Deserts

Do you think of a desert as a hot, dry place where sand stretches as far as you can see? The Sahara in North Africa is like that, but most deserts are not. All deserts are dry, but some deserts are very cold. Plants and animals live in most deserts. People have learned to live in deserts all over the world.
Most deserts form because of air movements over the planet. Masses of dry air create deserts. Water gets squeezed out of the air as it passes over the mountains, and a desert forms on the other side of the mountains. Deserts can also form along some seacoasts where there are currents of cold water. There are two main bands of desert areas, one north of the equator and one south of the equator. The equator is an imaginary line that goes around Earth’s middle.

TAKING AIR WITH YOU

You can go to places where there is no air. There is no air underwater, but you can dive underwater. You can stay underwater a short time just by holding your breath. Air tanks let you stay underwater for a long time. Scuba divers wear tanks on their backs. The tanks are filled with gases that make up air. The divers breathe the gases through hoses.
There is less and less air the higher up you go. People gasp for breath at the tops of tall mountains. Airplanes must carry air. Once the airplane gets up high, air is pumped into the cabin where passengers sit. Astronauts have to take all the air they need with them—there’s no air in space!

AIR

Take a really deep breath. Feel how your chest gets bigger and bigger. Your chest gets bigger because your lungs are filling up with air. You cannot see air, but air is all around you. You can feel it when the wind blows. Earth’s atmosphere is made of air. An atmosphere is made up of the gases that surround a planet.
Air is a mixture of several different gases. The main gases in air are nitrogen, oxygen, and argon. Air also contains smaller amounts of hydrogen, carbon dioxide, water vapor, helium, and other gases. Oxygen is the most important gas for animals. Animals must breathe oxygen in order to live.
Carbon dioxide is the most important gas for plants. Plants use carbon dioxide and sunlight to make food. Plants give off oxygen. Animals turn the oxygen back into carbon dioxide when they breathe.

COAL

Coal is mostly made up of the element carbon. When carbon burns, it releases a large amount of energy as heat. That’s what makes coal such a useful fuel. Coal is a fossil fuel. That means it comes from the remains of ancient life buried deep in Earth’s crust. The coal we use today started out as plants that grew in swamps millions of years ago. When the plants died, they settled to the swamp bottom. Over time, layers of mud and rock formed. They compressed and hardened the plant material. Heat and pressure caused chemical changes. Gradually, the once-living matter became coal.

REEFS IN DANGER

Scientists fear that many coral reefs are in danger. Many reefs have had a problem called bleaching. This occurs when the zooxanthellae, the algae that live in polyps, die off and the reef changes color. Then the coral polyps die. No one knows what causes bleaching.
A starfish called the Crown of Thorns starfish is also a threat to reefs. Sometimes too many of these starfish suddenly show up on a reef. The starfish kill the coral. No one knows why there are so many starfish.
Pollution is also a threat to coral reefs. Conservationists and governments are working to protect the Great Barrier Reef and other coral reefs.

THREE KINDS OF REEFS

There are three kinds of coral reefs: fringing reefs, barrier reefs, and atolls. All three kinds grow in warm places. Coral reefs cannot form in water colder than about 68° Fahrenheit (about 20° Celsius). Reefs form in clear, shallow water. They need sunlight in order for plants and animals to live there.
Fringing reefs are close to shore. There is no lagoon or other body of water between a fringing reef and the shore. Barrier reefs are farther out in the ocean. There is usually a lagoon between a barrier reef and the shore. Barrier reefs can be huge. The largest group of reefs in the world is Australia’s Great Barrier Reef. It covers thousands of square kilometers. Atolls are really the tops of volcanoes that sank below the sea. The reef grows on the rim of the volcano. Inside the reef is a lagoon.

KINDS OF CORAL

There are hundreds of different kinds of coral. Hard coral or stony coral is the kind of coral that builds reefs. These corals have hard outer skeletons. Other corals do not have hard outer skeletons and look like fans or flowers. Some kinds of coral look like the branches of a tree. Other kinds can sting you if you touch them.

Coral Reef

Imagine you are snorkeling in the warm ocean water around a tropical coral reef. You put on your mask and swim fins. You float around looking at the reef below you. The coral reef looks like strangely shaped rocks sticking up from the ocean floor. Crooked coral that looks like tree limbs twists up from cracks and caves in the reef. A big piece of coral that looks like a brain lies on the bottom. Orange and pink coral shaped like fans wave in the currents. Fish of all different shades and varieties of color swim near the reef.
Coral reefs play an important role in ocean life. Many kinds of plants, fish, and other animals live on and around a coral reef. Even the reef itself is made mostly of tiny coral animals, both living and dead.

RUNOFF: MOVING AROUND ON LAND

Water that falls on land always flows from high places to lower ones. This flow is called runoff. Precipitation that falls on land runs downhill. The water cuts channels as it flows.
Some water seeps into the ground. It fills cracks between rocks. Underground water also flows from places that are full to places that have less water.
Water from land flows into streams. Streams flow down mountains. Streams join together to make rivers and eventually the water flows into storage in the ocean. Then the water cycle starts all over again.

PRECIPITATION: BACK TO EARTH

Water returns to Earth as precipitation—rain, snow, or other moisture. Precipitation requires ice or liquid water. Water vapor can change into tiny ice crystals or drops of water when the air gets cold enough. Clouds are collections of tiny ice crystals or water droplets.
When the ice crystals or drops of water in a cloud get heavy enough, they fall to Earth as precipitation. Rain, snow, sleet, and hail are all forms of precipitation. Most precipitation falls into the oceans and goes right back into storage.

EVAPORATION: INTO THE AIR

Water goes from storage into the atmosphere (the air that surrounds Earth) by a process called evaporation. When water evaporates, it changes from a liquid into an invisible gas. The gas is called water vapor. Water vapor goes up into the atmosphere.
Most of the water that gets into the air evaporates from the surface of the oceans. Water also evaporates from rivers and lakes. Water can also go from ice caps and icebergs into the air. Ice changing into water vapor is called sublimation.

IN STORAGE

The water cycle has four stages: storage, evaporation, precipitation, and runoff. Most of the water on Earth is in the first stage, storage. Water on Earth gets stored in oceans, lakes, rivers, ice, and even underground. The oceans store the majority of this water.

Water Cycle

Maybe you recycle cans, glass, and paper. Did you know that nature recycles, too? One of the things nature recycles is water. Water goes from the ocean, lakes, and rivers into the air. Water falls from the air as rain or snow. Rain or snow eventually find their way back to the ocean. Nature’s recycling program for water is called the water cycle.

COULD WE RUN OUT OF WATER?

Nature recycles water all the time. Water in oceans, lakes, and rivers evaporates, or turns into a gas and rises into the air. The water vapor eventually turns back into a liquid and falls as rain. The water cycle keeps the total amount of water on Earth the same. But most of this water is salt water in the ocean. People need fresh water for drinking and for growing food on farms. Ocean water is too salty to drink. It is too salty to use for watering plants. Some places have more fresh water than others. People who live near big lakes or rivers have more fresh water than people who live in the desert. Places where a lot of rain falls have more fresh water. Places that usually have enough fresh water sometimes have a drought. Very little rain falls during a drought. People run short of water. People everywhere should be careful not to waste water.

DRINKING WATER FOUND ON EARTH

Not all water is safe to drink. Water in lakes and rivers can be polluted. It can have harmful chemicals or germs that cause disease. Long ago, many people living in cities got sick or died from drinking dirty water. Scientists have learned how to clean, or purify, drinking water. They learned that boiling water could kill germs. They learned that adding certain chemicals could kill germs. Engineers learned how to keep dirty water in sewers, away from drinking water. Governments passed laws to keep factories from polluting water. People still get sick from drinking polluted water. Many poor people still do not have pure drinking water.

DRINKING WATER FOUND ON EARTH

Not all water is safe to drink. Water in lakes and rivers can be polluted. It can have harmful chemicals or germs that cause disease. Long ago, many people living in cities got sick or died from drinking dirty water. Scientists have learned how to clean, or purify, drinking water. They learned that boiling water could kill germs. They learned that adding certain chemicals could kill germs. Engineers learned how to keep dirty water in sewers, away from drinking water. Governments passed laws to keep factories from polluting water. People still get sick from drinking polluted water. Many poor people still do not have pure drinking water.

WATER FOUND ON EARTH

Liquid water fills the ocean, lakes, ponds, rivers, and swamps. Water droplets form rain clouds. Liquid water makes beads of dew on the grass. It seeps down into the ground. It fills underground lakes and streams. Ice falls as hail or crystals of snow. Ice forms on ponds and frosty windowpanes. Huge sheets of ice make glaciers and icecaps at the North and South poles. Water vapor is always present in the air. Water vapor makes clouds in the sky. Water vapor makes fog that hangs close to the ground. It is the steam that comes out of a teakettle. v

WATER FOUND ON EARTH

Liquid water fills the ocean, lakes, ponds, rivers, and swamps. Water droplets form rain clouds. Liquid water makes beads of dew on the grass. It seeps down into the ground. It fills underground lakes and streams. Ice falls as hail or crystals of snow. Ice forms on ponds and frosty windowpanes. Huge sheets of ice make glaciers and icecaps at the North and South poles. Water vapor is always present in the air. Water vapor makes clouds in the sky. Water vapor makes fog that hangs close to the ground. It is the steam that comes out of a teakettle. v

WATER

Think about the different ways you use water. You drink water when you are thirsty. You take a bath and wash your clothes with water. You water the grass or other plants. You swim in water. Water pouring over huge dams may even make the electricity that lights up your home. About three-quarters of Earth’s surface is water. Living things are mostly made up of water. Without water, there Wooster is a chemical. Chemists say water is a compound, a combination of different materials. Water is a combination of oxygen and hydrogen atoms. An atom is a tiny bit of matter much too small to see. Water is made of one atom of oxygen and two atoms of hydrogen. The three atoms make the tiniest possible drop of water, called a molecule. Water can be a liquid, a solid, or a gas. Liquid water flows. Solid water is ice. Water in the form of a gas is called water vapor.uld be no life on Earth.

THE SUN’S ENERGY GETS INTO FOOD

The Sun provides the energy that starts the whole process. A plant uses sunlight to make its own food. The energy is stored in the plant. An insect eats the plant. The insect stores the energy in its body. Then the energy is transferred to a fish that eats the insect. When you eat the fish, your body gets the energy stored in that fish. When you eat salad, fruits, and potatoes, you take in the energy stored in these plants. When you eat fish, beef, or chicken, you take in the energy stored in these animals. When you eat your dinner, your body is getting energy that first came from the Sun. You use this energy to do your schoolwork. You use this energy to run and play.

FOOD WEB

A food web is made of many food chains in a community of plants and animals. There are many tiny animals near the beginning of a food web. There are fewer but larger animals higher up in a food web. There are many more insects than fish in a food web. There are also more small fish than big fish. Human beings are at the very top of the food web. No animals are higher up to make us their steady diet. Decomposers play important roles in some food webs. Bacteria and fungi are decomposers. Decomposers eat dead plants and animals and cause them to rot and decay. They also eat animal wastes. They break things down into chemical parts called nutrients. The nutrients go back into the soil. Plants take up water and nutrients to make food. Nutrients move through food webs over and over again.

Food Chain

A tiny insect nibbles on some leaves. The insect skims over a lake. A little fish swimming below spots the insect on top of the water. The fish zooms up and eats the insect. Later, a slightly larger fish eats the little fish. Then, the slightly larger fish gets eaten by a really big fish. You are in a boat on the lake fishing. You catch the big fish, cook it, and eat it for dinner.Food chain is the way energy goes from one living thing to another through food. Plants are the first step in most food chains. Plants use the energy in sunlight to make their own food. Plants store the energy in their leaves and stems. Plants are called primary producers in food chains.Animals eat the plants that use the Sun’s energy to grow. Animals are called consumers. Animals that eat plants are primary consumers. Animals that eat other animals are secondary consumers. Animals store the energy in their bodies. Energy flows from plants to bigger and bigger animals through the steps of eating and being eaten. Each part of the food chain is directly connected to the other, just like the links in a chain.

ATMOSPHERES ON OTHER PLANETS

Any planet that has gas around it has an atmosphere. Mercury, the planet closest to the Sun has almost no atmosphere. Pluto, the planet farthest from the Sun, is so cold that sometimes its atmosphere freezes. The gases in Pluto’s atmosphere turn to ice. There are colorful bands of clouds in the atmospheres of some planets. A gas called methane makes the atmospheres of Neptune and Uranus look smooth and blue. Jupiter has a swirling storm in its atmosphere called the Great Red Spot that may be like a giant hurricane.

LAYER CAKE OF AIR

Earth’s atmosphere extends about 6,000 miles (9,600 kilometers) above the surface of Earth, where we live. You can think of the atmosphere as having several layers. Most of our weather comes from winds, temperature changes, and water vapor in the layer nearest Earth’s surface. This layer is called the troposphere. Most of the clouds you see in the sky are floating in the troposphere. The stratosphere is the layer above the troposphere. Jet airplanes fly in the stratosphere because there are few clouds up so high and the ride is usually less bumpy. Earth’s ozone layer is in the stratosphere. The ozone layer absorbs, or soaks up, harmful rays from the Sun. These harmful rays would probably destroy life if they reached Earth’s surface. The atmosphere gets thinner and thinner in the next layers up, the mesosphere and thermosphere. The top layer of Earth’s atmosphere is the exosphere. The atmosphere ends here, about 6,000 miles (9,600 kilometers) above Earth’s surface. The thin air here gradually merges with outer space.

THE WEIGHT OF AIR

Air has weight. You cannot feel the weight of air, but all the air in the atmosphere presses downward. This weight is called atmospheric pressure. Atmospheric pressure depends on how much gas is in the atmosphere. The higher you go, the less air there is and the lower the atmospheric pressure gets. The atmosphere is heaviest and the atmospheric pressure highest close to Earth. Differences in air temperature close to Earth form areas of high and low pressure. Warm air is light and rises upward. It makes low-pressure areas. Cold air is heavy and sinks. It makes high-pressure areas.WEATHER AND THE ATMOSPHEREAir in the atmosphere is always moving. You can feel air blowing on your face. You can see air scattering autumn leaves and making tree branches sway. Moving air is called wind. The wind blows where areas of high and low atmospheric pressure meet. As warm air rises, cold air rushes in to take its place. Big areas of high and low atmospheric pressure cause storms. Thunderstorms often occur where big areas of high and low pressure come together. Huge thunderclouds form in these places. Water vapor in the atmosphere makes clouds. Water vapor is a gas. As the gas cools, it turns to liquid water. The water falls to Earth as rain or snow.

Atmosphere

Every time you take a breath, you are inhaling Earth’s atmosphere. You cannot see, smell, or taste Earth’s atmosphere. It is the air all around you. Other planets also have an atmosphere. An atmosphere is a blanket of gases that wraps around a planet or any other object in space.EARTH’S ATMOSPHERE IS AIREarth’s atmosphere is made up of a mix of gases called air. Air contains more nitrogen than any other gas. Nitrogen makes up 78 percent of the air. Oxygen, the gas that is most important for keeping you alive, makes up 21 percent. Earth is the only planet to have so much oxygen in its atmosphere. Water vapor and other gases are also present in small amounts in Earth’s atmosphere. The pull of gravity holds the atmosphere in place. Without gravity, the air in Earth’s atmosphere would float off into space. Gravity is the force that also keeps you from floating away from Earth.

Greenhouse Effect

Greenhouse Effect, the capacity of certain gases in the atmosphere to trap heat emitted from Earth’s surface, thereby insulating and warming the planet. Without the thermal blanketing of the natural greenhouse effect, Earth’s climate would be about 33°C (about 59°F) cooler-too cold for most living organisms to survive.The greenhouse effect has warmed Earth for over 4 billion years. Now scientists are growing increasingly concerned that human activities may be modifying this natural process, with potentially dangerous consequences. Since the advent of the Industrial Revolution in the 1700s, humans have devised many inventions that burn fossil fuels such as coal, oil, and natural gas. Burning these fossil fuels, as well as other activities such as clearing land for agriculture or urban settlements, releases some of the same gases that trap heat in the atmosphere, including carbon dioxide, methane, and nitrous oxide. These atmospheric gases have risen to levels higher than at any time in at least the last 650,000 years. As these gases build up in the atmosphere, they trap more heat near Earth’s surface, causing Earth’s climate to become warmer than it would naturally.Scientists call this unnatural heating effect global warming and blame it for an increase in Earth’s surface temperature of about 1°F over the last 100 years. Scientists project global temperatures to continue rising during the 21st century. Warmer temperatures could melt parts of polar ice caps and most mountain glaciers, causing a rise in sea level that would flood coastal regions. Global warming could also affect weather patterns causing, among other problems, prolonged drought or increased flooding in some of the world’s leading agricultural regions.

Acide Rain

Acid Rain, form of air pollution in which airborne acids produced by electric utility plants and other sources fall to Earth in distant regions. The corrosive nature of acid rain causes widespread damage to the environment. The problem begins with the production of sulfur dioxide and nitrogen oxides from the burning of fossil fuels, such as coal, natural gas, and oil, and from certain kinds of manufacturing. Sulfur dioxide and nitrogen oxides react with water and other chemicals in the air to form sulfuric acid, nitric acid, and other pollutants. These acid pollutants reach high into the atmosphere, travel with the wind for hundreds of miles, and eventually return to the ground by way of rain, snow, or fog, and as invisible “dry” forms.Damage from acid rain has been widespread in eastern North America and throughout Europe, and in Japan, China, and Southeast Asia. Acid rain leaches nutrients from soils, slows the growth of trees, and makes lakes uninhabitable for fish and other wildlife. In cities, acid pollutants corrode almost everything they touch, accelerating natural wear and tear on structures such as buildings and statues. Acids combine with other chemicals to form urban smog, which attacks the lungs, causing illness and premature deaths

Forest

Forest, plant community, predominantly of trees or other woody vegetation, occupying an extensive area of land. In its natural state, a forest remains in a relatively fixed, self-regulated condition over a long period of time. Climate, soil, and the topography of the region determine the characteristic trees of a forest. In local environments, dominant species of trees are characteristically associated with certain shrubs and herbs. The type of vegetation on the forest floor is influenced by the larger and taller plants, but because low vegetation affects the organic composition of the soil, the influence is reciprocal. Disturbances such as a forest fire or timber harvesting may result in a shift to another forest type (see Forest Fires; Lumber Industry). Left undisturbed, ecological succession will eventually result in a climax forest community (see Ecology). Human intervention is practiced to maintain some desirable forest types.

Water Pollution

Estimates suggest that nearly 1.5 billion people worldwide lack safe drinking water and that at least 5 million deaths per year can be attributed to waterborne diseases. Water pollution may come from point sources or non point sources. Point sources discharge pollutants from specific locations, such as factories, sewage treatment plants, and oil tankers. The technology exists to monitor and regulate point sources of pollution, although in some areas this occurs only sporadically. Pollution from non point sources occurs when rainfall or snow melt moves over and through the ground. As the runoff moves, it picks up and carries away pollutants, such as pesticides and fertilizers, depositing the pollutants into lakes, rivers, wetlands, coastal waters, and even underground sources of drinking water. Pollution arising from non point sources accounts for a majority of the contaminants in streams and lakes.With almost 80 percent of the planet covered by oceans, people have long acted as if those bodies of water could serve as a limitless dumping ground for wastes. However, raw sewage, garbage, and oil spills have begun to overwhelm the diluting capabilities of the oceans, and most coastal waters are now polluted, threatening marine wildlife. Beaches around the world close regularly, often because the surrounding waters contain high levels of bacteria from sewage disposal.

Air Pollution

A significant portion of industry and transportation burns fossil fuels, such as gasoline. When these fuels burn, chemicals and particulate matter are released into the atmosphere. Although a vast number of substances contribute to air pollution, the most common air pollutants contain carbon, sulfur, and nitrogen. These chemicals interact with one another and with ultraviolet radiation in sunlight in dangerous ways. Smog, usually found in urban areas with large numbers of automobiles, forms when nitrogen oxides react with hydrocarbons in the air to produce aldehydes and ketones. Smog can cause serious health problems.

Acid rain forms when sulfur dioxide and nitrous oxide transform into sulfuric acid and nitric acid in the atmosphere and come back to Earth in precipitation. Acid rain has made numerous lakes so acidic that they no longer support fish populations. Acid rain is also responsible for the decline of many forest ecosystems worldwide, including Germany’s Black Forest and forests throughout the eastern United States.

Habitat Destruction and Species Extinction

Plant and animal species are dying out at an unprecedented rate (see Endangered Species). Estimates range that from 4,000 to as many as 50,000 species per year become extinct. The leading cause of extinction is habitat destruction, particularly of the world’s richest ecosystems-tropical rain forests and coral reefs. If the world’s rain forests continue to be cut down at the current rate, they may completely disappear by the year 2030. In addition, if the world’s population continues to grow at its present rate and puts even more pressure on these habitats, they might well be destroyed sooner.

Global Warming

Global Warming or Climate Change, measurable increases in the average temperature of Earth’s atmosphere, oceans, and landmasses. Scientists believe Earth is currently facing a period of rapid warming brought on by rising levels of heat-trapping gases, known as greenhouse gases, in the atmosphere.Greenhouse gases retain the radiant energy (heat) provided to Earth by the Sun in a process known as the greenhouse effect. Greenhouse gases occur naturally, and without them the planet would be too cold to sustain life as we know it. Since the beginning of the Industrial Revolution in the mid-1700s, however, human activities have added more and more of these gases into the atmosphere. For example, levels of carbon dioxide, a powerful greenhouse gas, have risen by 35 percent since 1750, largely from the burning of fossil fuels such as coal, oil, and natural gas. With more greenhouse gases in the mix, the atmosphere acts like a thickening blanket and traps more heat.Depletion of the ozone layerThe ozone layer, a thin band in the stratosphere (layer of the upper atmosphere), serves to shield Earth from the Sun’s harmful ultraviolet rays. In the 1970s, scientists discovered that chlorofluorocarbons (CFCs)-chemicals used in refrigeration, air-conditioning systems, cleaning solvents, and aerosol sprays-destroy the ozone layer. CFCs release chlorine into the atmosphere; chlorine, in turn, breaks down ozone molecules. Because chlorine is not affected by its interaction with ozone, each chlorine molecule has the ability to destroy a large amount of ozone for an extended period of time.The consequences of continued depletion of the ozone layer would be dramatic. Increased ultraviolet radiation would lead to a growing number of skin cancers and cataracts and also reduce the ability of immune systems to respond to infection. Additionally, growth of the world’s oceanic plankton, the base of most marine food chains, would decline. Plankton contains photosynthetic organisms that break down carbon dioxide. If plankton populations decline, it may lead to increased carbon dioxide levels in the atmosphere and thus to global warming. Recent studies suggest that global warming, in turn, may increase the amount of ozone destroyed. Even if the manufacture of CFCs is immediately banned, the chlorine already released into the atmosphere will continue to destroy the ozone layer for many decades.

Population Growth

Human population growth is at the root of virtually all of the world’s environmental problems. Although the growth rate of the world’s population has slowed slightly since the 1990s, the world’s population increases by about 77 million human beings each year. As the number of people increases, crowding generates pollution, destroys more habitats, and uses up additional natural resources. Although rates of population increase are now much slower in the developed world than in the developing world, it would be a mistake to assume that population growth is primarily a problem of developing countries. In fact, because larger amounts of resources per person are used in developed nations, each individual from the developed world has a much greater environmental impact than does a person from a developing country. Conservation strategies that would not significantly alter lifestyles but that would greatly lessen environmental impact are essential in the developed world.In the developing world, meanwhile, the most important factors necessary to lower population growth rates are democracy and social justice. Studies show that population growth rates have fallen in developing areas where several social conditions exist. In these areas, literacy rates have increased and women receive economic status equal to that of men, enabling women to hold jobs and own property. In addition, birth control information in these areas is more widely available, and women are free to make their own reproductive decisions.

FACTORS THREATENING THE ENVIRONMENT

Population Growth
Global Warming
Depletion of the ozone layer
Habitat Destruction and Species Extinction
Air Pollution
Water Pollution
Groundwater Depletion and Contamination
Chemical Risksi. Environmental Racism
Energy production

Introduction

Environment, all of the external factors affecting an organism. These factors may be other biotic factors or abiotic factors, such as temperature, rainfall, day length, wind, and ocean currents. The interactions of organisms with biotic and abiotic factors form an ecosystem. Even minute changes in any one factor in an ecosystem can influence whether or not a particular plant or animal species will be successful in its environment. Organisms and their environment constantly interact, and both are changed by this interaction. Like all other living creatures, humans have clearly changed their environment, but they have done so generally on a grander scale than have all other species. Some of these human-induced changes-such as the destruction of the world’s tropical rain forests to create farms or grazing land for cattle-have led to altered climate patterns. In turn, altered climate patterns have changed the way animals and plants are distributed in different ecosystems.