Chapter 28

1. Chapter 28 Energy Flow and Nutrient Cycling in Ecosystems 0

2. How Do Nutrients and Energy Move Through Ecosystems? • All ecosystems consist of two components • Biotic - living organisms in a given area—bacteria, fungi, protists, plants, and animals • Abiotic - all nonliving physical or chemical aspects of the environment, such as the climate, light, temperature, availability of water, and minerals in the soil

3. How Do Nutrients and Energy Move Through Ecosystems? • Nutrients are atoms and molecules that organisms obtain from their environment • The same nutrients have been sustaining life on Earth for about 3.5 billion years • Your body includes oxygen, carbon, hydrogen, and nitrogen atoms that were once part of a dinosaur or a wooly mammoth • Nutrients are transported around the Earth, but they never leave Earth

4. How Do Nutrients and Energy Move Through Ecosystems? • Energy, in contrast, takes a one-way journey through ecosystems • Solar energy is captured by photosynthetic bacteria, algae, and plants, and then flows from organism to organism • Eventually, all of life’s energy is converted to heat that is given off to the environment and cannot be used to drive the chemical reactions of living organisms • Life requires a continuous input of energy

5. Figure 28-1 Energy flow, nutrient cycling, and feeding relationships in ecosystems energy fromsunlight producers primaryconsumers nutrients detritivores anddecomposers higher-levelconsumers solar energy heat energy energy stored inchemical bonds nutrients

6. How Does Energy Flow Through Ecosystems? • Much of the energy reaching Earth from the sun is reflected back into space by the atmosphere, clouds, and the Earth’s surface • Some is absorbed by the Earth to warm the planet • Less than 0.03% of the energy reaching Earth from the sun is captured by photosynthetic organisms, and supports life on Earth

7. How Does Energy Flow Through Ecosystems? • Energy enters ecosystems through photosynthesis • Plants, algae, and photosynthetic bacteria acquire nutrients such as carbon, nitrogen, oxygen, and phosphorus from the abiotic portions of ecosystems • Photosynthesizersbring energy and nutrients into ecosystems

8. How Does Energy Flow Through Ecosystems? • Energy is passed from one trophic level to the next • Each category of organisms is called a trophic level • Producers (or autotrophs) photosynthesizing organisms • Consumers (or heterotrophs) cannot photosynthesize • They acquire energy and nutrients from molecules in the bodies of other organisms

9. How Does Energy Flow Through Ecosystems? • Energy is passed from one trophic level to the next (continued) • There are several levels of consumers • Primary consumers (herbivores)feed directly and exclusively on producers • Carnivores act as secondary consumers when they prey on herbivores • Some carnivores eat other carnivores and are called tertiary consumers

10. How Does Energy Flow Through Ecosystems? • Net primary production is a measure of the energy stored in producers • The amount of life that a particular ecosystem can support is determined by the energy captured by the producers in that ecosystem • Biomass, or dry biological material, is usually a good measure of the energy stored in organisms’ bodies tundra(140) continentalshelf (140) coniferousforest (800) openocean(125) temperatedeciduousforest (1,200) tropical rainforest (2,200) estuary(1,500) grassland (600) desert (90)

11. How Does Energy Flow Through Ecosystems? • The net primary production of an ecosystem is influenced by many factors • The amount of sunlight • The availability of water and nutrients • The temperature • An ecosystem’s contribution to Earth’s total production is determined by the ecosystem’s productivity and by the portion of Earth that the ecosystem covers

12. How Does Energy Flow Through Ecosystems? tertiary consumer(fourth trophic level) • Food chains and food webs describe the feeding relationships within communities • A food chain is a linear feeding relationship with just one representative at each trophiclevel secondary consumer(third trophic level) primary consumer(second trophic level) producer(first trophic level) A simple terrestrial food chain

13. Figure 28-3b A simple marine food chain phytoplankton zooplankton secondary consumer(third trophic level) producer(first trophic level) primary consumer(second trophic level) tertiary consumer(fourth trophic level) quaternary consumer(fifth trophic level) A simple marine food chain

14. How Does Energy Flow Through Ecosystems? • Food chains and food webs describe the feeding relationships within communities (continued) • Animals in natural communities often do not fit neatly into the categories of primary, secondary, and tertiary consumers depicted in simple food chains • A food web shows many interconnected food chains, and actual feeding relationships in a community • Some animals, such as raccoons, bears, rats, and humans, are omnivores (“everything eaters”) and act as primary, secondary, and tertiary consumers

15. Figure 28-4 A simplified grassland food web

16. How Does Energy Flow Through Ecosystems? • Detritivores and decomposers release nutrients for reuse • Among the most important strands in a food web are the detritivores and decomposers • Detritivores (“debris eaters”) are an army of mostly small and often unnoticed organisms • Nematode worms and Earthworms • Vultures • Millipedes • Dung beetles • Slugs

17. How Does Energy Flow Through Ecosystems? • Detritivores and decomposers release nutrients for reuse (continued) • Decomposers are primarily fungi and bacteria • They feed on the same material as detritivores • They do not ingest chunks of organic matter • They secrete digestive enzymes outside their bodies, where the enzymes break down nearby organic material • Decomposers absorb some of the resulting nutrient molecules but leave the rest

18. How Does Energy Flow Through Ecosystems? • Detritivoresand decomposers are absolutely essential to life on Earth • Without detritivores and decomposers, ecosystems would gradually be buried by accumulated wastes and dead bodies, whose nutrients would be unavailable to enrich the soil and water

19. How Does Energy Flow Through Ecosystems? • Energy transfer through trophic levels is inefficient • Second Law of Thermodynamics • Inefficiency is a rule in living systems • Waste is heat produced by all biochemical reactions that keep cells alive • Only a fraction of the energy captured by producers of the first trophic level can be used by organisms in the second trophic level

20. How Does Energy Flow Through Ecosystems? • Energy transfer through trophic levels is inefficient (continued) • The average net energy transfer between trophic levels is roughly 10% efficient and is known as the “10% law” • An energy pyramid illustrates the energy relationships between trophic levels—widest at the base, and progressively narrowing in higher trophiclevels • A biomass pyramid for a community has the same general shape

21. Figure 28-5 An energy pyramid for a grassland ecosystem tertiaryconsumer(1 calorie) secondaryconsumer(10 calories) primaryconsumer(100 calories) producers(1,000 calories)

22. How Does Energy Flow Through Ecosystems? • Energy transfer through trophic levels is inefficient (continued) • The most abundant organisms are plants • The most abundant animals are herbivores • Carnivores are relatively scarce because there is far less energy available to support them • Energy losses within and between trophic levels mean that long-lived animals at higher trophic levels eat many times their body weight in food

23. How Does Energy Flow Through Ecosystems? • Energy transfer through trophic levels is inefficient (continued) • If the food contains certain types of toxic substances, they may be stored and become more concentrated • This biological magnification can lead to harmful and even fatal effects • Mercury in fish

24. How Do Nutrients Cycle Within and Among Ecosystems? • Nutrient cycles, also called biogeochemical cycles, describe the pathways that nutrients follow as they move from their major sources in the abiotic parts of ecosystems, called reservoirs, through living communities and back again

25. How Do Nutrients Cycle Within and Among Ecosystems? • The hydrologic cycle has its major reservoir in the oceans • The water cycle, or hydrologic cycle, is the pathway that water takes as it travels from its major reservoir—the oceans—through the atmosphere, to reservoirs in freshwater lakes, rivers, and groundwater, and then back again to the oceans

26. How Do Nutrients Cycle Within and Among Ecosystems? • The hydrologic cycle • The hydrologic cycle would continue even if life on Earth disappeared because the biotic portion of ecosystems plays a small role in the hydrologic cycle • The hydrologic cycle is crucial for terrestrial communities because it continually restores the fresh water needed for land-based life • The oceans cover 70% of the Earth’s surface and contain more than 97% of Earth’s water • Solar energy evaporates water, and it comes back to Earth as precipitation

27. Figure 28-6 The hydrologic cycle reservoirs reservoirs water vapor inthe atmosphere processes processes precipitationover land precipitationover the ocean evaporationfrom the landand from theleaves of plants evaporationfrom the ocean evaporation fromlakes and rivers lakes and rivers runofffrom riversand land water inthe ocean seepage through soilinto groundwater extraction foragriculture groundwater,includingaquifers

28. How Do Nutrients Cycle Within and Among Ecosystems? • The carbon cycle has major reservoirs in the atmosphere and oceans • Carbon atoms form the framework of all organic molecules • The carbon cycle is the pathway that carbon takes from its major short-term reservoirs in the atmosphere and oceans, through producers and into the bodies of consumers, detritivores, and decomposers, and then back again to its reservoirs

29. Figure 28-7 The carbon cycle reservoirs CO2 in theatmosphere processes trophic levels burningfossil fuels CO2 dissolvedin the ocean respiration fire photosynthesis producers consumers detritivoresand decomposers fossil fuels(coal, oil, natural gas) decomposition

30. How Do Nutrients Cycle Within and Among Ecosystems? • The carbon cycle • The complementary processes of uptake by photosynthesis and release by cellular respiration continually recycle carbon from the abiotic to the biotic portions of an ecosystem and back again

31. How Do Nutrients Cycle Within and Among Ecosystems? • The carbon cycle • Much of Earth’s carbon is bound up in limestone rock, formed from calcium carbonate (CaCO3) deposited on the ocean floor in the shells of prehistoric phytoplankton • This cycling requires millions of years • Fossil fuels, which include coal, oil, and natural gas, are additional long-term reservoirs for carbon

32. How Do Nutrients Cycle Within and Among Ecosystems? • The nitrogen cycle has its major reservoir in the atmosphere • Nitrogen is a crucial component of proteins, many vitamins, nucleotides (such as ATP), and nucleic acids (such as DNA) • The nitrogen cycle is the pathway taken by nitrogen from its primary reservoir—nitrogen gas (N2) in the atmosphere—to much smaller reservoirs of ammonia and nitrate in soil and water, through producers, consumers, detritivores and decomposers, and back to its reservoirs

33. How Do Nutrients Cycle Within and Among Ecosystems? • The nitrogen cycle • While nitrogen gas (N2) makes up 78% of the atmosphere, this form of nitrogen cannot be utilized by plants • Plants utilize nitrate (NO3) or ammonia (NH3) as their nitrogen source • N2 is converted to ammonia by specific bacteria during a process called nitrogen fixation

34. Figure 28-8 The nitrogen cycle reservoirs N2 in theatmosphere processes trophic levels burningfossil fuels lightning application ofmanufactured fertilizer producers consumers nitrogen-fixingbacteria in soiland legume roots ammonia andnitrates in water uptake byproducers detritivoresand decomposers decomposition denitrifyingbacteria ammoniaand nitratesin soil

35. How Do Nutrients Cycle Within and Among Ecosystems? • The nitrogen cycle • People significantly manipulate the nitrogen cycle, both deliberately and unintentionally • Plant legumes to fertilize fields • About 150 million tons of nitrogen-based fertilizer are applied to farms each year • The heat produced by burning fossil fuels combines atmospheric N2 and O2, generating nitrogen oxides that form nitrates • Human activities now dominate the nitrogen cycle

36. How Do Nutrients Cycle Within and Among Ecosystems? • The phosphorus cycle has its major reservoir in rock, bound to oxygen as phosphate • Phosphorus is found in biological molecules such as nucleic acids and the phospholipids of cell membranes • It also forms a major component of vertebrate teeth and bones • The phosphorus cycle is the pathway taken by phosphorus from its primary reservoir in rocks to much smaller reservoirs in soil and water, producers, consumers, detritivores and decomposers and back

37. Figure 28-9 The phosphorus cycle reservoirs processes trophic levels geologicaluplift phosphatein rock application ofmanufacturedfertilizer runofffrom rivers consumers runoff fromfertilizedfields producers uptake byproducers phosphatein water detritivores anddecomposers formation ofphosphate-containingrock phosphatein soil phosphatein sediment decomposition

38. Review • Why is energy flow not cyclical like nutrients? • Name the trophic levels in a community. • Why are detritivores and decomposers essential to ecosystem function? • What are the four major nutrient cycles?

39. What Happens When Humans Disrupt Nutrient Cycles? • As the human population grew and technology increased, people began to act more independently of natural ecosystem processes • The Industrial Revolution resulted in a tremendous increase in our reliance on energy stored in fossil fuels for heat, light, transportation, industry, and agriculture

40. What Happens When Humans Disrupt Nutrient Cycles? • Overloading the nitrogen and phosphorus cycles damages aquatic ecosystems • Fertilizers are applied to farm fields • Water dissolves and carries away some of the phosphate and nitrogen-based fertilizer • Overstimulatingthe growth of phytoplankton in the ocean “bloom”

41. What Happens When Humans Disrupt Nutrient Cycles? • Overloading the nitrogen and phosphorus cycles damages aquatic ecosystems (continued) • The phytoplankton die, and their bodies sink into deeper water and provide food for decomposer bacteria • The decomposers use up most of the available oxygen, and other aquatic organisms, such as invertebrates and fish, die, creating “dead zones” in many waters (Gulf of Mexico)

42. What Happens When Humans Disrupt Nutrient Cycles? • Overloading the sulfur and nitrogen cycles causes acid deposition • Burning of sulfur-containing fossil fuels, primarily coal, accounts for about 75% of all sulfur dioxide emissions worldwide • Days later and often hundreds of miles from the source, these acids fall to Earth in rain or snow

43. What Happens When Humans Disrupt Nutrient Cycles? • Interfering with the carbon cycle is warming Earth’s climate • Natural process called the greenhouse effect, which keeps our atmosphere relatively warm and allows life on Earth as we know it • For Earth’s temperature to remain constant, the total amount of energy entering and leaving Earth’s atmosphere must be equal

44. Figure 28-13 The greenhouse effect Most heat is radiatedinto space Sun Sunlight energyenters the atmosphere Some atmospheric heat isretained by greenhouse gases Some energyis reflected backinto space volcanoes forestfires Heat isradiated back intothe atmosphere Most sunlight strikesEarth’s surface and isconverted into heat power plantsand factories vehicleemissions agriculturalactivities homes and otherbuildings

45. What Happens When Humans Disrupt Nutrient Cycles? • Interfering with the carbon cycle is warming Earth’s climate (continued) • If atmospheric concentrations of greenhouse gases increase, more heat is retained than is radiated into space, causing Earth to warm • Greenhouse gases are increasing because people burn fossil fuels, releasing CO2 • Other important greenhouse gases include methane (CH4), released by agricultural activities and burning fossil fuels

46. What Happens When Humans Disrupt Nutrient Cycles? • Burning fossil fuels is causing climate change • Climate scientists predict that the warming atmosphere will cause more severe storms, including stronger hurricanes • Greater amounts of rain or snow will fall in single storms • More frequent and more prolonged droughts will occur • Increased CO2 makes the oceans more acidic