How populations How populations growgrow

Ch 15 Ch 15

B3.5 B3.5

What is a populationWhat is a population

PopulationPopulation – consists of all the – consists of all the individuals of a species that live individuals of a species that live together in one place at one time. together in one place at one time.

DemographyDemography – the statistical study – the statistical study of all populations. of all populations.

DemographerDemographer - Study the - Study the composition of a population and try composition of a population and try to predict how the size of the to predict how the size of the population will change. population will change.

Three features of a Three features of a populationpopulation

1.1. Population sizePopulation size – the number of – the number of individuals in a population individuals in a population

Can affect the population’s ability to Can affect the population’s ability to survive. survive.

Natural disturbances (fires and flood) Natural disturbances (fires and flood) are more of a danger to a small are more of a danger to a small population than a large population.population than a large population.

Small populations tend have more Small populations tend have more inbreedinginbreeding

Example …Example …

Cheetah (Cheetah (Acinonyx Acinonyx jubatusjubatus))

Very small populationVery small population Genetically identicalGenetically identical A disaster (new disease) could cause A disaster (new disease) could cause

their extinction their extinction

Three features of a Three features of a populationpopulation

2. 2. Population densityPopulation density – is the number of – is the number of individuals that live in a given area. individuals that live in a given area. Spread out population (dispersed widely) Spread out population (dispersed widely)

won’t interact and breed.won’t interact and breed.

3. 3. DispersionDispersion – is the way the individuals – is the way the individuals of the population are arranged in space.of the population are arranged in space.

Spacing of populations affect how they Spacing of populations affect how they interact with each other and the interact with each other and the environment.environment.

Modeling population Modeling population growth growth

Population modelPopulation model – is the – is the hypothetical population that hypothetical population that attempts to exhibit the key attempts to exhibit the key characteristic of a real population. characteristic of a real population.

Growth rateGrowth rate – simple model – simple model describes the rate of population describes the rate of population growth as the difference between growth as the difference between the birthrate and the death rate. the birthrate and the death rate.

Growth rate and population Growth rate and population sizesize

Exponential growth curveExponential growth curve – is a – is a curve in which the rate of a curve in which the rate of a population stays the same, as a population stays the same, as a result the population size increasing result the population size increasing steadily. steadily.

Carrying capacityCarrying capacity – the population – the population size that an environment can size that an environment can sustain. sustain.

MONEY SAVED by NOT SMOKING

$0.00

$10,000.00

$20,000.00

$30,000.00

$40,000.00

$50,000.00

$60,000.00

1 2 3 4 5 6 7 8 9 10

Years

Do

llar

s

4 Packs/Day

3 Packs/Day

2 Packs/Day

1 Pack/Day

Resources and Resources and population sizepopulation size

Density dependent resourcesDensity dependent resources – – resources that are depleted at a rate that resources that are depleted at a rate that depends on the population density of the depends on the population density of the population that use them.population that use them. Limited resources, food and water Limited resources, food and water

Logistic modelLogistic model – is a population model in – is a population model in which exponential growth is limited by a which exponential growth is limited by a density dependent factor.density dependent factor. Excellent estimate of population growth in Excellent estimate of population growth in

nature.nature. Competition for food, shelter, mates and Competition for food, shelter, mates and

limited resources tends to increase as a limited resources tends to increase as a population approaches it carrying capacity. population approaches it carrying capacity.

Logistic model Logistic model

Growth patterns in real Growth patterns in real populationspopulations

Density independent factorsDensity independent factors – – growth of an organism that is limited growth of an organism that is limited by environmental conditions. by environmental conditions. Weather and climateWeather and climate

Example, mosquito populations increase in Example, mosquito populations increase in the summer when it is warn and decrease in the summer when it is warn and decrease in the winter.the winter.

R-strategiesR-strategies – grow exponentially – grow exponentially when environmental conditions when environmental conditions allow them to reproduce.allow them to reproduce.

R-strategies R-strategies Short life spanShort life span Reproduce and mature early and have Reproduce and mature early and have

many offspring with little or no parental many offspring with little or no parental care.care. Example cockroaches (Example cockroaches (American cockroach

, , Periplaneta americanaPeriplaneta americana, ), )

K-strategies – organisms that grow K-strategies – organisms that grow slowly with long life span, fewer slowly with long life span, fewer offspring, slow maturing process and offspring, slow maturing process and reproduction late in life. reproduction late in life. Example Example Fin WhaleFin Whale ( (Balaenoptera Balaenoptera

physalusphysalus) )