Population Ecology and Ecosystems Concepts and Applications: Chapters 40 & 43 Basic Concepts: Chapters 27 & 30 Concepts and Applications: Chapters 40 & 43 Basic Concepts: Chapters 27 & 30

Ecology Certain ecological principles govern the growth and sustainability of all populations Human populations are no exception Certain ecological principles govern the growth and sustainability of all populations Human populations are no exception Ecology: The study of how organisms interact with one another and with their environment Population Ecology

Human Population Problems Over 6 billion people alive About 2 billion live in poverty Most resources are consumed by the relatively few people in developed countries Over 6 billion people alive About 2 billion live in poverty Most resources are consumed by the relatively few people in developed countries Population Ecology

Population A group of individuals of the same species occupying a given area Can be described by demographics –Vital statistics such as size, density, distribution, and age structure A group of individuals of the same species occupying a given area Can be described by demographics –Vital statistics such as size, density, distribution, and age structure Population Ecology

Population Age Structure Divide population into age categories Population’s reproductive base includes members of the reproductive and pre- reproductive age categories Divide population into age categories Population’s reproductive base includes members of the reproductive and pre- reproductive age categories Population Ecology

Density & Distribution Number of individuals in some specified area of habitat Crude density information is more useful if combined with distribution data Number of individuals in some specified area of habitat Crude density information is more useful if combined with distribution data Population Ecology Fig 40.2

Determining Population Size Direct counts are most accurate but seldom feasible Can sample an area, then extrapolate Capture-recapture method is used for mobile species Direct counts are most accurate but seldom feasible Can sample an area, then extrapolate Capture-recapture method is used for mobile species Mark and Recapture # marked Captured = Number released Total Captured Total Pop Population Ecology

Assumptions in Capture-Recapture Marking has no effect on mortality Marking has no effect on likelihood to being captured There is no immigration or emigration between sampling times Marking has no effect on mortality Marking has no effect on likelihood to being captured There is no immigration or emigration between sampling times Population Ecology

Changes in Population Size Immigration adds individuals Emigration subtracts individuals Births add individuals Deaths subtract individuals Immigration adds individuals Emigration subtracts individuals Births add individuals Deaths subtract individuals Population Ecology

Zero Population Growth- ZPG Interval in which number of births is balanced by number of deaths Assume no change as a result of migration Population size remains stable Interval in which number of births is balanced by number of deaths Assume no change as a result of migration Population size remains stable Population Ecology

Per Capita Rates Rates per individual Total number of events in a time interval divided by the number of individuals Per capita birth rate per month = Number of births per month Population size Rates per individual Total number of events in a time interval divided by the number of individuals Per capita birth rate per month = Number of births per month Population size Population Ecology

Exponential Growth Population size expands by ever increasing increments during successive intervals The larger the population gets, the more individuals there are to reproduce Population size expands by ever increasing increments during successive intervals The larger the population gets, the more individuals there are to reproduce Population Ecology Fig 40.4

r r Net reproduction per individual per unit time Variable combines per capita birth and death rates (assuming both constant) Can be used to calculate rate of growth of a population Net reproduction per individual per unit time Variable combines per capita birth and death rates (assuming both constant) Can be used to calculate rate of growth of a population Population Ecology

Exponential Growth Equation G = rN G is population growth per unit time r is net reproduction per individual per unit time N is population size G = rN G is population growth per unit time r is net reproduction per individual per unit time N is population size Population Ecology

Biotic Potential Maximum rate of increase per individual under ideal conditions Varies between species In nature, biotic potential is rarely reached Maximum rate of increase per individual under ideal conditions Varies between species In nature, biotic potential is rarely reached Population Ecology

Limiting Factors Any essential resource that is in short supply All limiting factors acting on a population dictate sustainable population size Any essential resource that is in short supply All limiting factors acting on a population dictate sustainable population size Space Food Shelter Temperature Mates Pollution Disease Space Food Shelter Temperature Mates Pollution Disease Population Ecology

Carrying Capacity (K) Maximum number of individuals that can be sustained in a particular habitat Logistic growth occurs when population size is limited by carrying capacity Maximum number of individuals that can be sustained in a particular habitat Logistic growth occurs when population size is limited by carrying capacity Population Ecology

Logistic Growth Equation G = r max N (K-N/K) G = population growth per unit time r max = maximum population growth rate per unit time N = number of individuals K = carrying capacity G = r max N (K-N/K) G = population growth per unit time r max = maximum population growth rate per unit time N = number of individuals K = carrying capacity Population Ecology

Logistic Growth As size of the population increases, rate of reproduction decreases When the population reaches carrying capacity, population growth ceases As size of the population increases, rate of reproduction decreases When the population reaches carrying capacity, population growth ceases Population Ecology

Overshooting Capacity Population may temporarily increase above carrying capacity Overshoot is usually followed by a crash; dramatic increase in deaths Population may temporarily increase above carrying capacity Overshoot is usually followed by a crash; dramatic increase in deaths Population Ecology Fig 40.7

Resetting the Carrying Capacity Major changes in environment can change the carrying capacity of a local system Population Ecology Fig 40.6

Density-Dependent Controls Logistic growth equation deals with density-dependent controls Limiting factors become more intense as population size increases Disease, competition, parasites, toxic effects of waste products Population Ecology

Density-Independent Controls Factors unaffected by population density Natural disasters or climate changes affect large and small populations alike Population Ecology

Life History Patterns Patterns of timing of reproduction and survivorship Vary among species Summarized in survivorship curves and life tables Patterns of timing of reproduction and survivorship Vary among species Summarized in survivorship curves and life tables Population Ecology

Life Table Tracks age-specific patterns Population is divided into age categories Birth rates and mortality risks are calculated for each age category Tracks age-specific patterns Population is divided into age categories Birth rates and mortality risks are calculated for each age category Population Ecology

Survivorship Curves Population Ecology Fig 40.8

Human Population Growth Population now exceeds 6 billion Rates of increase vary among countries Average annual increase is 1.26 percent Population continues to increase exponentially Population now exceeds 6 billion Rates of increase vary among countries Average annual increase is 1.26 percent Population continues to increase exponentially Population Ecology

Fig. 40.9, p. 695 Human Population Growth Population Ecology

How Humans have Side-Stepped density dependent controls Expanded into new habitats Agriculture increased carrying capacity; use of fossil fuels aided increase Hygiene and medicine lessened effects of density-dependent controls Expanded into new habitats Agriculture increased carrying capacity; use of fossil fuels aided increase Hygiene and medicine lessened effects of density-dependent controls Population Ecology

Future Growth Exponential growth cannot continue forever Breakthroughs in technology may further increase carrying capacity Eventually, density- dependent factors will slow growth Exponential growth cannot continue forever Breakthroughs in technology may further increase carrying capacity Eventually, density- dependent factors will slow growth Population Momentum Lowering fertility rates cannot immediately slow population growth rate. Why? If every couple had just two children, population would still keep growing for another 60 years Lowering fertility rates cannot immediately slow population growth rate. Why? If every couple had just two children, population would still keep growing for another 60 years Population Ecology

Resource Consumption United States has 4.7 percent of the world’s population Americans have a disproportionately large effect on the world’s resources Per capita, Americans consume more resources and create more pollution than citizens of less developed nations United States has 4.7 percent of the world’s population Americans have a disproportionately large effect on the world’s resources Per capita, Americans consume more resources and create more pollution than citizens of less developed nations Population Ecology

Effects of Economic Development Total fertility rates (TFRs) are highest in developing countries, lowest in developed countries When individuals are economically secure, they are under less pressure to have large families Total fertility rates (TFRs) are highest in developing countries, lowest in developed countries When individuals are economically secure, they are under less pressure to have large families Population Ecology

Slowing Growth in China World’s most extensive family planning program Government rewards small family size, penalizes larger families, provides free birth control, abortion, sterilization Since 1972, TFR down to 1.8 from 5.7 World’s most extensive family planning program Government rewards small family size, penalizes larger families, provides free birth control, abortion, sterilization Since 1972, TFR down to 1.8 from 5.7 Population Ecology

Community Ecology Community: Populations of all species in a habitat. Niche: Sum total of all a species activities and relationships as species do what they do. –Fundamental, Realized Community: Populations of all species in a habitat. Niche: Sum total of all a species activities and relationships as species do what they do. –Fundamental, Realized Community Ecology

Types of Interactions Neutral Commensalism Mutualism Competition Predation Parasitism Neutral Commensalism Mutualism Competition Predation Parasitism Who benefits? Spp 1Spp 2 00 Y0 YY NN YN YN Community Ecology

Competition Competitive Exclusion –Paramecium Resource Partitioning –Fruit eating birds, Barnacles Competitive Exclusion –Paramecium Resource Partitioning –Fruit eating birds, Barnacles Community Ecology

Predator-Prey Interactions The Classic Lynx / Hare system Community Ecology

Ecosystems Energy is transferred from the SUN to all organisms Primary Producers Consumers Decomposers Energy is LOST with each transition Energy is transferred from the SUN to all organisms Primary Producers Consumers Decomposers Energy is LOST with each transition Ecosystems

Food Webs A composite picture of an ecosystem’s membership and their interaction Ecosystems Fig. 43.6, p. 740 Do not post photos on Internet

Food Webs can be Disrupted Natural Disasters External inputs –Pesticides, Pollution Natural Disasters External inputs –Pesticides, Pollution Ecosystems

Fig , p. 746 The Hydrologic Cycle

Other Cycles Carbon Nitrogen Phosphorus Carbon Nitrogen Phosphorus Ecosystems

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