WHICH SENTENCE IS CORRECT?

SHE IS FROM USA. SHE IS AMERICAN

SHE IS FROM FRANCE. SHE IS POLISH

SHE IS FROM USA. SHE IS AMERICAN.

HE IS FROM USA. SHE IS AMERICAN

WHICH NEGATIVE FORM IS CORRECT?

LUCY ISN`T FROM CUBA. SHE IS FROM ITALY.

LUCY ISN`T FROM CUBA. HE IS FROM POLAND.

WHICH QUESTION IS CORRECT?

IS NEW YORK FAR FROM WASHINGTON?

ARE QUITO THE CAPITAL OF ECUADOR?

LEVEL 1 GROUP 123 QUIZ UNIT 1

QUIZ 1 LEVEL 6 GROUP 3603

QUIZ 1 (UNIT 1) GROUP 103-3303 LEVEL 3

GROUP 3602 QUIZ 1 LEVEL 6 UNIT 6

LEVEL 3 QUIZ 1 EXTENSIVE COURSE E-J 2022 GROUP 69

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

Studying population involves examining various aspects of the demographic composition, dynamics, and characteristics of a group of individuals within a specific geographic area. Here are key areas to explore when studying population: Demography: Population Size: Analyze the total number of individuals in a given area or community. Population Distribution: Examine how the population is spread across different regions or areas. Population Density: Explore the concentration of people in a particular area relative to the size of that area. Population Growth and Decline: Birth Rate: Study the number of live births per 1,000 people in a given year. Death Rate: Examine the number of deaths per 1,000 people in a given year. Migration: Explore patterns of people moving into and out of a specific area. Age Structure: Age Distribution: Analyze the distribution of individuals across different age groups in a population. Dependency Ratio: Examine the ratio of dependent individuals (young and elderly) to the working-age population. Gender Composition: Sex Ratio: Study the ratio of males to females in a population. Population Pyramids: Use population pyramids to visualize the age and gender structure of a population. Fertility and Family Planning: Total Fertility Rate (TFR): Explore the average number of children a woman is expected to have during her reproductive years. Contraceptive Use: Analyze the prevalence of contraceptive methods in a population. Mortality and Health: Life Expectancy: Examine the average number of years a person can expect to live. Infant and Child Mortality: Study the number of deaths among infants and children under the age of five. Urbanization: Urban vs. Rural Population: Analyze the distribution of people in urban and rural areas. Rate of Urbanization: Explore the speed at which people are moving from rural to urban areas. Education: Literacy Rates: Examine the percentage of the population that can read and write. Educational Attainment: Study the level of education achieved by individuals within the population. Socioeconomic Factors: Income Distribution: Explore the distribution of income among the population. Employment Rates: Analyze the percentage of the working-age population that is employed. Cultural and Ethnic Composition: Ethnic Diversity: Examine the presence of various ethnic groups within the population. Healthcare and Quality of Life: Access to Healthcare: Study the availability and accessibility of healthcare services. Quality of Life Indicators: Explore factors such as housing, sanitation, and overall living conditions. Population Policies and Government Interventions: Study the impact of government policies on population dynamics, including family planning programs and immigration policies. Environmental Impact: Explore the relationship between population growth and its impact on the environment, including resource consumption and pollution. Global Population Trends: Examine global population trends and their implications, including aging populations and population growth in developing countries. Studying population involves a multidisciplinary approach that incorporates elements from demography, sociology, geography, economics, and public health. Researchers and policymakers use this information to make informed decisions about resource allocation, development planning, and social policies.

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