Population GrowthChapter 14, sections 3, 4, and 5

Density• Population

density is a measurement of the number of individuals living in a defined space.

• # of individuals / area = population density

Geographic Dispersion• Population dispersion is the way in which

individuals of a population are spread out in an area.

Uniform dispersion Random dispersion Clumped dispersion

Population Disperson

• Clumped: individuals may live close together for mating, protection, food

• Uniform: territoriality / competition for limited resources cause individuals to live at specific distances from each other

• Random: individuals spread randomly within the area

Survivorship Curves• Number of surviving members over time

Survivorship Curves – Type I• Type I (i.e. –

humans): – Common for large

mammals – Low infant mortality– Population generally

survives to old age– Most parents care for

young (protection of young ensures they survive to adulthood

Survivorship Curves – Type II

• Type II Curves– Birds, small mammals,

some reptiles– Survivorship is roughly

the same throughout organism’s life (equal chance of living and dying)

Survivorship Curves – Type III• Type III

– High birth rate – High infant

mortality rate– Invertebrates,

fish, amphibians, plants

– Many will die from predation

– Some will survive to adulthood

Changes in Population Size• Increase in

Population Size– Immigration –

movement of individuals INTO a population

– Birth – additional individuals born

• Decrease in Population Size– Emigration –

movement of individuals OUT of population

– Death – individuals dying

J Curves (Exponential Growth)• Exponential Growth

Curve– Occurs when

resources are abundant

– Rapid growth occurs– Can occur when non-

native species is introduced to environment

– Often crashes when population outstrips resources

S Curves (Logistic Growth)• Logistic Growth

Curve:– Brief period of

slow growth– Brief period of

exponential growth

– Leveling off at a stable size

Carrying Capacity• Maximum number of

individuals of a particular species that the environment can normally and consistently support.

• This can change with changes in environmental conditions

• When capacity suddenly drops, the population can crash

Carrying capacity

Limiting Factors:

• Factors that limit the size of a population

• Two types:– Density –

Dependent (generally biotic)

– Density – Independent (generally abiotic)

Types of Limiting Factors

• Density Dependent: those whose impact worsens as the density of the population increases– Competition– Predation– Parasitism and

disease

• Density Independent: those whose limiting impact happens regardless of the population density– Unusual weather– Natural disasters– Human activities

Predator – Prey • Populations of

predators and their prey are closely linked – as the prey population rises, the predator population rises shortly after….then the prey population decreases and shortly after, the predator population decreases