Ecosystems, Energy, and Matter An ecosystem consists of all the organisms living in a community

1. Ecosystems, Energy, and Matter • An ecosystem consists of all the organisms living in a community

2. Regardless of an ecosystem’s size, its dynamics involve two main processes: energy flow and chemical cycling

3. Ecosystems and Physical Laws • The laws of physics and chemistry apply to ecosystems particularly in regard to the flow of energy • Energy is conserved but degraded to heat during ecosystem processes

4. Trophic Relationships • Energy and nutrients pass from primary producers (autotrophs) to primary consumers (herbivores) and then to secondary consumers (carnivores) • Plants are the main producers on land, while in water, photosynthetic protists and cyanobacteria (phytoplankton) are the main producers

5. The ultimate source of energy for most ecosystems is the sun

6. All other trophic levels are made of consumers or heterotrophs, which eat other organisms • Primary consumers eat plants or other producers, so are herbivores • Secondary consumers eat primary consumers, and are carnivores • Quaternary consumers eat tertiary consumers

7. Energy flows through an ecosystem • Entering as light and exiting as heat

8. Nutrients cycle within an ecosystem

9. Decomposition • Decomposition is the breakdown of organic material into inorganic matter, and connects all trophic levels • Detritus (dead organisms, wastes, plant litter)

10. Detritivores, mainly bacteria and fungi, are special consumers that recycle essential chemical elements by decomposing organic material and returning elements to inorganic reservoirs

11. Some energy moves through ecosystems as waste or excretion • Decomposers also release energy remaining in detritus (undigested food in wastes, and dead organisms)

12. The Global Energy Budget • The amount of solar radiation reaching the surface of the Earth limits the photosynthetic output of ecosystems • Most is absorbed, scattered, or reflected by the atmosphere or by the earth’s surface • Of all the visible light that reaches leaves and other autotrophs,only ~1.2% is converted to chemical energy by photosynthesis • This 1.2% on a global scale produces 170 billion tons of organic material (biomass)per year in the biosphere

13. The amount of (mass) living organic material in an ecosystem is called biomass • Typically, only about 5-20% of the sun’s energy trapped by plants during photosynthesis is transferred to the primary consumers that eat plants • Respiration breaks down glucose made during photosynthesis and releases energy, this energy is lost as heat or used for maintenance by plants (growth, repair, reproduction)

14. Biomass and Energy • Biomass is the total mass of organic matter such as carbohydrates, lipids, and proteins • Dry weight (mass) is is the weight of the organic matter minus the weight of the water in that matter, since water is inorganic and does not contain usable energy • Biomass is expressed as g/m2/y • Biomass can be used as a measure of the amount of energy available in an ecosystem

15. Gross and Net Primary Production • Primary productivity is the rate at which producers convert solar energy to chemical energy • Total primary production in an ecosystem is known as that ecosystem’s gross primary production (GPP) • Gross production = total amount of energy trapped in the organic matter produced by plants/per area/per time

16. Net primary production (NPP) is equal to gross production minus the energy used by the primary producers for respiration • Only net production is available to consumers

17. Different ecosystems vary considerably in their net primary production • And in their contribution to the total NPP on Earth

18. Energy transfer between trophic levels is usually about 10% efficient • The 90% decline is an average, this ranges from ~95% to 80% • The trend of energy flow declining significantly with each higher trophic level holds for all ecosystems

19. Energy cannot be created or destroyed, though it can be changed from one form to another • All energy transformations involve the conversion of some energy to heat, which is lost from the ecosystem • In most ecosystems, herbivores manage to eat only a fraction of the plant material produced, they also don’t digest all of what they consume

20. Cellular respiration breaks down organic compounds to inorganic wastes and heat • Of all the energy taken in, only the chemical energy left over and stored after respiration can add to the biomass of the trophic level • Only this energy that is stored as biomass is available to the next trophic level

21. Production Efficiency • When a caterpillar feeds on a plant leaf only about one-sixth (16%) of the energy in the leaf is used for secondary production

22. Most food chains are limited to 3-5 trophic levels, because there is not enough energy at the top level to support another trophic level

23. At each trophic level energy is lost as metabolic heat during maintenance (respiration) • The energy passed to the next trophic level becomes wastes, metabolic heat or is passed to the next trophic level • Eventually, all energy flowing through ecosystems is lost as metabolic heat

24. Pyramids of energy • This loss of energy with each transfer in a food chain can be represented by a pyramid of energy

25. Pyramids of Biomass • One important ecological consequence of low trophic efficiencies can be represented in a biomass pyramid • During respiration, glucose is broken down into water and carbon dioxide which is released back into the environment, resulting in a loss of biomass

26. Most biomass pyramids • Show a sharp decrease at successively higher trophic levels

27. Certain aquatic ecosystems • Have inverted biomass pyramids

28. Pyramids of Numbers • A pyramid of numbers represents the number of individual organisms in each trophic level

29. The dynamics of energy flow through ecosystems have important implications for the human population

30. Worldwide agriculture could successfully feed many more people if humans all fed more efficiently, eating only plant material

31. Humans have about 10X more energy available to them when they eat grain, than when they eat grain-fed cattle • It may actually take 100X more energy to feed humans on cattle, than on plants directly

32. Energy Flow • Eventually the ecosystem would run out of energy if not supplied by a continuous inflow of energy from an outside source like the sun • Energy flows in one direction thru ecosystems

33. Chemical Cycling • Chemicals are cycled between abiotic components (air, soil, water) and biotic components of the ecosystem • There are no extraterrestrial sources of water or other chemical nutrients, therefore life depends on the recycling of chemicals

34. Nutrient circuits that cycle matter through an ecosystem involve both biotic and abiotic components and are often called biogeochemical cycles

35. A general model of nutrient cycling • Includes the main reservoirs of elements and the processes that transfer elements between reservoirs

36. Water Cycle • Water moves in a global cycle driven by solar energy • Three processes occur in the water cycle: 1.evaporation 2.precipitation 3.transpiration

37. Carbon Cycle • Photosynthesis converts CO2 from atmosphere into organic compounds which are then eaten by consumers, which are then eaten by other consumers and so on • Detritivores decompose detritus and return carbon to atmosphere • Cellular respiration by plants, animals breaks down organic compounds back into CO2 and returns it to the atmosphere

38. Phosphorus Cycle • Rocks are main abiotic reservoir • Erosion adds phosphate to soil • Consumers obtain phosphorus by eating plants or consumers • Decomposition returns phosphates to soil • Some phosphates precipitate out of solution at bottom of lakes and oceans and become part of new rocks

39. Nitrogen Cycle • Most of the nitrogen cycling in natural ecosystems involves local cycles between organisms and soil or water • Atmosphere is 80% nitrogen (N2 gas) • Most living organisms cannot use nitrogen in this form

40. Four main processes occur in the nitrogen cycle • Nitrogen fixation • Bacteria in the soil or in root nodules of legumes convert atmospheric N2 to ammonia (NH3) which becomes NH4+ • Nitrification • Plants use nitrogen to make proteins, which are eaten by and passed on to consumers

41. Ammonification • Detritivores decompose nitrogen-containing detritus back into ammonium • Denitrification • Soil nitrates are converted back into atmospheric N2 gas by bacteria

42. Decomposition and Nutrient Cycling Rates • Decomposers (detritivores) play a key role • In the general pattern of chemical cycling

43. The rates at which nutrients cycle in different ecosystems • Are extremely variable, mostly as a result of differences in rates of decomposition

44. In one experiment, the trees in one valley were cut down • And the valley was sprayed with herbicides

45. Net losses of water and minerals were studied • And found to be greater than in an undisturbed area • These results showed how human activity • Can affect ecosystems

46. As the human population has grown in size • Our activities have disrupted the trophic structure, energy flow, and chemical cycling of ecosystems in most parts of the world

47. Nutrient Enrichment • In addition to transporting nutrients from one location to another • Humans have added entirely new materials, some of them toxins, to ecosystems

48. Agriculture and Nitrogen Cycling • Agriculture constantly removes nutrients from ecosystems • That would ordinarily be cycled back into the soil

49. Nitrogen is the main nutrient lost through agriculture • Industrially produced fertilizer is typically used to replace lost nitrogen • But the effects on an ecosystem can be harmful

50. Phosphates from fertilizers and detergents runoff and end up in waterways