Chapter 22: Ecosystems and the Biosphere 22-1 Energy Transfer 22-2 Ecosystem Recycling 22-3 Terrestrial Ecosystems 22-4 Aquatic Ecosystems
22-1 Energy Transfer I. Energy Transfer • Energy FLOWS from SUN AUTOTROPHS HETEROTROPHS; (e.g., ecosystem’s structure is HOW energy is TRANSFERRED).
II. Producers (2 Classes solar dependent AND independent) • Plants, bacteria, protists, transfer NRG into NUTRIENTS (i.e., they “produce” food).
(1) Photosynthesis (sunlight-DEPENDENT producers) • Sunlight as NRG source, biochemical reactions lead to carbohydrates.
(2) Chemosynthesis (sunlight-INDEPENDENT producers) • PRODUCE carbohydrates through NRG released from CHEMICALS (e.g., hydrogen sulfide).
(A) Measuring Productivity (How much NRG is available in an ecosystem?) • Differences in abiotic factors ALL influence PRODUCTIVITY.
(1) Gross Primary Productivity (GPP units: kcal/m2/y or g/m2/y) • RATE at which PRODUCERS in an ecosystem CAPTURE NRG.
(2) Net Primary Productivity (GPP units: kcal/m2/y or g/m2/y) • RATE at which captured NRG is USED to make BIOMASS. (i.e., ONLY NRG in BIOMASS is available to other organisms)
(3) Biomass (the volume an organism takes up) • MATERIAL available in an ecosystem for FOOD (i.e., producers ADD biomass ORGANIC COMPOUNDS)
III. Consumers (i.e., primary, secondary, tertiary, quaternary) • Different types based upon WHERE they obtain nourishment. (i.e., NRG is obtained by consumption NOT production)
(1) Herbivores (predators—primary consumers) • Consume PRODUCERS for NRG.
(2) Carnivores (predators—secondary or tertiary consumers) • Consumer OTHER consumers for NRG.
(3) Omnivores (opportunistic predators—either primary or secondary) • Consume BOTH producers AND consumers for NRG.
(4) Detritivores (mostly non-predators) • Consume “GARBAGE” of an ecosystem • (i.e., dead organisms, fallen leaves and branches, and animal wastes).
(5) Decomposers (class of detritivores—RECYCLERS of an ecosystem) • Initiate DECAY by breaking down dead tissues into NUTRIENTS.
IV. Energy Flow • NUTRIENTS are metabolized and NRG is transferred. (i.e., NRG flows through an ecosystem) (1) Trophic Level (the NRG level) • An organism’s POSITION in the sequence of NRG transfers.
(A) Food Chains and Food Webs • Represent an organism’s POSITION in sequence of NRG flow.
(1) Food Chain (LINEAR NRG transfer) • Single pathway of feeding relationships among organisms in ecosystem. (2) Food Web (INTERCONNECTED NRG transfer) • Shows HOW food chains in an ecosystem are interconnected.
(B) Quantity of Energy Transfers • ONLY 10-15% of TOTAL NRG in a trophic level is PASSED on to the NEXT trophic level.
Ex: Consider what happens when a DEER eats 1,000 kcal of LEAVES (biomass) from a TREE. • About 350 kcal are LOST by the deer through urine and feces. • Another 480 kcal are LOST as metabolic heat (the deer is an endotherm) • Therefore, ONLY about 170 kcal are actually STORED as BIOMASS that can be consumed for NRG at the NEXT trophic level ABOVE.
(C) Short Food Chains • LOW rate of NRG transfer between trophic levels EXPLAINS why some ecosystems RARELY contain more than a FEW TROPHIC levels. Ex: If you go on an African Safari, you would see about 1,000 zebras, gazelles, wildebeest, and other herbivores for EVERY lion or leopard you see, and there are FAR MORE grasses, trees, and shrubs than there are herbivores. (i.e., the HIGHER trophic levels contain LESS energy and, as a consequence, HIGHER LEVELS can support FEWER individuals).
22-2 Ecosystem Recycling I. Biogeochemical Cycle (Abiotic-Biotic-Abiotic) • UNLIKE NRG flow, WATER, C, N, Ca, and P can be RECYCLED. (via biogeochemical cycles)
Critical Thinking (1) Nitrogen, water, and carbon are recycled and reused within an ecosystem, BUT energy is not. Explain as to why energy cannot be recycled?
II. The Water Cycle (evaporation-transpiration-precipitation) • WATER defines the PRODUCTIVITY of TERRESTRIAL ecosystems (i.e., Remember, CELLS are MADE of 70-90% water.)
(1) Ground Water (in addition to water vapor AND bodies of water) • In SOIL or UNDERGROUND inside POROUS rock, flows in RESERVOIRS.
(2) Transpiration (water VAPOR) • ~ 90% returns to ATMOSPHERE via PLANTS during transpiration. • Plants: Release H2O vapor through STOMATA in leaves (majority). • Animals: Release H2O during breathing (vapor), sweating, and excretion.
III. The Carbon Cycle • Photosynthesis (ABSORBS), Respiration (RELEASES), and Combustion of Fossil Fuels (RELEASES).