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Population Dynamics

Population Dynamics. Exponential Growth and Doubling Times. Exponential Growth: Growth at a constant rate of increase per unit of time Geometric Growth: Same as exponential growth Sequence of growth follows a geometric pattern of increase

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Population Dynamics

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  1. Population Dynamics

  2. Exponential Growth and Doubling Times • Exponential Growth: Growth at a constant rate of increase per unit of time • Geometric Growth: Same as exponential growth • Sequence of growth follows a geometric pattern of increase • Arithmetic Growth: Growth increases at a constant amount per unit of time 6.4

  3. J curve: Growth curve produced by a constant rate of growth • Represents theoretical unlimited growth • It represents the biotic potential

  4. Biotic Potential • The maximum reproductive rate of an organism having no limiting factors. • If all the individuals in the population survived and reproduced at the maximum rate. • It is a reference value allowing one to determine if the observed growth rate is close to the biotic potential.

  5. Population Oscillations and Irruptive Growth • Dieback: When death rates begin to surpass birth rates • Overshoot: The extent to which a population exceeds the carrying capacity of its environment • Malthusian (Irruptive) Growth:Pattern of population explosion followed by a population crash

  6. Growth to a Stable Population • Logistic Growth:Constantly changing rate • When growth slows as populations approach the carrying capacity of the environment • Environmental Resistance: Factors that tend to reduce population growth rates 6.7 • S curve: Population growth and stabilization in response to environmental resistance

  7. Carrying capacity • The maximum number of individuals of a certain species that an environment can support. • It reflects the limits imposed on population growth by finite space and finite resources.

  8. Lifestyle greatly affects carrying capacity It is estimated that 10-15 acres are necessary to sustain one person with an affluent lifestyle To support the 5.6 billion humans at such a lifestyle would require 3 times as much productive land In these terms, the earth can support only 1.8 billion people

  9. Environmental resistance can include any of the following. • food runs out • waste accumulates and becomes toxic • living space runs out • over-crowding makes the population an easy target for parasites and predators • disease • predation

  10. Calculating % Growth Rates (GR) • Population Growth for a Specific Location % GR= (birth +immigration)- (deaths+emmigration) 100

  11. % Global Population Growth Rate % growth rate = (birth rate %-death rate percent) i.e. 6 births/100 people each year 4 deaths/100 people each year this is a rate of increase of 2%

  12. Calculating Doubling Time DT = _____70_____ % growth rate 70 is a demographic constant

  13. Factors that Increase or Decrease Populations • Natality , Fecundity and Fertility • Immigration and Emigration • Mortality and Survivorship • Age Structure

  14. Natality, Fecundity, and Fertility • Natality: Production of new individuals by birth, hatching, germination, or cloning • Main source of addition to most biological populations • Fecundity: Physical ability to reproduce “Potential” • Fertility: Measure of actual number of offspring produced “Actual or Realized”

  15. Migration • Immigration: movement of organisms into a new ecosystem • Emigration: movement of organisms outof an ecosystem **Migration is not a factor when determining Global Population Growth Rates

  16. Mortality and Survivorship • Mortality: Death rate • Determined by dividing number of organisms that die in a certain time period by the number alive at the beginning of the period 6.9 • Survivorship: Percentage of a cohort that survives to a certain age

  17. Life Span vs Life Expectancy • Life Span: Longest period of life reached by a given type of organism 6.10 • Life Expectancy: The probable # of years of survival for an individual of a given age

  18. Age Structure • Population Momentum: Large number of prereproductive individuals • Rapid increase in natality once youngsters reach reproductive age 6.11

  19. Factors That Regulate Population Growth • Density-Dependent: Effects are stronger or a higher proportion of the population is affected as population density increases • Density-Independent: The effect is the same or a constant proportion of the population is affected regardless of population density

  20. More….. • Intrinsic: Factors operating within individual organisms or between organisms in the same species • Extrinsic: Imposed from outside the population • Biotic: Caused by living organisms • Abiotic: Caused by nonliving components of the environment

  21. Characteristics of contrasting reproductive strategies

  22. Density-Independent Factors • Factors that affect natality of mortality independently of populations density abiotic

  23. Density-Dependent Factors • Factors that reduce population size by decreasing natality or increasing mortality • Tend to be biotic • Interspecific Interactions: Two species compete for the same environmental resources in an ecosystem 6.12 • May be beneficial or neutral, such as mutualism

  24. Intraspecific Interactions • Individuals within a population compete for resources • Territoriality is an example • Stress and Crowding • Stress Shock: A loose set of physical, psychological, and/or behavioral changes thought to result from the stress of excess competition and extreme closeness to other members of the same species

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