Chapter 55

• An ecosystem consists of all the organisms living in matter an area, aswell as the abiotic factors with which they interact.
• The arctic fox was introduced on subarctic islands around 1900 to establish populations for the fur trade

  • surprising outcome: the conversion of grassland to tundra in many places on the island
• Arctic terns, a prey source for the foxes, and major guano generators that provide nutrients for grasslands
• Ecosystem dynamics involve two main processes: energy flow and chemical cycling.
• Energy flows through ecosystems, while chemicals cycle within ecosystems.
• Ecologists study the transformations of energy and matter in an ecosystem and map the movements of chemical elements.
• The first law of thermodynamics states that energy cannot be created or destroyed, only transferred or transformed.
• Energy enters an ecosystem as solar radiation, is conserved, and is lost from organisms as heat.
• The second law of thermodynamics states that every exchange of energy increases the entropy of the universe.
• In an ecosystem, energy conversions are not completely efficient; some energy is always lost as heat.
• The law of conservation of mass states that matter cannot be created or destroyed.
• Chemical elements are continually recycled within ecosystems.
• Ecosystems are open systems, absorbing energy and mass and releasing heat and waste products.
• Energy and nutrients pass from primary producers (autotrophs) to primary consumers (herbivores) to secondary consumers (carnivores) to tertiary consumers (carnivores that feed on other carnivores).
• Detritivores, or decomposers, are heterotrophs that derive their energy from detritus, nonliving organic matter.
• Prokaryotes and fungi are the main decomposers in ecosystems.
• In most ecosystems, primary production is the amount of light energy converted to chemical energy by autotrophs during a given time period.
• The amount of solar radiation reaching Earth’s surface limits the photosynthetic output of ecosystems.
• Only a small fraction of solar energy actually strikes photosynthetic organisms, and even less is of a usable wavelength. Only about 1% of light striking photosynthetic organisms is converted to chemical energy.
• Total primary production is known as the ecosystems gross primary production (GPP).
• GPP is measured as the conversion of energy from light (or chemicals) to the chemical energy of organic molecules per unit time.
• Net primary production (NPP) is GPP minus energy used by autotrophs for respiration (Ra).
• NPP equation
• aerobic cellular respiration equation
• photosynthesis equation
• NPP is the amount of new biomass added in a given time period, not the total biomass of autotrophs.
• Satellite data indicate that ecosystems vary greatly in their NPP and contribution to the total NPP on Earth.
• Net ecosystem production (NEP) is a measure of the total biomass accumulation during a given period.
• NEP is gross primary production minus the total respiration of all organisms (RT) in an ecosystem.
• NEP equation
• NEP is estimated by comparing CO2 and O2 entering or leaving an ecosystem. If more CO2 enters than leaves, the system is storing carbon.
• In marine and freshwater ecosystems, both light and nutrients control primary production.
• Depth of light penetration affects primary production in the photic zone of an ocean or lake.
• More than light, nutrients limit primary production in most oceans and lakes.
• Nitrogen and phosphorous are the nutrients that most often limit marine production.
• In lakes, phosphorus limits cyanobacterial growth more often thannitrogen. This has led to the use of phosphate-free detergents.
• In terrestrial ecosystems, temperature and moisture affect primary production on a large scale.
• NPP increases with precipitation.
• Increasing temperature and solar energy also increase NPP.
• Soil nutrients can limit primary production in terrestrial ecosystems.