1 Ecosystems Chapter 54

What you need to know How energy flows through the ecosystem The difference between gross primary productivity and net primary productivity The carbon and nitrogen biogeochemical cycles How energy flows through the ecosystem The difference between gross primary productivity and net primary productivity The carbon and nitrogen biogeochemical cycles 2

Ecosystem The sum of all the organisms living within its boundaries (biotic community) and all the abiotic factors with which they interact Two key parts: 1.Energy flow 2.Chemical cycling The sum of all the organisms living within its boundaries (biotic community) and all the abiotic factors with which they interact Two key parts: 1.Energy flow 2.Chemical cycling 3

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1. Energy Flow Traced through feeding relationships (trophic levels) of food chains and webs Energy cannot be recycled It must be resupplied (sunlight 99.9%) Traced through feeding relationships (trophic levels) of food chains and webs Energy cannot be recycled It must be resupplied (sunlight 99.9%) 5

Energy Pyramid Bottom Level: primary producers (aka autotrophs) support all other organisms Upper levels: consumers (aka heterotrophs) –Herbivores (primary consumers) eat primary producers –Carnivores that eat primary consumers are secondary consumers, carnivores that eat secondary consumers are tertiary consumers Bottom Level: primary producers (aka autotrophs) support all other organisms Upper levels: consumers (aka heterotrophs) –Herbivores (primary consumers) eat primary producers –Carnivores that eat primary consumers are secondary consumers, carnivores that eat secondary consumers are tertiary consumers 6

Detritivores Decomposers that get their energy from detritus Detritus is nonliving organic material such as the remains of dead organisms, feces, dead leaves, and wood Critical organisms recycle organic material from all trophic levels and deposit the nutrients back into the soil for use by producers Decomposers that get their energy from detritus Detritus is nonliving organic material such as the remains of dead organisms, feces, dead leaves, and wood Critical organisms recycle organic material from all trophic levels and deposit the nutrients back into the soil for use by producers 7

Primary Production The amount of light* energy converted to chemical energy by autotrophs Spending limit for energy budget Total primary production in an ecosystem is gross primary production (GPP) GPP is not all available to consumers (some is used by the autotrophs) The amount of light* energy converted to chemical energy by autotrophs Spending limit for energy budget Total primary production in an ecosystem is gross primary production (GPP) GPP is not all available to consumers (some is used by the autotrophs) 8

Primary Production Net primary production (NPP) = GPP minus the energy used for respiration ® by the autotrophs NPP = GPP - R Aquatic ecosystems depend on nutrients (nitrogen and phosphorus) and light availability (photic zone) Terrestrial ecosystems depend on temperature and moisture Net primary production (NPP) = GPP minus the energy used for respiration ® by the autotrophs NPP = GPP - R Aquatic ecosystems depend on nutrients (nitrogen and phosphorus) and light availability (photic zone) Terrestrial ecosystems depend on temperature and moisture 9

Energy Transfer 10% of energy is transferred from primary producers to primary consumers –Only 1% makes it to the secondary consumers Keeps food chains short 10% of energy is transferred from primary producers to primary consumers –Only 1% makes it to the secondary consumers Keeps food chains short 10

2. Chemical Cycling Biogeochemical cycles are nutrient cycles that contain both biotic and abiotic components: Water cycle recycles fresh water Phosphorus cycle moves nitrogen throughout terrestrial and aquatic ecosystems Carbon cycle is a balance between photosynthesis and cellular respiration Nitrogen cycle moves nitrogen from the atmosphere through the living world –Common limiting factor for plant growth (makes this cycle especially important) Biogeochemical cycles are nutrient cycles that contain both biotic and abiotic components: Water cycle recycles fresh water Phosphorus cycle moves nitrogen throughout terrestrial and aquatic ecosystems Carbon cycle is a balance between photosynthesis and cellular respiration Nitrogen cycle moves nitrogen from the atmosphere through the living world –Common limiting factor for plant growth (makes this cycle especially important) 11

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Nitrogen Cycle Most nitrogen is N 2 (unusable by plants) Nitrogen fixation: Bacteria convert N 2 into usable forms of nitrogen –Nitrification is the process by which ammonium is oxidized to nitrite and then nitrate –Plants can absorb ammonium and nitrates Denitrification by bacteria releases nitrogen to the atmosphere (N 2 ) Most nitrogen is N 2 (unusable by plants) Nitrogen fixation: Bacteria convert N 2 into usable forms of nitrogen –Nitrification is the process by which ammonium is oxidized to nitrite and then nitrate –Plants can absorb ammonium and nitrates Denitrification by bacteria releases nitrogen to the atmosphere (N 2 ) 16

Human Activities Acid precipitation – rain, snow, or fog with a pH lower than 5.6 –Created by the burning of wood and fossil fuels which mix into sulfuric and nitric acid Biological magnification – toxins become more concentrated in higher trophic levels Greenhouse effect – blanket of CO 2 traps heat (global warming) Ozone layer reduces UV light Acid precipitation – rain, snow, or fog with a pH lower than 5.6 –Created by the burning of wood and fossil fuels which mix into sulfuric and nitric acid Biological magnification – toxins become more concentrated in higher trophic levels Greenhouse effect – blanket of CO 2 traps heat (global warming) Ozone layer reduces UV light 17