Chapter 42 Review: Cool Ecosystem An ecosystem consists of all the organisms living in a community, as well as the abiotic factors with which they interact An example is the unusual community of organisms, including chemoautotrophic bacteria, living below a glacier in Antarctica 1

Conservation of Energy Laws of physics and chemistry apply to ecosystems, particularly energy flow The first law of thermodynamics states that energy cannot be created or destroyed, only transferred or transformed Energy enters an ecosystem as solar radiation, is transformed into chemical energy by photosynthetic organisms, and is dissipated as heat 2

The second law of thermodynamics states that every exchange of energy increases the entropy of the universe In an ecosystem, energy conversions are not completely efficient, and some energy is always lost as heat Continuous input from the sun is required to maintain energy flow in Earth’s ecosystems 3

Conservation of Mass The law of conservation of mass states that matter cannot be created or destroyed Chemical elements are continually recycled within ecosystems In a forest ecosystem, most nutrients enter as dust or solutes in rain and are carried away in water Ecosystems are open systems, absorbing energy and mass and releasing heat and waste products 4

Ecosystems can be sources or sinks for particular elements If a mineral nutrient’s outputs exceed its inputs it will limit production in that system 5

Energy and nutrients pass from primary producers primary consumers (herbivores) secondary consumers (carnivores) tertiary consumers (carnivores that feed on other carnivores) 6

Prokaryotes and fungi are important detritivores Detritivores, or decomposers, are consumers that derive their energy from detritus, nonliving organic matter Prokaryotes and fungi are important detritivores Decomposition connects all trophic levels; detritivores are fed upon by secondary and tertiary consumers 7

Energy and other limiting factors control primary production in ecosystems In most ecosystems, primary production is the amount of light energy converted to chemical energy by autotrophs during a given time period In a few ecosystems, chemoautotrophs are the primary producers 8

Ecosystem Energy Budgets The extent of photosynthetic production sets the spending limit for an ecosystem’s energy budget 9

The Global Energy Budget The amount of solar radiation reaching Earth’s surface limits the photosynthetic output of ecosystems Only a small fraction of solar energy actually strikes photosynthetic organisms, and even less is of a usable wavelength 10

Gross and Net Production Total primary production is known as the ecosystem’s gross primary production (GPP) GPP is measured as the conversion of chemical energy from photosynthesis per unit time 11

Net primary production (NPP) is GPP minus energy used by primary producers for “autotrophic respiration” (Ra) NPP is expressed as Energy per unit area per unit time (J/m2  yr), or Biomass added per unit area per unit time (g/m2  yr) NPP = GPP − Ra 12

NPP is the amount of new biomass added in a given time period Only NPP is available to consumers Standing crop is the total biomass of photosynthetic autotrophs at a given time Ecosystems vary greatly in NPP and contribution to the total NPP on Earth 13

Net primary production (kg carbon/m2 • yr) Figure 42.6 Net primary production (kg carbon/m2 • yr) 3 2 1 Figure 42.6 Global net primary production 14

Net ecosystem production (NEP) is a measure of the total biomass accumulation during a given period NEP is gross primary production minus the total respiration of all organisms (producers and consumers) in an ecosystem (RT) NEP = GPP − RT 15

NEP is estimated by comparing the net flux of CO2 and O2 in an ecosystem, two molecules connected by photosynthesis The release of O2 by a system is an indication that it is also storing CO2 16

Nutrient Limitation A limiting nutrient is the element that must be added for production to increase in an area Nitrogen and phosphorous are the nutrients that most often limit marine production In some areas, sewage runoff has caused eutrophication of lakes, which can lead to loss of most fish species In lakes, phosphorus limits cyanobacterial growth more often than nitrogen 17

Energy transfer between trophic levels is typically only 10% efficient Secondary production of an ecosystem is the amount of chemical energy in food converted to new biomass during a given period of time 18

Production Efficiency When a caterpillar feeds on a leaf, only about one-sixth of the leaf’s energy is used for secondary production Net secondary production is the energy stored in biomass An organism’s production efficiency is the fraction of energy stored in food that is not used for respiration Production efficiency = Net secondary production × 100% Assimilation of primary production 19

secondary production) Figure 42.9 Plant material eaten by caterpillar 200 J 67 J Cellular respiration Figure 42.9 Energy partitioning within a link of the food chain 100 J Feces 33 J Not assimilated Growth (new biomass; secondary production) Assimilated 20

Insects and microorganisms have efficiencies of 40% or more Birds and mammals have efficiencies in the range of 13% because of the high cost of endothermy Insects and microorganisms have efficiencies of 40% or more 21

Trophic Efficiency and Ecological Pyramids Trophic efficiency is the percentage of production transferred from one trophic level to the next, usually about 10% Trophic efficiencies take into account energy lost through respiration and contained in feces, as well as the energy stored in unconsumed portions of the food source Trophic efficiency is multiplied over the length of a food chain 22

Approximately 0.1% of chemical energy fixed by photosynthesis reaches a tertiary consumer A pyramid of net production represents the loss of energy with each transfer in a food chain 23

Tertiary consumers 10 J Secondary consumers 100 J Primary consumers Figure 42.10 Tertiary consumers 10 J Secondary consumers 100 J Primary consumers 1,000 J Primary producers Figure 42.10 An idealized pyramid of net production 10,000 J 1,000,000 J of sunlight 24

Turnover time is the ratio of the standing crop biomass to production Certain aquatic ecosystems have inverted biomass pyramids: producers (phytoplankton) are consumed so quickly that they are outweighed by primary consumers Turnover time is the ratio of the standing crop biomass to production Turnover time = Standing crop (g/m2) Production (g/m2  day) 25

Water is essential to all organisms The Water Cycle Water is essential to all organisms Liquid water is the primary physical phase in which water is used The oceans contain 97% of the biosphere’s water; 2% is in glaciers and polar ice caps, and 1% is in lakes, rivers, and groundwater Water moves by the processes of evaporation, transpiration, condensation, precipitation, and movement through surface and groundwater Animation: Carbon Cycle 26

The water cycle Movement over land by wind Precipitation over land Figure 42.13a Movement over land by wind Precipitation over land Precipitation over ocean Evaporation from ocean Evapotranspiration from land Figure 42.13a Exploring water and nutrient cycling (part 1: water) Percolation through soil Runoff and groundwater The water cycle 27

Carbon-based organic molecules are essential to all organisms The Carbon Cycle Carbon-based organic molecules are essential to all organisms Photosynthetic organisms convert CO2 to organic molecules that are used by heterotrophs Carbon reservoirs include fossil fuels, soils and sediments, solutes in oceans, plant and animal biomass, the atmosphere, and sedimentary rocks 28

CO2 is taken up by the process of photosynthesis and released into the atmosphere through cellular respiration Volcanic activity and the burning of fossil fuels also contribute CO2 to the atmosphere 29

The carbon cycle CO2 in atmosphere Photosynthesis Photo- synthesis Figure 42.13b CO2 in atmosphere Photosynthesis Photo- synthesis Cellular respiration Burning of fossil fuels and wood Phyto- plankton Consumers Figure 42.13b Exploring water and nutrient cycling (part 2: carbon) Consumers Decomposition The carbon cycle 30

Nitrogen is a component of amino acids, proteins, and nucleic acids The Nitrogen Cycle Nitrogen is a component of amino acids, proteins, and nucleic acids The main reservoir of nitrogen is the atmosphere (N2), though this nitrogen must be converted to NH4+ or NO3− for uptake by plants, via nitrogen fixation by bacteria 31

Denitrification converts NO3− back to N2 Organic nitrogen is decomposed to NH4+ by ammonification, and NH4+ is decomposed to NO3− by nitrification Denitrification converts NO3− back to N2 32

The nitrogen cycle N2 in atmosphere Reactive N gases Industrial Figure 42.13c N2 in atmosphere Reactive N gases Industrial fixation Denitrification N fertilizers Fixation Runoff Dissolved organic N NO3− Terrestrial cycling N2 NO3− NH4 Aquatic cycling Denitri- fication Figure 42.13c Exploring water and nutrient cycling (part 3: nitrogen) Decomposition and sedimentation Decom- position Assimilation NO3− Fixation in root nodules Uptake of amino acids Ammoni- fication Nitrification NH4 The nitrogen cycle 33

Phosphate (PO43−) is the most important inorganic form of phosphorus The Phosphorus Cycle Phosphorus is a major constituent of nucleic acids, phospholipids, and ATP Phosphate (PO43−) is the most important inorganic form of phosphorus The largest reservoirs are sedimentary rocks of marine origin, the soil, oceans, and organisms Phosphate binds with soil particles, and movement is often localized 34

The phosphorus cycle Wind-blown dust Geologic uplift Weathering Figure 42.13d Wind-blown dust Geologic uplift Weathering of rocks Runoff Consumption Decomposition Plant uptake of PO43− Plankton Dissolved PO43− Uptake Leaching Figure 42.13d Exploring water and nutrient cycling (part 4: phosphorus) Sedimentation Decomposition The phosphorus cycle 35