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SUSTAINING THE MILLER/SPOOLMAN EARTH | G. TYLER MILLER | SCOTT E. SPOOLMAN 11e 4 Community Ecology, Population Ecology, and the Human Population © Cengage Learning 2015 4-1 What Roles Do Species Play in Ecosystems? • Each species plays a role in its ecosystem – Ecological niche (niche) • Species’ way of life in a community: everything that affects survival and reproduction, e.g., sunlight, water, space, food, predators, and temperature – Generalist species • Broad niches: wide range of tolerance – Specialist species • Narrow niches: narrow range of tolerance © Cengage Learning 2015 Black skimmer seizes small fish at water surface Flamingo feeds on minute organisms in mud Stepped Art Fig. 4-1 Brown pelican dives for fish, Avocet sweeps bill which it locates through mud and from the air surface water in search of small crustaceans, insects, and seeds Scaup and other diving ducks feed on mollusks, crustaceans, and aquatic vegetation Louisiana heron wades into water to seize small fish Herring gull is a Ruddy tireless turnstone scavenger searches Dowitcher probes under shells deeply into mud in and pebbles search of snails, for small marine worms, and invertebrates small crustaceans Oystercatcher feeds on clams, mussels, and other shellfish into which it pries its narrow beak Knot (sandpiper) picks up worms and small crustaceans left by receding tide Piping plover feeds on insects and tiny crustaceans on sandy beaches Case Study: The Giant Panda—A Highly Endangered Specialist • 1,600 to 3,000 giant pandas in the wild – Most in China • Specialist species – Requires bamboo stalks and leaves as food • Low reproductive rate • Threats – Limited range of bamboo forests – Poaching © Cengage Learning 2015 Species Can Play Four Major Roles within Ecosystems • Native species • Nonnative species (invasive, alien, and exotic species) • Indicator species • Keystone species © Cengage Learning 2015 Indicator Species Serve as Biological Smoke Alarms • Indicator species – Provide early warning of damage to a community – Widespread – Affected quickly by environmental changes – Examples: • Birds • Butterflies • Some amphibians © Cengage Learning 2015 Science Focus: Why Are Amphibians Vanishing? • Natural and human-caused factors − Parasites − Viral and fungal diseases – Increases in UV radiation – Pollution − Parasites – Overhunting − Habitat loss and fragmentation – Nonnative predators and competitors − Prolonged drought © Cengage Learning 2015 Keystone and Foundation Species Play Critical Roles in Their Ecosystems • Keystone species – Roles have a large effect on the types and abundances of other species • Pollinators • Top predators – Vulnerable to extinction • Loss of a keystone species can lead to population crashes and other species’ extinctions © Cengage Learning 2015 Case Study: Why Should We Protect Sharks? • Keystone species • Shark studies could help save human lives – Sharks rarely get cancer – Highly effective immune system • Three largest species – Plant-eaters • 100 million sharks killed every year – Among most vulnerable and least protected © Cengage Learning 2015 4-2 How Do Species Interact? • Species interact in five major ways – Interspecific competition • Resource partitioning – Predation – Parasitism – Mutualism – Commensalism © Cengage Learning 2015 Blackburnian BlackWarbler throated Green Warbler Cape May Warbler Baybreasted Warbler Resource partitioning Fig. 4-2 Yellowrumped Warbler Most Consumer Species Feed on Organisms of Other Species • Predation – Predator–prey relationships – Plays a role in evolution by natural selection – Predators play an important ecological role © Cengage Learning 2015 Some Species Feed off Other Species by Living on or in Them • Parasitism • Parasite is usually much smaller than the host • Parasite rarely kills the host – In some cases, parasites help to keep the hosts’ populations in check + © Cengage Learning 2015 - In Some Interactions, Both Species Benefit • • • • • Mutualism Nutrition and protection relationship Gut inhabitant mutualism Mutual exploitation Example: clownfish and sea anemones © Cengage Learning 2015 + + In Some Interactions, One Species Benefits and the Other Is Not Harmed • Commensalism • Example: epiphytes attach to the trunks of large trees in tropical forests + 0 © Cengage Learning 2015 4-3 How Do Communities and Ecosystems Respond to Changing Conditions? • Communities and ecosystems change over time: ecological succession – Primary succession – Secondary succession • Primary succession and secondary succession – Tend to increase biodiversity and interactions among species © Cengage Learning 2015 Lichens and Exposed mosses rocks Fig. 4-4 Small herbs and shrubs Heath mat Jack pine, black spruce, and aspen Balsam fir, paper birch, and white spruce forest community Annual weeds Stepped Art Fig. 4-5 Perennial weeds and grasses Shrubs and small pine seedlings Young pine forest with developing understory of oak and hickory trees Mature oak and hickory forest 4-4 What Limits the Growth of Populations? • Populations can grow, shrink, or remain stable – Population change = (births + immigration) – (deaths + emigration) • Biotic potential • Intrinsic rate of increase – Population growth rate with unlimited resources © Cengage Learning 2015 Populations Can Grow, Shrink, or Remain Stable • Limiting factors – Physical or chemical environmental conditions • Environmental resistance – All factors that act to limit the growth of a population • Carrying capacity – Maximum population a given habitat can sustain © Cengage Learning 2015 Number of sheep (millions) 2.0 1.5 1.0 Population overshoots carrying capacity Carrying capacity Population recovers and Population runs stabilizes Exponential out of resources growth and crashes .5 1800 Fig. 4-6 Environmental resistance 1825 1850 1875 Year 1900 1925 When a Population Exceeds Its Habitat’s Carrying Capacity It Can Crash • A population exceeds the area’s carrying capacity – Population crash (dieback) – Damage may reduce area’s carrying capacity • Area’s carrying capacity – Can rise or decline seasonally and from year to year © Cengage Learning 2015 Population overshoots carrying capacity Number of reindeer 2,000 1,500 Population crashes 1,000 500 0 Fig. 4-7 Carrying capacity 1910 1920 1930 Year 1940 1950 Species Have Different Reproductive Patterns • Opportunist species – Many, usually small, offspring – Little or no parental care – Massive deaths of offspring – Examples: algae, bacteria, and insects © Cengage Learning 2015 Species Have Different Reproductive Patterns • Competitor species – Reproduce later in life – Small number of offspring with long life spans – Young offspring develop inside their mothers – Long time to maturity – Protected by parents and potentially groups – Examples: elephants, whales, and humans © Cengage Learning 2015 4-5 What Factors Influence the Size of the Human Population? • Human population growth continues but it is unevenly distributed – Reasons for human population increase • Movement into new habitats and climate zones • Emergence of early and modern agriculture methods • Control of infectious diseases through sanitation systems, antibiotics, and vaccines © Cengage Learning 2015 Human Population Growth Continues but It Is Unevenly Distributed • World population is growing exponentially – Rate of 1.2 percent a year – Projected population by 2050: 9.6 billion – More-developed countries (2012): 0.1 percent yearly growth rate – Less-developed countries (2012): 1.5 percent yearly growth rate • Least equipped to deal with rapid growth © Cengage Learning 2015 World population (in billions) Population in less-developed countries Population in more-developed countries Year Fig. 4-9 Fig. 6-3, p. 123 Women Having Fewer Babies but Not Few Enough to Stabilize the World’s Population • Fertility rate • Replacement-level fertility rate – Rate is higher in less-developed countries • Total fertility rate (TFR) – Plays a key role in determining population size How many children does a woman need to have to keep the population the same? © Cengage Learning 2015 Case Study: The U.S. Population— Third-Largest and Growing • Population still growing – 76 million in 1900 – 310 million in 2010 • Drop in TFR in U.S. – Population growth rate has slowed • The U.S. has the world’s largest total and per capita ecological footprint © Cengage Learning 2015 Births per woman Fig. 4-11 Baby boom (1946–64) Replacement level 47 years Life expectancy 77 years Married women working outside the home 8% 81% 15% High school graduates 83% 10% Homes with flush toilets Homes with electricity Living in suburbs Hourly manufacturing job wage (adjusted for inflation) Homicides per 100,000 people Stepped Art Fig. 4-12 98% 2% 99% 10% 52% $3 1900 2000 $15 1.2 5.8 Several Factors Affect Birth Rates and Fertility Rates • • • • • Children as part of the labor force Cost of raising and educating children Availability of private and public pension Urbanization Educational and employment opportunities for women © Cengage Learning 2015 Several Factors Affect Birth Rates and Fertility Rates • Availability of legal abortions • Availability of reliable birth control methods • Religious beliefs, traditions, and cultural norms © Cengage Learning 2015 Several Factors Affect Death Rates • Life expectancy – U.S. ranks 32nd among nations • Infant mortality rate – Based on live births that die in first year – Impacted by undernutrition and malnutrition – U.S. ranks 44th among nations due to • Inadequate health care for poor women during pregnancy and for infants after birth • Drug addiction among pregnant women © Cengage Learning 2015 Migration Affects an Area’s Population Size • Immigration and emigration • Reasons for movement – Economic – Religious – Ethnic – Political – Wars – Environmental © Cengage Learning 2015 World population (in billions) Science Focus: Projecting Population Change UN high-fertility variant (2008 revision) U.S. Census Bureau (2008 update) UN medium-fertility variant (2008 revision) IIASA (2007 update) UN low-fertility variant (2008 revision) Year Fig. 4-B Population Age Structure Can Affect Growth or Decline • Age structure categories – Prereproductive ages (0-14) – Reproductive ages (15-44) – Postreproductive ages (45 and older) • Seniors (ages 65+) – Fastest-growing age group in the U.S. © Cengage Learning 2015 Male Female Expanding Rapidly Guatemala Nigeria Saudi Arabia Prereproductive ages 0–14 Fig. 4-13 Male Female Expanding Slowly United States Australia China Reproductive ages 15–44 Male Female Male Stable Japan Italy Greece Female Declining Germany Bulgaria Russia Postreproductive ages 45–85+ Fig. 6-11, p. 131 Case Study: The American Baby Boom Growing senior population: the graying of America Fig. 4-14 Populations Made Up of Mostly Older People Can Decline Rapidly • Severe effects – Fewer adults working and paying taxes to support an increasing elderly population • Countries facing rapid decline – Japan, Russia, Germany, Bulgaria, Hungary, Ukraine, Serbia, Greece, Portugal, and Italy © Cengage Learning 2015 Some Problems with Rapid Population Decline Can threaten economic growth Labor shortages Less government revenues with fewer workers Less entrepreneurship and new business formation Less likelihood for new technology development Increasing public deficits to fund higher pension and health-care costs Pensions may be cut and retirement age increased Fig. 4-15 4-6 How Can We Slow Human Population Growth? • Is the earth overpopulated? An important controversy – Can the world provide an adequate standard of living for a projected 2.5 billion more people by 2050 without causing widespread environmental damage? • Population regulation – Opponents and proponents © Cengage Learning 2015 Birth rate and death rate (number per 1,000 per year) Stage 1 Preindustrial Stage 2 Transitional Population grows very slowly because of a high birth rate (to compensate for high infant 80 mortality) and a 70 high death rate Stage 3 Industrial Population grows rapidly because birth rates are high and death rates drop because of improved food production and health Stage 4 Postindustrial Population growth slows as both birth and death rates drop because of improved food production, health, and education Population growth levels off and then declines as birth rates equal and then fall below death rates Total population 60 Birth rate 50 40 30 Death rate 20 10 0 Low Increasing Very high Decreasing Growth rate over time Stepped Art Fig. 4-17 Low Zero Negative Empowering Women Helps to Slow Population Growth • Factors that decrease total fertility rates – Education – Paying jobs – Rights supported • Women’s roles – Do most of the domestic work and child care – Provide unpaid health care within families • Bottom-up change in taking charge © Cengage Learning 2015 Family Planning Can Provide Several Benefits • Educational and clinical services – Responsible for a 56 percent drop in TFRs in less-developed countries (1960-2012) • Issues in less-developed countries – 42 percent of all pregnancies unplanned, 26 percent end with abortion – Many couples lack access to family planning © Cengage Learning 2015 Is It Possible to Reduce Population Growth? • United Nations’ Conference on Population and Development goals by 2015 – Provide universal access to family planning and reproductive health care – Improve health care for infants, children, and pregnant women – Implement national population policies – Improve the status of women © Cengage Learning 2015 Is It Possible to Reduce Population Growth? • Goals by 2015 – Increase the involvement of men in child-rearing – Sharply reduce poverty – Sharply reduce unsustainable patterns of production and consumption © Cengage Learning 2015 Case Study: India’s Attempts to Slow Its Population Growth • Projected 1.69 billion people by 2015 – Most populous country • Problems: poverty, malnutrition, environmental degradation • Factors for larger families – Poor couples want many children • Work and care for parents in old age – Bias toward having male children © Cengage Learning 2015 Case Study ─ Slowing Population Growth in China: the One-Child Policy • Projected 1.4 billion people by 2026 • Promotes one-child families – Free sterilization, contraceptives, and abortion • Fast-growing economy since 1980 – Rapidly growing middle class – Need for more environmentally sustainable economic development • Concerns regarding the graying of China © Cengage Learning 2015