Ecosystems Chapter 31. Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display

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1 Ecosystems Chapter 31

2 31.1 Energy Flows Through Ecosystems Ecology Study of interactions of living organisms with one another and their physical environment Community Collection of all organisms living together in an area Habitat The place where an organism lives Ecosystem A largely self-sustaining collection of organisms and their physical environment

3 The Path of Energy in Ecosystems Energy flows into the biological world from the sun Producers capture sunlight and transform it into chemical energy by photosynthesis Also called autotrophs Consumers obtain their energy from consuming plants or other animals Also called heterotrophs

4 A trophic, or feeding, level consists of all organisms feeding at the same energy level Food chain Passage of food energy through ecosystem trophic levels in a linear path Fig. 31.1

5 Fig Because animals eat at different trophic levels, most ecosystems have paths of energy that are not linear A complicated path of energy flow is called a food web

6 Producers Green plants and algae Use solar energy to build energy-rich carbohydrates Herbivores Animals that eat plants The primary consumers of ecosystems Carnivores Animals that eat herbivores The secondary consumers of ecosystems Omnivores are animals that eat both plants and animals Tertiary consumers are animals that eat other carnivores Detritivores Organisms that eat dead organisms Decomposers Organisms that break down organic substances

7 Energy Flows Through Trophic Levels Primary productivity Total amount of light energy converted to organic compounds in a given area per unit time Net primary productivity Primary productivity minus energy expended by the photosynthetic organisms to fuel metabolism Biomass Total weight of all organisms in an ecosystem

8 About one order of magnitude of available energy is lost from one trophic level to the next Reason why food chains generally consist of only 3 or 4 steps Biomass available at the next trophic level Cayuga Lake In NY Fig How heterotrophs use food energy Fig Energy loss in an ecosystem

9 31.2 Ecological Pyramids A plant fixes about 1% of the sun s energy that falls on its green parts Successive members of a food chain incorporate ~ 10% of energy available in organisms they consume Therefore, there are far more individuals at the lower tropic levels The biomass of the lower trophic levels also tends to be greater These relationships appear in a diagram as pyramids

10 Fairly large animals Fig Ecological pyramids Found in larger numbers, but still contain 90% less energy Inverted pyramid

11 31.3 The Water Cycle Unlike energy, the physical components of ecosystems are passed around and reused Recycling or cycling In each cycle the chemical resides for a time in an organism, then returns to the non-living environment A biogeochemical cycle Water cycles within ecosystems in two ways Environmental water cycle Organismic water cycle

12 Environmental Water Cycle Water vapor condenses and falls to earth Reenters atmosphere by evaporation Fig Transpiration Evaporation Solar energy Precipitation Oceans Runoff Lakes Percolation in soil Groundwater Aquifer

13 31.4 The Carbon Cycle The carbon cycle is begun by plants who use CO 2 to build organic molecules Carbon atoms are returned to the atmosphere by Respiration Most organisms extract energy from food and release CO 2 as a by-product Combustion Burning of wood or fossil fuels (coal or oil) releases trapped carbon in the form of CO 2 Erosion When limestone (calcium carbonate in sediment) erodes, CO 2 is released

14 Fig The carbon cycle Diffusion CO 2 in atmosphere Respiration Photosynthesis Combustion of fuels Industry and home Plants Animals Dissolved CO 2 Bicarbonates Photosynthesis Animals Plants and algae Death and decay Carbonates in sediment Death Fossil fuels (oil, gas, coal)

15 31.5 Soil Nutrients and Other Chemical Cycles Many other chemicals cycle through the ecosystem Nitrogen Phosphorus Sulfur

16 The Nitrogen Cycle The atmosphere is 78% nitrogen gas (N 2 ) However, most organisms are unable to use N 2 The triple covalent bond is very difficult to break Some bacteria can break the triple bond and bind its N atoms to hydrogen forming ammonia (NH 3 ) This process is termed nitrogen fixation Animals eat plants that have taken up fixed nitrogen Nitrogen reenters the ecosystem through Animal excretion Decomposition by detritivores and decomposers

17 Fig The nitrogen cycle

18 The Phosphorus Cycle Phosphorus (P) has no atmospheric form Exists mostly as the mineral calcium phosphate Phosphate ions are absorbed by plant roots and used to build organic molecules like ATP and DNA When animals and plants die and decay, bacteria convert organic phosphorus into ions Low phosphorus levels in freshwater lakes limits the overgrowth of algae An excessive increase in phosphorus, or other nutrients, is called eutrophication

19 Fig The phosphorus cycle Loss in drainage Plants Decomposers (bacteria and fungi) Phosphates in solution Land animals Soluble soil phosphate Rocks and minerals Animal tissue and feces Urine Decomposers (bacteria and fungi) Animal tissue and feces Aquatic animals Plants and algae Precipitates Loss to deep sediment

20 The Sulfur Cycle Sulfur is pumped into the atmosphere by coal-burning power plants Large amounts can harm an ecosystem Excess sulfur combines with water vapor to produce sulfuric acid This acid then reenters the ecosystem as precipitation Acid rain