Chapter 54

1. Chapter 54 Ecosystems (all organisms living in a community as well as all the abiotic factors they interact with.

2. Ecosystem Ecology Emphasizes: 1.) Energy flow: energy enters in form of sunlight, converted to chemical energy by autotrophs (producers), passed to heterotrophs (consumers) in food compounds & dissipated (lost) as heat. a.) Energy cannot be created or destroyed – just transformed. b.) Energy conversions are not completely efficient.

3. Ecosystem Ecology cont’d… 2.) Chemical cycling: Elements such as C & N are cycled among abiotic & biotic ecosystem components. a.) An atom of carbon moves from trophic level to trophic level and eventually to decomposers & then back into the food chain through producers over and over again. Distinctions b/w energy & matter: Ecosystems require a constant influx of energy b/c it is not recycled. Elements (matter) are cycled within ecosystems.

4. Ecosystem Ecology cont’d… 3.) Trophic relationships a.) Primary producers: autotrophs that support all other trophic levels b.) Primary consumers: herbivores – eat plants/primary producers c.) Secondary consumers: carnivores that eat herbivores d.) Tertiary consumers: carnivores that eat other carnivores/secondary

5. Ecosystem Ecology cont’d… e.) Detritovores/decomposers: consumers that get their energy from detritus: nonliving organic material such as the remains of dead organisms, feces, fallen leaves, etc. *Super Important!*

6. Concept Check 1.) Why is the transfer of energy in an ecosystem referred to as energy flow, not energy cycling? 2.) Predict what would happen to an ecosystem if there were no detritovores.

7. Production in Ecosystems 1.) Primary production: the amount of light energy converted to chemical energy (organic compounds) during a given time period. a.) This sets the “spending limit” for the “energy budget” of an entire ecosystem.

9. Production in Ecosystems b.) Of the visible light that reaches producers, about 1-2% is converted to chemical energy through photosynthesis c.) That’s enough though to create 170 billion tons of organic material/year!

10. Production in Ecosystems 2.) Gross Primary Production (GPP): the total primary production in an ecosystem. a.) Not all of this is stored as organic material in producers b/c the producers have to use some as fuel for their cellular respiration. 3.) Net Primary Production (NPP): equals GPP minus the energy used by primary producers for respiration (R). a.) This is an important measurement – reflects what is available to consumers!

12. Production in Ecosystems b.) Can be expressed as energy per unit area per unit time (J/m2/yr) c.) Can also be expressed as biomass (weight) of vegetation added to ecosystem per unit area per unit time (g/m2/yr) d.) NPP varies from one ecosystem to the next

13. Production in Ecosystems i.) Tropical rain forests, coral reefs have high NPP. ii.) How much each ecosystem contributes to GLOBAL NPP depends on how big it is. Even though per unit area the open ocean has a low NPP, b/c it is so big it contributes more NPP than any other ecosystem.

14. Production in Ecosystems

15. Primary Production in Aquatic Ecosystems 1.) Primary production in aquatic ecosystems is limited not only by light availability/penetration but also by nutrient availability. a.) Limiting nutrient: the element that must be added in order for production to increase in a certain area. i.) N and P are most often the limiting nutrients in marine ecosystems. Fe can also be a limiting nutrient. ii.) Adding limiting nutrients typically causes the pop of cyanobacteria to explode. These bacteria “fix” N making it available to all other phytoplankton whose pop then also explodes.

16. Primary Production in Aquatic Ecosystems b.) Practical implications: i.) When sewage and/or fertilizer (containing N & P) from fields runs off into freshwater lakes & rivers, it can cause an explosion of cyanobacteria which is called eutrophication or cultural eutrophication. ii.) This can severely disrupt an ecosystem

18. Primary Production in Terrestrial and Wetland Ecosystems 1.) Temperature and moisture are the key factors controlling primary production in terrestrial ecosystems. a.) Warm, wet tropical rainforest = high productivity. Deserts & tundra = low productivity. Intermediate is temperate forests & grasslands. b.) Actual evapotranspiration: the annual amount of water transpired by plants & evaporated from a landscape. i.) Transpiration: water loss from plants through pores in leaves called stomata. c.) Actual evapotranspiration increases with the amount of precipitation in a region & the amount of solar energy available that drives evaporation & transpiration. So, tropical rain forests have HIGH evapotranspiration & high productivity.

19. Concept Check 1.) Why is only a small portion of the solar energy that strikes Earth’s atmosphere stored by primary producers? 2.) How could ecologists experimentally determine the nutrient limiting primary production in an ecosystem?

20. Concept Check con’td… 3.) Why does the open ocean account for almost 25% of Earth’s primary production despite its relatively low rate of primary production? 4.) Why is an ecosystem’s net primary production lower than its gross primary production?

21. Energy Transfer Between Trophic Levels 1.) Secondary Production: the amount of chemical energy in consumers’ food that is converted to their own new biomass during a given time period.

22. Energy Transfer Between Trophic Levels 2.) Production efficiency: the fraction of energy stored in food that is not used for respiration. a.) Production eff. = Net secondary production Assimilation of primary prod. i.) Net secondary production = the energy stored in biomass (represented by growth/reproduction). ii.) Assimilation = total energy taken in &used for growth/reproduction & respiration.

23. Energy Transfer Between Trophic Levels b.) For the caterpillar, the production efficiency is 33%. i.) Of the 100 J of energy actually taken in, 67 J are used for cell resp and only 33 J are used for growth/reproduction. (Don’t count the energy that goes to feces…)

24. Energy Transfer Between Trophic Levels c.) Birds & mammals typically have a production efficiency of only 1-3% because they use so much energy to maintain a constant body temperature. i.) Endotherms: maintain constant body temp. d.) Fish have a production efficiency around 10% and insects around 40%. ii.) Ectotherms: body temp fluctuates with temp of environment

25. Trophic Efficiency Definition: the % of production transferred from one trophic level to the next. 1.) Takes into account the energy lost through respiration & contained in feces & the energy in a lower trophic level that is not consumed at the next trophic level. 2.) Ranges from 5-20%. a.) This means that 80-95% of the energy available at one trophic level is not transferred to the next. b.) The loss is multiplied at each step of a food chain: i.) If 10% of energy is transferred from primary prod to primary consumers and 10% of that energy is transferred To secondary consumers, then really only 1% of NPP is available to secondary consumers.

26. Trophic Efficiency c.) So, about 0.1% of energy fixed by photosynthesis can flow to a tertiary consumer. i.) This loss of energy probably explains why most food webs are only about 4 – 5 trophic levels long.

27. Pyramid of Production 1.) Used to represent the loss of energy at each trophic level. 2.) Size of each block is proportional to the net production of trophic level.

28. Pyramid of Biomass 1.) Each tier of pyramid represents the standing crop biomass of one trophic level. a.) Standing crop: the total dry weight of all organisms. 2.) Most biomass pyramids narrow from primary producers to top level consumers because energy transfers are so inefficient. a.) Some aquatic ecosystems are inverted b/c phytoplankton grow, reproduce & are eaten so quickly that they never build a huge biomass.

29. Most biomass pyramids are similar to example (a) above. Some aquatic ecosystems may resemble example (b).

30. Pyramid of Numbers 1.) Represents the number of individual organisms present in each trophic level. a.) Narrows toward top b/c top consumers tend to be large and fewer in numbers.

31. Eat less meat & eat more plants! The way energy flows through an ecosystem implies a lot about how we should feed our population… 1.) Eating meat is an inefficient way to tap into photosynthetic production. 2.) You obtain far more calories by eating a certain amount of grain directly as a primary consumer than by processing that same amount of grain through another trophic level and eating meat from grain fed animals. 3.) We could feed MANY more people & use a lot less land if we all fed as primary consumers – i.e. if we were all vegetarians.

32. The Green World Hypothesis If so many primary consumers feed on the producers then why are ecosystems still so green? 1.) According to the GWH terrestrial herbivores consume relatively little plant biomass b/c they are held in check by predators, parasites, disease, etc.

33. Concept Check 1.) If an insect that eats plant seeds containing 100 J of energy uses 30 J of that energy for respiration and excretes 50 J in its feces, what is the insect’s net secondary production? What is its production efficiency? a.) Net secondary = 20 J = 20% 100J b.) Prod. Efficiency = 20 J = 40% 50 J

34. Concept Check Why does the production pyramid have the same general shape as the biomass pyramid in most ecosystems? Under what circumstances might the shapes of the two pyramids differ?

35. Nutrient Cycling While energy flows THROUGH ecosystems, nutrients can cycle within them. Nutrient cycles are called biogeochemical cycles because these circuits involve both biotic & abiotic components.

36. The Water Cycle

37. The Carbon Cycle

38. The Nitrogen Cycle *Important! Most N is in atmosphere. Only becomes available to plants via nitrogen fixation which is carried out by special bacteria. We get all our nitrogen by eating plants or animals that eat plants.

39. The Phosphorous Cycle Phosphate is absorbed by plants – that’s how we get it. Again, from eating plants or eating animals that eat plants.

40. Why do we care about C, N & P? 1.) Carbon: the basis of ALL organic molecules (all the molecules that we are made of). 2.) Nitrogen: component of amino acids, proteins & nucleic acids. 3.) Phosphorous: component of nucleic acids, phospholipids & ATP.

41. Too many humans = Disruption of Biogeochemical cycles!

42. Nutrient Enrichment 1.) Human activities often remove nutrients from one ecosystem & deposit them in another. a.) Agriculture: nutrients in farm soil (maybe artificial – fertilizers) run off into lakes or streams = cultural eutrophication. i.) Cultural eutrophication disrupts fish populations – often wiping them out. All the excess plants/algae die and then decompose. The decomposers use up all oxygen – kills fish.

43. Acid Precipitation 1.) Burning fossil fuels releases sulfur & nitrogen oxide. a.) Reacts with water in atmosphere forming sulfuric & nitric acid – then falls to earth as acid precipitation. 2.) Lowers aquatic ecosystem pH & disrupts soil chemistry. 3.) Industry in one area usually produces acid precipitation that falls in another.

44. Toxins in Environment 1.) We release an immense amount of synthetic chemicals into ecosystems – many of which are toxic (we don’t know or we don’t care). 2.) Organisms can metabolize & excrete some but others accumulate in organisms’ tissues. 3.) Toxins that accumulate become more and more concentrated at higher and higher trophic levels = biological magnification. a.) Occurs b/c the biomass at any given trophic level is produced from a much larger biomass ingested from the level below.

45. Biological Magnification of DDT DDT used to control mosquitoes. DDT softened bird eggshells – shells broke = huge decline in reproduction. Rachel Carson’s Silent Spring drew attention to problem.

47. http://www.storyofstuff.com/ http://www.chrisjordan.com/

48. Atmospheric Carbon Dioxide 1.) Atmospheric levels of carbon dioxide are on the rise. 2.) The Greenhouse Effect & Global Warming a.) Much of the solar radiation that strikes Earth is reflected back into space. b.) However, gases in Earth’s atmosphere such as carbon dioxide and water vapor absorb much of the reflected radiation – this warms the Earth = very important. i.) If not for this greenhouse effect the average temperature on Earth would be below zero!

50. Atmospheric Carbon Dioxide c.) There has been a huge increase in the concentration of atmospheric carbon dioxide (due to human burning of fossil fuels mainly). d.) Increase carbon dioxide concentration = increase in global temperature = melting of polar ice caps (?), flooding of coastal areas (?), changes in global climate patterns (?) …yikes.