Group of individuals Populations - Davis School District · Group of individuals same species same area same time ... member of the Galapagos Islands . The decline ... 9 billion by

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PopulationsChapter 4

Group of individuals

same species

same area

same time

Population

Characteristics of Populations

• Geographic distribution or Population range.

• Describes the area inhabited by a population. Where something lives and reproduces.

• Vary in size; a few inches, to millions of Square miles.

••

Population density

Number of individuals per area.• Low density- resources are scant.• High density- resources are plentiful.

Population Dispersion• The pattern of spacing of a population

within an area.

Growth Rate

• Number of births• Number of deaths•• Number of individuals move out of an

area (Emigration)•• Number of individuals that move into an

area (Immigration)•• ** Populations never stay the same

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Exponential Growth• Population reproduce at a constant rate.

• Under ideal conditions

• Unlimited resources

• ** Exponential growth does not continue in a natural population.

J –shaped curve

Constant reproduction rate.

Factors that lead to exponential growth:

Unlimited resourcesShelterFoodMates

No predators

Will eventually lead to a population crash.

No population has a continuous supply of resources.

Logistic GrowthWhen a population’s growth slows or stops.

“Carrying Capacity”Largest number of individuals of a population

that a given area can support.

Logistic growth

S-shaped curveSigmoid curve

Realistic growth pattern of populations.Factors:

Limited resourcesFoodShelterMates

Predators

Populations reach its carrying capacity.

Do populations of species affect each other in an ecosystem?

Yes

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Sea Otters Kelp Forests

Sea Urchins

• ***** Do cats in Borneo

Carrying capacity

The maximum number of individuals of a given species that can be sustainedindefinitely in a given space.

Each environment will

have a limit as to how

many organisms can

live in that particular

environment.

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Limits to growth“Limiting Factors”

Factors that causes population growth To decrease.

Density-dependent factors

Limiting factors that depends on the number of organisms in a population.

– These factors only become limiting when a population reaches a certain level.

Competitionfood, water, space, sunlight, mates

• Occurs among individuals of the same species.

• Occurs among different species.

Disease & Parasites

• As populations grow their distribution becomes more “Clumped” together.

• This makes it easier

• for disease and

• parasites to get

• passed through

• a population at a

• greater speed.

Predation

• Populations are often controlled by a predator-prey relationship.

• As the prey population grow so do the predator.

• As the prey declines

• so do the predators.

Density-Independent factors•

Factors that affect all populations in similar ways.

These factors do not depend on the number of species in a population.

•• ** Environments are always changing.

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Climate

Seasonal cycles

Droughts

Floods

Too Hot

Severe Frost

Natural Disaster

• Earthquakes

• Hurricanes

• Fires

• Mud slides

• Tornados

This graph shows the decline in the population of one of Darwin's finches (Geospiza fortis) on Daphne Major, a tiny 100 acres member of the Galapagos Islands. The decline (from 1400 to 200 individuals) occurred because of a severe drought that reduced the quantity of seeds on which this species feeds. The drought ended in 1978, but even with ample food once again available the finch population recovered only slowly.

Human Activities

Over hunting (poaching)

Habitat destruction

Pollution

Farming

Factors

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Human Population Growth

Facts:Currently at 6.8 billion

Growing at an exponential rate.

1-2% per year

Expected to get to 9 billion by 2050**Only organism who

has not reached a carrying capacity.

• The global population reached one billion

in 1850.

• In 1930, some 80 years later, it passed

two billion.

• Sixty years later, in 1987, the world

population was five billion.

• 12 years later, in October 1999, it is

estimated to have passed six billion.

• An eventual world population of 8-12

billion is expected by the end of the

century.

Human Populations

• Population is growing

• at a rate of 3

• people per second.

• Mass production of food

– Green Revolution

– Better medicineIntroduction of antibioticMortality went down

Growth rate stayed the

same at about 1-2%

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Future Population Growth

2050 -11 billion people

• Where is it going to be?

– Developing countries

• Europe will see a decline in populations.

– Problems?

• US should remain even.

US Population Growth

• US is the third largest country behind China

and India.

– Current population is 311 million

• Birth rates are dropping

– In 1970-

• 2.1 children/woman

• Replacement fertility

– 2010

• 2.03 children/woman

• Is there a Carrying Capacity for Homo

sapiens?

• If so, what is it - and when will we reach

or overshoot this limit?

• There are no easy answers to the

questions:

• “How many people can the earth

support?”, and “At what level of well-being?”.