0:19:45but give the plant nutrients in the form of faeces and leftover food,
0:19:45 > 0:19:49and the bromeliad relies upon the tree to keep it near the sunlight.
0:19:53 > 0:19:56The tree tops are where it's really at.
0:19:56 > 0:20:00So successful are these high-rise communities
0:20:00 > 0:20:03that researchers discovered a single tree in the Amazon
0:20:03 > 0:20:06to be home to nearly 2,000 species of insect and spider.
0:20:06 > 0:20:11Only 100 of these were already known to science.
0:20:14 > 0:20:18With such limited resources and so many mouths to feed,
0:20:18 > 0:20:20once the plants have secured nutrients,
0:20:20 > 0:20:23they have to keep hold of them.
0:20:26 > 0:20:30Many Amazon plants use poisons to protect their leaves
0:20:30 > 0:20:33from the hungry vegetarians.
0:20:33 > 0:20:36But again nature finds a way.
0:20:38 > 0:20:44The piping guan only eats the tender new tips that hold the least poison.
0:20:46 > 0:20:48Most leaf eaters eat some then move on
0:20:48 > 0:20:52before they get too large a dose from any given tree.
0:20:53 > 0:20:55The white faced saki monkey, however,
0:20:55 > 0:20:59has evolved a highly specialised digestive system
0:20:59 > 0:21:03that can cope with virtually any toxin found in the rainforest.
0:21:06 > 0:21:10And there is another primate here, one of the smallest in the world,
0:21:10 > 0:21:13that has found a different way around the tree's poisonous defences.
0:21:18 > 0:21:22Pygmy marmosets are omnivorous, eating both plants and insects
0:21:22 > 0:21:25but their favourite food is tree gum,
0:21:25 > 0:21:28produced by the trees when their trunks are damaged.
0:21:28 > 0:21:32The marmosets have learnt to keep this food supply going
0:21:32 > 0:21:34by reopening previous wounds on the tree
0:21:34 > 0:21:39and they have evolved special teeth to do so.
0:21:42 > 0:21:45These tiny monkeys, which could fit inside a tea cup,
0:21:45 > 0:21:48have learnt how to exploit a particular food source
0:21:48 > 0:21:50at the tree's expense.
0:21:58 > 0:22:00Rather than fighting back,
0:22:00 > 0:22:03some plants have developed relationships with animals
0:22:03 > 0:22:05that benefit both parties.
0:22:07 > 0:22:10They grow tasty, energy-rich fruit.
0:22:11 > 0:22:1644 different species of bird and monkey can feed on a single tree.
0:22:19 > 0:22:23And the benefit for the tree is that contained inside the fruit
0:22:23 > 0:22:26are seeds that cannot be digested.
0:22:27 > 0:22:30So as the vegetarians move off through the forest,
0:22:30 > 0:22:33what has gone in has to come out.
0:22:34 > 0:22:38And the minute it hits the floor, in come the forests street cleaners.
0:22:41 > 0:22:45Dung beetles detect the bounty immediately.
0:22:46 > 0:22:48The males meticulously ball it up
0:22:48 > 0:22:52and roll it away with their hind legs.
0:22:52 > 0:22:57However, it is a lot easier to steal someone else's
0:22:57 > 0:22:58than to make your own.
0:22:58 > 0:23:03And the bigger the ball, the better the chances of attracting a female.
0:23:04 > 0:23:07Once he's clear, the beetle rolls his ball away,
0:23:07 > 0:23:12burying it in a safe place so that the female can lay her eggs inside
0:23:12 > 0:23:17and the tree's seed is planted with its own source of fertiliser.
0:23:20 > 0:23:22So in this relationship,
0:23:22 > 0:23:26the trees are connected to both the fruit eaters and the recycling team
0:23:26 > 0:23:28and they all benefit.
0:23:33 > 0:23:37There is one species of plant that has taken this one stage further
0:23:37 > 0:23:42and developed a much more direct and surprising relationship to get ahead.
0:23:45 > 0:23:48This might appear to be a natural forest clearing,
0:23:48 > 0:23:53but in fact it is inhabited by only one species of plant.
0:23:54 > 0:23:59One species of plant and thousands of ants.
0:24:01 > 0:24:06In this bizarre relationship, the plant has enlisted the ants' help
0:24:06 > 0:24:08in a very surprising way.
0:24:11 > 0:24:14The ants inject formic acid directly into the leaves and stems
0:24:14 > 0:24:17of any other plants that try and grow in the clearing,
0:24:17 > 0:24:20killing off all but their host plant.
0:24:26 > 0:24:31And the ants don't stop there. They also provide protection.
0:24:33 > 0:24:37They attack any animals that try and feed on the plant's leaves.
0:24:40 > 0:24:43Even giants many thousands of times their size
0:24:43 > 0:24:46are not immune to a bit of ankle biting.
0:24:51 > 0:24:54This is a great service if you are a plant in this competitive environment,
0:24:54 > 0:24:58but what do the ants get in return?
0:25:00 > 0:25:03The plant has small openings and swellings along its branches.
0:25:03 > 0:25:07These tiny cavities provide the ants with a home,
0:25:07 > 0:25:12protecting them from predators and giving them a safe place
0:25:12 > 0:25:14to rear their young.
0:25:16 > 0:25:19It's a collaboration developed over millennia and another example
0:25:19 > 0:25:23of how to survive out here, by building a successful relationship.
0:25:26 > 0:25:29And it is one of these relationships that holds the key
0:25:29 > 0:25:33to the success of this entire ecosystem.
0:25:33 > 0:25:39But it is not colourful, or obvious, and happens completely out of sight.
0:25:46 > 0:25:51Within the soil, the trees hide a symbiotic relationship
0:25:51 > 0:25:54with a fascinating fungus.
0:25:54 > 0:25:57The fungus are attached to their roots
0:25:57 > 0:26:01and absorb the available nutrients far faster than the trees
0:26:01 > 0:26:05because they have a huge surface area.
0:26:05 > 0:26:08They efficiently take elements like phosphorus, potassium
0:26:08 > 0:26:11and calcium out of the soil and into the tree
0:26:11 > 0:26:14before the rain gets a chance to wash it all away.
0:26:15 > 0:26:20But this relationship is mutually beneficial. Both parties benefit.
0:26:21 > 0:26:24In return, the tree supplies the fungus with sugars and starches
0:26:24 > 0:26:27that it can't obtain itself.
0:26:29 > 0:26:32One could not survive without the other
0:26:32 > 0:26:36and the rainforest as we know it would not exist.
0:26:40 > 0:26:42The delicacy of this relationship
0:26:42 > 0:26:46and the importance it has on this microworld is clearly demonstrated
0:26:46 > 0:26:49where the rainforest has been cut down for agriculture.
0:26:53 > 0:26:57The rain quickly washes away the little goodness held in the soil,
0:26:57 > 0:27:00and the sun bakes the ground solid.
0:27:02 > 0:27:06With no trees to shade the ground or to provide essential sugars,
0:27:06 > 0:27:09the fungus in the soil dies out.
0:27:09 > 0:27:13Leaving the soil barren, untenable for trees to recolonise.
0:27:15 > 0:27:19Without this partnership there would be no rainforest
0:27:19 > 0:27:23and so many species rely on this ecosystem.
0:27:28 > 0:27:33The Amazon rainforest is a complex web of inter-connectivity,
0:27:33 > 0:27:38where many organisms rely on the others to survive.
0:27:48 > 0:27:52The more diverse the microworld, the more robust it is to change.
0:27:56 > 0:28:00But as we have discovered, even our biggest and most diverse ecosystem
0:28:00 > 0:28:02relies on a fragile balance
0:28:02 > 0:28:06between the environment and the species that live within it.
0:28:08 > 0:28:12And without one surprising alliance between a tree and a fungus,
0:28:12 > 0:28:15life in our microworld would not exist at all.
0:28:19 > 0:28:22But it does and it has created
0:28:22 > 0:28:27one of the most incredible and intricate microworlds on our planet.
0:28:33 > 0:28:35Subtitles by Red Bee Media Ltd