Population Ecology & Food Web

1. Population Ecology & Food Web 6c. Students know how fluctuations in population size in an ecosystem are determined by the relative rates of birth, immigration, emigration, and death. 6d. Students know how water, carbon, and nitrogen cycle between abiotic resources and organic matter in the ecosystem and how oxygen cycles through photosynthesis and respiration. 6e.Students know a vital part of an ecosystem is the stability of its producers and decomposers. 6f. Students know at each link in a food web some energy is stored in newly made structures but much energy is dissipated into the environment as heat. This dissipation may be represented in an energy pyramid.

2. Energy flow and chemical cycling are the two fundamental processes in ecosystems • A community interacts with abiotic factors, forming an ecosystem • Energy flows from the sun, through plants, animals, and decomposers, and is lost as heat • Chemicals are recycled between air, water, soil, and organisms

3. A terrarium ecosystem Chemical cycling(C, N, etc.) Chemicalenergy Heatenergy Lightenergy

4. Trophic structure is a key factor in ecosystem dynamics • A food chain is the stepwise flow of energy and nutrients • from plants (producers) • to herbivores (primary consumers) • to carnivores (secondary and higher-level consumers)

5. TROPHIC LEVEL Quaternaryconsumers Carnivore Carnivore Tertiaryconsumers Carnivore Carnivore Secondaryconsumers Carnivore Carnivore A TERRESTRIAL FOOD CHAIN AN AQUATIC FOOD CHAIN Primaryconsumers Herbivore Zooplankton Producers Plant Phytoplankton

6. Decomposition is the breakdown of organic compounds into inorganic compounds • Decomposition is essential for the continuation of life on Earth • Detritivores decompose waste matter and recycle nutrients • Examples: animal scavengers, fungi, and prokaryotes

7. Food chains interconnect, forming food webs • A food web is a network of interconnecting food chains • It is a more realistic view of the trophic structure of an ecosystem than a food chain

8. Wastes anddead organisms Tertiaryandsecondaryconsumers Secondaryandprimaryconsumers Primaryconsumers Producers Detritivores (Plants, algae,phytoplankton) (Prokaryotes, fungi,certain animals)

9. Energy supply limits the length of food chains • Biomass is the amount of living organic material in an ecosystem • Primary production is the rate at which producers convert sunlight to chemical energy • The primary production of the entire biosphere is about 170 billion tons of biomass per year

10. A pyramid of production reveals the flow of energy from producers to primary consumers and to higher trophic levels Tertiaryconsumers 10 kcal Secondaryconsumers 100 kcal Primaryconsumers 1,000kcal Producers 10,000 kcal 1,000,000 kcal of sunlight

11. Only about 10% of the energy in food is stored at each trophic level and available to the next level • This stepwise energy loss limits most food chains to 3 - 5 levels • There is simply not enough energy at the very top of an ecological pyramid to support another trophic level

12. Connection: A production pyramid explains why meat is a luxury for humans • The dynamics of energy flow apply to the human population as much as to other organisms • When we eat grain or fruit, we are primary consumers • When we eat beef or other meat from herbivores, we are secondary consumers • When we eat fish like trout or salmon (which eat insects and other small animals), we are tertiary or quaternary consumers

13. Because the production pyramid tapers so sharply, a field of corn or other plant crops can support many more vegetarians than meat-eaters TROPHIC LEVEL Humanmeat-eaters Secondaryconsumers Primaryconsumers Humanvegetarians Cattle Corn Corn Producers

14. Chemicals are recycled between organic matter and abiotic reservoirs • Ecosystems require daily infusions of energy • The sun supplies the Earth with energy • But there are no extraterrestrial sources of water or other chemical nutrients • Nutrients must be recycled between organisms and abiotic reservoirs • Abiotic reservoirs are parts of the ecosystem where a chemical accumulates

15. There are four main abiotic reservoirs • Water cycle • Carbon cycle • Nitrogen cycle • Phosphorus cycle

16. Water moves through the biosphere in a global cycle • Heat from the sun drives the global water cycle • Precipitation • Evaporation • Transpiration

17. Solar heat Net movementof water vaporby wind Water vaporover the sea Water vaporover the land Evaporationandtranspiration Precipitationover the land Precipitationover the sea Evaporationfrom the sea Oceans Surface waterand groundwater Flow of waterfrom land to sea

18. The carbon cycle depends on photosynthesis and respiration • Carbon is taken from the atmosphere by photosynthesis • It is used to make organic molecules • It is returned to the atmosphere by cellular respiration

19. CO2 in atmosphere Burning Cellular respiration Plants,algae,cyanobacteria Photosynthesis Higher-levelconsumers Primaryconsumers Wood andfossil fuels Decomposition Detritivores(soil microbesand others) Detritus

20. The nitrogen cycle relies heavily on bacteria • Nitrogen is plentiful in the atmosphere as N2 • But plants cannot use N2 • Various bacteria in soil (and legume root nodules) convert N2 to nitrogen compounds that plants can use • Ammonium (NH4+) and nitrate (NO3–)

21. Some bacteria break down organic matter and recycle nitrogen as ammonium or nitrate to plants • Other bacteria return N2 to the atmosphere

22. Nitrogen (N2) in atmosphere Amino acidsand proteins inplants and animals Assimilationby plants Nitrogenfixation Denitrifyingbacteria Detritus Nitrogen-fixingbacteria in rootnodules of legumes Nitrates(NO3–) Detritivores Nitrogen-fixingbacteria in soil Decomposition Nitrifyingbacteria Nitrogenfixation Ammonium (NH4+)