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

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

Population Dynamics

Chapter 6


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


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.


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


Population Measures

• Doubling Time of a population: 70/annual percentage growth rate.

• Biotic Potential - Maximum reproductive rate of an organism.



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.



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.


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.


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.


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


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


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.


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.


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


Survivorship Curves


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.


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.



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.


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.


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


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


Documents

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