Presentation on theme: "Applying Population Ecology: The Human Population"— Presentation transcript:
1 Applying Population Ecology: The Human Population G. Tyler Miller’sLiving in the Environment14th EditionChapter 9Applying Population Ecology: The Human PopulationChapter 10
2 Chapter 9 Key Concepts – Population Ecology Factors affecting population sizeSpecies reproductive patternsSpecies survivorship patternsConservation biology and human impacts on ecosystemsPopulation Dynamics and Carrying CapacityPopulation dynamicsBiotic potential (intrinsic rate of increase [rmax])Environmental resistanceCarrying capacityExponential and Logistic GrowthPopulation Density
3 The Study of Population Dynamics Populations change in size, density, dispersion and age structure.Population density —the number of individuals of a population that inhabit a certain unit of land or water area.Population dispersion —refers to how individuals of a population are spaced within a region.Age structure of a population is usually described as thepre-reproductive stage, the reproductive stage and the post-reproductive stage. A population with a large reproductive stage is likely to increase, while a population with a large post-reproductive stage is likely to decrease.
4 Population SizeFour variables influence/govern population size: (1) births, (2) deaths, (3) immigration, and (4) emigration.Increase in population occurs by birth and immigration.Decrease in population occurs by death and emigration.Rapidly growing populations have four characteristics:Individuals in the population reproduce early in life.Individuals have short periods between generations.Individuals have long reproductive lives.Individuals produce multiple offspring each time they reproduce.
5 Biotic Potential vs. Environmental Resistance The biotic potential max (rmax) is the population's capacity for growth. The intrinsic rate of increase (r) is the rate of population growth with unlimited resources.environmental resistanceconsists of factors that limit population growth.limiting FactorsNo population can grow indefinitely due to limited resources such as light, water, and nutrients and also due to competitors and/or predators.
6 Limiting Factors Examples: ExtrinsicBiotic – Density DependentAbiotic – Density IndependentIntrinsicSocial HierarchyGender changingDensity-independent population controls affect a population's size regardless of its density. These are abiotic factors in the community.Density-dependent factors or population controls have a greater affect on the population as its density increases. Infectious disease is an example of density-dependent population control.
7 Environmental resistance Biotic Potential v. Environmental Resistance (Logistic Population Growth)Carrying capacity (K)is determined by biotic potential and environmental resistance.(K) is is the number of a species individuals that can be sustained indefinitely in a specific space.As a population reaches itscarrying capacity, itsgrowth rate will decreasebecause resourcesbecome more scarce.Environmental resistanceCarrying capacity (K)Population size (N)BioticpotentialExponentialgrowthFigure 9-4 Page 166Time (t)
8 Natural Population Curves Population sizes may stay about the same, suddenly increase and then decrease, vary in regular cycles, or change erratically.Four general types of population fluctuations in nature are (1) stable, (2) irruptive, (3) cyclic, and (4) irregular.A stable population fluctuates slightly above and below carrying capacity and is characteristic of many species Living under fairly constant environmental conditions.Fig. 9-7 p. 168Some species have a fairly stable population sizeThat may occasionally irrupt to a high peak and thencrash to below carrying capacity. This ischaracteristic of short-lived, rapidly reproducingspecies.Cyclic fluctuations occur over a regular time period,generally a multiple year cycle.Irregular behavior is poorly understood. Somescientists attribute irregular behavior to chaos in thesystem; others disagree.
10 The Role of Predation in Controlling Population Size Interactions between predators and their prey change in cycles and appear to be caused by species interactions, but other factors may be involved.The hypothesis of top-down control of prey by predators may not be the only explanation for the boom-and-bust cycles seen in these populations. This may also be related to the food supply of prey.The bottom-up control hypothesis states that plants are consumed too rapidly by prey for replacement to keep up. This may lead to a crash of herbivores, and that may lead to a crash of higher predators.Fig. 9-8 p. 168These are not mutually exclusive hypotheses; more probably have interaction between predation and food supplies.
11 Population dispersion Fig. 9-2 p. 164clumping dispersion the most common dispersion pattern for populations. In this type of dispersion, individuals "flock together.“uniform dispersion a type of population dispersion in which the members of the population are uniformly spaced throughout their geographic region.random dispersion a type of population dispersion in which the position of each individual is not determined or influenced by the other members of the population.Most species live in clumps or groups; reasons may include:Availability of resources varies from place to place.Living in groups offers better protection from predators.Some predator species live in packs to better have a chance to get a meal.Temporary groups may form for mating and caring for young.Uniform pattern distribution may occur where a resource, such as water, is scarce.
12 Reproductive Patterns and Survival Some species reproduce without having sex, and others reproduce by having sex.Asexual reproduction does not utilize sex; each cell can divide and produce two identical cells that are replicas of the original cell.Sexual reproduction occurs when gametes from each parent combine toproduce offspring with a combination of genetic traits from each parent.Three disadvantages to sexual reproduction:Males do not give birth; females have to produce twice the offspring tomaintain the same number of young as an asexual organism.Chance of genetic errors/defects increase during splitting and recombination.Courtship/mating consume energy and time, transmit disease, and inflict injury on males in some casesTwo important advantages are genetic diversity for survival of species in the face of changes in environment and males may help with food gathering and/or rearing of young.
13 Reproductive Patterns and Survival Fig p. 170Reproductive patterns can be classified into two fundamental reproductive patterns: r-selected and K-selected species.Availability of a suitable habitat for individuals of a population ultimately determines the population size.
14 Reproductive Strategies r-Selected species are opportunists and reproduce when conditions are favorable or when disturbance opens a niche for invasion. Most species of this type go through irregular and unstable boom-and-bust cycles in population size.K-selected species generally follow a logistic growth curve. Many of the larger species with long generation times and a low reproductive rate are prone to extinction.
15 Survivorship CurvesPopulations of different species vary in how long individual members typically live.A survivorship curve is one way to represent age structure of a population.Three generalized types of survivorship curves are: late loss, early loss, and constant loss.A life table shows the numbers of individuals at each age on a survivorship curve.Insurance companies use life tables to determine the cost of insurance policies.Fig p. 171
16 Effects of Genetic Variations on Population Size Variations in genetic diversity can affect the survival of small, isolatedpopulations. Several factors can play a role in loss of genetic diversityand survival of a small population.The founder effect is when a few individuals move to a new locationthat is isolated from the original population. There is limited geneticdiversity in such a population.A demographic bottleneck occurs when only a few individualssurvive a catastrophe.Genetic drift is a third factor and involves random changes in genefrequencies in a population. This may help or hurt the survival of thepopulation.Inbreeding occurs when members of a small population mate oneanother; this may increase the numbers of defective genes in a population.Metapopulations occur where some mobile populations occasionally exchangegenes when some members get together. Conservation biologists use thisinformation to establish migration routes that will enhance population size,genetic diversity, and survival of related local populations.
17 Human Impacts on Ecosystems Habitat degradation and fragmentationHumans have altered nature in ways that threaten the survival of many species, including our own species.Humans have directly affected changes on about 83% of the earth's land surface.Ecosystem simplificationGenetic resistancePredator eliminationIntroduction of non-native speciesOverharvesting renewable resourcesInterference with ecological systems
18 Human Impacts on Ecosystems Humans have altered nature to meet needs and wants in nine major ways.1. Destruction, fragmentation, and degrading of wildlife habitats have reduced biodiversity.2. The simplification and homogenization of natural ecosystems by clearing land and planting a single species (monoculture) reduces numbers of species and interactions. Opportunistic species and pest organisms are costing time, energy, and money to control. Invasion of pathogenic organisms is another threat.3. Destruction of the earth's net primary productivity is a third type of alteration.4. Certain types of intervention have unintentionally strengthened pest species and disease-causing bacteria.5. Some predator species have been deliberately eliminated from ranching areas.6. Alterations have occurred due to the introduction of nonnative (invasive) or new species into an ecosystem.
19 Human Impacts on Ecosystems 7. A number of renewable resources have been over-harvested, such as overgrazing of grasslands, over-hunting of wildlife, and pumping out aquifers for freshwater faster than they can recharge.8. Some human activities also interfere with normal chemical cycling and energy flows in ecosystems9. Human-dominated ecosystems are increasingly dependent on nonrenewable energy from fossil fuels that produce pollution and add greenhouse gases to the atmosphere.Alteration of natural ecosystems needs to be slowed down, and we need to maintain a balance between simplified, human-altered ecosystems and more complex, natural ecosystems
20 Learning from NatureDependence on NatureInterdependenceUnpredictabilityLimited resourcesRecycle wastesSee Connections p. 173
21 Learning from Nature By mimicking four major ways that nature has adapted andsustained itself, we can developmore sustainable economies.We are totally dependent on thesun and Earth for life. We are anexpendable species.Everything is interconnected andinterdependent. What connectionsare strongest, most important,and most vulnerable are thosethat we must discover.Any intrusion into nature hasunexpected and unintended sideeffects. We must not deplete anddegrade the earth's natural capital.
22 Principles of Sustainability SolutionsPrinciples of SustainabilityHow Nature WorksLessons for UsRely mostly on renewable solar energy.Prevent and reduce pollution and recycle and reuse resources.Preserve biodiversity by protecting ecosystem services and preventing premature extinctionof species.Reduce births and wasteful resource use to prevent environmental overload and depletion anddegradation of resources.Runs on renewable solar energy.Recycles nutrients and wastes. There is little waste in nature.Uses biodiversity to maintain itself and adapt to new environmental conditions.Controls a species population size and resource use by interactions with its environment and other species.Figure 9-15 Page 174
23 Applying Population Ecology: The Human Population Chapter 10 Key ConceptsFactors affecting human population sizeHuman population problemsManaging population growth
24 Factors Affecting Human Population Size Demography is the study of the size, composition, and distribution of human populations and the causes and consequences of changes in these characteristics.Population change equationPopulationChange=(Births + Immigration) – (Deaths + Emigration)Crude birth rate (BR) The crude birth rate is the number of live births per 1,000 people in a population in a specific year.|Crude death rate (DR) The crude death rate is the number of deaths per 1,000 people in a population in a specific year
25 Describing Population Changes Doubling Times “Rule of 70”: Doubling time is one measure of population growth.Fertility-is the number of births that occur to an individual woman in a population.Replacement-level Fertility —the number of children a couple must have in order to replace themselves in a population.Total Fertility Rate (TFR) —the number of children a woman will bear during her lifetime; this information is based on an analysis of data from preceding years in the population in question.Who is Over Populated?
26 Factors Affecting Human Population Size (2005 Data) There are currently more births than deaths throughout the world.1. The annual rate of natural population change (%) equals birth rate minus death rate divided by 1,000 persons multiplied by 100.2. The rate of the world's population growth has decreased.The annual population growth dropped by almost half between 1963 and 2004, from 2.2% to 1.2%. But during this same period, the population base doubled from 3.2 to 6.4 billion.There is a big difference in the exponential population growth rates of developed and developing countries, with developed countries growing at 0.25% and developing countries growing at 1.46%— almost six times faster.The six fastest growing countries in terms of population are: India, China, Pakistan, Nigeria, Bangladesh, and Indonesia.The populations of China and India comprise 38% of the world's population. The next most populated country is the United Stated with 4.6% of the world's population.
27 Factors Affecting Birth Rates and Total Fertility Rates Many factors influence birth and fertility rates.More children work in developing countries; they are important to the labor force.The economic cost of raising and educating children determines their numbers. The more children cost, the less children people tend to have.If there are available private/public pension systems, adults have fewer children because they don't need children to take care of them in old age.People in urban areas usually have better access to family planning, so they have fewer children.
28 If women have educational and economic choices, they tend to have fewer children. When the infant mortality rate is low, people have fewer children because children are not being lost to death.The older the age at which women marry, the fewer children they bear.If abortions are available and legal, women have fewer children.The availability of reliable birth control allows women to space children and determine the number of children they bear.
29 Births per thousand population U.S. Birth Rates:Fig. 10-8, p. 18032302826Births per thousand population242220DemographictransitionEnd of World War II18Depression16Baby boomBaby bustEcho baby boom1419101920193019401950196019701980199020002010YearFrom , the United States had a sharp rise in birth rate, called the baby-boom period. At its peak, the TFR reached 3.7 children per woman. There has been a gradual decline since then. The population growth of the United States is still greater than any other developed country and is not close to leveling off.
30 Factors Affecting Human Population Size About 2.7 million people were added to the U.S. population in Fifty-five percent of this population growth came from more births than deaths, and forty-five percent came from immigration.Other major developed countries have slower population growth, and most are expected to have declining populations after 2010The high U.S. per capita resource rate use produces enormous environmental impact.
31 Immigration Policy Arguments to limit immigration into the U.S. Limitations would aid in stabilizing the population sooner.Limitations would help reduce the enormous environmental impact of the U.S.Arguments for generous immigration policies in the U.S.Historically, the U.S. has been the land of opportunity for the world's poor.Immigrants do work that Americans won't do or handle jobs for which there are not enough trained natives.Immigrants contribute to the economy and pay taxes.
32 Factors Affecting Human Population Size Factors, which have caused a decline in death rates, are the following:Better food supplies and nutrition and safer water supplies contribute to people living longer.Advances in medicine and public health and improved sanitation and personal hygiene also contribute to people living longer.Life expectancy is the average number of years a newborn can expect to live.Infant mortality rate (IMR) is the number of babies out of every 1,000 born who die before their first birthday.a. This rate reflects a country's level of nutrition and health care.b. It is the single best measure of a society's quality of life.U.S. infant mortality rate is higher than 35 other countries due to:a. inadequate health care for poor women and for their babies,b. drug addiction among pregnant women, andc. a high birth rate among teenagers.
33 Population Age Structure Rapid GrowthGuatemalaNigeriaSaudi ArabiaSlow GrowthUnited StatesAustraliaCanadaMaleFemaleZero GrowthSpainAustriaGreeceNegative GrowthGermanyBulgariaSwedenFig p. 184
35 Relative population size Birth rate and death rate The Demographic TransitionFig p. 189LowHighRelative population size(number per 1,000 per year)Birth rate and death rate8070605040302010Stage 1PreindustrialStage 2TransindustrialStage 3IndustrialStage 4Postindustrialgrowth rateIncreasing GrowthVery highDecreasingZeroNegativeBirth rateTotal populationDeath rateTime
36 Solutions: Influencing Population Size MigrationEnvironmental refugeesReducing birthsFamily planningEmpowerment of womenEconomic rewards and penalties
37 Case Study: Slowing Population Growth in India Generally disappointing results:Poor planningBureaucratic inefficiencyLow status of womenExtreme povertyLack of supportWorld in the Balance - India
38 Case Study: Slowing Population Growth in China Economic incentivesFree medical carePreferential treatmentLocally administeredVery intrusive and coerciveWorld in the Balance - China
39 Population Growth in Sub-Saharan Africa How do different populations compare?Sub-Saharan Africa
40 Cutting Global Population Growth Family planningImprove health careElevate the status of womenIncrease educationInvolve men in parentingReduce povertySustainability