Population
Dynamics
Exponential Growth and
Doubling Times
Exponential Growth: Growth at a constant
rate of increase per unit of time
 Geometric Growth: Same as exponential
growth

–

Sequence of growth follows a geometric pattern
of increase
Arithmetic Growth: Growth increases at a
constant amount per unit of time 6.4

J curve: Growth curve produced by a
constant rate of growth
–
–
Represents theoretical unlimited growth
It represents the biotic potential
Biotic Potential
The maximum reproductive rate of an
organism having no limiting factors.
 If all the individuals in the population survived
and reproduced at the maximum rate.
 It is a reference value allowing one to
determine if the observed growth rate is close
to the biotic potential.

Population Oscillations and
Irruptive Growth
Dieback: When death rates begin to surpass
birth rates
 Overshoot: The extent to which a
population exceeds the carrying capacity of
its environment
 Malthusian (Irruptive) Growth: Pattern of
population explosion followed by a
population crash

Growth to a Stable Population

Logistic Growth: Constantly changing rate
–
When growth slows as populations approach
the carrying capacity of the environment
Environmental Resistance: Factors that
tend to reduce population growth rates 6.7
 S curve: Population growth and
stabilization in response to environmental
resistance

Carrying capacity
The maximum number of individuals of a
certain species that an environment can
support.
 It reflects the limits imposed on population
growth by finite space and finite resources.

Lifestyle greatly affects
carrying capacity
It is estimated that 10-15 acres are necessary
to sustain one person with an affluent
lifestyle
To support the 5.6 billion humans at such a
lifestyle would require 3 times as much
productive land
In these terms, the earth can support only 1.8
billion people
Environmental resistance can
include any of the following.
food runs out
 waste accumulates and becomes toxic
 living space runs out
 over-crowding makes the population an
easy target for parasites and predators
 disease
 predation

Calculating % Growth Rates (GR)

Population Growth for a Specific Location
% GR= (birth +immigration)- (deaths+emmigration)
100
% Global Population Growth Rate
% growth rate = (birth rate %-death rate
percent)
i.e.
6 births/100 people each year
4 deaths/100 people each year
this is a rate of increase of 2%
Calculating Doubling Time
DT =
_____70_____
% growth rate
70 is a demographic constant
Factors that Increase or Decrease
Populations
Natality , Fecundity and Fertility
 Immigration and Emigration
 Mortality and Survivorship
 Age Structure

Natality, Fecundity, and
Fertility

Natality: Production of new individuals by
birth, hatching, germination, or cloning
–
Main source of addition to most biological
populations
Fecundity: Physical ability to reproduce
“Potential”
 Fertility: Measure of actual number of
offspring produced “Actual or Realized”

Migration

Immigration: movement of organisms into
a new ecosystem

Emigration: movement of organisms out of
an ecosystem
**Migration is not a factor when determining Global
Population Growth Rates
Mortality and Survivorship

Mortality: Death rate
–

Determined by dividing number of organisms
that die in a certain time period by the number
alive at the beginning of the period 6.9
Survivorship: Percentage of a cohort that
survives to a certain age
Life Span vs Life Expectancy
Life Span: Longest period of life reached
by a given type of organism 6.10
 Life Expectancy: The probable # of years
of survival for an individual of a given age

Age Structure

Population Momentum: Large number of
prereproductive individuals
–
Rapid increase in natality once youngsters
reach reproductive age 6.11
Factors That Regulate
Population Growth
Density-Dependent: Effects are stronger
or a higher proportion of the population is
affected as population density increases
 Density-Independent: The effect is the
same or a constant proportion of the
population is affected regardless of
population density

More…..
Intrinsic: Factors operating within
individual organisms or between organisms
in the same species
 Extrinsic: Imposed from outside the
population
 Biotic: Caused by living organisms
 Abiotic: Caused by nonliving components
of the environment

Characteristics of contrasting
reproductive strategies
Extrinsically Controlled Growth Intrinsically Controlled Growth
Short Life
Long Life
Rapid growth
Slower growth
Early maturity
Late maturity
Little parental care or protection
High parental care and protection
Little investment in individual offspring
High investment in individual offspring
Adapted to unstable environment
Adapted to stable environment
Pioneers, colonizers
Later Stages of succession
Niche generalists
Niche specialist
Prey
Predators
Regulated mainly by extrinsic factors
Regulated mainly by intrinsic factors
Low trophic levels
High trophic levels
Density-Independent Factors

Factors that affect natality of mortality
independently of populations density
abiotic
Density-Dependent Factors

Factors that reduce population size by
decreasing natality or increasing mortality
–

Tend to be biotic
Interspecific Interactions: Two species
compete for the same environmental
resources in an ecosystem 6.12
–
May be beneficial or neutral, such as mutualism

Intraspecific Interactions
–
–

Individuals within a population compete for
resources
Territoriality is an example
Stress and Crowding
–
Stress Shock: A loose set of physical,
psychological, and/or behavioral changes
thought to result from the stress of excess
competition and extreme closeness to other
members of the same species