Understanding Populations

Key Concept: As the human population grows, the demand for Earth’s resources increases

Earth’s human carrying capacity is unknown.

Population

• …..is all members of a species living in the same place at the same time.

Population Density

• is a measurement of population per unit area or unit volume

Geographic dispersion of a population shows how individuals in a population

are spaced. • Population dispersion

refers to how a population is spread in an area.

Clumpeddispersion

Uniformdispersion

Randomdispersion

Density Dependent

• ….deaths occur more quickly in a crowded population than in a sparse population.

• Example: black plague

• Density-dependent limiting factors are affected by the number of individuals in a given area.

– parasitism and disease

– predation– competition

• Predation occurs when one organism captures and eats another.

Competition and predation are two important ways in which organisms interact

• Competition occurs when two organisms fight for the same limited resource

– Intraspecificcompetition

– Interspecificcompetition

• There are three major types of symbiotic relationships.– Mutualism: both organisms benefit

– Commensalism: one organism benefits, the other is unharmed

Human Our eyelashes are home to tiny mitesthat feast on oil secretions and dead skin. Without harming us, up to 20 mites may be living in one eyelash follicle.

Demodicids Eyelash mites find all they need to survive in the tiny folliclesof eyelashes. Magnified here 225 times, these creatures measure 0.4 mm in length and can be seen only with a microscope.

+

Organism benefits+

Ø

Ø Organism is not affected

Commensalism

• There are three major types of symbiotic relationships.

– Parasitism: one organism benefits, the other is harmed

• There are three major types of symbiotic relationships.

Organism benefits0

_

Organism is not affected

Hornworm caterpillarThe host hornworm will eventually die as its organs are consumedby wasp larvae.

Braconid waspBraconid larvae feed on their host and release themselves shortly before reachingthe pupae stage of development.

_

Parasitism

+

0

Density Independent

• …..a certain proportion of a population dies regardless of the population’s density.

• Severe weather• Natural disasters• Human impact

How Does a Population Grow?

• Change in population size equals the number of births minus the number of deaths.

Reproductive Potential

• ....maximum number of offspring that each member of the population can produce.

• Elephants 750 yrs for a pair to produce 19 million descendants.

• Bacterium can produce 19 million descendants in a few days or weeks.

Population growth is based on available resources.

• Exponential growth is a rapid population increase due to an abundance of resources.

Exponential Growth

• …populations growing fast and faster.

What if…..

Q: What would the graph look like if it showed linear (or arithmetic) growth?

A: ..a straight line, increasing by the same amount during each time period.

Q: How does exponential growth relate to reproductive potential?

A: most organisms have the potential to reproduce “multiples” of themselves.

Problems with Rapid Growth

• Infrastructure no longer meets needs

• Shortage of fuel wood• Unsafe water• Impacts on land

Changes in a population’s size are determined by immigration, births,

emigration, and deaths. • The size of a population is

always changing.• Four factors affect the size of a

population.

– immigration– births– emigration– deaths

• Survivorship curves can be type I, II or III.– Type I—low level of infant mortality and an older

population– common to large mammals and humans– Type II—survivorship rate is equal at all stages of life– common to birds

and reptiles– Type III—very

high birth rate, very high infant mortality

– common to invertebrates and plants

Other Factors Impacting Growth

• Carrying Capacity• Resource Limits• Competition within a

population• ---direct: cannibalism,

predation• ---indirect: territory

• Carrying capacity is the maximum number of individuals in a population that the environment can support.

• A population crash is a dramatic decline in the size of a population over a short period of time.

How might an introduced species disrupt an ecosystem?

• Native species may not be adapted to…. -----compete

---defend against it

---capture it as prey

Remember the cane toad?

• Technology has helped to increase Earth’s carrying capacity.– gas-powered farm equipment– medical advancements

The growing human population exerts pressure on Earth’s

natural resources.

• Nonrenewable resources are used faster than they form.– coal– oil

• Renewable resources cannot be used up or can replenish themselves over time.

– wind– water– sunlight

• Growing use of nonrenewable resources may lead to a crisis.

• Resources must be properly managed.

Effective management of Earth’s resources will help meet the

needs of the future. • Earth’s resources must be used

responsibly.

• Careless use of resources makes them unavailable to future generations.