Ecology

• Population


  All the individuals of a species that live together in one place at one time
• Population growth and decline

  • Depend on the stability of an organism's food chain
  • Small populations tend to be more endangered from natural disturbances than large populations
  • Small populations tend to experience more inbreeding, reducing fitness
• Factors determining population growth

  1. Number of births

  2. Number of deaths

  3. Number of individuals that enter or leave a population
• r (rate of growth)

  Birthrate - death rate
• Immigration


  Movement of individuals into an area (growth)
• Emigration


  Movement of individuals out of an area (decline)
• Exponential growth


  • If conditions are ideal with unlimited resources, a population will grow exponentially
  • Resembles J-shaped curve
• Logistic growth


  • Slow growth that is controlled by the availability of resources
  • Resembles a stretched out letter S
• Carrying capacity


  The largest population size that a given environment can sustain
• Population density


  The number of individuals that live in a given area
• Geographic distribution (dispersion)


  The area inhabited by a population
• Limiting factor


  An aspect that causes population growth to decrease
• Density-dependent factors


  • Limited resources whose rates of depletion depend on the density of the population using them
  • Competition is a major force for evolutionary change
• Predation-prey relationship


  • The numbers increase or decrease depending on the abundance of resources
  • The cycle of predator and prey populations repeats indefinitely unless an outside force interferes with the natural sequence
• Parasitism


  Similar to predators in that they often weaken the host causing disease or death (decline)
• Density-independent factors


  • Growth is limited by environmental conditions
  • Conditions include unusual weather, natural disasters, seasonal cycles, and human activities
• The size of the human population tends to increase with time
• Birthrates, death rates, and the age structure of a population help predict why some countries have high growth rates while other countries grow more slowly
• Earth's main resources necessary for long term survival of humans and other species

  • Breathable air
  • Drinkable water
  • Fertile soil
• Human activities that affect the biosphere

  • Hunting and gathering
  • Agriculture
  • Industry and urban development
• Renewable resources


  Can regenerate if they are alive or can be replenished by biogeochemical cycles if they are nonliving
• Human activities can affect the quality and supply of renewable resources such as land, forests, fisheries, air, and fresh water
• Nonrenewable resources


  Cannot be replenished by natural processes (e.g. fossil fuels, coal, oil, and natural gas)
• Sustainable development


  A way of using natural resources without depleting them, providing for human needs without causing long term environmental harm
• Biodiversity is one of Earth's greatest natural resources
• Benefits of biodiversity


  • Foods
  • Industrial products
  • Medicines
• Biodiversity can be reduced by altering habitats, hunting species to extinction, introducing toxic compounds into food webs, and introducing foreign species to new environments
• Endangered species


  A species whose population size is declining in a way that places it in danger of extinction
• Extinction


  When an organism disappears from all or part of its range forever
• Weather


  The day-to-day condition of Earth's atmosphere at a particular time and place
• Climate


  The average, year-to-year conditions of temperature and precipitation in a particular region
• Main climate zones


  • Polar
  • Temperate
  • Tropical
• Angle of sunlight directed at different latitudes


  Results in the delivery of more heat to the equator than to the poles
• Greenhouse effect


  CO2, H2O vapor, methane, and other gases in the atmosphere allow solar radiation to enter the biosphere but slows the loss of heat to space
• Greenhouse effect helps maintain Earth's temperature range
• Transport of heat


  Unequal heating of the Earth's surface drives wind and ocean currents
• Land masses can interfere with the movement of air
• Biotic factors


  All living organisms in an ecological community
• Abiotic factors


  Nonliving factors such as climate, land masses, soil, etc.
• Together, biotic & abiotic factors determine the survival of an organism