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Chapter 54

Unit 9 - Chapter 54 Bio 1M03 .docx

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James S Quinn

Bio 1M03 Unit Nine: Ecology Chapter 54: Ecosystems  Ecosystem – the organisms that live in an area together with their physical, or abiotic, environment 54.1 Energy Flow and Trophic Structure  Ecosystems have four components that are linked by a flow of energy 1. The abiotic environment  Includes soil, climate, the atmosphere, the Sun and the particulate matter and solutes in water 2. Primary producers  Autotroph – organism can synthesize own food (sugar) from inorganic sources (eg/ solar energy through photosynthesis, chemical energy contained in inorganic compounds such as2H , 4H 2 H S)  Use chemical energy (sugar) in two ways  Support maintenance or respiratory costs  Makes growth and reproduction possible o Net Primary Product (NPP) – energy invested in new tissue; represents the amount of energy that is available to consumers and decomposers 3. Consumers  Eat living organisms  Herbivores – eat plants  Carnivores – eat animals 4. Decomposers (detritivores)  Obtain energy by feeding on the dead remains of other organisms or waste products Global Patterns in Productivity  NPP on land declines from the equator toward the poles (desert are exceptions – not productive)  Marine productivity is highest along coastlines – can be high near the poles  Open ocean is as productive as a desert (not very productive)  Productivity of terrestrial ecosystems  limited by a combination of temperature and availability of water and sunlight  Marine Ecosystems (Open Ocean) – low productivit limited by availability of nutrients o Neritic and intertidal zones along coasts receive nutrients from  Rivers that carry and deposit nutrients from terrestrial ecosystems  Near shore ocean currents that bring nutrients from the cold, deep water of the oceanic zone back up to the surface  Both are absent in the surface waters of open ocean – explains low productivity o Nutrients found in organisms near the surface of open ocean (where sunlight is abundant), constantly fall to dark, deeper waters in the form of dead cells and are lost o Iron, zinc and magnesium are important; required for enzyme cofactors How Does Energy Flow Through an Ecosystem?  NPP results in biomass  chemical energy in primary producers eventually moves on to primary consumers or primary decomposers o Biomass – organic material that non-photosynthetic organisms can eat  Herbivores (primary consumers) – consume only a small percentage of plant tissue; rest of tissue dies  Primary decomposers consume detritus (the dead tissues that are not consumed by herbivores) 1 Bio 1M03 How Does Energy Flow through an Ecosystem?  Trophic (“feeding”) Level – organisms that obtain their energy from the same type of source  Food Chain – connects trophic levels in a particular ecosystem; describe how energy moves from one trophic level to another o Grazing Food Chain – collection of organisms that eat plants, along with organisms that eat herbivores  Secondary consumers – organisms that eat herbivores  Organisms at top trophic level are not killed and eaten by any other organism but enter the decomposer food chain when they die (along with biomass from dead primary producers and other consumers) o Decomposer Food Chain – starts with primary decomposer; includes primary consumers that specialize in eating primary decomposers  At higher levels, decomposer chain and grazing chain merge  Food Web – compact way of summarizing energy flows and documenting the complex trophic interactions that occur in communities Why Is Energy Lost at Each Tropic Level?  The total biomass produced each year declines from lower trophic levels up to the higher levels o Much of the NPP produced is unavailable to primary consumers (eg/ lignin on wood is indigestible) o NPP that is consumed by herbivores is lost as heat or used in metabolism o Many herbivores (primary consumers) defend themselves against secondary consumers or die of other causes o Some energy that is consumed by secondary consumers is lost as heat, used in metabolism or used to capture prey Limitations to Food Chain Length – food chains have one to six links  Hypothesis 1: Energy Transfer o As energy is transferred up the food chain, a large fraction of energy is lost o Prediction: There should be more trophic levels in ecosystems with higher productivity or higher efficiency of energy transfer  no evidence  Hypothesis 2: Stability o Long food chains are easily disrupted by droughts, floods or other disturbances; thus are eliminated o Long food chains take longer to return to previous state following a disturbance than short food chains 2 Bio 1M03 o Long food chains are unlikely to persist in a variable environment o Prediction: Length of food chain should increase with the stability of the environment  proven; still testing  Hypothesis 3: Environmental Complexity o Food chain length is a function of an ecosystems physical structure; three dimensional ecosystems (e/g forests) should have longer food chains than two dimensional sites (eg/ grasslands, tundra) o Prediction: Food webs are longer in three-dimensional ecosystems  proven Analyzing Energy Flow: A Case History – Hubbard Broke Experimental Forest in New Hampshire  General Principles (Review) 1. In terrestrial and marina ecosystems – NPP varies with region and biome 2. Land – limitations to productivity are warmth and moisture 3. Aquatic Habitats – limitation to productivity is nutrient availability 4. Chemical energy in biomass flows into consumer or decomposer food web, then passed up a series of trophic levels 5. Terrestrial Ecosystems – total biomass declines with each trophic level  Gross Primary Productivity – total amount of photosynthesis in a given area and time period o Found to be 10 400 kcal/m2  Gross Photosynthetic Efficiency – efficiency with which pants use the total amount of energy available to them, as the ratio of gross photosynthesis to solar radiation in kilocalories per square meter o 10 400 kcal/m / 1 254 000 kcal/m = 0.8% 2  1 254 000 kcal/m = amount of sun that reached the forest How Does Energy Flow Through The Hubbard Brook Ecosystem?  Energy that entered the consumer food web varied from 1% - 40%  Eg/ Chipmunks – seed predators; primary consumers 2 o Harvest 31 kcal/m of energy o 17.7% is unused and excreted o 80.7& is lost to respiration and other maintenance processes o 1.6% if the yearly 31 kcal/m goes into production of new chipmunk tissue by growth and reproduction  Secondary Production – production of new tissue by primary consumers o Higher in ectotherms and than endotherms; ectotherms rely principally on heat gained from the environment and do not oxidize sugars to keep warm, devote less energy to cellular respiration  About 75% of total NPP is not eaten while alive – energy enters decomposer food web and is passed up subsequent trophic levels o Energy enters decomposer food web and is passed up subsequent trophic levels, just as it is in the consumer food web o Large amount of energy leaves the decomposer food web in the form of detritus that washes into streams – major source of energy for aquatic organisms 54.2 Biogeochemical Cycles  Biogeochemical (“life-Earth-chemical” Cycle – path that an element takes as it moves from abiotic systems through organisms and back again o Carbon, Nitrogen, Phosphorus, Calcium and other elements act as nutrients and are also reused as they cycle through the trophic levels and air, water and soil (not just energy)  Focus on 1. The nature and size of reservoirs (areas where elements are stored for a period of time)  In the case of carbon; the biomass of living organisms, sediments, soils, coal and oil 2. The rate at which elements move between reservoirs, and the factors that influence these rates  Global photosynthetic rates measure the rate of carbon flow from2CO in the atmosphere to living biomass 3 Bio 1M03  When fossil fuels burn, carbon that was buried in coal or petroleum move into the atmosphere as CO2 3. Interaction between the biogeochemical cycle and other cycles  Eg/ how changes in the nitrogen cycle affect carbon Biogeochemical Cycles in Ecosystems 1. Nutrients are taken up from the soil by plants and assimilated into plant tissue 2. Plant is eaten – nutrients pass to the animal members of the ecosystems consumer food web 3. Plant dies – nutrients enter the decomposer food web 4. Once plant is consumed by animal – nutrients are excreted in fecal matter or urine and are taken up by a parasite or predator, or added to the dead biomass reservoir when animal dies 5. Nutrients in plant litter, animal excretions and dead animal bodies are used by bacteria, archaea, roundworms, fungi, other primary decomposers 6. The microscopic decomposers and the ions and molecules they release combine to form the soil organic matter 7. Soil organic matter – complex mixture of partially and completely decomposed detritus 8. Humus – completely decayed organic matter; rich in humic acids (a family of carbon-containing molecules) 9. Eventually nutrients in soil organic matter are converted to an inorganic form o Eg/ Cellular respiration by soil-dwelling bacteri+ and archaea con-erts the nitrogen present in animal acids that are found in detritus to ammonium (NH4) or nitrate (NO3) ions  nutrients available for plant uptake  Nutrients are reused – but not completely  Nutrients lea
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