Are we over carrying capacity?
Population density/consumption patterns
Quality of life issues
Impact on landscapes & resourcesLake Chad
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What is “overpopulation”?
how does it occur?
Outline
Basic Dynamics of Population Growth– Exponential vs. Arithmetic Growth– Malthusian vs. Logistic Growth
Complex Patterns of Population ChangeRegulating 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 lifeRapid growthEarly maturityMany small offspringLittle parental careLittle investment in individual offspring.
Adapted to unstable environment.Pioneers, colonizersNiche generalistsPreyRegulated mainly by extrinsic factors.Low trophic level
Biotic Potential and Carrying CapacityBiotic 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 lifeSlower growthLate maturityFewer large offspringHigh parental care and protection.High investment in individual offspring.
Adapted to stable environment.Later stages of succession.Niche specialistsPredatorsRegulated 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 White-tailed Deer in Knox County?