CHAPTER 3

• Tropical rain forests


  • Cover only about 7% of the earth's land
  • Contain up to one-half of the world's known terrestrial plant and animal species
• Disruption of tropical rain forests

  • Reduces biodiversity
  • Accelerates climate change
  • Changes regional weather patterns
• Major components of the earth's life-support system

  • Atmosphere (air)
  • Hydrosphere (water)
  • Geosphere (rocks, minerals, and soil)
  • Biosphere (living things)
• Troposphere


  Innermost layer of the atmosphere, contains the air we breathe
• Stratosphere


  Contains the ozone layer, filters sun's harmful UV radiation
• Hydrosphere


  All water vapor, liquid water, and ice
• Oceans contain 97% of the planet's water
• Geosphere


  Upper portion of crust contains nutrients organisms need to live, grow, and reproduce
• Biosphere


  Parts of atmosphere, hydrosphere, and geosphere where life is found
• Factors that sustain the Earth's life

  • One-way flow of high-quality energy from the sun
  • Cycling of nutrients through parts of the biosphere
  • Gravity holds the earth's atmosphere
• Levels of matter studied by ecologists

  • Biosphere
  • Ecosystems
  • Communities
  • Populations
  • Organisms
• Producers (autotrophs)


  Organisms that make needed nutrients from their environment through photosynthesis
• Consumers (heterotrophs)


  Organisms that cannot produce the nutrients they need
• Types of consumers


  • Primary consumers (herbivores)
  • Carnivores
  • Omnivores
• Decomposers


  Consumers that release nutrients from wastes or remains of plants or animals
• Aerobic respiration


  Using oxygen to turn glucose back to carbon dioxide and water, releases energy
• Anaerobic respiration and fermentation

  Used by some decomposers in the absence of oxygen, releases methane gas, ethyl alcohol, acetic acid, and hydrogen sulfide
• Soil


  • Complex mixture of rock, particles, mineral nutrients, organic matter, water, air, and living organisms
  • Soil formation begins with weathering of bedrock into small pieces
  • Mature soils contain several layers (horizons) that differ in texture, composition, and thickness
• Formation of 1 inch of topsoil can take hundreds to thousands of years
• Soil becomes nonrenewable if we deplete faster than it can be replenished
• Food chain


  Movement of energy and nutrients from one trophic level to the next

  
• Food web


  Network of interconnected food chains
• Every use and transfer of energy involves energy loss as heat
• Pyramid of energy flow

  90% of energy lost with each transfer, less chemical energy for higher trophic levels
• Biomass


  Total mass of organisms in a given trophic level
• Gross primary productivity (GPP) is the rate at which an ecosystem's producers convert solar energy to stored chemical energy, measured in units such as kcal/m2/year
• Net primary productivity (NPP)


  The rate at which an ecosystem's producers convert solar energy to chemical energy, minus the rate at which they use the stored energy for aerobic respiration
• Terrestrial ecosystems and aquatic life zones differ in their NPP
• The planet's NPP ultimately limits the number of consumers (including humans) that can survive on the earth
• Nutrients cycle within and among ecosystems, driven by incoming solar energy and gravity, and can be altered by human activity
• Nutrient cycles

  • Water
  • Carbon
  • Nitrogen
  • Phosphorus
• The water cycle

  1. Evaporation

  2. Precipitation

  3. Surface runoff

  4. Groundwater storage
• Ways humans alter the water cycle

  • Withdrawing large amounts of freshwater at rates faster than nature can replace it
  • Clearing vegetation, increasing runoff and decreasing infiltration
  • Draining and filling wetlands for farming and urban development, reducing flood control and water absorption
• Properties of water include being a liquid over a large temperature range, storing a large amount of heat, taking lots of energy to evaporate, dissolving a variety of compounds, filtering out UV radiation, and expanding when it freezes
• The carbon cycle

  1. Photosynthesis removes CO2 from atmosphere

  2. Aerobic respiration adds CO2 to atmosphere

  3. Carbon in dead plant matter and algae converted to fossil fuels over millions of years

  4. Some CO2 dissolves in the ocean and is stored in marine sediments

  
• Humans have added large quantities of CO2 to the atmosphere at a faster rate than natural processes can remove, resulting in a warming atmosphere and changing climate
• Clearing vegetation reduces the ability to remove excess CO2 from the atmosphere
• The nitrogen cycle

  1. Lightning and specialized bacteria convert atmospheric nitrogen to useful forms

  2. Plants use nitrogen compounds to produce proteins, nucleic acids, and vitamins

  3. Bacteria convert nitrogen compounds back into nitrogen gas
• Human alteration of the nitrogen cycle includes burning fuels creating nitric oxide, removing large amounts of nitrogen from the atmosphere to make fertilizers, and adding excess nitrates to aquatic ecosystems
• Human nitrogen inputs to the environment have risen sharply and are expected to continue rising