Food Chains and Food Webs

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Food Chains and Food Webs

  1. 1. Food Webs and Ecological Pyramids
  2. 2. <ul><li>Every species interacts with other species and with its environment in a unique way. </li></ul>
  3. 3. <ul><li>These interactions define the ecological niche of a species - the role of a species within an ecosystem. </li></ul>
  4. 4. Ecological Niche <ul><li>For example, the ecological niche of a black bear is as follows: </li></ul><ul><ul><li>black bears feed on nuts and berries as well as insects and other small animals </li></ul></ul><ul><ul><li>bears carry seeds over long distances in their digestive systems before they are expelled and germinate </li></ul></ul>
  5. 5. Ecological Niche <ul><li>For example, the ecological niche of a black bear is as follows: </li></ul><ul><ul><li>bears hibernate during the winter </li></ul></ul><ul><ul><li>they have few predators, but are fed on by blood-sucking insects and other parasites </li></ul></ul>
  6. 6. <ul><li>A key feature of any ecosystem is the feeding roles of each species. </li></ul><ul><li>We have already distinguished between producers and consumers, however consumers can be further subdivided depending on what types of organisms they eat. </li></ul>Ecological Niche
  7. 7. Ecological Niche animal that feeds on the remains of another organism scavenger animal that eats both plants and animals omnivore animal that eats other animals carnivore animal that eats plants or other producers herbivore Definition Feeding Role
  8. 8. <ul><li>The most common interactions between species are through feeding relationships. </li></ul>
  9. 9. <ul><li>The easiest way to display these relationships is with food chains. </li></ul><ul><li>Food chains illustrate who eats whom in an ecosystem. </li></ul>Food Chains
  10. 10. <ul><li>Food chains show how energy passes through an ecosystem. </li></ul><ul><li>Energy is continually lost from all levels of the food chain. </li></ul>Food Chains
  11. 11. <ul><li>Ecologists refer to the trophic level, or feeding level, to describe the position of an organism along a food chain. </li></ul>Trophic Levels Tertiary consumers (carnivores) Secondary consumers (carnivores or omnivores) Primary consumers (herbivores) Primary producers 1st Trophic Level 2nd Trophic Level 3rd Trophic Level 4th Trophic Level
  12. 12. <ul><li>Producers occupy the lowest, or first, trophic level. Herbivores occupy the second trophic level, and carnivores occupy the third and fourth trophic levels. </li></ul>Trophic Levels Tertiary consumers (carnivores) Secondary consumers (carnivores or omnivores) Primary consumers (herbivores) Primary producers 1st Trophic Level 2nd Trophic Level 3rd Trophic Level 4th Trophic Level
  13. 13. <ul><li>Food chains do not exist in nature. They are only used to show simple feeding relationships. </li></ul><ul><li>Food chains are part of more complex sets of relationships that exist among species. </li></ul>Food Webs
  14. 14. <ul><li>A more accurate, but still incomplete, way to illustrate interactions is with a food web. A food web shows a series of interconnecting food chains. </li></ul>Food Webs
  15. 15. <ul><li>Food webs are highly complex, with consumers feeding on many different species. </li></ul><ul><li>The large number of interactions tends to reduce the vulnerability of any one species to the loss or decline of another species. </li></ul>Food Webs
  16. 16. <ul><li>Food webs are useful tools to figure out what may happen when a species is removed from or added to an ecosystem. </li></ul>Food Webs
  17. 17. <ul><li>For example, if a species is removed from a food web, the species it feeds on may increase dramatically in numbers. </li></ul>
  18. 18. <ul><li>Conversely, the population of a newly introduced species may disrupt the entire food chain. </li></ul>Food Webs For this reason, complex food webs are thought to be more stable than simple food webs.
  19. 19. Before
  20. 20. After
  21. 21. <ul><li>Another way ecologists illustrate how ecosystems function is through ecological pyramids. </li></ul>Ecological Pyramids
  22. 22. <ul><li>Ecological pyramids display relationships between trophic levels in an ecosystem. </li></ul>Ecological Pyramids
  23. 23. <ul><li>The three types of ecological pyramids are energy, numbers and biomass. </li></ul>Ecological Pyramids energy pyramid pyramid of numbers pyramid of biomass
  24. 24. <ul><li>The size of each layer in the energy pyramid represents the amount of energy available at that trophic level. </li></ul>Energy Pyramids An energy pyramid illustrates energy loss and transfer between trophic levels.
  25. 25. <ul><li>Only about 10% of the energy taken in by the individuals at one trophic level is passed on to individuals at the next trophic level. </li></ul>Energy Pyramids 1000 kJ 100 kJ 10 kJ
  26. 26. <ul><li>Species in the highest trophic levels have less energy available to them than species near the bottom. </li></ul>Energy Pyramids This often results in their populations being much smaller than species lower in the food chain (i.e. an ecosystem will have fewer predators than herbivores).
  27. 27. <ul><li>Biomass is the total mass of all living organisms in a given area. A pyramid of biomass shows the total mass of organisms in each trophic level. </li></ul>Pyramid of Biomass
  28. 28. <ul><li>A pyramid of numbers shows the number of individuals of all populations in each trophic level. </li></ul>Pyramid of Numbers
  29. 29. <ul><li>http://www.explorelearning.com/index.cfm?method=cResource.dspDetail&ResourceID=381 </li></ul>Food Web Gizmo

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