Are we over carrying capacity?

Population density/consumption patterns

Quality of life issues

Impact on landscapes & resourcesLake Chad

6

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 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 White-tailed Deer in Knox County?