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BI 101 Food webs and Ecosystems Copyright © 2011 Pearson Education, Inc. Learning objectives • Describe the flow of energy through the ecosystem, and understand how this affects the biomass of tropic levels • Understand the cycling of nutrients such as carbon and water • Recognize how impacts to the nutrient cycles affect the whole community Copyright © 2011 Pearson Education, Inc. Levels of study in Ecology Organism Population √ Community √ Ecosystem Biosphere Copyright © 2011 Pearson Education, Inc. What is an ecosystem? Figure 28-4b A simple marine food chain phytoplankton zooplankton secondary consumer (3rd trophic level) producer (1st trophic level) primary consumer (2nd trophic level) tertiary consumer (4th trophic level) quaternary consumer (5th trophic level) (b) A simple marine food chain Copyright © 2011 Pearson Education, Inc. Figure 28-5 A simplified grassland food web Copyright © 2011 Pearson Education, Inc. Primary producers—the autotrophs • Auto = self + trophy = nourishment • Organisms take nourishment directly from the environment Phytoplankton—ocean http://www.njscuba. net/biology/eco_wat er.html Copyright © 2011 Pearson Education, Inc. Terrestrial plants http://www.100m ag.com/know00 2.html Consumers—heterotrophs • Hetero = other + trophy = nourishment Copyright © 2011 Pearson Education, Inc. Copyright © TheTertiary McGraw-Hill Companies, Inc. Permission required for reproduction or display. consumer Trophic levels within an ecosystem Detrivores (also known as scavengers) are special consumers that eat dead organisms Decomposers are organism that break down organic substances, making them available to other organisms bacteria and fungi are the principal Copyright © 2011 Pearson Education, Inc. Sun Trophic level 4 Top carnivore Secondary consumer Trophic level 3 Carnivore Primary consumer Trophic level 2 Herbivore Producer Trophic level 1 Decomposers Fungi Bacteria 8 Detrital food web Copyright © 2011 Pearson Education, Inc. Energy pathways in ecosystems • All ecosystems need energy so its living members can grow and reproduce • Source of energy = the sun • One-way path • Flows through various organisms, and eventually dissipates into the environment as heat Copyright © 2011 Pearson Education, Inc. Energy Flows Through Ecosystems How heterotrophs use (and lose) food energy Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17% Growth 33% Cellular respiration 50% Feces Much of the energy captured by plants is lost as energy passes through the ecosystem Copyright © 2011 Pearson Education, Inc. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Algae and cyanobacteria Energy loss in an ecosystem Small heterotrophs Trout Smelt Human 1.2 calories 6 calories 1000 calories 150 calories 30 calories 12 Copyright © 2011 Pearson Education, Inc. Copyright © 2011 Pearson Education, Inc. Food Supply – Energy Pyramid Energy is used much more efficiently if humans eat plants (first tropic level) instead of meat (second tropic level). A given area of farmland can support more people if the crops are fed directly to people rather than to livestock that people then eat. For example if a man needs 3,000 Calories per day, then 30,000 Cal beef are needed, which in turn need 300,000 Cal of corn. This works out to be 1.5 acres of corn per day per person. If the person ate corn directly then 10 people could be supported by the same 1.5 acres of corn. Copyright © 2011 Pearson Education, Inc. Biogeochemical Cycles • In contrast to the one-way flow of energy, materials (such as water, carbon and nitrogen) cycle through ecosystems. – Water cycle – Carbon cycle – Nitrogen cycle – Phosphorus cycle Copyright © 2011 Pearson Education, Inc. Figure 28-7 The hydrologic cycle reservoirs processes water vapor in the atmosphere precipitation over land precipitation over the ocean evaporation from land and transpiration from plants evaporation from the ocean evaporation from lakes and rivers lakes and rivers seepage into soil groundwater, including aquifers Copyright © 2011 Pearson Education, Inc. runoff from rivers and land extraction for agriculture water in the ocean Burning or clear-cutting forests breaks the water cycle Copyright © 2011 Pearson Education, Inc. Figure 28-8 The carbon cycle reservoirs CO2 in the atmosphere processes trophic levels burning fossil fuels CO2 dissolved in the ocean respiration fire photosynthesis producers consumers detritus feeders and decomposers decomposition Copyright © 2011 Pearson Education, Inc. fossil fuels (coal, oil, natural gas) Figure 28-14 Greenhouse gases and global warming 5 Most heat is radiated back into space Sun 1 Sunlight energy enters the atmosphere 6 Some atmospheric heat is retained by greenhouse gases 2 Some energy is reflected back into space volcanoes 3 Most sunlight strikes Earth’s surface and is converted into heat vehicle emissions Copyright © 2011 Pearson Education, Inc. 4 Heat is radiated back into the atmosphere agricultural activities forest fires power plants and factories homes and buildings Figure 28-15 Global warming parallels atmospheric Copyright © 2011 Pearson Education, Inc. Figure 28-9 The nitrogen cycle reservoirs N2 in the atmosphere processes trophic levels burning fossil fuels lightning application of manufactured fertilizer consumers ammonia and nitrates in water producers uptake by producers detritus feeders and decomposers nitrogen-fixing bacteria in soil and legume roots decomposition denitrifying bacteria Copyright © 2011 Pearson Education, Inc. ammonia and nitrates in soil Figure 28-10 The phosphorus cycle reservoirs processes trophic levels phosphate in rock geological uplift application of manufactured fertilizer runoff from rivers consumers producers detritus feeders and decomposers decomposition Copyright © 2011 Pearson Education, Inc. runoff from fertilized fields uptake by producers phosphate in water phosphate in soil phosphate in sediment formation of phosphate-containing rock