5-2 What Limits the Growth of Populations? Concept 5-2 No population can continue to grow indefinitely because of limitations on resources and because of competition among species for those resources.

Most Populations Live Together in Clumps or Patches (1) Population: group of interbreeding individuals of the same species Population distribution 1.Clumping 2.Uniform dispersion 3.Random dispersion

Most Populations Live Together in Clumps or Patches (2) Why clumping? 1.Species tend to cluster where resources are available 2.Groups have a better chance of finding clumped resources 3.Protects some animals from predators 4.Packs allow some to get prey

Population of Snow Geese Fig. 5-11, p. 112

Generalized Dispersion Patterns Fig. 5-12, p. 112

Populations Can Grow, Shrink, or Remain Stable (1) Population size governed by Births Deaths Immigration Emigration Population change = (births + immigration) – (deaths + emigration)

Populations Can Grow, Shrink, or Remain Stable (2) Age structure Pre-reproductive age Reproductive age Post-reproductive age

Some Factors Can Limit Population Size Range of tolerance Variations in physical and chemical environment Limiting factor principle Too much or too little of any physical or chemical factor can limit or prevent growth of a population, even if all other factors are at or near the optimal range of tolerance Precipitation Nutrients Sunlight, etc

Trout Tolerance of Temperature Fig. 5-13, p. 113

No Population Can Grow Indefinitely: J-Curves and S-Curves (1) Size of populations controlled by limiting factors: Light Water Space Nutrients Exposure to too many competitors, predators or infectious diseases

No Population Can Grow Indefinitely: J-Curves and S-Curves (2) Environmental resistance All factors that act to limit the growth of a population Carrying capacity (K) Maximum population a given habitat can sustain

No Population Can Grow Indefinitely: J-Curves and S-Curves (3) Exponential growth Starts slowly, then accelerates to carrying capacity when meets environmental resistance Logistic growth Decreased population growth rate as population size reaches carrying capacity

Logistic Growth of Sheep in Tasmania Fig. 5-15, p. 115

2.0 Population overshoots carrying capacity Carrying capacity 1.5 Population recovers and stabilizes Number of sheep (millions).5 Exponential growth Population runs out of resources and crashes Year

Fig. 5-15, p Population overshoots carrying capacity Carrying capacity 1.5 Population recovers and stabilizes Number of sheep (millions).5 Exponential growth Population runs out of resources and crashes Year

Science Focus: Why Do California’s Sea Otters Face an Uncertain Future? Low biotic potential Prey for orcas Cat parasites Thorny-headed worms Toxic algae blooms PCBs and other toxins Oil spills

Population Size of Southern Sea Otters Off the Coast of So. California (U.S.) Fig. 5-B, p. 114

Case Study: Exploding White-Tailed Deer Population in the U.S. 1900: deer habitat destruction and uncontrolled hunting 1920s–1930s: laws to protect the deer Current population explosion for deer Spread Lyme disease Deer-vehicle accidents Eating garden plants and shrubs Ways to control the deer population

Mature Male White-Tailed Deer Fig. 5-16, p. 115

When a Population Exceeds Its Habitat’s Carrying Capacity, Its Population Can Crash A population exceeds the area’s carrying capacity Reproductive time lag may lead to overshoot Population crash Damage may reduce area’s carrying capacity

Exponential Growth, Overshoot, and Population Crash of a Reindeer Fig. 5-17, p. 116

2,000 Population overshoots carrying capacity 1,500 Population crashes 1, Carrying capacity Number of reindeer Year

Species Have Different Reproductive Patterns (1) Some species Many, usually small, offspring Little or no parental care Massive deaths of offspring Insects, bacteria, algae

Species Have Different Reproductive Patterns (2) Other species Reproduce later in life Small number of offspring with long life spans Young offspring grow inside mother Long time to maturity Protected by parents, and potentially groups Humans Elephants

Under Some Circumstances Population Density Affects Population Size Density-dependent population controls Predation Parasitism Infectious disease Competition for resources

Several Different Types of Population Change Occur in Nature Stable Irruptive Population surge, followed by crash Cyclic fluctuations, boom-and-bust cycles Top-down population regulation Bottom-up population regulation Irregular

Population Cycles for the Snowshoe Hare and Canada Lynx Fig. 5-18, p. 118

Hare Lynx Population size (thousands) Year

Humans Are Not Exempt from Nature’s Population Controls Ireland Potato crop in 1845 Bubonic plague Fourteenth century AIDS Global epidemic

LIVING IN THE ENVIRONMENT 17 TH MILLER/SPOOLMAN Chapter 6 The Human Population and Its Impact

6-1 How Many People Can the Earth Support? Concept 6-1 We do not know how long we can continue increasing the earth’s carrying capacity for humans without seriously degrading the life-support system that keeps us and many other species alive.

Core Case Study: Slowing Population Growth in China: A Success Story 1.3 billion people Promotes one-child families Contraception, abortion, sterilization Fast-growing economy Serious resource and environmental problems

Crowded Street in China Fig. 6-1, p. 125

Human Population Growth Continues but It Is Unevenly Distributed (1) Reasons for human population increase Movement into new habitats and climate zones Early and modern agriculture methods Control of infectious diseases through Sanitation systems Antibiotics Vaccines Health care Most population growth over last 100 years due to drop in death rates

Human Population Growth Continues but It Is Unevenly Distributed (2) Population growth in developing countries is increasing 9 times faster than developed countries % of growth in developing countries billion people Should the optimum sustainable population be based on cultural carrying capacity?

Human Population Growth Fig. 1-18, p. 21

Fig. 6-2, p Average annual global growth rate (percent) Year 1950

Population Time Line: 10,000 BC Figure 3, Supplement 9

Annual Growth Rate of World Population, Fig. 6-2, p. 127

Where Population Growth Occurred, Fig. 6-3, p. 127

Population in less-developed countries World population (in billions) 2 1 Population in more-developed countries Year

Five Most Populous Countries, 2010 and 2050 Fig. 6-4, p. 127

2010 China1.3 billion United States 310 million India 1.2 billion Indonesia 235 million Brazil 193 million 2050 India 1.7 billion China 1.4 billion United States 439 million Pakistan 335 million Indonesia 309 million

Fig. 6-A, p UN high-fertility variant (2008 revision) U.S. Census Bureau (2008 update) 10 UN low-fertility variant (2008 revision) IIASA (2007 update) 9 8 World population (in billions) Year UN medium-fertility variant (2008 revision)

Science Focus: Projecting Population Change Why range of billion for 2050? Demographers must: 1.Determine reliability of current estimates 2.Make assumptions about fertility trends 3.Deal with different databases and sets of assumptions

World Population Projections to 2050 Fig. 6-A, p. 128

Science Focus: How Long Can The Human Population Keep Growing? Thomas Malthus and population growth: 1798 Overpopulation and overconsumption Will technology increase human carrying capacity? Can the human population grow indefinitely?

Natural Capital Degradation: Altering Nature to Meet Our Needs Fig. 6-B, p. 129

Natural Capital Degradation Altering Nature to Meet Our Needs Reducing biodiversity Increasing use of net primary productivity Increasing genetic resistance in pest species and disease-causing bacteria Eliminating many natural predators Introducing harmful species into natural communities Using some renewable resources faster than they can be replenished Disrupting natural chemical cycling and energy flow Relying mostly on polluting and climate-changing fossil fuels