Bodies of the bird

Figure 18-11 represents the amount of energy stored as organic material in each trophic level in an ecosystem. The pyramid shape of the diagram indicates the low percentage of energy transfer from one level to the next. On average, 10 percent of the total energy consumed in one trophic level is incor- porated into the organisms in the next. Why is the percentage of energy transfer so low? One reason is that some of the organisms in a trophic level escape being eaten. They eventually die and become food for decomposers, but the energy contained in their bodies does not pass to a higher trophic level. Even when an organism is eaten, some of the molecules in its body will be in a form that the consumer cannot break down and use. For example, a cougar cannot extract energy from the antlers, hooves, and hair of a deer. Also, the energy used by prey for cellu- lar respiration cannot be used by predators to synthesize new bio- mass. Finally, no transformation or transfer of energy is 100 percent efficient. Every time energy is transformed, such as during the reactions of metabolism, some energy is lost as heat. Limitations of Trophic Levels The low rate of energy transfer between trophic levels explains why ecosystems rarely contain more than a few trophic levels. Because only about 10 percent of the energy available at one trophic level is transferred to the next trophic level, there is not enough energy in the top trophic level to support more levels. Organisms at the lowest trophic level are usually much more abundant than organisms at the highest level. In Africa, for exam- ple, you will see about 1,000 zebras, gazelles, and other herbivores for every lion or leopard you see, and there are far more grasses and shrubs than there are herbivores. Higher trophic levels con- tain less energy, so, they can support fewer individuals.A population is a group of organisms that belong to the same species and live in a particular place at the same time. All of the bass living in a pond during a certain period of time make up a pop- ulation because they are isolated in the pond and do not interact with bass living in other ponds. The boundaries of a population may be imposed by a feature of the environment, such as a lake shore, or they can be arbitrarily chosen to simplify a study of the population. The humans shown in Figure 19-1 are part of the pop- ulation of a city. The properties of populations differ from those of individuals. An individual may be born, it may reproduce, or it may die. A population study focuses on a population as a whole—how many individuals are born, how many die, and so on. Population Size A population’s size is the number of individuals that the population contains. Size is a fundamental and important population property but can be difficult to measure directly. If a population is small and composed of immobile organisms, such as plants, its size can be determined simply by counting individuals. Often, though, individ- uals are too abundant, too widespread, or too mobile to be counted easily, and scientists must estimate the number of individuals in the population. Suppose that a scientist wants to know how many oak trees live in a 10 km2 patch of forest. Instead of searching the entire patch of forest and counting all the oak trees, the scientist could count the trees in a smaller section of the forest, such as a 1 km2 area. The scientist could then use this value to estimate the population of the larger area. SECTION 1 OBJECTIVES ● Describe the main properties that scientists measure when they study populations. ● Compare the three general patterns of population dispersion. ● Identify the measurements used to describe changing populations. ● Compare the three general types of survivorship curves. VOCABULARY population population density dispersion birth rate death rate life expectancy age structure survivorship curve FIGURE 19-1 A population can be widely distributed, as Earth’s human population is, or confined to a small area, as species of fish in a lake are. Copyright © by Holt, Rinehart and Winston. All rights reserved. 382 CHAPTER 19 If the small patch contains 25 oaks, an area 10 times larger would likely contain 10 times as many oak trees. A similar kind of sampling technique might be used to estimate the size of the pop- ulation shown in Figure 19-2. To use this kind of estimate, the sci- entist must assume that the distribution of individuals in the entire population is the same as that in the sampled group. Estimates of population size are based on many such assumptions, so all esti- mates have the potential for error. Population Density Population density measures how crowded a population is. This measurement is always expressed as the number of individuals per unit of area or volume. For example, the population density of humans in the United States is about 30 people per square kilome- ter. Table 19-1 shows the population sizes and densities of humans in several countries in 2003. These estimates are calculated for the total land area. Some areas of a country may be sparsely popu- lated, while other areas are very densely populated. Dispersion A third population property is dispersion (di-SPUHR-zhuhn). Dispersion is the spatial distribution of individuals within the popu- lation. In a clumped distribution, individuals are clustered together. In a uniform distribution, individuals are separated by a fairly con- sistent distance. In a random distribution, each individual’s location is independent of the locations of other individuals in the popula- tion. Figure 19-3 illustrates the three possible patterns of dispersion. Clumped distributions often occur when resources such as food or living space are clumped. Clumped distributions may also occur because of a species’ social behavior, such as when animals gather into herds or flocks. Uniform distributions may result from social behavior in which individuals within the same habitat stay as far away from each other as possible. For example, a bird may locate its nest so as to maximize the distance from the nests of other birds. These migrating wildebeests in East Africa are too numerous and mobile to be counted. Scientists must use sampling methods at several locations to monitor changes in the population size of the animals. FIGURE 19-2 TABLE 19-1 Population Size and Density of Some Countries Population size Population density Country (in millions) (in individuals/km2) China 1,289 135 India 1,069 325 United States 292 30 Russia 146 8 Japan 128 337 Mexico 105 54 Kenya 32 54 Australia 20 3 dispersion from the Latin dis-, meaning “out,” and spargere, meaning “to scatter” Word Roots and Origins Copyright © by Holt, Rinehart and Winston. All rights reserved. POPULATIONS 383 The social interactions of birds called gannets, which are shown in Figure 19-3b, result in a uniform distribution. Each gannet chooses a small nesting area on the coast and defends it from other gannets. In this way, each gannet tries to maximize its distance from all of its neighbors, which causes a uniform distribution of individuals. Few populations are truly randomly dispersed. Rather, they show degrees of clumping or uniformity. The dispersion pattern of a population sometimes depends on the scale at which the popu- lation is observed. The gannets shown in Figure 19-3b are uni- formly distributed on a scale of a few meters. However, if the entire island on which the gannets live is observed, the distribution appears clumped because the birds live only near the shore. POPULATION DYNAMICS All populations are dynamic—they change in size and composition over time. To understand these changes, scientists must know more than the population’s size, density, and dispersion. One important measure is the birth rate, the number of births occur- ring in a period of time. In the United States, for example, there are about 4 million births per year. A second important measure is the death rate, or mortality rate, which is the number of deaths in a

Astonishing Animals Our planet is full of weird and wonderful creatures. Meet three of them – animals with surprising bodies, habits and abilities. The animal that can’t be true When in 1798 zoologists in Britain first saw the skin of an Australian platypus and a drawing of the animal, they were sure it was a hoax. A creature like that could not exist. Why not? First, it has fur, like cats or dogs, but also a flat bill like a duck, and a big thick tail like a beaver. Secondly, it lays eggs and looks after them like a bird, but when the young come out of the eggs, the mother feeds them with her milk. On top of everything, the platypus has a poisonous sting – like a snake! It cannot kill a human, but it’s very painful. Champion Runner You probably know the cheetah is the fastest runner among animals. It can run up to 100 kilometres per hour. But after some 200 metres, it needs to lie down and rest. The pronghorn, which lives in the prairies of North America, can run a few kilometres at ninety kilometres per hour, and fifteen kilometres at sixty-five kilometres per hour. Its whole body – heart, lungs, legs – is a perfect machine for long-distance running. But why? It doesn’t need to run this fast now, but 18,000 years ago there were cheetahs in America. The pronghorn probably evolved to escape them. This beautiful animal is not well-known in Europe, but in America it is a symbol of the prairie life. You can see it in the emblem of the province of Alberta, Canada. Aliens in the ocean An octopus has no fixed shape or colour. In danger, it will change both. It can become like its surroundings and difficult to see. Or it can look like a dangerous animal, such as a sea snake, and scare an attacker away. Octopuses are also intelligent. Their brains are large in proportion to their body size. They can use tools and solve problems: for example, open bottles to get food, or use clever strategies to escape from an aquarium. It seems they are unhappy in a zoo or lab. But they are so different from humans that it is difficult for us to understand their intelligence. In fact, it is a bit like meeting intelligent aliens.

Animals, Animals There are many kinds of animals. The elk is in the deer family. Male elk have large antlers. Elk are excellent swimmers and can run very fast. Giraffes are very tall with long necks. Giraffes have spots all over their bodies and short horns on their heads. Giraffes live in savannas and open woodlands. Elephants are the largest land animals alive today. Elephants have long trunks and ivory tusks. They live in grasslands and forests. Snow leopards live on cold mountains. They have thick fur to stay warm. They hunt wild goats, sheep, and other animals. This camel has a long winter coat. When it is well fed, its humps stand up. The humps fall to one side if the camel has not eaten. Camels live in both hot and cold deserts. The fox is in the dog family. It lives in a burrow. Foxes eat small animals, insects, fruits, and eggs. Unlike dogs, foxes like to hunt alone. The zebra is in the horse family. Zebras have white and black stripes and live in grasslands. Their manes stand straight up on their necks. The great gray kangaroo carries its babies in its pouch. It uses its strong back legs to hop. Kangaroos eat grass and other plants. The hippopotamus spends most of its time in water. It has almost no hair and eats grass and water plants. Its eyes and nostrils stick out so that it can see and breathe when underwater. Polar bears live in cold places. They have thick fur. They eat seals, walruses, small mammals, birds, and fish. There are many kinds of animals.

Describe how landforms and bodies of water affect the living components of the environment; 2. compare different types of rocks collected in terms of color, texture, and grain size; 3. classify common rocks from provided samples using a simple rock classification system; 4. explain how soil is formed by the weathering of rocks and minerals; 5. investigate how fast erosion transports Earth materials in different places;

Think about the geography and location of the city or town you live in. Are there bodies of water like rivers and lakes or a coast nearby? Perhaps you live in a place with vast open fields suitable for farming or raising livestock. The natural environment is important when understanding how cities and towns developed. The earliest North American colonies depended on their natural environment. The type of soil, climate, length of seasons, and proximity to bodies of water all played a role in how each colony prospered. By the 1700’s, the American colonies grew into three distinct regions. The New England, Middle, and Southern regions each had different geographical and cultural characteristics that determined the development of their economy, society, and relationships to each other. The New England Colonies included Connecticut, Rhode Island, Massachusetts, and New Hampshire. The geography of this region featured dense forests and hills. Combined with the hard rocky land, cold climate and long winters, New England was a poor area for large farming operations. However, many colonists known as "yeoman farmers" had small family-owned farms that grew a variety of crops. Many other colonists relied on fishing and whaling off the New England coast. Others settled in small towns and became craftsmen or merchants. The forests provided excellent lumber for building boats and homes for the growing population. Many of the settlers to the New England Colonies were Puritans, hardworking, and very religious. Close families and strong communities were very important to them. The Middle Colonies included Pennsylvania, Delaware, New York, and New Jersey. The geography of this region featured a warmer climate with fertile soil, flat land, easily navigable rivers, and wide valleys making it perfect for farming and growing crops. Wealthy farmers grew cash crops and raised livestock. Mining and trading were also important aspects of the economy here. Over time, cities grew, and urban merchants sold and traded goods with people throughout the other colonies. Compared to other regions, the people of the middle colonies supported religious freedom and tolerance and had a diverse population with settlers arriving from many areas in Europe. The Southern Colonies included the first English colony of Virginia, and grew to include Maryland, North Carolina, South Carolina, and Georgia. The geography included rich, fertile soil with broad coastal plains that made it possible for large plantations to grow tobacco, rice, and indigo. Most of these plantations featured a labor force of enslaved Black people. These enslaved men, women, and children had few, if any, rights and often saw their families torn apart at the whim of the plantation owner. Enslaved children were even put to work as young as age three, weeding fields, carrying drinking water, or helping in the home. Smaller farms owned by subsistence farmers also existed across the Southern Colonies. Often, the people working these would grow crops for their families with little left over to sell or trade. Indentured servants also arrived in the South who would work for 5-7 years in exchange for their passage to North America. The Church of England (also known as the Anglican Church) was the dominant religion in the region. Most settlers to the South did not come for religious freedom like they did in the northern colonies. Therefore, they often maintained their allegiance to the established Church of England.

MEANING OF POLLUTION Pollution is the release of harmful substances into the environment and making it unsafe for human and animals. TYPES OF POLLUTION 1. WATER POLLUTION: This is the release of harmful substances into bodies of water. Examples of water pollutants are urine, bathing, excretion from man and animals, dumping of refuse into the rivers, lakes etc. 2. AIR POLLUTION: This is the release of harmful substances into the atmosphere making it unfit to breathe in. Examples of air pollutants are : smoke of vehicles, smoke from industries, oil burning, smoke from firewood, dead animals etc. 3. NOISE POLLUTION: This is a kind of pollution from the constant loudness of music or rowdiness. It disturbs the mind and prevents people from sleeping, resting or reasoning properly. THE FOLLOWING ARE THE EFFECTS OF POLLUTION 1. It makes the water unfit for drinking 2. It causes dysentery, typhoid fever and cholera. 3. It causes sneezing, blood poisoning, cough and lung diseases. 4. It causes headaches and sleeplessness. 5. It makes the air dirty and bad for breathing into the body. CONTROL OF POLLUTION ARE AS FOLLOWS: 1. Refuse should be dump in a proper place 2. Industries should be located far away from where people live. 3. Modern toilets should be built. 4. Regular cleaning of the surroundings.

Geography: the study of Earth’s physical and cultural features Landforms: the natural features of the land’s surface Climate: the average weather conditions in a certain area over a long period of time Environment: All the living and nonliving things that affect life in an area Region: An area with one or more features that make it different from other surrounding areas Map Key / Map Legend: box that explains the meaning of different symbols used on the map Map Scale: tool that measures the relationship between the distance of locations on the map and the distance of locations in real life Compass Rose: a circle that shows the key directions on a map Hemispheres: halves of the Earth Continent: one of seven large landmasses on Earth Oceans: large bodies of water that cover 71% of the Earth’s surface Latitude: imaginary horizontal lines that measure distance north and south of the Equator Equator: central line of latitude that is measured at 0° Longitude: imaginary vertical lines that measure distance east and west of the Prime Meridian Prime Meridian: the central line of longitude, which is measured at 0° and runs through Greenwich, United Kingdom Map: illustration of a specific area on Earth that is often portrayed on a flat surface Physical Map: a type of map that shows the natural landforms and terrain of a location Political Map: a type of map that identifies cities, states, and countries Globe: a spherical model that is the most accurate representation of Earth

Changes in the reproductive system There are also important changes that take place inside the bodies of boys and girls during puberty. These changes happen in the reproductive system and make it possible for a boy to become a father and for a girl to become a mother when they are older. The main job of the reproductive system is to make special cells called sex cells that are needed for reproduction. In males, the sex cells are called sperm. In females, the sex cells are called eggs or ova (one egg is called an ovum). During reproduction, a sperm and an egg join together to form a new living being that will grow into baby. This process is called fertilisation. A boy’s body starts to make sperm during puberty. In girls, ova start to develop. Menstruation in girls starts about a year after puberty begins. This is when an unfertilised egg is released from the body together with the lining of the uterus, which causes some bleeding. Menstruation happens about once a month but is often not regular until a girl is older.

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