Chapter 45Population Ecology: A Summary

AP BiologySpring 2011

Population Demographics

•Population density: number of individuals per a certain area

Population Demographics

•Population distribution: where individuals are positioned in a certain area▫3 types

Population Demographics

•Clumped distribution: pattern is one where all individuals are in a small area▫Ex. Surrounding water supply

Population Demographics

•Uniform distribution: individuals are evenly spaced

Population Demographics

•Random distribution: individuals have no uniformity to their placement

Elusive Heads to Count•Quadrants are plots of land of a standard

size used for counting the number of organisms

•The capture-recapture method is used to estimate the size of a population of animals▫Sample size must be large enough to gather

significant information ▫The animals captured must have no bias, such

as being easier or more difficult to catch

Population Size and Exponential Growth

•Members of a population may leave (emigration) or enter a new population (immigration)▫Ms. Warren

emigrated from Canada, and immigrated to the US

Population Size and Exponential Growth •Zero population growth: number of

individuals born equals the number dying •Per capita growth

rate: equals the birth rate minus the death rate ▫If per capita growth rate

is more than zero, the population is exhibiting exponential growth J shaped curve

Population Size and Exponential Growth •Biotic potential: indicates the largest

amount of increase that can occur in that particular population

Limits on Population Growth

•Carrying capacity: largest number of individuals that a certain environment can support ▫S shaped

curve indicative of how a population naturally changes

Limits on Population Growth

•Limiting factors: components that are not plentiful and may restrict population growth ▫Density dependent factors▫Density independent factors

Limits on Population Growth

•Density dependent factors: those that become more critical as the population increases▫Ex. Food, water, incidence of disease

Limits on Population Growth

•Density independent factors: those that are not influenced by the size of a population ▫Ex. Floods, fires, earthquakes, natural

disasters

Life History Patterns •Life tables: illustrate the number of

individuals that survive in various age categories

•Survivorship curve: visual representation of age-specific survival of a population

Life History Patterns

•Type 1 curve: shows tat the individuals usually survive until old age ▫Animals exhibiting type 1 curve produce

small amount of offspring that require much care

▫Ex. Humans▫These animals exhibit K-selection, few

offspring needing much care

Life History Patterns

•Type 2 curve: illustrates that the survival rate does not relate to age▫Ex. Squirrels

Life History Patterns

•Type 3 curve: chows that the majority of individuals do not survive to maturity ▫Animals exhibiting type 3 produce many

offspring that do not require much care▫Ex. Sea urchins ▫These animals exhibit R-selection with

many offspring needing little care

Life History Patterns

Natural Selection and Life Histories •Life history traits can change as a

response to an alteration in the types of predators ▫Ex. Shown by 2 isolated populations of

guppies where there were different predators

▫The life history of the cod population in the North Atlantic changed due to over-fishing

Human Population Growth

•Human population’s current rate of increase is approximately 1.1%

•This rate of growth is due to the fact that humans can spread easily into new habitats

•Man has developed fire, tool making abilities that are passed on from one generation to the next

Human Population Growth •Humans have developed new technologies

to increase the carrying capacity of the environment▫Man learned how to cultivate crops, raise

livestock

Human Population Growth

•Human population has learned how to overcome some limiting factors▫Man learned how to combat many diseases

and use fossil fuels for energy production •Density dependent factors may become of

the utmost importance due to overpopulation

Fertility Rates and Age Structure •Total fertility rate: the average number of children born to each woman of reproductive age

•The fertility rate worldwide has decreased from 6.5 to 2.7 in the last 50 years

•This decrease still puts the worldwide fertility rate above the number that keeps the population at a constant level

Fertility Rates and Age Structure •One third of the world’s population is not

yet in the reproductive category•China has initiated a system of rewards to

encourage a lower national fertility rate

Population Growth and Economic Effects •Demographic transition model:

connects industrial development and changes in population growth rates

Population Growth and Economic Effects •In countries where industrialization has

not yet occurred, the birth rate is high ▫Children are needed to perform duties on a

farm ▫Ex. Many African countries

•In industrial nations, the birth rate declines, ex. United States▫Industrialized nations use a larger

percentage of resources of the world •In post-industrialized nations, the

population size may increase

Rise of the Seniors

•The amount of individuals over age 65 is increasing

•Fertility rates are declining•Individuals are living longer due to

medical advances•Society may have trouble supporting the

increase in retired individuals