Are we over carrying capacity?
Population density/consumption patterns
Quality of life issues
Impact on landscapes & resources
Lake Chad
What is “overpopulation”?
how does it occur?
6
Outline
Basic Dynamics of Population Growth
– Exponential vs. Arithmetic Growth
– Malthusian vs. Logistic Growth
Complex Patterns of Population Change
Regulating Population Growth
– Density Dependence vs. Independence
How do we apply possibilities to a specific
case?
DYNAMICS OF POPULATION
GROWTH
Exponential Growth - Growth at a constant
rate of increase per unit time (Geometric)
Arithmetic Growth - Growth at a constant
amount per unit time (independent of base)
Exponential Growth and Doubling
Times
Number of individuals added to a
population at the beginning of exponential
growth is relatively small.
But numbers increase quickly as the
reproductive base of the population grows.
– J curve is the result of exponential growth
Doubling Time of a population:
– 70/annual percentage growth rate.
Irruptive Growth
Malthusian Growth (Irruptive) - Population
explosions followed by population crashes.
– Malthus concluded human populations tend to grow
exponentially until they exhaust their resources and
then crash.
– Non-human examples are common, but may be
influenced by predators or parasites, not just resources
Irruptive population examples
Malthusian Strategies
Short life
Rapid growth
Early maturity
Many small
offspring
Little parental care
Little investment in
individual offspring.
Adapted to
unstable
environment.
Pioneers,
colonizers
Niche generalists
Prey
Regulated mainly
by extrinsic factors.
Low trophic level
Biotic Potential and Carrying Capacity
Biotic Potential - Maximum reproductive rate of
an organism (births minus deaths in optimal
conditions).
Carrying Capacity - Maximum number of
individuals of any species that can be indefinitely
supported
Growth to a Stable Population
Logistic Growth - Growth rates regulated
by internal and external factors until
coming into equilibrium with environmental
resources.
– Growth rate slows as population approaches
carrying capacity.
– S curve
Environmental Resistance - Any
environmental factor that reduces
population growth.
Logistic Strategies
Long life
Slower growth
Late maturity
Fewer large
offspring
High parental care
and protection.
High investment in
individual offspring.
Adapted to stable
environment.
Later stages of
succession.
Niche specialists
Predators
Regulated mainly
by intrinsic factors.
High trophic level
Population Oscillations around Carrying
Capacity
Overshoot - Measure of extent to which
population exceeds carrying capacity of its
environment.
Dieback - Negative growth curve.
– Severity of dieback generally related to the
extent of overshoot.
FACTORS THAT ADD TO
POPULATIONS
Natality - Production of new individuals .
– Fecundity - Physical ability to reproduce.
– Fertility - Measure of actual number of
offspring produced.
Immigration - Organisms introduced into
new ecosystems.
LOSSES: Mortality and Emigration
Mortality - Death Rate.
– Survivorship - Percentage of cohort surviving to a
certain age.
– Life expectancy - Probable number of years of
survival for an individual of a given age.
Increases as humans age.
– Life Span - Longest period of life reached by a
given type of organism.
Emigration - Movement of individuals out of a
population.
FACTORS THAT REGULATE
ADDITIONS AND LOSSES
Intrinsic factors - Operate within or between
individual organisms in the same species.
Extrinsic factors - Imposed from outside the
population.
Biotic factors - Caused by living organisms.
Abiotic factors - Caused by non-living
environmental components.
Density-Independent Regulatory
Factors
Constant proportion of the population is
affected regardless of population density.
Tend to be abiotic components affecting
mortality.
The risk (per individual) is unrelated to the
density of individuals (e.g, tsunami).
Density-Dependent Factors
Intensity changes as the population
density changes.
Tend to reduce population size by
decreasing natality or increasing mortality.
– Interspecific Interactions
Predator-Prey oscillations
– Intraspecific Interactions
Territoriality
– Stress and Crowding
Stress-related diseases
Given a long list of possible factors promoting
growth, for a specific case, what leads to
overpopulation or extinction?
Identify most likely influences
– (create a simplified “model”)
Test the predictions of the model
Example, what are the most likely
influences on population levels of Whitetailed Deer in Knox County?