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Population Ecologyand Ecosystems

Concepts and Applications: Chapters 40 & 43

Basic Concepts: Chapters 27 & 30

http://darwin.bio.uci.edu/~sustain/bio65/lec16/b65lec16.htm

Ecology

• 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

PopulationEcology

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

PopulationEcology

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

PopulationEcology

Population Age Structure

• Divide population into age categories

• Population’s reproductive base includes

members of the reproductive and pre-

reproductive age categories

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Density & Distribution

• Number of individuals in some specified area of habitat

• Crude density information is more useful if combined with distribution data

PopulationEcology

Fig 40.2

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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

Mark and Recapture

# marked Captured = Number releasedTotal Captured Total Pop

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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

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Changes in Population Size

• Immigration adds individuals

• Emigration subtracts individuals

• Births add individuals

• Deaths subtract individuals

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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

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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

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Exponential Growth

• Population size expands by ever increasing increments during successive intervals

• The larger the population gets, the more individuals there are to reproduce

PopulationEcology

Fig 40.4

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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

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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

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Biotic Potential

• Maximum rate of increase per individual

under ideal conditions

• Varies between species

• In nature, biotic potential is rarely reached

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Limiting Factors

• 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

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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

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Logistic Growth Equation

G = rmax N (K-N/K)

• G = population growth per unit time

• rmax = maximum population growth rate per unit time

• N = number of individuals

• K = carrying capacity

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Logistic Growth

• As size of the population increases, rate of reproduction decreases

• When the population reaches carrying capacity, population growth ceases

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Overshooting Capacity

• Population may temporarily increase above carrying capacity

• Overshoot is usually followed by a crash; dramatic increase in deaths

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Fig 40.7

Resetting the Carrying Capacity

• Major changes in environment can change the carrying capacity of a local system

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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

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Density-Independent Controls

• Factors unaffected by population density

• Natural disasters or climate changes affect

large and small populations alike

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Life History Patterns

• Patterns of timing of reproduction

and survivorship

• Vary among species

• Summarized in survivorship curves

and life tables

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Life Table

• Tracks age-specific patterns

• Population is divided into age categories

• Birth rates and mortality risks are calculated

for each age category

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Survivorship Curves

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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

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Fig. 40.9, p. 695

Human Population GrowthPopulationEcology

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

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Future 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

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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

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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

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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

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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 Ecology

Types of Interactions

• Neutral• Commensalism• Mutualism• Competition• Predation• Parasitism

Who benefits?Spp 1 Spp 2

0 0Y 0Y YN NY NY N

Community Ecology

Competition

• Competitive Exclusion– Paramecium

• Resource Partitioning– Fruit eating birds,

Barnacles

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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

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

Ecosystems

Ecosystems

Fig. 43.14, p. 746

The Hydrologic Cycle

Other Cycles

• Carbon• Nitrogen• Phosphorus

Ecosystems

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Quiz