Complementary texts to the videos

Ecology

Complementary texts to the video clips

Text 1: Brazil nut trees

Rainforests are characterized by a unique vegetative structure consisting of several vertical layers including the overstory, canopy, understory, shrub layer, and ground level. One of the largest trees in the rainforest that makes up a large portion of the canopy is the Brazil nut tree (Bertholletia excelsa). These trees are dependent on several animal species for their survival such as the agouti, a ground-dwelling rodent, for a key part of their life cycle. The agouti is the only animal with teeth strong enough to open their grapefruit-sized seed pods. While the agouti eats some of the Brazil nut's seeds, it also scatters the seeds across the forest by burying caches far away from the parent tree. These seeds then germinate and form the next generation of trees. For pollination, Brazil nut trees are dependent on Euglossine orchid bees. Without these large-bodied bees, Brazil nut reproduction is not possible. For this reason, there has been little success growing Brazil nut trees in plantations as they only appear to grow in primary rainforest.

Text 2: Nitrogen in the savanna biome

Nutrients, along with fire, water and herbivory, are one of savanna ecology's big 4

Nitrogen, although the most abundant gas in the atmosphere (nearly 80% of air is nitrogen), is one of the three commonest elements limiting plant growth (the others are the P - phosphorus - and K - potassium - of traditional NPK fertilisers). It's vitally important to life, because it's a major component of protein, but most of that nitrogen in the world is in fact useless for plants or animals being what we call inorganic. Before plants or animals can make use of it a chemical transformation needs to occur from the inorganic form, to a form that is bound to hydrogen or oxygen atoms and can be used by plants. The most important process that converts N2 in the air to nitrogen-containing molecules that can be taken up by plants is driven by various types of bacteria; in particular there's a group called Archaea that we now think probably aren't bacteria at all that play an absolutely critical role in this process.

Once in the soil, nitrogen can be picked up by plants, which may in turn be eaten by animals who defecate and eventually die allowing (mainly) bacteria to recycle the organic nitrogen to the soil. There's some loss in the process (other bacteria are called denitrifying bacteria because they return the organic nitrogen to N2) so there's no continual build-up of organic nitrogen in the soil and, as we know, it's often limiting to plant growth - add a nitrogen fertiliser to savanna and plants grow better. But its distribution across the landscape isn't even and this is where it gets interesting - the full range of processes operating in the savanna affects both the fine and large-scale distribution of nitrogen which, in turn, affects the distribution of plants and animals across the landscape.

Large-scale patterns that are ultimately related to geology may include the following:

 higher lands regularly have nitrogen washed out of them with nitrogen accumulating at valley bottoms -

where broad-leaved woodlands can be found, for example.

 The underlyinggeology itself affects the soil type, which determines how long nitrogen stays in the soil

 Rainfall gradients can also be important, as rain can wash organic forms of nitrogen from the atmosphere to the ground, with the effect that wetter areas often have more nitrogen deposition than drier areas.

But within these areas there are a large number of fine-scale processes that mean that even within low nutrient areas there can be particular hotspots that are, actually, richer and more fertile than the generally higher nutrient areas: termites are particularly important at concentrating nitrogen around termite mounds. Large animals also develop grazing lawns encouraging grass with higher nitrogen content to keep growing. Also, the work of dung beetles is a further process that creates fine-scale variations in nitrogen content in the soil. And of course, nitrogen fixing legumes - all those trees that are formally known as Acacias - make a huge difference.

Text 3: The Role of Mycorrhizae in Forestry

There is a group of fungi which grow associated with plant roots in a symbiotic relationship. These are called mycorrhizae fungus root. A large volume of the soil is penetrated by fine, highly branched fungal hyphae which are "extensions" of the tree's own root system. As the fungal hyphae are very absorptive, and more efficient than the plant's roots themselves, they take up mineral nutrients from the soil and then pass some of these minerals to the plant. In return, the fungi receive sugars and other nutrients from the plant's photosynthetic processes. Hence the symbiotic relationship.

Mycorrhizae also contain nitrogen fixing bacteria which fix atmospheric nitrogen. Nitrogen, in a usable form is one of the plant's most important requirements. However, plants are defendant upon the activity of soil microorganisms which incorporate nitrogen through this form of nitrogen fixation. After, nitrogen fixation has occurred usable nitrogen compounds, N02 and NH3 are available for both the micro-organism and the plants. This, after the nitrogen fixing bacteria in the mycorrhizae harvest nitrogen from the air, the nitrogen is used both by the fungus and the host tree.

The most common trees in this type of relationship are woody plants. In particular : Pine, Fir, Spruce, Larch, Douglas Fir and Hemlock. These trees depend on these mycorrhizae forming fungi for nutrient uptake. It is believed that this occurrence occurred as far back as 400 million years ago, traceable back to the early fossils of the rooting systems of plants.

Mycorrhizal fungi also produce hormones which encourage the production of new root tips of the tree and therefore increase the tree's useful life span. In addition, a mycorrhizal infection is beneficial to plant in situation where nutrients are deficient or the plant faces strong competition from other organisms. This results in an

increased surface area available for mineral and water uptake. Hence, it is evident that the mycorrhizal

relationship with certain trees is beneficial to both organisms. The fungi gain valuable sugars and nutrients from the host and the tree experiences enhanced growth for a variety of reasons if the fungus is present.

Mycorrhizae have a link with the Northern Flying Squirrel. The squirrel is common in northern Canada, Alaska and North-Western United States of America. This squirrel is nocturnal and its diet consists mainly of fungus, hence it is a "mycophagist". Mycorrhizal hypogeous fungi - those which fruit below the ground, form the principle diet of the squirrel.

Exactly what is the main link between the hypogeous ‚ mycorrhizal fungi and the flying squirrel?? Let us examine this relationship: The squirrels nest and reproduce in the tree canopy. At night, they descend to the ground and feed on hypogeous sporocarps. These sporocarps contain nutrients which are beneficial to the small animals, such as the squirrels which eat them. But they also contain water, nitrogen fixing bacteria, fungal spores and yeast. After the sporocarps are consumed by the squirrels, pieces of them move to the stomach where the fungal tissue is digested. They then move to the small intestine where they are absorbed, and finally into the cecum where they are concentrated and mixed. The sporocarps are later released as pellets, after spending more than a month after ingestion. These pellets are excreted through the rectum and still contain the fungal spores, nitrogen fixing bacteria and yeast. Each pellet contains four important components to the forest :

 spores of the hypogeous mycorrhizal fungi

 yeast

 nitrogen-fixing bacteria

 the nutritional needs of the nitrogen-fixing bacteria.

These pellets may be dispersed throughout the forest in various ways allowing for the reproduction of the mycorrhizae fungi depending on where the pellets fall. If they land near a rootlet of a tree, the root might become host to a new colony of mycorrhizal fungus as spores germinate. Hence, the Flying Squirrel is an important component within the forest system.

We must remember how fundamentally connected these organisms are in order to maintain the delicately balanced ecosystem of the forests. If we do not ensure the survival of one species, another will surely perish. Thus fungi, seemingly insignificant organisms, have a vital role in the huge cycle of life.

Text 4: Environmental Case Study. Why Trees Need Salmon

need salmon to remain healthy, and that bears play an important intermediary role in this dynamic relationship.

The yearly return of salmon from the open Pacific Ocean to coastal waters of western North America is one of nature’s grand displays. Salmon (Onchorhyncus sp.) are anadromous: They hatch in freshwater lakes and streams, spend most of their lives at sea, then return to the stream where they were born, to breed and die. To reproduce successfully, these fish require clear, cold, shaded streams and clean gravel riverbeds. If forests are stripped from riverbanks and surrounding hillsides, sediment washes down into streams, clogging gravel beds and suffocating eggs. Open to the sunlight, the water warms, lowering its oxygen levels, and reducing survival rates of eggs and young fish.

Every year, as millions of fish return to spawn and die in rivers of the Pacific Northwest, they provide a bonanza for bears, eagles, and other species. Ecologist Tom Reimchen estimates that each bear fishing in British Columbia’s rivers catches about 700 fish during the 45-day spawn, and that 70 percent of the bear’s annual protein comes from salmon. After a quick bite on the head to kill the fish, the bears drag their prey back into the forest, where they can feed undisturbed. Some bears have been observed carrying fish as much as 800 m (0.5 mi) from the river before feeding on them.

Bears don’t eat everything they catch. They leave about half of each carcass to be scavenged by eagles, martens, crows, ravens and gulls. A diversity of insects, including flies and beetles, also feed on the leftovers. Within a week, all the soft tissue is consumed, leaving only a bony skeleton. Reimchen calculates that between the nutrients leeching directly from decomposing carcasses and the excreta from bears and other scavengers, the fish provide about 120 kg of nitrogen per hectare of forest along salmon spawning rivers. This is comparable to the rate of fertilizer applied by industry to commercial forest plantations.

Altogether, British Columbia’s 80,000 to 120,000 brown and black bears could be transferring 60 million kg of salmon tissue into the rainforest every year.

How do ecologists know that trees absorb nitrogen from salmon? Analyzing different kinds of nitrogen atoms, researchers can distinguish between marine-derived nitrogen (MDN) and that from terrestrial sources. Marine phytoplankton (tiny floating plant cells) have more of a rare, heavy form of nitrogen called 15N compared to most terrestrial vegetation, in which 14N, the more common, lighter form, predominates. Using a machine called a mass spectrometer, researchers can separate and measure the kinds and amounts of nitrogen in different tissues. We’ll discuss different forms of atoms (called isotopes) later in this chapter. Because salmon spend most of their lives feeding on dense clouds of plankton far out to sea, they have higher ratio of 15N/14N in their bodies than do most freshwater or terrestrial organisms. When the fish die and decompose, they contribute their nitrogen to the ecosystem. Bears and other scavengers distribute this nitrogen throughout the forest where they drop fish carcasses or defecate in the woods.

Robert Naiman and James Helfield from the University of Washington found that foliage of spruce trees growing in bear-impacted areas is significantly enriched with MDN relative to similar trees growing at comparable distances from streams with and without spawning salmon. These results suggest that in feeding on salmon, bears play an important role in transferring MDN from the stream to the riparian (streamside) forest. Nitrogen is often a limiting nutrient for rainforest vegetation. Tree ring studies show that when salmon are abundant, trees grow up to three times as fast as when salmon are scarce. For some streamside trees, researchers estimate that between one-quarter to one-half of all their nitrogen is derived from salmon. Not only do salmon replenish the forest, but they also vitalize the streams and lakes with carbon, nitrogen, phosphorous, and micronutrients. Nearly 50 percent of the nutrients that juvenile salmon consume comes from dead parents.

This research is important because salmon stocks are dwindling throughout the Pacific Northwest. In Washington, Oregon, and California, most salmon populations have fallen by 90 percent from their historic numbers, and some stocks are now extinct. Because of the close relationship of salmon and the trees, biologists argue, forest, wildlife, and fish management need to be integrated. Each population—rainforest trees, bears, hatchlings, and ocean-going fish—affects the stability of the others.

Salmon need healthy forests and streams to reproduce successfully, and forests and bears need abundant salmon. Stream ecosystems need standing trees to retain soil and provide shade. So healthy streams depend on fish, just as the fish depend on the streams. As this case shows, the flow of nutrients and energy between organisms can be intricate and complex. Relationships between apparently separate environments, such as rivers and forests, can be equally complex and important.

For more information, see

Helfield, J. M., and R. J. Naiman. 2001. Effects of salmon-derived nitrogen on riparian forest growth and implications for stream productivity. Ecology 82(9):2403–9.

Text 5: The Crab and The Tiger

Normally, plants access oxygen through their roots from tiny pockets of air in the soil. But in the sticky ooze of the Sunderbans, these pockets are virtually non-existent. But then, the mangrove is a pretty special plant.

You see, all of these spikes sticking out of the soil here are roots, and they act a bit like snorkels, sucking in oxygen out of the air when the plant can't get it out of this thick mud. But then, the mangrove doesn't just rely on it snorkels. There is something else going on here, something you can only appreciate at low tide.

They're called fiddler crabs because they have this vastly-enlarged front claw. And when they are feeding, it looks like they're playing the fiddle. They also wave them at any adversaries in a relative show of size and strength. In fact, when they are fully grown, that claw can represent 65% of the crab's bodyweight quite an investment for something to wave around at your enemies. These fiddlers are displaying to defend their territories. And their most valuable real estate is underground.

This little fiddler is excavating mud to create a burrow. When he's finished, it's going to be more than half a metre deep. His burrow gives some somewhere to hide from predators, like this stork. And when the tide comes in, from predatory fish.

These Leaf-eaters live in communal burrows, and together, their tunnels form an underground labyrinth. All of these burrows are vital for the mangrove. At low tide, they channel an air supply through the mud, direct to the roots. And it's not just oxygen. The crabs even supply the trees with food. The first ingredient is all those smelly bacteria.

Look really carefully, and you can see this crab feeding. It's picking up particles of soil and passing them to its mandibles. When it gets enough, it forms them into a ball, and it gradually removes all of the organic material, detritus and bacteria, and then it discards the ball. And you can see those that it's processed lying on the surface here. And if the crabs didn't do this, this mud wouldn't be very nice a nasty, sulphurous ooze. Racing against the tide, this fiddler is taking bacteria-rich mud back to his burrow. Here, he'll recycle it and release nutrients for the roots of the mangrove.

Further up the beach, this leaf-eater is also working hard to gather his food before the tide steals it. These crabs collect a staggering 80% of the leaves that fall here in the Sundarbans and they store them at the bottom of their burrows. Where they, too, will essentially fertilise the mangrove. But best of all, the burrows even help control the saltiness of the swamp. When the tide comes in, toxic seawater flows into the burrows and mixes with fresh water. And this allows the mangrove to expend less of its energy excreting salt, and more on actually growing. Without these burrows, the Sunderbans simply couldn't survive. Together, the crabs make a vast network a sort of Sunderbans tube system. The scale of the tube system is unbelievable. Just one square metre can have 300 tunnels. Crabs are ecosystem engineers. Without the many millions of them, living in this mangrove, the Sunderbans simply couldn't work. That's why the tiger needs the crab.

So the Tiger needs the crab. But it's more magical than that. And there's an even more unusual relationship One that protects the Sunderbans from a lethal threat. Thanks to the crabs gardening the mangroves, the Sunderbans support some large herbivores. But too many eating too much would soon damage the forest, so it needs protection.

The monkeys have sounded a warning. This family of chital deer won't be staying much longer. It's the very presence of these terrifying predators that protects the Sundarbans. You see, in any ecosystem, top predators exert what we call "an ecology of fear". And this influences the behaviour and movement of their prey. Here, that may be monkeys, or dear, or humans. In the Sunderbans the Tigers keep large numbers of people out of the forest, and they also keep all the herbivores on the move, so they don't damage the trees. So, anyway, the tiger needs the crab to help build this place, but then the crab needs the tiger to help protect it. You've got to admit, that's pretty neat.

And the result is this the largest mangrove forest in the world! This mangrove ecosystem is dependent on a complex web of relationships between species as diverse as crabs and Tigers to make it functional. But surprisingly, these connections don't end here, because what happens on the coast, where the river meets the sea, actually has a profound effect on what happens out there.

Text 6: The Deep Ocean

All of the silt, the sediment, and recycled organic material, that's washed down from the wetlands, the mangroves and the coral reef, where has it all gone? Has it just washed out into the open ocean, to be lost for ever? And if it has, what are the animals that live here feeding upon?

Well, potentially, it could have been a great waste of food, if it weren't for the way that the water moves. All of those valuable nutrients fall like marine snow on the seabed, far below. But they're not lost forever. Deep sea currents of unimaginable power, stir up the oceans on a global scale. It may take centuries, but carried by these upwelling currents, many of those lost nutrients eventually resurface. A sudden bounty of all the ingredients needed to sustain life. And a feast for all the microscopic algae phytoplankton.

The plankton that live here on the surface are dependent on these upwellings of nutrients. And when they are able to combine them with bright sunlight, their population explodes. These multiplying plankton soon attract millions of small crustaceans, krill, larvae of all kinds and many other creatures. And together, they combine to create the biggest frenzy of life on our planet a plankton bloom.

And plankton blooms attracts some of the most awe-inspiring creatures. Here, in the Indian Ocean, I've come to witness one of the most enchanting. The manta ray. They fly through the water, filtering and feeding on the plankton. They can eat 30kg a day. And it's not just rays. The plankton bloom has attracted the world's largest fish. This whale shark, may have swum thousands of kilometres, just to feast on this plankton bloom. And this great spectacle of life is all thanks to connections that stretch back, right across our planet.

Although the debris of life on Earth ultimately ends up here, in the ocean. And that's why the marine environment is so dependent on healthy terrestrial ecosystems places like the Pantanal wetlands and the mangroves in the Sunderbans. That's why the ray needs snail. A giant fish needs a moderately-sized mollusc, thousands of miles away. Unexpected, and undeniably complex, but a certainly beautiful connection.