cunningham - cunningham - saigo: environmental science 7 th ed. population dynamics chapter 6
TRANSCRIPT
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Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Population Dynamics
Chapter 6
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Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
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
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Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
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.
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Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
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
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Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Population Measures
• Doubling Time of a population: 70/annual percentage growth rate.
• Biotic Potential - Maximum reproductive rate of an organism.
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Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
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Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
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.
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Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
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Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
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.
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Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
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.
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Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
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.
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Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
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
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Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
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
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Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
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.
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Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
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.
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Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
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
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Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Survivorship Curves
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Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
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.
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Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
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.
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Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
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Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
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.
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Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
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.
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Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
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
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Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
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
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Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.