34 Now the crickets don’t have enough food so their numbers go down
35 ..and so on. Numbers of each species have an effect on the numbers of the other species in the web.
36 Use the food web worksheet to predict what might happen in the following situations: A) There is very little rain and much of the Marsh Grass and Cattail die off.B) Humans nearby bring cats into the area.C) The frogs eats some poisoned slugs from a garden
37 Transfer of EnergyWhen a zebra eats the grass, it does not obtain all of the energy the grass has (much of it is not eaten)When a lion eats a zebra, it does not get all of the energy from the zebra (much of it is lost as heat)
38 No organism EVER receives all of the energy from the organism they just ate Only 10% of the energy from one trophic level is transferred to the next – this is called the 10% law
39 Key Points to Remember… Energy moves from one organisms to another when it is eatenEach step in this transfer of energy is known as a trophic levelThe main trophic levels are producers, consumers, and decomposers
40 DDT affect on Food WebsDDT: Used in the 40’s and 50’s as a pesticide .Outlawed in 70’s: collects in fats of organisms and cannot be broken down.Marine microorganisms greatly affectedcollected in plankton and green algaeslows photosynthesis – not deathMostly noted in birds eggsthinning of eggshellsBrown Pelican: nestsonly 1 chick survived
42 BiomassThe total mass of the organic matter at each trophic level is called biomassBiomass is just another term for potential energy – energy that is to be eaten and used.The transfer of energy from one level to another is very inefficient (10% Law)
44 Ecological PyramidAn ecological pyramid shows the relationship between consumers and producers at different trophic levels in an ecosystemShows the relative amounts of energy or matter contained at each trophic levelThe Pyramid shows which level has the most energy and the highest number of organisms
47 Ecological Pyramid Which level has the most energy? Which level has the most organisms?Which level has the least organisms?Which level has the least energy?
48 This powerpoint was kindly donated to www.worldofteaching.com is home to over a thousand powerpoints submitted by teachers. This is a completely free site and requires no registration. Please visit and I hope it will help in your teaching.