1. Chapter 54 Ecosystems Chapter 54 Ecosystems

2. Ecosystems • Consist of all the organisms living in a community as well as the abiotic factors in which they interact. • For ecosystems to remain stable, there must be a continuous input of energy AND nutrient cycling.

4. Primary Production • Primary producers (autotrophs) ultimately support all other trophic levels. • The amount of light energy converted into chemical energy during a given time is termed  Primary productivity • Photosynthesis sets the “spending” limit for the energy budget of the ecosystem.

5. Photosynthetic product is the starting point for ecosystem metabolism and energy flow. • Most primary producers use light energy to synthesize energy rich organic molecules, that can be converted into ATP  “SPENDING LIMIT” • The total amount of solar radiation that comes at the planet strikes bare ground and bodies of water that either absorb or reflect the energy.

6. Gross and Net Primary Productivity • Total primary production in an ecosystem is known as  gross primary production (GPP). • Gross primary production minus the energy used by the primary producers for respiration (R) Net primary production (NPP). NPP = GPP - R

7. Primary production in aquatic ecosystems • In aquatic ecosystems, light and nutrients are limiting factors. • More than half of the solar radiation is absorbed in the first meter of water; only 5-10% may reach 20 meters (photic zone). • Limiting nutrients are those elements that must be added in order for production to increase.

9. Marine Ecosystems • Most limiting nutrient is nitrogen • Very low concentration in the photic zone but high in deeper regions where light does not penetrate. • Some reasons why nitrogen is limiting is because molybdenum, phosphorus, or energy constraints can be limiting to nitrogen fixers, which makes for lower nitrogen fixation.

10. There is also significantly higher denitrification in marine sediments than in freshwater sediments, as marine sediments are largely anoxic.

11. Nutrient limitation is also common in freshwater lakes • Freshwater phosphorus limitation is due to the fact that the majority of phosphorus inputs into aquatic ecosystems comes from the weathering of primary minerals in marine sediments, not in freshwater systems.

12. Nutrient limitation is also common in freshwater lakes; • eutrophication: “well nourished”; high nutrient lakes lead to high concentrations of phytoplankton, which in turns causes oxygen depletion. • Oligotrophic: low nutrient concentration, low plant growth, high oxygen concentration.

15. Energy Transfer • Secondary production defines the process of chemical energy in food that is converted to new biomass. • Production efficiency is the fraction of energy stored in food that in NOT used for respiration. Production efficiency = net secondary production/assimilation of primary production

17. Production efficiency can be used to measure the organisms efficiency in energy transformation. • Endotherms have an efficiency of 1%-3%, whereas ectotherms maintain 10% efficiency. Insects can maintain up to 40%!!!