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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