Population Dynamics

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Population Dynamics
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Outline

• Dynamics of Population Growth
• Factors That Increase or Decrease Populations
• Factors That Regulate Population Growth
• Conservation Biology

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DYNAMICS OF POPULATION GROWTH

• Exponential Growth - Growth at a constant rate of
  increase per unit time. (Geometric)
• dN/dt rN

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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.

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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.

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Boom and Bust Cycles

• 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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Growth to a Stable Population

• Logistic Growth - Growth rates regulated by
  internal and external factors until coming into
  equilibrium with environmental resources.
• dN/dt r N (1 - N/K)
• Growth rate slows as population approaches
  carrying capacity.
• S curve
• Environmental Resistance - Any environmental
  factor that reduces population growth.

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r-Adapted Species

• 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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K-Adapted Species

• 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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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.

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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.

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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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Survivorship Curves
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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.

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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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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

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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.

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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.

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Genetic Drift
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Population Viability Analysis

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

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Metapopulations

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

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Summary

• Dynamics of Population Growth
• Factors That Increase or Decrease Populations
• Factors That Regulate Population Growth
• Conservation Biology

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