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Take a few moments to review the discussions before you start this chapter.

The primary migration corridor is from the north of the circle to the south of the Tropic of Cancer. Millions of geese will follow the Mississippi, Pacific, Central, or Atlantic flyways.

Birds can travel up to 650 miles in a single day at speeds of up to 55 miles per hour. The migrations will cover thousands of miles.

They stop at key staging points to rest and feed during the winter. Wetlands, marshes, grasslands, and chaparral regions are vital for their migration. The high concentration of birds makes them more vulnerable to disease. Bald eagles and humans are some of the natural predators. Waterfowl hunting in Illinois contributes to the state's economy.

The birds migrate toward their breeding grounds after wintering in the southern part of their range. The winter migration takes them through the same flyways and staging points. From the middle of March to the middle of May is when it happens. The new birds have grown enough to start the cycle over again. The survival of this species depends on a variety of biomes.

The prevailing weather conditions in a region are called climate.

Because the Earth is a sphere, it gets both direct sunlight at the equator and indirect sunlight at the poles. The tropics are between the north and south of the equator. The tropics are warmer than the north and south of 23.5degS.

Because the Earth is a sphere, beams of solar energy hitting the Earth near one of the poles are spread over a wider area than similar beams hitting the Earth at the equator. The seasons of the Northern and Southern Hemispheres are due to the tilt of the Earth.

The tilt of the Earth causes one pole or the other to be tilted toward the sun, except at the spring and fall equinoxes. The seasons occur in all parts of the Earth except at the equator. When the Northern Hemisphere is having winter, the Southern Hemisphere is having summer.

All air movements would occur in two different directions if the Earth were a solid, uniform ball. Warm air at the equator would move toward the poles, where it would cool and sink. zones of lower air pressure are created by rising air. The flow of warm and cold air is changed into three large circulation cells in each hemisphere because of the Earth's rotation.

The Earth rotates on its axis, so air ascends and descends as shown. The trade winds move from the northeast to the west in the Northern Hemisphere and from the southeast to the west in the Southern Hemisphere. The westerlies are moving toward the east.

The sun heats the air at the equator. Warm, moist air rises, and as it cools, it loses most of its rain-like qualities. The equator has the greatest amount of rain. The rising air flows toward the poles, but at 30 degrees north and south, it cools and sinks into the Earth's surface. Areas of high pressure are created when the dry air descends. The high-pressure regions are low in precipitation. The great deserts of Africa, Australia, and the Americas can be found at these latitudes.

The air moves toward the poles and equator at the Earth's surface.

Water and land get absorbed as dry air moves across the Earth. The warm air rises and cools in the north and south at 60 degrees north and south. The great forests of the temperate zone are supported by this moist air. Part of the rising air goes toward the equator and the other goes toward the poles. The poles have low amounts of precipitation.

The winds are affected by the spinning of the Earth. Large-scale winds bend clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere. The curving pattern of the winds, ocean currents, and cyclones is the result of the Earth rotating in an eastward direction. The winds blow from the east to the south in the Southern Hemisphere and from the east to the north in the Northern Hemisphere. There are calm regions at the equator.

Sailors depended on trade winds to fill their sails.

The prevailing westerlies blow from west to east in the north and south latitudes. The Pacific Northwest has a massive evergreen forest, which is located on the west coast of the continents. The polar easterlies blow from the east to the west at higher latitudes.

The presence of mountains is a physical feature that affects the climate. As air rises over a coastal mountain range, it cools. The windward side of the mountain gets more rain than the other side. On the interior side of the mountain or leeward side, the air descends, absorbs water from the ground, and produces clear weather.

When winds from the sea cross a coastal mountain range, they rise and release their water as they cool this side of a mountain, called the windward side.

In the Hawaiian Islands, the windward side of the mountains gets more rain than the leeward side, with an average of 50 cm of rain a year. The western side of the Sierra Nevada Mountains is lush, while the eastern side is semidesert.

The temperature of the oceans is stable.

The heat of the ocean is more slowly than the heat of the land. There is a weather pattern that is not observed inland. During the day, the land warms more quickly than the ocean, and the air above the land rises, pulling a cool sea breeze in from the ocean. The breeze blows from the land to the sea at night.

India and other countries in southern Asia have a monsoon climate in which wet ocean winds blow for almost half the year.

During the spring, the land is hotter than the Indian Ocean.

The monsoon season begins when the warm air loses its humidity. On the windward side of hills, the rain is heavy. Cherrapunji, a city in northern India, gets an average of 1,090 cm of rain a year because of its high altitude. The weather pattern will change by November. Dry winds blow from the Asian continent across the Indian Ocean because the land is cooler than the ocean. In the winter, the air is dry, the skies are cloudless, and the temperatures are pleasant. Rice is the main crop of India when the monsoon rains.

The "lake effect" is a term used in the United States to describe warm and moist winds blowing over the Great Lakes in the winter. The snow starts to fall when the winds rise. Buffalo, New York, receives heavy snowfalls due to the lake effect, and snow is on the ground there for an average of 90 to 140 days a year.

The equator has a warm climate.

There are two physical features that can affect the weather.

The distribution of the major twinnings.

The key characteristics of the land are listed.

Climate and geography are the main factors that determine major terrestrial ecosystems. A has a mix of plants and animals that are adapted to living in a certain region.

The change from one area to another is gradual according to the mean annual shows. There is a connection between the other ecosystems of the biosphere.

The dashed line encircles a wide range of environments in which either grasses or plants can dominate the area.

The global map shows that the same type of biome can occur in different parts of the world.

Differences in climate determine the distribution of the biomes and their corresponding populations. The altitude and latitude play a role in determining the temperature.

The same sequence is seen when ascending a mountain. The lack of landmasses in the Southern Hemisphere makes it hard to reach a region similar to a forest or tundra when going from the equator to the South Pole.

The vegetation is partly determined by temperature, so it changes with altitude. It is possible to find grassland at the base of mountains because of the role precipitation plays.

Canada geese are able to migrate from one region to another, as described in the opening essay. The geese breed in one area but spend their time in another. The Nature of Science feature describes how the analysis of DNA is helping to clarify migration patterns and species relationships.

The features of the major biomes begin with the tundra.

Much of the year is cold and dark in thearctic tundra. It has harsh winters and short summers. The tundra could be considered a desert because it only gets 20 cm of rain a year, but melting snow creates a landscape of pools and bogs in the summer. Only the topmost layer of soil thaws, while the permanently frozen layer of permafrost results in minimal drainage. The soil in the tundra is poor.

The vegetation in this area consists of mosses, grasses, and shrubs. There are pools of water on the permanently frozen ground. During the summer, Caribou will feed on grasses and shrubs, while in the winter they migrate south.

The growing season in the tundra is too short. The roots can't become anchored in the shallow boggy soil during the summer because they can't penetrate the permafrost. The ground is covered with grasses and sedges in the summer.

There are animals in the tundra year-round. The mouselike lemming stays beneath the snow, the ptarmigan burrows in the snow during storms, and the musk ox conserves heat because of its short, squat body. There are animals that live in the tundra. In the summer, the tundra is home to many insects and birds. Reindeer in Asia and Europe also migrate to and from the tundra, as do the wolves that prey on them. There are polar bears near the coast. All species can live in extreme cold with a short growing season.

There are long, cold, snowy winters iniferous forests.

The taiga typifies the forest with its cone-bearing trees. The leaves and bark of these trees are thick so they are well adapted to the cold. The leaves can hold the weight of snow. The forest floor is covered with mosses and lichens beneath a layer of needles. Birds and animals live around the lakes and streams. These mammals are preyed on by wolves. The mountain lion and the wolverine can be found in a montane forest. The taiga, or boreal forest, is south of the tundra and covers more than 10% of the Earth's landmasses. There are no large landmasses in the Southern Hemisphere.

The taiga spans northern Europe, Asia, and North America.

Scientists were amazed to find that most of the turtles that are killed in nets and hooks in the Mediterranean Sea are from beaches in the southeastern United States.

The decline in loggerheads on southeastern U.S. beaches may be related to the decline in Mediterranean fishing.

They are the largest cat in the world. Their range goes from as far north as Mexico to as far south as Argentina. They are currently listed as "Near Threatened" by the International Union for the Conservation of Nature. In order to conserve a top-level predator that has an extensive range, it requires support from all of the countries that are home to jaguars.

Detailed genetic analysis of jaguars has indicated that they are all the same species, even if they live in Mexico, Argentina, or anywhere in between.

The only wide-ranging carnivore in the world that has genetic continuity across their entire range is them.

The Jaguar Corridor Initiative is a result of this genetic information. The goal of the initiative is to create a genetic corridor that links jaguar populations in all of the 18 countries in Latin America, from Mexico to Argentina, and hopefully ensuring the survival of this species.

Scientists from the United States and New Zealand carried out discreet experiments in a Japanese hotel room on whale sushi bought in local markets, in a classic example of how DNA analysis could be used to protect species from future ruin. A staple of the Japanese diet, sushi is a rice and fish mixture wrapped in seaweed. The 16 pieces of whale sushi the scientists examined were all from whales that are protected under an international moratorium on whaling. David Woodruff is a biology professor at the University of California, San Diego.

The Mediterranean Sea has many loggerhead turtles from the southeastern United States. All jaguars are the same species, no matter where they are found.

Four of the samples were from fin whales and one was from a beaked whale. The technique could be used to monitor and verify catches.

The Fish and Wildlife Service forensics laboratory is on the lookout for wildlife crimes in the United States and 122 other countries that send samples to him for analysis. "DNA is one of the most powerful tools we have," says a former California police crime-lab director.

For the obvious reason that we can match those samples to a crime scene, the lab has blood samples for all of the wolves being released into the park. There are many cases in the lab that he can't discuss. He likes to tell the story of the first case. California wildlife authorities contacted Goddard shortly after the lab opened.

A trophy-sized deer was taken from a hunter.

The agents couldn't match the gut pile to the carcass on the property. Two witnesses denied that the deer had been shot.

The lab analysis made a perfect match between the tissue from the gut pile and the tissue from the carcass.

The forest that runs along the west coast of Page sucks in water when they meet the coastal mountain range. The environment has produced some of the tallest conifer trees in the world. Some trees are as old as 800 years in this forest. It is an evergreen forest because of the abundance of green plants.

There are many species of animals in the rain forest.

The growing season is between 140 and 300 days. Oak, beech, sycamore, and maple have broad leaves.

Deciduous forests can be found south of the taiga in eastern North America, eastern Asia, and much of Europe.

The first to receive sunlight is the canopy of the tallest trees. A layer of trees called understory trees get their energy from the sun. There are shrubs and plants beneath the trees that may flower in the spring. There is still another layer of plant growth beneath the shrub layer. There is a variety of habitats for insects and birds. There are many ground animals. Squirrels, rabbits, woodchucks, and chipmunks are small animals. Birds such as turkeys, pheasants, and grouse are preyed on. In contrast to the taiga, the winters are not as cold. Frogs and turtles prefer the water.

After the leaves turn brilliant colors and fall to the ground, a rich layer of humus is formed. When the rich soil is washed away by the spring rains, the minerals are taken back up into the forest system by the deep tree roots.

These are the most fertile land areas on the planet. 50% of the Earth's biodiversity can be found in the tropical rain forests. Tropical rain forests can be found in South America, Africa, and the Indo-Malayan region.

A tropical rain forest has many levels of life, including the forest floor, understory, and canopy. Most of the sunlight is blocked by the canopy of the forest floor. The plants in the understory are specialized for shade. The most productive level of the tropical rain forest is the canopy.

The canopy, understory, and forest floor are the primary levels in a tropical rain forest. Some organisms spend their entire lives in one level, and the canopy contains levels as well. The hanging vines produce leaves in the canopy. Epiphytes are air plants that grow on trees.

The broadleaf evergreen trees can grow up to 50 m in height. The trunks of tall trees have been girded to prevent them from falling. As the tree grows, lianas help strengthen the trunk. A 10 km2 area of a tropical rain forest may contain 750 species of trees and 1,500 species of flowering plants.

Some animals live on the forest floor, but most live in the trees. Most of the insect species have not been identified yet.

The ants are found in the trees, and they play a vital role in the decomposition of plant material. The various birds, such as hummingbirds, parakeets, parrots, and toucans, are often beautifully colored. There are many types of snakes and lizards. Chimpanzees, sloths, and monkeys feed on the fruits of the trees. The big cats are the jaguars in South America and the leopards in Africa and Asia.

Animals and plants spend their entire lives in the canopy.

Epiphytes are plants that grow on other plants but have roots of their own, which absorb water and minerals from the air. The bromeliads form vases of leaves to catch rain and debris. Pineapples, orchids, and ferns are related to the most common epiphytes.

Tropical forests that have wet and dry seasons are found in India, Southeast Asia, West Africa, South and Central America, the West Indies, and northern Australia. There are many layers of growth beneath the trees.

The soil of a tropical rain forest is poor. Only a small amount of leaf litter makes it to the forest floor due to the high amount of herbivory. High temperatures, a long growing season, and nearly 12 hours of sunlight all contribute to high productivity. Slash-and-burn agriculture can be done on a small scale, but it becomes destructive and unsustainable on a large scale. The ash produced from cutting down trees provides food for several years. A new section of the forest must be cut and burned. In tropical humid forests, iron and aluminum oxides occur at the surface, causing a reddish stain known as laterite. Laterite bakes in the hot sunlight to a bricklike consistency, which will not support crops, when the trees are cleared.

The rain forest is estimated to have been destroyed by Page 884 second. 78 million acres is how much this rate equates to.

Rain forests will be destroyed beyond recovery unless strategies are put in place to conserve them. Ecologists estimate that there are 137 species that are driven to extinction every day in the rain forests.

Shrublands tend to have dry summers and receive most of their precipitation in the winter. shrubs are shorter than trees but have no central trunk. Shrubs have small but thick evergreen leaves, which are often coated with a waxy material.

Shrubs are able to grow quickly after a fire. The shrub stage is part of the process of both primary and secondary succession.

Shrublands can be found along the cape of South Africa, the western coast of North America, and the southwestern and southern shores of Australia. The seeds of many species need fire to grow. Some shrubs grow after a fire. The animals of the chaparral include mule deer, rodents, lizards, and greater roadrunners. California has chaparral regions.

The shrubs in this chaparral are adapted to regrowth quickly, even though they are subject to raging fires. The roadrunner found a home in the chaparral.

A northern shrub area that lies to the west of the Rocky Mountains is sometimes classified as a cold desert. sagebrush provides the resources to support various species of birds.

Grasslands are generally insufficient to support trees despite the fertile soil. It is too dry for forests and too wet for deserts to form in temperate areas.

Grasses are well adapted to a changing environment and can tolerate a high degree of flooding. Tall grasses that reach more than 2 m in height can flourish in high rain areas. The grasses are shorter in the dry areas.

Grasses are seasonal. When there is little grass for animals to eat, they migrate and hibernate.

There are winters that are bitterly cold and summers that are hot. The line between a forest and a prairie is roughly along the border between Illinois and Indiana. The tall-grass prairie gets more rain than the short-grass prairie. The Russian steppes, the South American pampas, and the North American prairies are some of the tevirate grasslands.

The tall-grass prairies are dotted with pines and junipers. Some areas are being reintroduced with bison. Small mammals, such as mice, prairie dogs, and rabbits, live belowground but feed aboveground.

Most of the grasslands have been converted to agricultural lands because of their fertile soils.

There are Savannas in regions where the dry season is followed by a hot rainy season. The savanna is characterized by large expanses of grasses. The plants of the savanna have deep root systems, which allow them to survive fire. There are savannas in central and southern Africa. There are savannas in Australia, Southeast Asia, and South America.

There are shrubs and trees in the African savanna. There is a large amount of animal species in this area.

Elephants and giraffes are browsers. The animals feed on the grasses. The plant litter that is not eaten by the grazers is attacked by a variety of small organisms. The source of food for the tyrannosaurus rex is the fungal gardens they tend. The animals support a large population of animals. The abundant herbivore populations found in the savanna are preyed upon by lions, hyenas, cheetahs, and leopards.

Deserts are characterized by days that are hot because of the lack of cloud cover, but nights are cold because heat escapes into the atmosphere. An annual rainfall of less than 25 cm is the result of the winds that descend in these regions.

Deserts can be found at latitudes of 30 degrees in both the Northern and Southern Hemispheres. Deserts cover 30% of the Earth's land surface.

The Sahara, which spans from the Atlantic coast of Africa to the Arabian peninsula, has little or no vegetation. Most deserts contain plants that are adapted to survive long dry spells, extreme heat, and extreme cold.

The ability to set seeds quickly in the spring is on the page. The spiny cacti, which have stems that store water and have the ability to run, are the best desert plants in North America. Nonsucculent shrubs, such as the sagebrush with silvery gray leaves and the spiny-branched ocotillo, are common.

Plants and animals live in the desert. The plants are either succulents, which retain water, or shrubs with small leaves, which don't lose much water. The kit fox is an example of a desert carnivore.

The animals are adapted to the environment. Desert animals that are nocturnal or burrowing have a protective outer body covering to conserve water. A desert has many insects that pass through the stages of development at the same time as the rain.

Start at the equator and move toward the North Pole.

Understand how ocean currents affect the weather over the continents.

There are two types of aquatic systems: freshwater and saltwater. There is a mixture of fresh and salt water.

Mountain streams have clear water that flows over waterfalls. As streams merge, a river forms and gets wider and deeper. Wetlands and estuaries can be found at the mouth of the river, where it divides into many channels. There is a high oxygen content in the water. The trout are a major predator. There is little oxygen and a lot of silt in the water.

Blue crabs are found in the water.

The salts are left behind when the sun's rays cause the water to evaporate. In Chapter 45 fresh water rises into the atmosphere, cools and falls as rain. When there is rain, some of the water sinks into the ground and saturates it. The water table is the layer of water in the ground.

All fresh water is returned to the sea when land is above sea level. It is contained in lakes and ponds along the way to the sea. There are underground rivers called aquifers. Water will rise to the level of the water table when the Earth has basins or channels.

Wetlands hold some amount of water during the year. Wetlands are classified by their vegetation. Wetlands that are frequently flooded by water are called marshes. They are characterized by the presence of rushes, reeds, and other grasses, which provide excellent habitat for ducks and small mammals. One of the most productive ecosystems is the marshes. The swamp trees include cypress, red maple, and tupelo. The American alligator is a top predator. The wetlands are characterized by acidic waters. Most of their water comes from precipitation. Orchids, cranberries, Venus flytraps, and pitcher plants are some of the plants that thrive in the bogs.

Humans have historically diverted rivers and filled wetlands with the idea that "useless land" was being improved. These activities can cause flooding and degrade the habitats for fish and other wildlife. Wetlands break down toxic waste and excess nutrients to purify waters. Wetlands absorb storm waters. They protect farms, cities, and towns from floods. Wetlands have been protected by federal and local laws.

Lakes are bodies of fresh water. The lakes are characterized by a small amount of organic matter and low productivity. Eutrophic lakes are characterized by plentiful organic matter and high productivity. These lakes are usually located in regions with high levels of nitrogen and other minerals.

Eutrophic lakes have large populations of plants that use up oxygen and leave little for fish to eat.

In the winter and summer, deep lakes have different vertical zones. There are three layers of water in the lakes in the summer.

The more dense water of the thermocline floats on top of the less dense water of the epilimnion.

During the spring and fall, the deep waters receive oxygen from the surface waters.

Phytoplankton use up a lot of different vitamins and minerals as they photosynthesize. This layer has a ready supply of oxygen. Oxygen is used up as decomposing occurs at the bottom of the lake. Decomposition releases vitamins and minerals. As the season goes on, the epilimnion becomes weak and the hypolimnion depletes of oxygen.

The epilimnion cools in the fall and warms in the spring. The upper epilimnion waters become cooler in the fall.

The temperature is uniform throughout the lake until the layers are mixed. The circulation of water is aided by the wind at this point. Oxygen and nutrients are distributed evenly.

Further cooling of the water below can be prevented by ice. This allows organisms to live in the water during the winter.

The cooler water on top sinks below the warmer water on the bottom in the spring. The temperature is uniform throughout the lake until the layers are mixed. The surface waters absorb solar radiation.

In the summer, coldwater fish move to the deeper water while in the winter they stay in the upper water. In the fall and spring, there is a lot of growth at the surface.

When a green scum or red tide appears on the water, they become more noticeable.

Life zones can be divided into lakes and ponds.

Plants and organisms live in the littoral zone. The fishes are in the sunlit limnetic zone.

The profundal and littoral zones are where the curafishes and molluscs are found. The pike are prized by fishermen. Largemouth bass are a type of ambush predator that waits among vegetation around the margins of lakes and pounces on passing prey. The birds are feeding in the littoral zone. The water strider can walk on water and live at the water-air interface. Small fishes, such as minnows and killifish, serve as food for larger fish in the limnetic zone. In the profundal zone, zooplankton, invertebrates, and fishes such as catfish and whitefish feed on debris that falls from higher zones.

The benthic zone is composed of silt, sand, and dead organic material.

Decomposers, such asbacteria, are found in the benthic zone and break down waste and dead organisms into food for the producers.

A portion of the ocean is where fresh water and salt water mix. Mangrove swamps are found in tropical and subtropical zones. The bays, fjords, and lagoons are classified as estuaries. The term estuary has a broad definition.

Migrant birds frequent mudflats. The coastlines of many tropical and subtropical lands are skirted by mangrove swamps. Some organisms live on the rocky coast. Organisms adapted to the estuarine environment benefit from the abundance of vitamins and minerals.

Estuaries are productive and diverse.

There is an abundance of food and habitat for animals in the estuaries. The estuarine environment is home to nearly two-thirds of marine fishes and shellfish, making it the nursery of the sea. There is an abundance of fish and shellfish.

As the tides roll in and out, the sea bombards the sandy shores.

The calcareous outer plates of barnacles remain in place even after the animal dies in the upper portion of the intertidal zone. In the middle of the intertidal zone, rockweed may overlie the barnacles. Below the intertidal zone, seaweeds anchor themselves to the rocks with holdfasts.

The ocean is home to many organisms.

Organisms can't attach themselves to shifting sands on a sandy beach, so most of the permanent residents are underground. Either they burrow during the day or stay within their burrows and tubes at night. Ghost crabs and sandhoppers burrow above the high tide mark and feed at night. Sandworms and ghost shrimp remain in their burrows in the intertidal zone and feed on whatever they can find. clams, cockles, and sand dollars are found. shorebirds visit the beaches and feed on fish.

There is food for zooplankton and small fishes here. These attract a lot of fish. As the water gets deeper, seaweed can be found growing on outcroppings. Sea stars, lobsters, crabs, and brittle stars prey on clams, worms, and sea urchins.

Coral reefs are found in shallow, warm, tropical waters. Their main components are stony corals, animals with a calcium carbonate (limestone) exoskeleton, and calcareous red and green algae. The corals feed at night while the algae grow during the day. Coral reefs are usually developed in shallow, sunlit waters.

There is a lot of life on the reef. The large number of crevices and caves give shelter to filter feeders and scavengers. The barracuda, moray eel, and shark are some of the top predators in coral reefs. There are many types of small, beautifully colored fishes here. These become food for larger fishes.

The majority of the ocean's volume is within the pelagic zones.

There are a lot of whales in this zone. Baleen whales eat small crustaceans from the water, while toothed sperm whales feed on squid.

The benthic division's epipelagic, mesopelagic, and bathypelagic zones are home to unique organisms.

Shrimps, squids, and fishes, including lantern and hatchet fishes, are some of the organisms that are translucent, red colored, or even luminescent.

Animals and fishes migrate from the mesopelagic zone to the surface at night.

There are animals in this zone. There are strange-looking fishes with distensible mouths and abdomens.

Many animals survive there by feeding on debris floating in the water. Sea lilies rise above the seafloor, sea cucumbers and sea urchins crawl around on the sea bottom, and tube worms burrow in the mud.

The flat plain is interrupted by mountain chains. Sulfate reacts with water and forms hydrogen sulfide along the axes of the ridges.

There are organisms at the vents that live mutualistically with Chemo autotrophicbacteria that obtain energy from oxidizing hydrogen sulfide.

They are the beginning of a food chain that includes huge tube worms, clams, crustaceans, and fishes. Light doesn't need light energy to exist in this environment.

We talked about food webs and energy flow in the section. The biomagnification of Mercury is discussed in the Biological Systems.

Mercury emissions into the environment can cause serious health effects for humans. Mercury emissions negatively impact fish and wildlife. Humans are at risk if they come into contact with fish and wildlife. Recent fish studies show that mercury is present in streams, wetlands, and lakes in the majority of the United States.

Mercury becomes a serious environmental risk when it is bioaccumulated. A bioaccumulation occurs when an organisms accumulates a contaminant faster than it can eliminate it. Most organisms can eliminate half the mercury in their bodies every 70 days if they don't eat any more during this time. Problems arise when organisms can't eliminate mercury.

The base of the food chain is where Mercury tends to enter and increase in concentration. The most vulnerable to high levels of mercury in their body tissues are top-level predator and organisms that have been around for a long time.

Humans are exposed to mercury due to eating contaminated fish or breathing mercury fumes.

Birth defects in infants and damage to the central nervous system can be caused by the form of mercury called methylmercury.

Every state in the United States has developed fish advisories for certain bodies of water. 45 states warn pregnant women to limit their fish consumption.

Mercury poisoning is not limited to aquatic species. In the northeastern United States and Canada there was research that showed the presence of mercury in a variety of birds. The consumption of contaminated fish can lead to high levels of mercury in the birds. The presence of mercury in the songbirds raised serious concerns among ecologists. Some theorize that songbirds in the northeast are consuming mercury when they feed on insects that have picked up the toxin from eating smaller insects. Concerns about mercury's ability to enter food webs and bioaccumulate in previously unknown ways have been raised.

Humans are to blame for mercury pollution. There are no limits to where mercury can be found. With coalburning power plants being the largest source of mercury emissions, it will be up to us to find a solution.

High levels of mercury can be found in tuna due to biomagnification. Fetal development can be affected by high levels of mercury in fish.

Climate is driven by the sun, but the oceans contribute to heat in the biosphere. The distribution of the sun's rays causes water to be warm at the equator and cooler at the poles. Warm air moves from the equator to the poles as air takes on the temperature of the water below. The ocean makes the winds blow. The oceans hold heat longer and remain cooler during periods of changing temperature than do the landmasses.

When wind blows across a large expanse of ocean for a long time, it causes the water to get wet.

The ocean currents are counterclockwise in the Southern Hemisphere and counterclockwise in the Northern Hemisphere. Warm water is taken from the equator to the poles. The Gulf Stream brings tropical Caribbean water to the east coast of North America and the higher latitudes of western Europe.

Without the Gulf Stream, Great Britain would be as cold as Greenland. The eastern coast of South America is warm by another major ocean current.

The locations and directions of the major ocean currents are indicated by the arrows on the map. Carrying warm water to cool latitudes and cool water to warm latitudes has a major effect on the world's climates.

There is a current in the Southern Hemisphere that goes toward the equator. Along the west coast of South America, the Humboldt Current carries cold water. The abundance of marine life in South America is due to the enriched waters. Birds deposit their droppings on the land where they are mined for a commercial source of phosphorus.

The phenomenon is called an El Nio-Southern Oscillation.

The position of a region on the Earth and the amount of solar radiation play a role in determining the region's weather patterns.

Warm air rises near the equator and then descends at 30 degrees north and south to the poles. The great deserts of the world are formed at 30 degrees latitudes when the air descends. The winds blow in opposite directions above and below the equator because of the Earth's rotation.

On the windward side, air rises over coastal ranges.

The pattern of the world's biomes is influenced by temperature and rain. When traveling up a mountain, the effect of temperature causes the same sequence of biomes.

Most of the water in the soil is frozen in the winter.

These are the most productive of all the biomes.

Some desert plants, such as cacti, are Succulents with thick stems and leaves, and others are shrubs that are deciduous during dry periods.

The freshwater and saltwater systems are divided.

There are three life zones in lakes and ponds. plankton and fishes live in the sunlit limnetic zone, while bottomdwelling organisms such as crayfishes and molluscs live in the profundal zone.

The oceans and coastal ecosystems are different. Estuaries are near the mouth of a river and are considered the nurseries of the sea.

The ocean is divided into two parts. The most life can be found in the epipelagic zone. The zone has organisms adapted to minimal or no light. The bathypelagic zone is dark. The continental shelf, continental slope, and the abyssal plain are on the ocean floor.

The base of these communities are the Chemoautotrophicbacteria. The ocean currents are moving in a circular pattern.

Pick the best answer for the question.

The seasons are explained by the distribution of temperature and rain.

The northern and southern hemispheres are between 30 and 60 degrees.

The rotation of the Earth causes this.

The winds blow from the ocean.

The tundra is only described by low-lying vegetation.

A tropical rain forest has a multilevel canopy.

The westerlies explain the mild climate of Great Britain.

The ocean current is prevented from upwelling.

The tropical rain forests are being bioprospected. These companies are looking for naturally occurring compounds in plants and animals that can be used as drugs.

Ski resorts, golf courses, and homeowners all contribute to water pollution. Some farmers are using irrigation methods that deliver water directly to plant roots, no-till agriculture that reduces the loss of topsoil, and integrated pest management, which relies heavily on good bugs to kill bad bugs. In some cases, encouraged by state and federal agents, dairy farmers have built sheds, concrete containments, and underground liquid storage tanks. The manure is trucked to the fields.

In Minnesota, builders are required to control soil erosion with filter fences, to steer rain away from exposed soil, and to plant protective buffers. Homeowners need to have a 25-foot and 50-foot setbacks from wetlands and lakes. They are encouraged to have their systems pumped out every 2 years.