Chapter 28 BSC 1005 Tidwell How Do Ecosystems Work Two basic laws underline ecosystem function o Nutrients constantly cycle and recycle o Energy moves in a continuous one way flow Nutrients environment and that are required for survival are atoms and molecules that organisms obtain from their living and nonliving The energy to drive life s activities come from the sun o The sun converts hydrogen to helium transforming a relatively small amount of matter into enormous quantities of energy o Since only a tiny fraction of solar energy is captured by plants life on Earth is supported by less than 0 03 of the energy reaching Earth from the sun Each category of organisms is called a trophic level o Producers autotrophs energy from the environment make their own food using inorganic nutrients and solar o Organisms that cannot photosynthesize are called consumers heterotrophs They require energy and nutrients from molecules in the bodies of other organisms o Primary consumers feed directly and exclusively on producers These herbivores include animals such as grasshoppers mice and zebras and form the second trophic level o Carnivores act as secondary consumers that prey on herbivores Carnivores such as spiders hawks cheetahs and salmon are higher level consumers Some carnivores eat other carnivores are called tertiary consumers o The energy that photosynthetic organisms store and make available to other members of the community over a given period is called net primary production o Tropical rain forests and estuaries coastal areas where rivers meet the ocean have an abundance of resources and have high productivities A food chain is a linear feeding relationship with just one representative at each trophic level o Aquatic food chains have phytoplankton as their dominant producers o Phytoplankton are consumed by zooplankton which consist of protists and small shrimp like crustaceans o Zooplankton are consumed by fish which are eventually eaten by larger fish A food web shows the actual feeding relationships in a community including its many interconnecting food chains Page 1 of 4 Chapter 28 BSC 1005 Tidwell Omnivores both plants and animals act as primary secondary and tertiary consumers because they consume Detritus feeder and decomposers release nutrients for reuse live on dead organic matter including the bodies of other o Detritus feeders organisms fallen leaves and fruit and wastes o Decomposers digest food outside of their bodies by secreting digestive enzymes They primarily consist of fungi and bacteria which liberate nutrients from the environment o Detritus feeders and decomposers convert the bodies of dead organisms into simple molecules such as carbon dioxide water and minerals The net energy transfer between trophic levels is roughly 10 efficient and is known as the 10 law o An energy pyramid illustrates the general energy relationships between trophic levels Biomass is the weight of living material at each trophic level o Because the dry weight of an organism s body at each trophic level is roughly proportional to the amount of energy stored at that level a biomass pyramid for a given community has the same shape as its energy pyramid o This pattern of energy transfer has some important ramifications Plants dominate most communities because they have the most energy available to them followed by herbivores and carnivores We can feed more people directly of grain that on meat from animals fed on grain Certain persistent toxic chemicals become increasingly concentrated in the bodies of animals that occupy higher trophic levels by a process called biological magnification Macronutrients hydrogen oxygen nitrogen phosphorus sulfur and calcium are required by organisms in large amounts and include water carbon Micronutrients trace amounts including zinc molybdenum iron selenium and iodine are required in Nutrient cycles biogeochemical cycles communities and the nonliving portions of ecosystems describe the pathways nutrients follow between o Reservoirs o Major reservoirs are usually in the abiotic environment are sources and storage sites of nutrients Page 2 of 4 Chapter 28 BSC 1005 Tidwell The water cycle hydrologic cycle describes the pathway that water takes as it travels from its major reservoir through the atmosphere to reservoirs in freshwater lakes rivers and groundwater and then back again o the oceans o The oceans contain more than 97 of Earth s water A small amount enters underground reservoirs called aquifers o Aquifers are tapped to supply water for irrigating crops Plants absorb water through roots but most is evaporated back to the atmosphere from leaves through a process called transpiration The carbon cycle has major reservoirs in the atmosphere oceans and fossil fuel o Chains of carbon atoms form the framework of all organic molecules the building blocks of life o The carbon cycle describes the movement of carbon from its major short term reservoirs in the atmosphere and oceans through producers and into the bodies of consumers and detritus feeders and then back to its reservoirs o Carbon enters communities through capture of CO2 during photosynthesis o Much of Earth s carbon is bound up in limestone rock o Fossil fuels subjected to high temperatures and pressures for millions of years are formed when the remains of prehistoric organisms are buried and Burning fossil fuels releases stored energy in hydrocarbons and releases carbon into the atmosphere as CO2 The nitrogen cycle is the process by which nitrogen moves from nitrogen gas in the atmosphere to reservoirs of ammonia and nitrate in the soil and water o While nitrogen gas N2 makes up 78 of the atmosphere Plants utilize nitrate NO3 or ammonia NH3 o Nitrogen is a crucial component of proteins many vitamins nucleotides ATP and nucleic acids fixation o N2 is converted to ammonia by specific bacteria during a process called nitrogen Some of these bacteria live in water and soil and convert the ammonia into nitrate that plants can directly use Others live in symbiotic associations with plants called legumes which include alfalfa soybeans clover and peas o Denitrifying bacteria break down nitrate and release N2 The phosphorus cycle describes the process by which phosphorus moves from phosphate rich rocks to reservoirs of phosphate in soil and water through producers and into consumers and detritus feeders and then back to its reservoirs o The phosphorus cycle has its major reservoir in rock bound to oxygen as 3