unregulated population growth

• Demography


  The study of population vital statistic and how they vary with age
• Life table


  Age-specific summary of the vital statistics of a population
• Cohort


  A group of individuals in a population born about the same time
• Survivorship (Ix)


  Proportion of individuals born that survive to age x
• Survivorship curves


  • Type I: Low death rates during early and middle life and a sharp increase in death rates later in life
  • Type II: Constant death rate over the life span
  • Type III: High death rates for the young; death rate steeply declines for survivors of early period die-off
• Reproductive table


  An age-specific summary of the reproductive rates in a population
• Exponential population growth


  Growth of a population with continuous generations in an ideal, unlimited environment, represented by a J-shaped curve when population size is plotted over time

  
• Geometric population growth


  Growth of a population with discrete generations in an ideal, unlimited environment
• Discrete generations


  Generations that have no overlap in reproduction
• Populations have the potential to expand greatly when resources are abundant
• Unregulated population growth in discrete time intervals = geometric growth

  
• Unregulated population growth in continuous time intervals = exponential growth

  
• Changes in population size

  Births + Immigrants entering population - Deaths - Emigrants leaving population = Change in population size
• Net reproductive rate (R0)

  • R0 < 1, population is decreasing
  • R0 = 1, population is stable
  • R0 > 1, population is increasing
• Instantaneous growth rate or intrinsic rate of increase (r)

  • r < 0, population is decreasing
  • r = 0, population is stable
  • r > 0, population is increasing

  
• Exponential population growth results in a J-shaped curve

  
• Unregulated population growth is characteristic of populations that are introduced to a new environment or rebounding after drastic reduction by a catastrophic event or experiencing a pulse of new nutrients
• Increasing population size gives rise to shortages in food and other limiting resources, greater intraspecific aggression, increased attention from predators, and greater risk of disease outbreaks, which can lower birth rates and elevate death rates