1. Population Dynamics

2. Outline
Dynamics of Population Growth
Exponential vs. Arithmetic Growth
Malthusian vs. Logistic Growth
Population Increase
Population Decrease
Survivorship
Regulating Population Growth
Density Dependence vs. Independence
Conservation Biology

3. 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.

4. 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 population, and thus the given percentage of that population, grows.
J curve
Doubling Time of a population:
70/annual percentage growth rate.

5. Biotic Potential and Carrying Capacity
Biotic Potential - Maximum reproductive rate of an organism.
Carrying Capacity - Maximum number of individuals of any species that can be indefinitely supported in a given area.

6. Population Oscillations
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.

7. Irruptive Growth
Malthusian Growth (Irruptive) - Population explosions followed by population crashes.
Malthus concluded human populations tend to grow until they exhaust their resources and then crash.

8. 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.

9. 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

10. 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

11. FACTORS THAT INCREASE OR DECREASE 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.

12. Mortality, Survivorship, 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.

13. Survivorship Curves
Four general patterns:
Full physiological life span.
Probability of death unrelated to age.
Mortality peaks both early and late in life.
Mortality peaks early in life.

14. Survivorship Curves

15. FACTORS THAT REGULATE POPULATION GROWTH
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.

16. Density Independent Factors
Constant proportion of the population is affected regardless of population density.
Tend to be abiotic components.
Do not directly regulate population size.

17. Density Dependent Factors
Higher proportion of population is affected as population density increases.
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

18. CONSERVATION BIOLOGY
Island biogeography - Small islands far from a mainland have fewer terrestrial species than larger, closer islands.
MacArthur and Wilson proposed that species diversity is a balance between colonization and extinction rates.

19. Conservation Genetics
Genetic Drift
Random reduction in gene frequency.
Founder Effect
Few individuals start a new population.
Demographic Bottleneck
Few individuals survive catastrophe.
Inbreeding
Mating between related individuals.

20. Genetic Drift

21. Population Viability Analysis
Minimum Viable Population is the minimum population size required for long-term viability of a species.

22. Metapopulations
A collection of populations that have regular or intermittent gene flow between geographically separate units.
Bay Checkerspot Butterfly
Source - Sink Model

23. Summary
Dynamics of Population Growth
Exponential vs. Arithmetic Growth
Malthusian vs. Logistic Growth
Population Increase
Population Decrease
Survivorship
Regulating Population Growth
Density Dependence vs. Independence
Conservation Biology