ch 18

• Ecology


  The study of interactions of living organisms with each other and with their environment
• Levels of ecology


  • Organism
  • Population
  • Community
  • Biome
  • Ecosystem
• Population


  All members of a species that inhabit a specific geographical area at a specific time
• Community


  A collection of the populations of all species that inhabit a specific geographical area
• Biome


  A large area characterized by a particular climate & vegetation
• Ecosystem


  An interactive collection of all of Earth's ecosystems/ biomes
• Population density


  The number of individuals of a species per unit land area or unit aquatic volume of habitat
• Measuring population density


  1. Quadrat sampling

  2. Line transect sampling

  3. Animal trapping
• Birth rate


  Number of births in a given time period divided by population size
• Death rate


  Number of deaths in a given time period divided by population size
• Intrinsic growth rate (r)


  Birth rate - Death rate
• Intrinsic growth rate (r)


  • If r>0, population grows
  • If r=0, population equilibrium
  • If r<0, population shrinks

  
• Intrinsic growth rate does not include migration into/out of population
• Intrinsic growth rate calculation


  • Population has 1000 individuals
  • 100 births in a year
  • Birth rate = 0.1
  • 80 deaths in a year
  • Death rate = 0.08
  • Intrinsic growth rate r = 0.1 - 0.08 = 0.02 or 2%

  
• Many young individuals indicates future population growth, few young and increased older individuals indicates future population declines
• Survivorship curve


  Shows the proportion of individuals alive at each age group in a population
• Three general patterns of survivorship curves


  • Type I
  • Type II
  • Type III
• Life history


  Summarizes typical events in an organism's life, including rate of development, average life span, social structure, reproductive events, and parental care
• Opportunistic (r-selected) species


  Live fast and cheap, proliferate when conditions are good
• Equilibrium (K-selected) species


  Live slow but expensive, can persist in good and bad conditions
• Survivorship curves can indicate general patterns in life history strategy
• Arithmetic growth


  A constant increase per unit time, not relevant to biological population growth
• Exponential growth


  An increase proportional to population size, usually occurs when resources are unlimited

  
• Logistic growth


  1. shaped curve where population growth slows as the population size approaches the environment's carrying capacity (K)
• Carrying capacity (K)


  The population size the environment can sustain
• Biotic factors


  Influence population size as it grows, e.g. a pathogen may kill more of a population when the density is high
• Abiotic factors


  Influence population size randomly, affecting all individuals equally regardless of population density
• Not all organisms follow predictable growth curves, some exhibit population cycles due to species interactions
• Less developed countries typically have higher birth rates and are projected to contribute most to global population growth in coming years
• Demographic transition


  A process required in many areas to reduce global population growth rates
• Demographic transitions typically occur in 3 stages as a country develops economically
• Leading causes of death in humans

  • High-income countries
  • Low-income countries
• Ecological footprint


  Estimates the average quantity of resources needed to support an individual's lifestyle in a particular country, including land use and energy consumption
• Ecological footprint increases with wealth and/or total population size