Biome CD-ROM Text Version 1/02 Integrated Science 2 Redwood High School Scene 1 What would you pack for an African safari? A hike in the Sonoran desert? A cross-country skiing trip at Banff National Park in Canada? Humans can survive in many different climates with the right equipment, but the plants and animals that live in these places must possess adaptations that help them survive. Based on climate and the predominant vegetation, we can divide the Earth s ecosystems into broad categories called biomes. In this program we will tour the Earth s biomes, discover the challenges of these unique environments and learn how organisms adapt to these challenges. But before you pack your shorts, parka, water bottle, or anything else you might need, let s examine the factors that influence climate. Scene 2 The term climate describes the temperature range, average annual precipitation, humidity, and amount of sunshine that a region typically experiences. Three main factors influence climate: solar energy, global patterns of air and ocean circulation, and geographical factors. Scene 3 Solar energy varies as the output of the sun changes over time, but the Earth s shape (or curvature), rotation, and orbit also influence the input of solar energy. The Earth s curvature causes the tropical regions, or the tropics to receive the greatest amount of solar energy, while the Polar Regions receives the least. The light is less intense near the poles, because the same amount of light must cover a larger relative area. The Earth s rotation around an invisible axis causes the differences between night and day. Finally, the Earth is tilted in relation to its orbit around the sun, and this creates the difference in solar energy between seasons and between hemispheres. The seasons for the Northern Hemisphere are shown on this diagram, but note that the Earth s tilt means that the seasons are just the opposite between hemispheres. For example, the summer solstice in the Northern Hemisphere is the winter solstice in the Southern Hemisphere. These three factors: 1) the Earth s shape or curvature, 2) its rotation, and 3) its tilt and orbit all influence solar input and drive the movement of air and water from warm to cold areas. Scene 4 Have you ever seen water droplets form on the outside of a cold beverage on a hot day? These droplets form because as warm, moist air comes in contact with the cold surface of the can or glass, water droplets condense and this process is called condensation. In the atmosphere, condensation can result in precipitation. Precipitation includes rain, snow, sleet, hail, or dew. The heat of the sun evaporates water from the oceans into the air. As this warm, moist air mixes with cold air, tiny droplets condense into clouds and may fall as precipitation. We will examine the formation of precipitation from two atmospheric processes: 1) Hadley Cells and 2) the movement of air masses and fronts. Scene 5 The abundant rainfall in the tropics and the scarce rainfall in the deserts come from circular air currents called Hadley Cells. The direct solar energy in tropical areas causes warm, moist air to rise. Air temperatures cool with elevation, and as this air cools, water condenses and rain falls. This now dry air eventually descends and warms, creating the hot dry climate of the great deserts. This cycle creates high pressure in the deserts and low pressure in the tropics, so air moves toward the equator and picks up moisture, completing the cycle. The Hadley Cell occurs on both sides of the thermal equator.
Scene 6 In temperate and Polar Regions, the movement of air masses influences weather more than the Hadley Cells. An air mass is a large body of air with similar temperature and moisture properties. The boundary between dissimilar air masses is called a front. Air masses can dramatically change air temperatures and generate powerful storm systems. When large air masses of different temperature and pressure collide, storm systems can form. High altitude winds called jet streams regularly push these storm systems far from their origin. Scene 7 Like air currents, ocean currents redistribute heat. Because the oceans warm and cool slower than the air, they tend to moderate the temperature of nearby landmasses. For example, the warm water of the Gulf Stream produces the relatively warm and moist weather of Northern Europe and the British Isles. On the other hand, cool currents usually bring cooler summer temperatures and drier weather. The California and Humboldt currents located on the western coasts of North and South America are two examples of cool currents. Scene 8 Geographical features, such as mountains and large water bodies, also influence climate. Let s look at California s Sierra Nevada Mountains as an example. Remember that air temperature decreases as elevation increases. As we climb up the mountain, the decrease in air temperature somewhat mimics the temperature changes we would see as we traveled toward the North Pole. The temperature decrease also influences precipitation. As the jet-stream blows Pacific-generated storms to the windward side of the Sierras, the mountains force air to higher elevations, where it cools and causes rain or snow to fall. Now dry, this air descends and creates the desert climate of the Great Basin on the leeward side of the mountains. This phenomenon is called a rainshadow effect. The temperature and precipitation differences produce vegetation characteristic for that climate. Scene 9 We have discovered the major factors that influence climate: solar energy, global patterns of air and ocean circulation, and geographical features. But relatively minor factors such as shade, soil moisture, wind exposure, and surrounding vegetation can modify the local climate enough to foster the survival of organisms otherwise suited to other climates. The term microclimate describes the actual conditions experienced by an organism at a particular area. As we examine each biome, think about the factors that might influence microclimates. Scene 10 A biome is a large terrestrial region with a defining climate that supports characteristic plants and animals with adaptations to that particular environment. We will focus on the four main terrestrial biomes: tundra, forest, grassland, and desert, but we will also examine the three main aquatic ecosystems: freshwater, estuarine, and marine. Terrestrial biomes are based on climate and vegetation, while aquatic ecosystems are based on physical and chemical factors. Scene 11 The concept of biomes helps us to understand the conditions found over large areas, but can you think of areas near your home that do not match the categories depicted? Local vegetation may not match the designated biome category for several reasons. First, biomes represent transitions where boundaries often slowly fade into the adjoining biome, like grassland merges with forest to produce savannas. Second, biome maps may omit small pockets of vegetation. For example, a stream in the desert may allow lush vegetation to thrive. Finally, we base biomes on the expected vegetation for a given climate, and not necessarily what currently exists. For example, a fire may clear a forest of trees, but eventually the forest will reappear. 2
Scene 12 We can define terrestrial biomes based solely on annual precipitation and annual average temperature. This graph gives us a hint of the typical climate conditions of each biome. The tropical rainforest is warm and wet, while all deserts are dry. During our tour, we will focus on the unique survival adaptations that allow plants and animals to cope with the characteristic climate of each biome. The climate also helps tell us what to bring. Our first stop, the tundra, is cold and dry so pack the warm clothes. Got your luggage packed? Let s go! Scene 13 Cold and dry weather characterizes the climate of the tundra biome. Alpine tundra dots the high mountains of the world, but most tundra lies above the Arctic Circle. Arctic winters are incredibly inhospitable, with up to 24 hours of darkness and bitterly cold, dry winds. Snowfall is less frequent and less heavy than people often realize. Furthermore, water is frozen as ice or snow, and is unavailable to organisms until temperatures rise in the summer. In fact, it is so cold that permafrost, or permanently frozen soil, lies under the surface. Fortunately you have arrived in the midst of the short, but intense summer. Despite the cold, dry winters, life flourishes in the summer. While you still need to dress for cool weather, summer days are not as cold as you might expect. As daylight gradually lengthens to nearly 24 hours, numerous small wet depressions form over the permafrost, and the tundra comes alive with insects, mammals, and birds. A swat at yet another mosquito reminds you of the abundant life on the busy summer tundra, but how do organisms survive the harsh winter? Scene 14 Tundra plants have special traits or adaptations to protect them from this harsh climate. We call any functional, structural, or behavioral change that aids in the survival and reproduction of an organism to a particular environment, an adaptation. For example, short plants with small, hairy leaves provide better protection from the blast of cold, dry winds than tall plants with large leaves. In order to reproduce during the short growing season, plants must either have adaptations that allow them to produce seeds in a short period of time, or grow from vegetative parts such as stems, leaves, or roots. Scene 15 Some animals also take advantage of the short growing season. The rapid plant growth in summer creates an attractive food source for insects and large migrating herds of musk ox and caribou. In winter, insects remain dormant to avoid cold temperatures, but in summer they emerge to feed on plants and animals, including you. Migrating birds feed on the abundant insects to fatten up for their long migrations ahead. With the abundance of animals, predators such as foxes and wolves thrive. Inevitably, winter returns and many animals migrate to warmer climates to avoid the cold winter. The animals that remain develop thick fur coats and special fat layers that insulate them from the extreme cold. Surprisingly, very few arctic mammals hibernate, presumably due to the danger of freezing during the long, cold winter. Scene 16 Depending on rainfall, temperature, and the seasonal variation of the two, at least four different forest biomes are possible: taiga, temperate forests, chaparral, and tropical rain forests. Let s tour each of these forest biomes, starting with the taiga. Scene 17 As we move south, the open spaces of the arctic tundra give way to occasional stunted trees and finally to a dense forest called taiga. Taiga makes a worldwide band of vegetation just south of the Arctic Circle. Taiga, which is sometimes called the boreal or northern coniferous forest, comes from the Russian word for mountain and taiga is found in many mountainous areas of the world. Like the tundra, taiga winters are cold, but with considerably more snow than the tundra. Although snow is cold, it insulates plants and soil from even colder temperatures and 3
chilling winds. Taiga summers are longer and warmer than those of the tundra. Scene 18 While walking under the dark canopy of the taiga, you would instantly notice the dominance of conifers, or conebearing trees. Certain conifers are well suited to this environment. Their conical, or Christmas-tree like shape and flexible branches shed snow and yield to strong winds, and their shallow root systems enable them to collect nutrients and water from the surface soil rather than the permafrost below. Much like the leaves of tundra plants, tough conifer needles tolerate drought and freezing temperatures, because they use little water and are structurally strong. Because most conifers are evergreen, they can produce food for the plant whenever water and sunlight are available, which is a definite advantage in this unpredictable climate. Scene 19 Many birds visit the taiga in the warmer summer months to feed on the abundant food and to breed, but migrate south to avoid the cold winter. However, winters in the taiga are not quite as cold as the tundra. In fact caribou migrate from the wind-swept open tundra to spend winters sheltered in the trees of the taiga. Many animals grow thick fur coats to protect them from the cold, but others seek shelter during the winter. Voles, for example, make snow tunnels to feed on old vegetation and gain shelter from the cold. Some animals, like this marmot, hibernate. Hibernation allows animals to enter a state of sleep with low metabolic requirements and avoid having to forage when food is scarce. Scene 20 Unlike the taiga, winter in a temperate forest will not necessarily turn you into an instant popsicle. Temperate forests have moderate temperatures and precipitation, but climate variations favor certain tree types. We can divide temperate forests into coniferous, mixed, and deciduous forests. Our tour of the taiga gave us a good introduction to coniferous trees, most of which are evergreen. Evergreen trees keep their leaves year round. Temperate coniferous forests tend to grow in areas with distinct dry periods and often represent the transition between temperate deciduous forests and taiga. Deciduous trees include broad-leaved trees that shed all of their leaves at once. Temperate deciduous forest are best represented in the Northern Hemisphere in areas with warm summers, cool winters, and relatively abundant precipitation spread evenly throughout the year. Mixed forests describe areas with relatively even numbers of coniferous and deciduous trees. Scene 21 As we shuffle through the colorful leaves of a temperate deciduous forest on a crisp fall day, we can note one of the most important features of this biome, namely that the temperate deciduous forests have a distinct annual rhythm and four seasons. The long growing season allows for a greater variety of plants than found in the taiga. Taiga typically consists of 2 vegetation layers of mosses and conifers, but temperate forests support several different vegetation layers of mosses, herbs, shrubs, and understory and overstory trees. The climate determines which trees dominate. The water retaining properties of conifer needles provide an advantage in areas with frequent dry periods or unpredictable weather. In contrast, broad leaves are sensitive to cold temperatures and require more water than needles. However, broad leaves capture sunlight more efficiently than small, needle-like leaves, and hold an advantage in areas with relatively long growing seasons and relatively abundant water. Deciduous plants lose their leaves and become dormant (much like hibernating animals) as a means to protect themselves from the cold or the lack of available water. Scene 22 Many temperate forest animals are well adapted for a life among trees. Most animals are well disguised and usually depend on an acute sense of hearing for protection. Some are good climbers. For instance, this squirrel uses its tail for balance as it scrambles along branches. Trees also provide shelter and support intricate food chains. Some insects feed on specific parts of trees, and in turn become food for the variety of birds that live in or 4
migrate to the temperate forests. This woodpecker is well adapted to drilling holes to find bark-dwelling insects and to hollow out shelters. In the late fall or early winter, some animals hibernate, some migrate to warmer climates, and yet others remain active through the winter. Scene 23 As the fall colors fade in the temperate deciduous forests, we leave for our next type of forest biome, the tropical rain forest. Unlike the temperate forests, the tropical rain forests generally lack distinct seasons, and day-length and temperature vary little during the year. In fact, temperatures usually differ more between day and night than between months. Rainfall is often heavy and falls throughout the year. You are now standing in a tropical forest, jungle-ready in lightweight longsleeved cotton clothing to keep cool, a mesh-netting hat to keep the insects out, and boots to repel water and snakes. As raindrops ricochet off the leaves above, a remarkable thought grabs you, something living is on, under, over, above, or in just about everything you see. Scene 24 With abundant water and warm temperatures, plants compete fiercely for sunlight. In between the forest floor and the canopy, multiple layers of plants capture any available light that slips through the blanket of leaves from the tall rainforest trees. When a tree falls, the other trees begin a race toward the sun to fill the gap. The competition for light is so fierce that some plants even grow on other plants. Unlike most plants, epiphytes do not grow in soil, but grow on a host plant s branches, collecting water and nutrients from rain and dust. However, not all plants grow harmlessly on the host tree. For example, birds deposit seeds of the strangler fig onto the branches of a host tree, and the roots grow around the tree and into the ground. As the fig grows, it shades out and eventually kills the host tree. Scene 25 From underground to the tops of trees, a dizzying variety of insects, reptiles, amphibians, mammals, and birds occupy every possible habitat of the tropical rainforest. Many rainforest animals have coevolved intricate relationships with other organisms and depend on other organisms to survive. For example, these leaf cutter ants chew leaves and feed the pulp to a specific fungus. The ants later harvest the fungus for food. Scene 26 Our next stop is the chaparral or Mediterranean Scrub. As the first rain of the season settles the dry dust, your guide tosses you a pair of tough, leather chaps to wear on a morning horseride in the chaparral. Unlike the rainforest, where the last rain was 3 o clock yesterday, this is the first rain since late spring, well over three months ago. Such dry periods are common in the chaparral. Although scattered drought tolerant trees grow here, dense, evergreen shrubs dominate chaparral vegetation. The chaps and long-sleeved shirt that you are wearing protect you from these spiny shrubs. Chaparral vegetation is found usually near coasts, and the cool, wet winters and hot, dry summers are usually the result of the offshore circulation of cool ocean water. Scene 27 Organisms exposed to similar environmental conditions often develop similar adaptations and begin to resemble each other even though they are not related to each other. This process is called convergent evolution. Chaparral plants from different continents are unrelated, yet they look similar to each other because of their adaptations for dry summers, wet winters, and frequent fires. To limit water requirements, many shrub leaves are typically light colored to reflect heat, small and waxy to limit evaporation, and evergreen to allow photosynthesis immediately after rain. In contrast, some plants are summer deciduous and drop their leaves to avoid the lack of water in the summer. Even though shrubs predominate, many annual plants grow during the wet winter and spring. Annuals are plants that complete their lifecycle in a single season. Finally, chaparral plants are well adapted to fire, and can quickly resprout or grow after a fire. 5
Scene 28 Because of the rather unusual climate, the chaparral supports an interesting variety of animals. Many chaparral areas are exceptionally rich in bird species. Chaparral areas also support browsers, such as mule deer, predators, such as mountain lions, and burrowing animals, such as ground squirrels. Browsers are animals that feed on the leaves of shrubs and trees. Reptiles such as lizards, turtles, and snakes are also common. Scene 29 Grasses grow in chaparral and other biomes, but they can also dominate other plants under the right climate. In the heart of a grassland you might feel that you are in a vast sea of grass. The lack of trees somehow makes the sky seem larger than anywhere else. Grasslands usually occupy the interior of continental areas and represent the transition between forests and deserts. Between grasslands and forests, are grassland areas with scattered trees called savanna. Perhaps the most famous savanna is the Serengeti in Africa. Fire, temperature extremes, and grazing are factors that shape grasslands and savannas. Scene 30 Unlike many other plants, grasses respond well to frequent grazing and fires, and are extremely well suited to this biome. The growing shoot of grasses lies protected near the base of the plant, and so grasses regrow even after the leaves are nibbled or burned off. Bison graze on large amounts of grass, and as they roam to new areas the grass regrows. Winds and dry conditions fuel fast moving fires, but grassland species resprout quickly once moisture returns. In fact, some grassland species require these conditions to grow. Finally, grasses and other species must withstand extreme climatic conditions. Only hardy plants can survive the drastic changes in temperature and precipitation that these areas experience. Scene 31 Grassland soils are among the most fertile in the world, and the abundant growth of grass supports some of the largest grazers and predators found anywhere. In North America, bison and pronghorn once roamed over vast grassland areas, but most of this fertile land has been converted to agricultural uses. In Africa, the savanna supports a great number of interesting animals because these animals feed on different plants. Because of the lack of cover, smaller animals often dig shelters underground for protection from the weather and predators, and larger animals often sport antlers or other means for protection. Scene 32 Hat, water, sunglasses, water hmm what else do you need?. In the dawn of an oncoming day, the desert morning does not feel hot, at least not yet. Yesterday s heat gave way to a rather cold night because the lack of vegetation and cloud cover lets heat escape. Although deserts can vary greatly in temperature from cold to hot, all deserts are dry and often sparsely vegetated. As mentioned earlier, the world s great deserts are found under the atmospheric high pressure that borders the tropics, but large deserts can also occur in the rain shadows of mountains. The desert contains many unique plants and animals well adapted to this harsh environment. Scene 33 Desert plants have many unique adaptations that make them among the most recognizable on Earth. Like chaparral plants, there are many examples of convergent evolution usually related to the efficient use of water. Desert plants often have small spines that reduce water loss, succulent stems that store water, and either shallow roots that quickly absorb rainfall or deep roots that can tap into underground water sources. When rains fall, most desert plants complete reproduction within a few weeks. This Ocotillo from the Sonoran desert blooms only after a rain and can bloom up to five times in wet years. Desert plants usually produce large amounts of hearty seeds. These seeds can wait decades for sufficient moisture to grow. 6
Scene 34 Other than a few notable exceptions, such as Bighorn sheep, camels, the Arabian oryx, and mule deer, few large mammals survive the difficulties in finding shade and food. Small birds and seed-eating rodents are more common. Perhaps the most conspicuous animals are the abundant lizards, snakes, and other reptiles that thrive in these conditions. Not surprisingly, animals that thrive in the desert conserve water and stay cool. To avoid the heat and moisture loss, some animals spend daylight hours in underground burrows and become more active after dusk. In addition, many desert animals have light colored bodies that reflect heat and longer limbs and ears that provide a larger surface area for cooling. Some animals are even more specialized for desert life. For example, the kangaroo rat obtains water from eating seeds, collects moisture from breathing, and recycles water from urine. Scene 35 You should keep in mind that biomes naturally change over long periods of time. Climate, in an area, can change from wet to dry, changing the vegetation that lives there. For example, thousands of years ago, the Great Basin in Nevada was once covered in forests, but now its desert. Human activities can also alter biomes. In fact some ecologists recognize an urban biome and an agricultural biome to describe areas of the Earth converted to these uses. Human activities that remove water or erode soil converted formerly productive land into desert-like land, in a process called desertification. Humans may also be altering the Earth s climate. Biomes continuously change over time, and organisms must continue to adapt to new challenges, but we need to curtail activities that adversely affect these biomes. Scene 36 Up to this point, we have focused on terrestrial biomes, but aquatic ecosystems cover much of the Earth, support unique species, and provide important ecological functions. In addition to the vast oceans, aquatic ecosystems occur in all of the biomes that we examined. Even deserts have aquatic systems. However, in contrast to terrestrial systems, we divide aquatic ecosystems into categories based on chemical or physical factors, because these factors capture the essence of aquatic systems better than categories based on climate. As we have seen, solar energy drives the cycling of water from ocean to atmosphere to land and eventually back to the sea. We will briefly examine the conditions of the major aquatic ecosystems as water completes this cycle: freshwater, estuarine, and marine, or oceanic systems. Scene 37 We can split freshwater systems into three basic categories: wetlands, lakes, and streams. Wetlands represent the transition between terrestrial and aquatic systems. Wetlands occur in a great variety of habitats that support many unique organisms. Survival requires that organisms be able to tolerate temperature extremes and dry periods. Lakes are still-water habitats that form where water collects. Most lakes have distinct zones of temperature, nutrient, and light availability that often change seasonally. Lake organisms are often adapted for specific zones. The presence of moving water governs stream systems. Stream habitats change frequently and organisms must adapt accordingly. Moving water means that streamdwelling organisms must swim well or attach themselves securely to the stream bottom. Scene 38 We call the place where fresh water meets the salty water of the ocean, an estuary. Because of the daily tidal influence, the salt content of the water can vary from fresh to salty in a matter of hours. Although these fluctuations would kill many organisms, the few hardy animals that tolerate these conditions thrive, and make estuaries among the most productive environments on Earth. Oysters, crabs, and many fish species live in estuaries, and other organisms reproduce in this productive ecosystem. Scene 39 7
The ocean is the largest ecosystem on Earth. We can divide the ocean or marine ecosystem into at least three units: the intertidal zones, coral reefs, and the open ocean. In addition, the oceans contain a variety of amazing communities such as kelp forests, submarine canyons, and sea floor vents. The intertidal zone describes a habitat of extremes. Intertidal zones alternate between full submersion in sea water to full exposure to air over the course of a few hours. Organisms in intertidal zones separate into bands based on their tolerance to punishing physical factors such as exposure to wind or waves. Coral reefs are like a frosted birthday cake with the skeletons of dead organisms comprising the cake and the living organisms making up the frosting. Coral reefs form in tropical waters, and with other species rich areas. Heavy competition forces many organisms to specialize and form complicated and interesting interactions with other species. Even though some of the largest creatures on Earth inhabit the ocean, the lack of nutrients and limited sunlight makes the open ocean an aquatic version of a desert. Water effectively filters sunlight, so photosynthesis is mostly limited to phytoplankton growing near the surface. Nutrients are in short supply because they settle to the ocean bottom where they are inaccessible to many living things. However, areas near land or areas with nutrient-rich upwellings are quite productive. Scene 40 Welcome back! In this program, you have learned about the Earth s terrestrial biomes and aquatic ecosystems. The adaptations of plants and animals tell us a lot about the climate and environmental conditions with which they must contend. In this program we explored terrestrial biomes including: the tundra, taiga, temperate forests, tropical rainforests, chaparral, grasslands, and deserts; and the three main aquatic systems: freshwater, estuarine, and marine. You should now be familiar with the environmental conditions in these biomes and some of the organisms that live there. We hope you enjoyed your travels and that you tour with us again! 8