1. Chapter 54 Ecosystems

2. An ecosystem consists of all the organisms living in a community as well as all the abiotic factors with which they interact Ecosystems can range from a microcosm to lakes and forests Most ecosystems are powered by energy from sunlight, which is transformed to chemical energy by autotrophs and passed to heterotrophs Most energy is continually dissipated in the form of heat

3. Ecosystem Dynamics

4. Decomposition Decomposition connects all trophic levels Detritivores that feed on plant remains often form a link between producers and consumers Fungi and prokaryotes (bacteria) are the most important decomposers; they convert organic material from all trophic levels to inorganic compounds that can be recycled by autotrophs

5. Laws of Physics and Chemistry The first law of thermodynamics states that energy cannot be created or destroyed, only transformed –Sunlight → chemical energy → heat The second law of thermodynamics states that in each energy conversion, some energy is lost as heat Ecologists trace the energy flow in ecosystems and the efficiency of ecological energy conversion

6. Primary Production Primary production is a measure of the amount of light energy converted to chemical energy – output by autotrophs Only about 1-2% of the solar radiation that strikes the earth is converted to chemical energy – varies with latitude The worldwide photosynthetic production is about 170 billion tons of organic material per year

7. Primary Production Net primary production is the gross primary production minus the energy used by plants in their own cellular respiration (R) –NPP = GPP - R Primary production can be expressed as energy per unit area per unit time (J/m 2 /yr) or as biomass measured in terms of dry weight of organic material added (g/m 2 /yr) Standing crop is the total biomass of plants in an ecosystem

8. Primary Production in Different Ecosystems

9. Regional Annual Net Primary Production

10. Primary Production in Marine Ecosystems In aquatic ecosystems, light and nutrients limit primary production Light only reaches the photic zone – more than half is absorbed in the first meter Nutrients limit marine production more than light Nitrogen and phosphorous, as well as iron, levels limit the growth of phytoplankton – known as limiting nutrients

11. Primary Production in Freshwater Ecosystems In freshwater ecosystems, light intensity, temperature, and availability of minerals affect production Eutrophication, the shift in composition of phytoplankton from green algae and diatoms to blooms of cyanobacteria, has been linked to phosphorous pollution from sewage and fertilizer runoff

12. Primary Production in Terrestrial Ecosystems Both water supply and temperature vary more in terrestrial ecosystems – production is related to precipitation and temperature Nitrogen or phosphorous is the limiting nutrient in many ecosystems

13. Secondary Production Secondary production – is the rate at which consumers produce new biomass from their food The efficiency of energy transfer between trophic levels is usually less than 20% Herbivores consume only a fraction of the plant material produced; they cannot digest all they eat; and much of the energy they do absorb is used for cellular respiration

14. Trophic Efficiency Trophic efficiency is the percentage of the energy of one trophic level that makes it to the next level, usually ranging from 5-20% The pyramid of production shows the multiplicative loss of energy via heat, respiration, and feces

15. The Biomass Pyramid A biomass pyramid illustrates the standing crop biomass of organisms at each trophic level.

16. Pyramid of Numbers The pyramid of numbers illustrates that higher trophic levels contain small numbers of individuals, resulting from the larger size of these animals and the greatly decreased energy availability illustrated by the pyramid of production

17. Cycling of Chemical Elements Biochemical cycles – chemical elements are passed between abiotic and biotic components of an ecosystem After chemicals are passed through the food chain, they are returned to the atmosphere, water, or soil through respiration and the action of decomposers

18. Cycling of Nutrients

19. The Water Cycle

20. The Carbon Cycle

21. The Nitrogen Cycle

22. The Phosphorous Cycle

23. Cycling of Nutrients Decomposition rates largely determine the rates of nutrient cycling Nutrient cycling is strongly regulated by vegetation

24. Human Impact on Ecosystems Human activity often intrudes in nutrient cycles by removing nutrients from one part of the biosphere and adding them to another Agricultural effects – harvesting of crops removes nutrients that would otherwise recycle into the soil – requires the addition of fertilizers Accelerated eutrophication – leads to oxygen shortages and fish kills Combustion of fossil fuels is the main cause of acid precipitation

25. Distribution of Acid Precipitation in the US

26. Human Impact on Ecosystems Toxins can become concentrated in successive trophic levels of food webs Biological magnification of DDT in a food chain

28. Human Impact on Ecosystems Rising atmospheric CO 2 – combustion of fossil fuels and burning of wood The greenhouse effect – CO 2 and water vapor in the atmosphere absorb infrared radiation reflected from Earth and re-reflect it back to Earth, causing an increase in temp. Global warming – caused by an increase in CO 2 levels –Climatologists predict a temp. rise of 2°C in the next 100 years if CO 2 levels continue to rise

29. The Greenhouse Effect

30. Increase in Atmospheric CO 2 and Average Temp. from 1958-2000

31. Depletion of the Ozone Layer The layer of ozone molecules (O 3 ) in the lower stratosphere absorb damaging ultraviolet radiation This layer has been gradually thinning since 1975, largely as a result of the accumulation of breakdown products of chlorofluorocarbons in the atmosphere Loss of the ozone layer leads to more intense UV radiation and an increase in skin cancer risk.

32. Depletion of the Ozone Layer