Transcript Population Size Factors

Population Growth Patterns
Population Size Factors
• Population sizes change based on resources
• Increase
– Immigration
– Births
• Decrease
– Emigration
– Deaths
Exponential Growth
• Growth rates
determined by
abundant resources
• Dramatic population
increases over time
• J-shaped curve
Logistic Growth
• Most populations
faced with limited
resources
– Factors: Disease, food,
predators, climate, space, mates
• Three stages
– 1) Slow growth
– 2) Exponential growth
– 3) Carrying Capacity:
greatest number of
individuals that a
population can sustain
• S-shaped curve
Population Crash
• Defined: Dramatic decline in the size of a population
• Usually over a short time period
• Causes: Environment changes, drop in resources
Limiting Factors
• Density Dependent:
factors that are affected
by the individuals in a
given area
–
–
–
–
Competition
Predation
Parasitism
Disease
• Density Independent:
environmental factors
that limit populations
– Climate/weather
– Natural disasters
– Human activity
Density Dependent
• Top graph: Two
species of
Paramecia were
grown in two
separate containers.
Both populations
thrived.
• Bottom graph: Due
to competition,
Paramecium
caudatum crashed
when grown in the
presence of
Paramecium aurelia
Density Independent
• This graph shows the decline
in the population of one of
Darwin's finches on Daphne
Major, a tiny (100-acre)
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.