Population Growth
Chapter 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 nonnative 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