Chapter 27 Population Growth Lectures by Gregory Ahearn

27. 1 How Are Populations Distributed In Space And Time? § Organisms arrange themselves in space in many different ways. § Ecologists recognize three major types of spatial distribution: • Clumped • Uniform • Random Copyright © 2009 Pearson Education Inc.

27. 1 How Are Populations Distributed In Space And Time? § Individuals in many populations clump together in groups, and include social groups such as elephant herds, wolf packs, lion prides, flocks of birds, and schools of fish. clumped (a) Clumped distribution Copyright © 2009 Pearson Education Inc. Fig. 27 -1 a

27. 1 How Are Populations Distributed In Space And Time? § What are the advantages of clumping? • Many eyes can search for localized food. • Part of a large group may reduce the odds that one individual will be killed by a predator. • A group may increase the individual’s chance of finding a mate. Copyright © 2009 Pearson Education Inc.

27. 1 How Are Populations Distributed In Space And Time? § Some individuals disperse themselves evenly. • Populations with uniform distributions maintain relatively even spacing between individuals. • This type of distribution occurs among animals that defend territories. • Male Galapagos iguanas establish regularly spaced breeding territories. Copyright © 2009 Pearson Education Inc.

27. 1 How Are Populations Distributed In Space And Time? § Creosote bushes release chemicals into the soil around them that inhibit germination of seeds from other plants. uniform (b) Uniform distribution Copyright © 2009 Pearson Education Inc. Fig. 27 -1 b

27. 1 How Are Populations Distributed In Space And Time? § In a few populations, individuals are distributed at random. • In a population with random distribution, the distance between individuals varies unpredictably. • Individuals in such populations do not form social groups. • The resources they need are not in short supply and are available throughout the year. Copyright © 2009 Pearson Education Inc.

27. 1 How Are Populations Distributed In Space And Time? § Trees and other plants in rain forests may be randomly distributed. random (c) Random distribution Copyright © 2009 Pearson Education Inc. Fig. 27 -1 c

27. 2 How Do Populations Grow? § Births, deaths, and migration determine population growth. • A population’s size remains stable if, on average, as many individuals join as leave. • Individuals enter a population by birth or immigration, and leave it by death or emigration. • A population grows when the number of births plus immigrants exceeds the number of deaths plus emigrants. • Populations shrink when the opposite occurs. Copyright © 2009 Pearson Education Inc.

27. 2 How Do Populations Grow? § A simple equation for the change in population size within a given period is as follows: • (births – deaths) + (immigrants – emigrants) = change in population size Copyright © 2009 Pearson Education Inc.

27. 2 How Do Populations Grow? § Population growth can be expressed as a rate. • The per capita growth rate (r) of a population is measure of how fast a population grows, expressed as a change in population size per individual per unit of time (that is, as a percentage). • This value is determined by subtracting the per capita death rate (d) from the per capita birth rate (b). • b (births) – d (deaths) = r (growth rate) Copyright © 2009 Pearson Education Inc.

27. 2 How Do Populations Grow? § Population growth can be expressed as a rate (continued). • For example, to calculate the annual growth rate of a human population of 10, 000 in which there are 1, 500 births and 500 deaths each year, we first calculate the annual per capita birth rate. • b = 1, 500 births/10, 000 people • = 0. 15 births person per year • Next, the annual per capita death rate. • d = 500 deaths/10, 000 people • = 0. 05 deaths person per year Copyright © 2009 Pearson Education Inc.

27. 2 How Do Populations Grow? § Population growth can be expressed as a rate (continued). • Finally, we calculate the per capita growth rate by subtracting the death rate from the birth rate. • r = 0. 15 births person per year – 0. 05 deaths person per year • = 0. 10 (that is, 10% increase per year) • If the death rate exceeds the birth rate, the growth rate will be negative and the population will shrink. Copyright © 2009 Pearson Education Inc.

27. 2 How Do Populations Grow? § A constant growth rate increases population size rapidly. • To calculate the number of individuals added to a population in a year, multiply the annual per capita growth rate (r) by the original population size (N). • Population growth = r. N • In our example, population growth in the first year (r. N) is 0. 10 x 10, 000 = 1, 000 people; at the end of year 1, the population has 11, 000 people. Copyright © 2009 Pearson Education Inc.

27. 2 How Do Populations Grow? § A constant growth rate increases population size rapidly (continued). • If the per capita growth rate r remains constant, the number of people added to the population increases each year. • This pattern of continuously accelerating increase in population size is exponential growth. Copyright © 2009 Pearson Education Inc.

27. 2 How Do Populations Grow? § A population’s growth rate depends on patterns of reproduction. • A population grows during periods when births exceed deaths. • Growth will persist if, on average, each individual produces more than one surviving offspring during its lifetime. • Each individual, of course, has the potential to replace itself many times during its lifetime. Copyright © 2009 Pearson Education Inc.

27. 2 How Do Populations Grow? § A population’s growth rate depends on patterns of reproduction. • Every species has a built-in capacity for population growth, but the speed of this potential growth varies among species, dependent upon the following factors. • The age of first reproduction • The frequency of reproduction • The average number of offspring produced each time • The length of an organism’s reproductive life span • The organism death rate Copyright © 2009 Pearson Education Inc.

27. 2 How Do Populations Grow? § Some species produce large numbers of offspring quickly. • The harmless bacterium Staphylococcus is found on the human body. • Each bacterial cell can divide every 20 minutes, doubling the population three times each hour. • The larger the population growth, the more cells there are to divide. Copyright © 2009 Pearson Education Inc.

27. 2 How Do Populations Grow? § Some species produce large numbers of offspring quickly (continued). • The growth rate is so great that, unchecked, the offspring of one bacterium could produce a layer around the Earth 7 feet deep in 48 hours. • Because this does not happen, many bacteria must die. Copyright © 2009 Pearson Education Inc.

27. 2 How Do Populations Grow? § Other species produce fewer but longerlived offspring. • The golden eagle is a long-lived, rather slowly reproducing species. • Figure 27 -2 compares the potential population growth of eagles with that of bacteria, assuming no deaths. • All three curves on this figure are J-shaped, indicating exponential growth. Copyright © 2009 Pearson Education Inc.

27. 2 How Do Populations Grow? § J-shaped exponential growth curves in bacteria number of individuals 1, 200 1, 100 1, 000 900 800 700 600 500 400 300 200 100 0 (a) Bacteria Copyright © 2009 Pearson Education Inc. Exponential growth curves are J-shaped 0 60 time number of (minutes) bacteria 0 1 20 2 40 4 60 8 80 16 100 32 120 64 140 128 160 256 180 512 200 1, 024 220 2, 048 120 180 240 time (minutes) Fig. 27 -2 a

27. 2 How Do Populations Grow? § Delayed onset of reproduction slows population growth. • Figure 27 -2 b shows what happens if there is a difference in the age at which individuals in a population begin reproduction. • Growth in both populations is exponential, but the population whose members begin reproduction later takes longer to reach a particular size. • For humans, delayed childbearing slows population growth. Copyright © 2009 Pearson Education Inc.

27. 2 How Do Populations Grow? number of individuals § J-shaped exponential growth curve in eagles 2, 000 1, 800 1, 600 1, 400 1, 200 1, 000 800 600 400 200 0 (i) Reproduction begins at 4 years (ii) number time of of (years) eagles (ii) 0 2 2 2 4 4 2 6 8 4 8 10 28 12 12 52 18 14 100 32 16 190 54 18 362 86 20 630 142 22 1, 314 238 24 2, 504 392 26 4, 770 644 28 9, 088 1, 066 30 17, 314 1, 764 Reproduction begins at 6 years (b) Eagles Copyright © 2009 Pearson Education Inc. 0 5 10 15 20 time (years) 25 30 Fig. 27 -2 b

27. 2 How Do Populations Grow? § Death rate also influences growth rate. • Figure 27 -3 compares three bacterial populations with different death rates. • The J shapes of the curves are the same. • However, the time required to reach any given population size is longer at higher death rates. Copyright © 2009 Pearson Education Inc.

27. 2 How Do Populations Grow? § The effects of death rates on population growth 2, 500 bacteria No deaths 10% die between doublings number of individuals 2, 000 25% die between doublings 1, 500 1, 000 500 0 0 Copyright © 2009 Pearson Education Inc. 1 2 3 time (hours) 4 5 6 Fig. 27 -3

27. 3 How Is Population Growth Regulated? § A population’s growth is influenced by its biotic potential—the maximum rate at which a population can increase, assuming ideal conditions that allow the highest possible birth rate and the lowest possible death rate. • The ultimate size of a population is also affected by limits that oppose this potential for growth. • These limits, which are set by the living and nonliving environments, are collectively known as environmental resistance. Copyright © 2009 Pearson Education Inc.

27. 3 How Is Population Growth Regulated? § Environmental resistance is imposed by several things. • • • Availability of food and space Interactions with competitors Predators Disease-causing organisms Natural catastrophes (e. g. , storms, fires, freezing weather, floods, and droughts) Copyright © 2009 Pearson Education Inc.

27. 3 How Is Population Growth Regulated? § Environmental resistance limits population size by the following factors: • Increasing death rates • Decreasing birth rates • Both factors together § For example, a drought might restrict growth of an animal population both by increasing the number of deaths from starvation, and by causing malnutrition that reduces the number of births. Copyright © 2009 Pearson Education Inc.

27. 3 How Is Population Growth Regulated? § Rapid growth cannot continue indefinitely. • Populations grow rapidly only under certain circumstances and only for a limited time before environmental resistance brings their expansion to a halt. Copyright © 2009 Pearson Education Inc.

27. 3 How Is Population Growth Regulated? § Some populations fluctuate cyclically. • Short-term explosive growth occurs in populations that undergo regular cycles of rapid population growth followed by a sudden, massive die-off—a boom-and-bust cycle. • Many such animals have seasonal population cycles that are linked to predictable changes in rainfall, temperature, or nutrient availability. Copyright © 2009 Pearson Education Inc.

27. 3 How Is Population Growth Regulated? § A boom-and-bust population cycle population density Nutrients are depleted Favorable growth conditions occur 0 Jan Copyright © 2009 Pearson Education Inc. Mar May “boom” Jul month “bust” Sep Nov Fig. 27 -4

27. 3 How Is Population Growth Regulated? § Some populations fluctuate cyclically (continued). • A lemming population may grow until the animals overgraze their fragile arctic tundra ecosystem. • Then, lack of food, increasing populations of predators, and social stress caused by overpopulation all contribute to a suddenly high death rate. • Eventually, the lemming population shrinks so much that number of predators declines. Copyright © 2009 Pearson Education Inc.

27. 3 How Is Population Growth Regulated? § Lemming population cycles Copyright © 2009

27. 3 How Is Population Growth Regulated? § Ecosystem changes may allow temporary rapid growth. • A population may grow rapidly if populationcontrolling factors, such as predators, are eliminated or if the food supply is increased. • Growth can also be explosive when individuals invade a new habitat that has favorable conditions and few competitors. • For example, a species’ population may grow explosively when people introduce the species into an ecosystem. Copyright © 2009 Pearson Education Inc.

27. 3 How Is Population Growth Regulated? § Environmental resistance limits population growth. • Populations that grow rapidly must eventually stabilize or crash. • They tend to stabilize at or below their ecosystem’s carrying capacity, the maximum population of a particular species that an ecosystem can support indefinitely. Copyright © 2009 Pearson Education Inc.

27. 3 How Is Population Growth Regulated? § Environmental resistance limits population growth (continued). • As a growing population approaches the carrying capacity of the environment, its growth rate gradually declines and finally stops when the population reaches a state of equilibrium. • In this equilibrium, the birth rate is balanced by the death rate, and population size is stable. • This type of population growth is represented graphically by an S-shaped growth curve. Copyright © 2009 Pearson Education Inc.

27. 3 How Is Population Growth Regulated? § An S-shaped logistic growth curve stabilizes at carrying capacity. number of individuals carrying capacity Growth rate slows Growth stops and the population stabilizes close to the carrying capacity Population grows rapidly 0 time (a) An S-shaped growth curve stabilizes at carrying capacity Copyright © 2009 Pearson Education Inc. Fig. 27 -6 a

27. 3 How Is Population Growth Regulated? § Environmental resistance limits population growth (continued). • A population may grow to a size larger than its ecosystem’s carrying capacity. • This overshooting of carrying capacity is necessarily temporary. • A small overshoot of carrying capacity is likely to be followed by a decrease in population size until the resources recover and the original carrying capacity is restored. Copyright © 2009 Pearson Education Inc.

27. 3 How Is Population Growth Regulated? § Consequences of exceeding carrying capacity Population overshoots the carrying capacity; the environment is damaged carrying capacity (original) carrying capacity (reduced) 0 Low damage; resources recover, and the population fluctuates Extreme damage; the population dies out High damage; the carrying capacity is permanently lowered time (b) Consequences of exceeding carrying capacity Copyright © 2009 Pearson Education Inc. Fig. 27 -6 b

27. 3 How Is Population Growth Regulated? § Environmental resistance limits population growth (continued). • The factors that usually maintain populations at or below the carrying capacity of their environment can be classified into two broad categories. • Density-independent factors limit population size regardless of the population density (number of individuals per given area). • Density-dependent factors increase in effectiveness as the population density increases. Copyright © 2009 Pearson Education Inc.

27. 3 How Is Population Growth Regulated? § Density-independent factors limit population size. • Natural events—including hurricanes, droughts, floods, and fire—can reduce the size of populations. • The effectiveness of such events in limiting the size of a population does not generally depend on the population’s density. Copyright © 2009 Pearson Education Inc.

27. 3 How Is Population Growth Regulated? § Density-independent factors limit population size (continued). • The most important natural densityindependent factor is weather. • Human activities, such as the use of pesticides and pollutants, can also limit population growth in ways independent of population density. Copyright © 2009 Pearson Education Inc.

27. 3 How Is Population Growth Regulated? § Density-dependent factors have a greater effect as population density increases. • Density-dependent factors become increasingly effective as population density increases, thus exerting negative feedback that limits the size of populations. • Conversely, density-dependent factors become less effective as population density decreases, allowing population size to stabilize or grow. Copyright © 2009 Pearson Education Inc.

27. 3 How Is Population Growth Regulated? § Density-dependent factors have greater effect as population density increases (continued). • The most important density-dependent factors are predation and competition. • In predation, one organism feeds on another, harming it in the process. • Often, one organism (the predator) kills another (its prey) in order to eat it, but the prey is not always killed. Copyright © 2009 Pearson Education Inc.

27. 3 How Is Population Growth Regulated? § Predators help control prey populations. Copyright

27. 3 How Is Population Growth Regulated? § Density-dependent factors have greater effect as population density increases (continued). • Prey also often survive the special form of predation known as parasitism. • In parasitism, the predator (the parasite) lives on or inside another organism (its host) and feeds on the host’s body without killing it—at least not immediately. Copyright © 2009 Pearson Education Inc.

27. 3 How Is Population Growth Regulated? § Predators exert density-dependent controls on populations. • Predation plays an increasingly important role in population control as prey populations increase. • The increased frequency of encounters with predators increases the prey populations’ death rate, because predators tend to eat larger numbers of whichever prey species is most abundant and easiest to find. • Increasing numbers of prey organisms also increase the numbers of predators, and this tends to control prey numbers. Copyright © 2009 Pearson Education Inc.

27. 3 How Is Population Growth Regulated? § Parasites spread faster when the host population density is high. • Like other forms of predation, parasitism is density-dependent. • Most parasites have limited ability to move, so they spread more readily from host to host at high host-population densities. • Parasites can affect the death rate of a host population because the damage inflicted by the parasite on its host’s body may kill the host. Copyright © 2009 Pearson Education Inc.

27. 3 How Is Population Growth Regulated? § Populations can soar or crash when predator-prey relationships are disrupted. • The population balance in ecosystems can be disrupted when predators are introduced to regions in which they were not previously present and where prey species have had no opportunity to evolve defenses against them. • Rats, snakes, and mongooses were introduced in Hawaii and many other Pacific islands, and have drastically reduced or exterminated many native bird populations. Copyright © 2009 Pearson Education Inc.

27. 3 How Is Population Growth Regulated? § Populations can soar or crash when predatorprey relationships are disrupted (continued). • Prey populations can grow out of control when introduced to areas where they have no predators. • The prickly pear cactus was introduced into Australia from Latin America, and, lacking predators, it spread uncontrollably. • In the 1920 s, a cactus moth was imported from Argentina to feed on the cacti. • Within a few years, the cacti were almost eliminated, and today, the moth keeps the population density of its prey very low. Copyright © 2009 Pearson Education Inc.

27. 3 How Is Population Growth Regulated? § Competition for resources helps curb population size. • The resources that determine the carrying capacity are limited. • Therefore, organisms must compete for access to resources, and the competition among individuals limits population size in a density-dependent manner. • There are two forms of competition: interspecific competition among individuals of different species, and intraspecific competition among individuals of the same species. Copyright © 2009 Pearson Education Inc.

27. 3 How Is Population Growth Regulated? § Competition may be indirect or direct. • Some organisms, including most plants and many insects, engage in scramble competition, a kind of free-for-all in which individuals independently seek resources without interacting directly. • For example, after gypsy moth caterpillars hatch from large masses of eggs laid on tree trucks, armies of caterpillars crawl up to the treetops to feed on leaves; many caterpillars die off before they can metamorphose into moths. Copyright © 2009 Pearson Education Inc.

27. 3 How Is Population Growth Regulated? § Scramble competition Copyright © 2009 Pearson

27. 3 How Is Population Growth Regulated? § Competition may be indirect or direct (continued). • Many animals have evolved contest competition, in which individuals interact to contest access to important resources. • Only the best competitors are able to defend adequate territories; poor competitors fail to secure territories and are unlikely to reproduce or survive. Copyright © 2009 Pearson Education Inc.

27. 3 How Is Population Growth Regulated? § Different age groups may experience different death rates. • The effects of population-limiting factors do not necessarily fall equally on all members of a population. • For example, the death rate in a population differs among individuals of different ages; survivorship varies with age. • A survivorship curve shows the likelihood that an individual will survive to a given age. Copyright © 2009 Pearson Education Inc.

27. 3 How Is Population Growth Regulated? § Survivorship in populations follows three basic patterns. • Convex late-loss survivorship curves reflect populations in which the death rate is low for juveniles and in which most individuals survive to old age. • These curves are characteristic of humans and other large, long-lived animals, such as elephants and mountain sheep. • These species produce relatively few offspring that receive a great deal of parental care. Copyright © 2009 Pearson Education Inc.

27. 3 How Is Population Growth Regulated? § Survivorship in populations follows three basic patterns (continued). • Early-loss survivorship produces a concave curve and is characteristic of organisms that produce large numbers of offspring that receive little or no parental care. • The death rate of juveniles is very high, but individuals than manage to reach adulthood have a good chance of surviving to old age. • Early-loss survivorship curves are common among invertebrates, plants, and fish. Copyright © 2009 Pearson Education Inc.

27. 3 How Is Population Growth Regulated? § Survivorship in populations follows three basic patterns (continued). • Populations with straight-line, constant-loss survivorship curves have a fairly constant death rate that does not vary much with age. • This pattern has been found in some bird and lizard species, and in populations of some asexually-reproducing invertebrate species. Copyright © 2009 Pearson Education Inc.

27. 3 How Is Population Growth Regulated? § Survivorship curves number of survivors 1, 000 100 late loss (human) constant loss (American robin) 10 0 Copyright © 2009 Pearson Education Inc. early loss (dandelion) age (in percentage of maximum life span) Fig. 27 -9

27. 4 How Is The Human Population Changing? § The graph of human population growth in Figure 27 -10 and the exponential growth curves in Figure 27 -2 a are similar—each are J shaped, characteristic of explosive growth. 7 2008 1999 5 1987 4 3 bubonic plague billions of people 6 1975 1960 2 1930 1 1830 0 12, 000 11, 000 10, 000 9000 8000 B. C. Technical and cultural advances Copyright © 2009 Pearson Education Inc. 7000 B. C. 6000 B. C. 5000 4000 3000 2000 B. C. Agricultural advances 1000 B. C. /A. D. 1000 A. D. 2000 A. D. Industrial and medical advances Fig. 27 -10

27. 4 How Is The Human Population Changing? PLAY Animation—Human Population Growth and Regulation

27. 4 How Is The Human Population Changing? § Survivorship in populations follows three basic patterns (continued). • According to the U. S. Census Bureau, world population currently grows at about 1. 2%, or almost 78 million people yearly. • Why hasn’t environmental resistance put an end to our tremendous population growth? Copyright © 2009 Pearson Education Inc.

27. 4 How Is The Human Population Changing? § Technological advances have increased Earth’s carrying capacity for humans. • Humans have responded to environmental resistance by devising ways to overcome it. • Human population growth has increased by a series of cultural “revolutions” in which the products of human culture conquered various aspects of environmental resistance and increased Earth’s carrying capacity for people. Copyright © 2009 Pearson Education Inc.

27. 4 How Is The Human Population Changing? § Early tools allowed human populations to spread and prosper. • Prehistoric people produced a tool-use revolution when they discovered fire, invented tools and weapons, built shelters, and designed protective clothing. • Tools and weapons allowed more effective hunting, and thereby increased the food supply. • These developments set the stage for future population growth. Copyright © 2009 Pearson Education Inc.

27. 4 How Is The Human Population Changing? § Agriculture fostered population growth. • By 8, 000 B. C. , cultivation of domesticated crops and animals had replaced hunting and gathering as humans’ primary means of acquiring food. • This agricultural revolution provided people with a larger, more dependable food supply, and further increased Earth’s carrying capacity for humans. • Increased food resulted in a long life span and more childbearing years, and the human population began to climb steadily. Copyright © 2009 Pearson Education Inc.

27. 4 How Is The Human Population Changing? § Explosive growth began with the Industrial Revolution. • Human population growth continued slowly for thousands of years until the industrial-medical revolution began in England in the mideighteenth century, spreading through Europe and North America in the nineteenth century. • This revolution marked the beginning of a period of extremely rapid population growth, as medical advances dramatically decreased the death rate. Copyright © 2009 Pearson Education Inc.

27. 4 How Is The Human Population Changing? § Population growth continues today but is unevenly distributed. • In Western Europe, the population explosion fostered by the declining death rates of the industrial-medical revolution was eventually followed by a decline in birth rates. • Birth rate decline in affluent societies has been attributed to better education, increased availability of contraceptives, a shift to a primary urban lifestyle, and more career options for women. • In most developed countries, population sizes have stabilized or even declined. Copyright © 2009 Pearson Education Inc.

27. 4 How Is The Human Population Changing? § Population growth continues today but is unevenly distributed (continued). • In developing countries—such as those in Central and South America, Asia, and Africa— the death rate has gone down and the life span has increased. • In agricultural societies, children are an important source of labor and provide support for elderly parents. Copyright © 2009 Pearson Education Inc.

population (billions) 27. 4 How Is The Human Population Changing? § By 2050, 8 billion people will be living in the developing nations. 10 9 8 7 6 5 4 3 2 1 0 2006: 6. 5 billion developing countries developed countries 1950 Copyright © 2009 Pearson Education Inc. 1970 2010 1990 year 2030 2050 Fig. 27 -11

27. 4 How Is The Human Population Changing? § The age structure of a population predicts its future growth. • The age structure of a population is determined by the numbers of males and females in each age group, and can be shown graphically in an age-structure diagram. • The shape of the diagram shows whether the population is expanding, stable, or shrinking. Copyright © 2009 Pearson Education Inc.

27. 4 How Is The Human Population Changing? § The age structure of a population predicts its future growth (continued). • The shape of an age-structure diagram is determined by the relative numbers of reproductive age adults and their children. • If the adults of reproductive age are producing just enough children to replace themselves, the population is said to have replacement level fertility (RLF). Copyright © 2009 Pearson Education Inc.

27. 4 How Is The Human Population Changing? § The age-structure diagram of such a population has relatively straight sides. 80+ Sweden 2007 75– 79 male 70– 74 65– 69 60– 64 55– 59 50– 54 45– 49 40– 44 35– 39 30– 34 25– 29 20– 24 15– 19 10– 14 5– 9 0– 4 12 10 8 6 4 female 2 0 2 percent (a) Population age structure for Sweden Copyright © 2009 Pearson Education Inc. 4 6 8 10 12 Fig. 27 -12 a

27. 4 How Is The Human Population Changing? § If children in the various age classes exceed the number of reproductive-age adults, the population is exceeding RLF and is expanding. Copyright © 2009 Pearson Education Inc.

27. 4 How Is The Human Population Changing? § The age-structure diagrams of such expanding populations have a pyramidal shape. 80+ Mexico 2007 75– 79 70– 74 65– 69 60– 64 55– 59 50– 54 45– 49 40– 44 35– 39 30– 34 25– 29 20– 24 15– 19 10– 14 5– 9 0– 4 12 male 10 8 female 6 4 2 0 2 percent (b) Population age structure for Mexico Copyright © 2009 Pearson Education Inc. 4 6 8 10 12 Fig. 27 -12 b

27. 4 How Is The Human Population Changing? § In shrinking populations, there are fewer children than reproducing adults, and the agestructure diagrams narrows at the base. 80+ Italy 2007 75– 79 70– 74 65– 69 male 60– 64 55– 59 50– 54 45– 49 40– 44 35– 39 30– 34 25– 29 20– 24 15– 19 10– 14 5– 9 0– 4 12 10 8 6 Copyright © 2009 Pearson Education Inc. female 4 2 0 2 4 percent (c) Population age structure for Italy 6 8 10 12 Fig. 27 -12 c

27. 4 How Is The Human Population Changing? § Almost all future population growth will be in developing countries. • Figure 27 -13 shows the average structures of the populations of developed and developing countries. • The outermost boundaries represent the projected population structure for the year 2050, and the innermost green areas give actual values for 2006. Copyright © 2009 Pearson Education Inc.

27. 4 How Is The Human Population Changing? § In 2006, developing countries had an average annual natural increase of 1. 45% and a doubling time of 50 years. age 2006 75 75 and older 60 60 - 74 45 45 - 59 30 30 - 44 15 15 - 29 0 male 2050 female 0 - 14 1, 000 900 800 700 600 500 400 300 200 100 (b) Developing countries Copyright © 2009 Pearson Education Inc. 0 100 200 300 400 500 600 700 800 900 1, 000 millions of people Fig. 27 -13 b

27. 4 How Is The Human Population Changing? § In developed countries, the numbers were 0. 07% and 985 years. age 2006 75 75 and older 60 60 - 74 45 45 - 59 30 30 - 44 15 15 - 29 0 male female postreproductive (45– 79 yr) reproductive (15– 44 yr) prereproductive (0– 14 yr) 0 - 14 1, 000 900 800 700 600 500 400 300 200 100 (a) Developed countries Copyright © 2009 Pearson Education Inc. 2050 0 100 200 300 400 500 600 700 800 900 1, 000 millions of people Fig. 27 -13 a

27. 4 How Is The Human Population Changing? § Almost all future population growth will be in developing countries. • More than 97% of the growth of the human population occurs in developing countries. • The growth would come as the children of the large families of the recent past entered their reproductive years and began having children, even if each couple only had one child. Copyright © 2009 Pearson Education Inc.

27. 4 How Is The Human Population Changing? § Population growth by world regions World average 1. 3% Developing countries 1. 6% world regions Africa 2. 4% Latin America/Caribbean 1. 7% Asia (excluding China and Japan) 1. 6% China 0. 6% Developed countries 0. 1% North America 0. 5% Europe – 0. 2% – 0. 5 Copyright © 2009 Pearson Education Inc. 0 0. 5 1. 0 annual natural increase 2. 0 2. 5 Fig. 27 -14

27. 4 How Is The Human Population Changing? § Fertility in Europe is below replacement level. • In Europe, the fertility rate is well below RLF, and several European countries have declines in population. • A low fertility rate also occurs in Japan, and the government there provides a variety of subsidies and incentives to encourage people to have larger families. • The situations in Europe and Japan reveal one of the key barriers to controlling the world’s population: Current economic structures are based on growing populations. Copyright © 2009 Pearson Education Inc.

27. 4 How Is The Human Population Changing? § The U. S. population is growing rapidly. • The United States is the fastest growing industrialized country in the world. • The U. S. has a current population of 300 million, a natural increase of 0. 6% annually, and the population grows at more than six times the average rate of developed countries. • Even with RLF, immigration will guarantee continued U. S. population growth. Copyright © 2009 Pearson Education Inc.

27. 4 How Is The Human Population Changing? § U. S. population growth Copyright

27. 4 How Is The Human Population Changing? § The U. S. population is growing rapidly (continued). • The average person in the U. S. uses five times as much energy as the average non-U. S. person; therefore, with less than 5% of the world’s population, the United States accounts for 25% of world energy use. • The ecological impact of the 2. 7 million people added annually to the U. S. population is far greater than the total ecological impact of the 18 million people added annually to India’s population. Copyright © 2009 Pearson Education Inc.