Population Dynamics

1. Population Dynamics Chapter 6 Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

2. Outline: • Dynamics of Population Growth • Exponential vs. Arithmetic Growth • Malthusian vs. Logistic Growth • Population Increase • Population Decrease • Survivorship • Age Structure • Regulating Population Growth • Density Dependence vs. Independence Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

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. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

4. Exponential Growth • 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-shaped curve Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

5. Population Measures • Doubling Time of a population: • 70/annual percentage growth rate. • Biotic Potential - Maximum reproductive rate of an organism. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

6. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

7. 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. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

8. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

9. Malthusian Growth • Malthusian Growth (Irruptive Growth) - Population explosions followed by population crashes. • Malthus concluded human populations tend to grow until they exhaust their resources and then crash. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

10. Logistic Growth • Logistic Growth - Growth rates regulated by internal and external factors until come into equilibrium with environmental resources. • Growth rate slows as population approaches carrying capacity. • S-Shaped curve • Environmental Resistance - Any environmental factor that reduces population growth. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

11. Chaotic and Catastrophic Dynamics • Chaotic Systems - Exhibit variability in a complex pattern not observable under normal human scales. • Edward Lorenz - Butterfly effect. • Catastrophic System - May jump from one steady state to another without any intermediate stages. • Balancing chair on two legs. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

12. 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 Malthusian Strategies Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

13. 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 Logistic Strategies Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

14. FACTORS INCREASING OR DECREASING 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. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

15. Population Decrease • 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. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

16. 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 Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

17. Survivorship Curves Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

18. Age Structure • Growing or declining populations usually have very different proportions of individuals in various age classes. • Rapidly expanding populations - Have large number of pre-reproductive individuals and thus have population momentum. • Diagram shows large base. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

19. Age Structure • Stationary Populations - Balanced when natality and mortality are equivalent. • Diagram shows no bulges. • Diminishing Populations - Natality has fallen below replacement level. • Diagram shows bulge in upper age classes. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

20. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

21. REGULATING 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. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

22. 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. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

23. Density Dependent Factors • Higher proportion of population is affected as population density increases. • Tend to reduce population size by decreasing natality or increasing mortality as population size increases. • Interspecific Interactions • Predator Prey oscillations • Intraspecific Interactions • Territoriality • Stress-related diseases Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

24. Summary: • Dynamics of Population Growth • Exponential vs. Arithmetic Growth • Malthusian vs. Logistic Growth • Population Increase • Population Decrease • Survivorship • Age Structure • Regulating Population Growth • Density Dependence vs. Independence Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

25. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.