Ecosystem Dynamics and Nutrient Cycles

Posted on Feb 15, 2025 in Biology

• Keystone species exert strong control on a community by their ecological roles, or niches.
• In contrast to dominant species, they are not usually abundant in a community.
• Ecosystem engineers (or “foundation species”) cause physical changes in the environment that affect community structure.
• Beaver dams can transform landscapes on a very large scale.
• 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.
• Autotrophs build molecules themselves using photosynthesis or chemosynthesis as an energy source.
• Heterotrophs depend on the biosynthetic output of other organisms.
• 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) and so on…
• Detritivores, or decomposers, are heterotrophs that derive their energy from detritus, nonliving organic matter.
• Prokaryotes and fungi are the main decomposers.
• Primary production makes up the bottom of the food chain.
• Total primary production is known as the ecosystem’s 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.
• NPP is the amount of new biomass added in a given time period.
• Only NPP is available to consumers.
• Tropical rain forests, estuaries, and coral reefs are among the most productive ecosystems per unit area.
• Marine ecosystems are relatively unproductive per unit area but contribute much to global net primary production because of their size.
• Secondary production of an ecosystem is the amount of chemical energy in food converted to new biomass during a given period of time.
• When a caterpillar feeds on a leaf, only about one-sixth of the leaf’s energy is used for secondary production.
• Trophic efficiency is the percentage of production transferred from one trophic level to the next.
• It is usually about 10%, with a range of 5% to 20%.
  • About 90% of energy is not transferred.
  • Approximately 0.1% of chemical energy fixed by photosynthesis reaches a tertiary consumer.
• The rate of decomposition is controlled by temperature, moisture, and nutrient availability.
• Nutrient cycles are called biogeochemical cycles because they involve both biotic and abiotic components.
• The oceans contain 97% of the biosphere’s water; 2% is in glaciers and polar ice caps, and 1% is in lakes, rivers, and groundwater.
• Photosynthetic organisms convert CO₂ to organic molecules that are consumed by heterotrophs.
• Carbon reservoirs include fossil fuels, soils and sediments, solutes in oceans, plant and animal biomass, the atmosphere, and sedimentary rocks.
• Nitrogen is a component of amino acids, proteins, and nucleic acids.
• The main reservoir of nitrogen is the atmosphere (N₂), though this nitrogen must be converted to NH₄⁺ or NO₃^– for uptake by plants, via nitrogen fixation by bacteria.
• Some bacteria can also use NO₂^–.
• Bioremediation is the use of organisms to detoxify ecosystems.