13.1 Population growth

Terms Explain biotic potential (r) Environmental resistance on population growthCarrying capacityNatality and mortalityGrowth curveExponential growth curveLogistic growth curveDensity dependent factorsDensity independent factors

• PopulationPopulation: group of individuals of the same species that live in a habitat

Population ecologyPopulation ecology studies interactions between members of a population & examines factors that affect population size (growth) & composition

Population growth involves:

i. biotic potential

ii. environmental resistance

iii. carrying capacity

iv. natality & mortality

v. population strategy

13.1 Population growth…13.1 Population growth…

• ‘The increase in the number of individuals of a population’

Growth at biotic potential

Growth with environmental resistance

(carrying capacity)

BIOTIC POTENTIAL ( BIOTIC POTENTIAL ( r r ))

• ‘The capacitycapacity of a population to increase in size to increase in size in ideal / optimum conditionsin ideal / optimum conditions’

• Gives the maximum rate for population growthmaximum rate for population growth when population density is low & resources are plentiful

• Described by a J-shaped growth curveJ-shaped growth curve

ENVIRONMENTAL RESISTANCEENVIRONMENTAL RESISTANCE

• ‘Environmental factorsEnvironmental factors that limit growthlimit growth of the population’

• The population will not be able to achieve its full biotic potential

• Growth rate may become zero

• Described by an S-shaped growth curveS-shaped growth curve

• Eg of environmental resistance: limiting resources (food, light, shelter), accumulating toxic waste, stress, predation & diseases

CARRYING CAPACITYCARRYING CAPACITY

• ‘The maximum population sizemaximum population size that a particular environment can supportenvironment can support’

• The area occupied by a population has limiting resources (eg: predation, disease,food, shelter, water and light)

• Carrying capacity is achieved when population growth slows & maintains at a nearly steady level

• Described by the stable equilibrium phaseequilibrium phase of the S-shaped growth curve

NATALITY & MORTALITYNATALITY & MORTALITY

• Natality: - ‘birth rate’

- the number of offspring producednumber of offspring produced during

a certain amount of time

• Mortality: - ‘death rate’

- the number of individuals dyingnumber of individuals dying during a

certain amount of time

• If natality > mortality, population size increases• If mortality > natality, population size decreases• If natality = mortality, population is stable

• Patterns of population growth are described by:

i. Exponential growth curve ( human population )

ii. Logistic growth curve ( S-shape:Paramecium )

Exponential Growth Curve (human population )Exponential Growth Curve (human population )

• The population size increases slowly during lag phase & then continuously grows very rapidly as time passes (log phase)

• Eg: human population growth

Logistic Growth Curve ( S-shape )Logistic Growth Curve ( S-shape )

• Consists of:

i. lag phaselag phase (individuals start to grow as they are adapting to the environment)

ii. exponential growth phaseexponential growth phase (growth is rapid as resources are still unlimited)

iii. linear phaselinear phase (environmental resistance starts to take effect as population approaching the carrying capacity)

iv. equilibrium phaseequilibrium phase (population becomes stable)• Eg: population growth of Paramecium in the lab shows

the S-shaped growth curve

LIMITING FACTORS AFFECTING THE LIMITING FACTORS AFFECTING THE POPULATION SIZEPOPULATION SIZE

• 2 types of limiting factors:

i. Density dependent factors Density dependent factors

- factors that limit population growth when population density / size increases

-eg: niche( predator-prey relationship, habitat ) territorial behaviour, competition and interspecific factors)

ii. Density independent factors Density independent factors

- factors that limit population growth irrespective of population size

- due to events that occur seasonally or unexpectedly

-eg: climate, natural disasters and pesticides )

Examples of Density dependent factors Density dependent factors

a) competitioncompetition- when pop. size ↑, competition ↑ for limited sources;

causing a decrease in pop. growth- 2 types (intraspecific & interspecific)

b) territorial behaviourterritorial behaviour- individuals (individually or in groups) select & defend a

territory large enough to provide basic necessities - the larger & more productive the territory, the better it is for

population growth

c) predator – prey relationshippredator – prey relationship- when pop. of prey ↑, pop. of predators ↑ & when pop. of

prey ↓, pop. of predators ↓

- usually shows fluctuation in pop. growth for both predators &

prey

• Example of independent factors

a) climate / weather climate / weather

b) natural disastersnatural disasters

d) pesticides