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Chapter 54 Ecosystems Trophic Relationships • Autotrophs are primary producers of the ecosystem • Heterotrophs – Primary consumers are herbivores – Secondary consumers eat herbivores – Tertiary consumers eat carnivores • Detritivores are decomposers that break down detritus The Global Energy Budget • Earth is bombarded with enough solar radiation daily that is equivalent to 100 million atomic bombs the size of Hiroshima • Only about 1% of visible light is captured for photosynthesis Primary Production • Gross Primary Production (GPP): total primary production – Amount of light energy that is converted to chemical energy by photosynthesis per unit time • Net Primary Production (NPP): gross primary production minus the energy used by primary producers for respiration (R): – NPP = GPP - R • NPP – Measurement of greatest interest to ecologists because it represents the storage of chemical energy that will be available for consumers in an ecosystem • Primary production is expressed in energy per unit area per unit time, or by biomass of vegetation added to the ecosystem per unit area per unit time – Expressed as the dry weight of organic matter Marine Limiting Factor • It is not light, as we would think • Limiting factor is actually nutrients – Nitrogen and Phosphorus Eutrophication • Changing of phytoplankton communities in lakes due to excess nutrients from dumping • Found that phosphorous was the limiting nutrient in lakes – Led to the production of phosphate-free detergent Terrestrial Limiting Factors • Temperature, moisture, and nutrients are the limiting factors Secondary Production • Amount of chemical energy in a consumers’ food that is converted to their own new biomass during a given time period Production Efficiency • Less than 20% of available energy is passed through trophic levels • Production efficiency: the fraction of food energy that is not used for respiration, and is taken in and used for growth, reproduction • Pyramid of production: multiplicative loss of energy from a food chain • Biomass pyramid: each tier represents the total dry weight of all organisms in a trophic level Green World Hypothesis • Herbivores consume relatively little plant biomass because they are held in check by a variety of factors, included predators, parasites, and disease – Defenses against herbivores – Nutrients, not energy supply, limit herbivores – Abiotic factors limit herbivores The Nitrogen Cycle • Atmosphere is 80% nitrogen, but not in a form that is usable by plants • Nitrogen Fixation: convert N2 to minerals that can be used to synthesize nitrogenous organic compounds such as amino acids – Only certain prokaryotes can do this The Phosphorous Cycle • Weathering of rocks adds phosphorous to the soil • Recycles locally among soil, plants, consumers Nutrient Cycling • Rate is largely determined by decomposition Human Impacts • Changes chemical cycles – Adding or subtracting nutrients to the cycle – Agriculture • Natural store of nutrients in soil is depleted • Use industrially synthesized fertilizers to combat it • Human activities have double the globe’s supply of fixed nitrogen available for producers – Excess nutrients in the water systems • Critical Load: amount of added nitrogen that can be absorbed by plants without damaging the ecosystem • Cultural Eutrophication: caused by sewage and factory run off Human Impacts • Fossil Fuels – Acid Precipitation: snow, rain, or fog that has a pH less than 5.6 • Drifts hundreds of kilometers from source • Toxins – Poisons cannot be degraded naturally • Mercury poisoning from plastic production – Accumulate in tissues, especially fat • DDT, PCB • Biological magnification – Eagle eggs are brittle Human Impacts • Rising CO2 – Leads to increased productivity by producers • Global Warming – Climatologists sample bubbles caught in glaciers to determine what the CO2 content was at the last ice age – Look at fossilized pollen to see how plants adapted to increased temperatures Human Impacts • Depletion of the ozone – Ozone absorbs UV radiation – Has been thinning since 1975 – CFC’s are a main contributor • Aerosol cans, refrigeration chemicals