Ecology

Strange Days on Planet Earth: Predators

Deep in the wilds of Venezuela, the natural order is being turned inside out. Miles of savanna and verdant forest have given way to small, scattered islands. Some of these islands are now overrun by bands of howler monkeys, a glut of iguanas and hordes of ravenous ants. What's driving this bizarre transformation? and could it be linked to other mysterious events around the world?

A team of scientists may have the answers. They believe that life on these islands is running amok in large part because the top predators are gone. In fact, in Venezuela and around the world, experts are learning that predators could play a crucial role in structuring entire ecosystems and when the predators disappear, the consequences may be dramatic.

It's not just on land that predators appear to be crucial. In the Caribbean, once-vibrant coral reefs are under attack by insidious algae. With the reefs suffocating under shaggy layers of algae, scientists are investigating the role that the loss of top predatory fish such as sharks, groupers and jacks have played in the reef's slow demise. As these large fish were decimated by fisheries, smaller fish became the next commercial target – including those vital grazers that kept fast-growing algae in check. With the grazers gone, the algae were free to take over.

Similarly, the majestic wilderness of Yellowstone National Park is also showing signs of change that some scientists trace to the depletion of natural predators. Familiar and revered forests have vanished. Researchers have recently put forth an amazing hypothesis linking these forest losses to the expulsion of the gray wolf some 70 years ago.

Wolves were once a vital part of North American ecosystems before bounty hunters, starting at the turn of the century, decimated their numbers.

A big question for biologists worldwide is what has been the effect of removing large carnivores? In Yellowstone, researchers have looked for answers in the way wolves impact the ecosystem. This impact starts with their kills.

In a lot of ways, a wolf kill is not an ending but a beginning. Every wolf kill becomes an epicenter of animal activity, replete with ravens, magpies, coyotes, bald eagles and grizzly bears that feed on the wolf-kill remains. These kills then become extremely important to the ecological community of Yellowstone. In this way, one wolf kill serves hundreds.

Perhaps, even more importantly, by hunting elk in particular, wolves literally may be reshaping the landscape. By keeping elk on the move, researchers say elk spend less time grazing on Yellowstone's aspen and willow trees.

Research suggests that the elimination of Yellowstone's wolves allowed the elk to browse aspens and willows unchecked. Though other factors may have played a role, it seems the disappearance of trees and streamside vegetation can, in fact, be traced to the missing wolves. Now, following the controversial reintroduction of wolves to the environment, where elk are on the run, trees and shrubs are starting to make a comeback.

Ecology 9: Population Growth

Students become familiar with the microorganism Paramecium caudatum by using microscopes to observe its feeding and searching behaviors. Students then compare two populations of Paramecium that have been growing in environments with different amounts of food. Students use microscopes to count the number of individuals in samples from these different environments. They collect and analyze the data to determine the effect of food availability on the growth of Paramecium populations. 

Strange Days on Planet Earth: Troubled Waters

A series of apparently unconnected crises among animal populations around the world turns out to be linked by water. The fourth hour of Strange Days on Planet Earth examines the evidence that pollutants are being spread throughout the world's water systems and explores what we can do to remedy the problem.

Around the world, at least 20 frog species have become extinct and many surviving populations are dying out. Clues to the disappearances may be found in the American heartland where some frog populations are declining dramatically. An investigation into this mystery has led one scientific team led by Tyrone Hayes to marshes and ponds, where a closer look at the Northern Leopard frog reveals anomalies inside the frog's reproductive organs. At the same time, US farms are producing about one trillion ears of corn every year often using manmade chemicals like Atrazine, which can reach the world's waterways by wind and rain. The team's research suggests that even tiny amounts of Atrazine can be dangerous to these aquatic animals.

Elsewhere, epidemiologists in Columbia, Missouri are investigating the effects of chemicals found in tap water. They have discovered evidence of human vulnerability, reporting high miscarriage rates in women who drink tap water with elevated levels of chlorine by-products. Now they are looking at the reproductive health of men in cities versus farm areas, finding lower sperm counts in rural areas where exposure to farming chemicals through tap water is more likely.

Farther north in the waters of Canada's St. Lawrence River, biologists have discovered pods of beluga whales with some of the highest cancer rates of any wild animal studied. Dozens of chemicals have been discovered in the bodies of these St. Lawrence belugas. Some dead belugas are so full of pollutants and chemical mixtures from the water that they technically qualify as hazardous waste. It's these chemical mixtures, as opposed to any one chemical in particular, that are causing some scientists to worry.

And near the Great Barrier Reef, scientists try to solve the mystery of a massive outbreak of Crown-of-Thorns Starfish, a species that has proliferated in recent years, destroying parts of the reef. Is this population explosion part of a natural cycle? Or could human activity be to blame? Some scientists believe the outbreaks could be related to nitrogen-rich agricultural runoff.

As invisible pollutants infiltrate our water, much of that water ends up flowing straight into our coastal zones. One school of thought is that pollutants are diluted to safe levels by the time they reach the open ocean. But are the creatures that live here really protected from chemicals? In the past decades, researchers have become aware that sharks, bluefin tuna, swordfish and killer whales all have pollutants in their tissues. Where are they being exposed? To find out, marine biologist Tierney Thys and her team with the Census of Marine Life oceanographic project try to discover where open-ocean animals spend their time. Thys uses new tracking devices to chart the travel habits of the animals, once widely believed to live primarily in the open ocean. Surprisingly, the tags reveal that these animals spend a lot of time near shore, in close proximity to where polluted runoff enters open water. The good news is that we are now locating the particular places where open-ocean species approach our shores to feed and from that information, we know where to concentrate our clean-up efforts.

Such research calls into question how we assess chemical safety. The water that animals rely on is part of a single interconnected system – the same network that provides our drinking water. Each of these stories may be part of a worldwide transformation in which Earth's vibrant waterways – its streams, rivers, estuaries and even oceans – have become massive delivery systems for invisible poisons. Yet even as the level of water-borne pollutants rises, scientists and farmers alike are discovering exciting new solutions.

Strange Days on Planet Earth: Invaders

Strange transformations are taking place around the world because of alien invaders. People in New Orleans no longer trust the floor beneath their feet. Their houses are collapsing — under siege by voracious termite hordes that scientists suspect began their journey half a world away.

In Tokyo Bay, General Douglas MacArthur presided over Japan's formal surrender in World War II. US forces in Japan and China packed up to return home, making crates from local wood. The crates wound up in garbage dumps near military bases in the American South. But the discarded containers were not necessarily empty – they were likely teeming with stowaways, aliens in the form of Formosan subterranean termites. Over time, the dangerous broods built up their numbers throughout New Orleans.

Given the magnitude of the infestation, scientists are now working to slow down the beast devouring the city by locating its supply lines. To control the termites, scientists hope to exploit one aspect of the insects' lives. Colonies are intensely social — a quality that explains the success of all termites. Most importantly, this means they share food. Using bait stations buried in locations across the city, scientists replace wood bait with poison-soaked paper. Workers carry it back to colony headquarters. In as little as three months, the nest could be destroyed.

Meanwhile, in Uganda, an alien interloper may be jeopardizing the very health of the nation. Cases of the tropical disease, schistosomiasis, have been on the rise and scientists suspect the alien water hyacinth plant is partly to blame. In a short time, this weed has clogged 80 percent of Uganda's shoreline, providing an ideal breeding ground for snails carrying this deadly disease. Plus as the menacing snails thrive, fish life suffers under the suffocating blanket of weeds and when the weeds rot, the drinking water coming straight from the lake is fouled, further weakening the health of all the lakeside inhabitants.

At his laboratory on the outskirts of Uganda's capital, researcher James Ogwang looks for a way to fight the invader. The weed has taken over, Ogwang believes, because it left its predators behind in its native Brazil. His theory: Why not import natural enemies?

Using a technique known as bio-control, Ogwang and his team carry 1,200 weevil insects to Uganda. After making sure the weevils do not have a taste for local crops, Ogwang's team breeds his insect army and releases it into the waters, where it eats and depletes the plants.

At the same time, in Hawai'i, a new species of plant threatens to remodel the landscape. Botanists are tracking a plant called Miconia that left its native Mexico on a ship bound for Europe in the mid-1800s. In 1961, a botanical garden in Hawai'i welcomed Miconia as a gift. Soon, the plant was being sold at nurseries, where it became a popular decoration. Its escape from backyards was facilitated by way of another introduced species, the Japanese white-eye, a bird that excels at spreading seeds. Now, only 40 years later, the invasive plant has spread over 10,000 acres on the Big Island and is shading out the native species. In its takeover, Miconia replaces the natives' deep roots with its own shallow root system, placing the steep slopes of Hawai'i at grave risk of landslides. To combat Miconia, researchers like David Duffy use state-of-the-art detection devices to map its growth in forests then uproot the plant, region by region.

Below is an example student project from several years ago:

Ecology 1: The Miracle Fish

This activity introduces students to the concept of ecology—the study of organisms and their interactions with other organisms and the environment—through a reading about the introduction of Nile perch into Lake Victoria in Africa. Students consider how this change to the biological component of the ecosystem has affected populations of other species of fish. After obtaining empirical evidence about past changes in the ecosystem, students construct arguments to predict what will happen in the future. Students then examine trade-offs and decide whether humans should have introduced Nile perch into Lake Victoria—a decision that is informed but not prescribed by science. This activity provides an opportunity to assess student work related to the crosscutting concept of connections to nature of science: Science addresses questions about the natural and material world, but while scientific knowledge can describe the consequences of actions, it does not necessarily prescribe the decisions that society takes.