1. Big on Biology A different kind of World Wide Web 9-12 Science Std: Bio 6f

2. Food Chains and Webs  Food chain: step-by-step sequence that links together organisms that feed on each other o Ex: bat ate a mosquito that had bitten a coyote that had eaten a grasshopper that had chewed a leaf

3. Different Food Chains Terrestrial (Land-Based) Marine (Water-Based)

4. o Food chain supposes that organisms eat only that one particular organism  We know that organisms can eat more than one type of organism  Makes links to different organisms to create more realistic picture of a food web  Food web: complex relationship formed by interconnecting food chains or feeding relationships signified by arrows

5. FOOD WEBS

7. Organisms in the Food Web  Two types of organisms based on where they get their energy (food): o 1. Autotrophs o 2. Heterotrophs

8. o1. Autotrophs: organisms capable of obtaining their energy from environment  Most get energy from photosynthesis when sunlight on plants makes sugar  Are called producers since they produce (make) their energy  Ex: all plants, phytoplankton, some bacteria

9. Aquatic Producers

10. o2. Heterotrophs: organisms that obtain energy from autotrophs or other heterotrophs  Are called consumers since they consume (eat) their energy  3 different kinds of consumers depending on where they feed in food web:  1. Primary consumers  2. Secondary consumers  3. Decomposers

11.  1. Primary (first-order) consumers: feed directly on autotrophs  Eat plants only so are considered herbivores (herb/plant eaters) Ex: mice, rabbits, deer, cows Cows are primary consumers because they eat only plants (producer autotrophs)

12. o2. Secondary (second-order) consumers: feed on primary consumers  Eat animals only so are considered carnivores (meat eaters) Ex: owls, lions, tigers

13.  Some secondary consumers can also be primary consumers since they are both herbivores and carnivores so are called omnivores Ex: humans, bears

14.  3. Decomposers: feed on remains or bodies of all organisms to make energy  Ex: bacteria, fungi (mushrooms), some insects

15. Food Chains All Have Decomposers that Can Feed on Any Member of a Food Chain

17. Alternative Pathways Maintain Stability in Food Webs  Having alternatives to eat can help stability of food web o Ex: if rabbits in some areas decrease in population, owls won’t starve, they can focus on mice  Less rabbits – more grass - more mice since more places for mice to hide in  If owls focus on mice, rabbit numbers have a chance to increase  Food web stays stable since numbers of all organisms will always go back to original

18. Maintaining Stability EAT Owl can eat rabbit or mouse

19.  Worldwide problem has arisen: land to grow producers is being taken over by urban cities o As human population grows, need more food to feed them, and according to food webs, all human food starts at producers

20.  No land means producers can’t grow  No primary consumers will survive  No secondary consumers will survive  No decomposers will survive

21. Deforestation

22. Questions?

23.  The removal of one part from an ecosystem, like the removal of a moving part from a car’s engine, can cause the collapse of an entire food chain.  In a food chain, there are predators and there are prey.  Prey – the organism that could be eaten by another organism  Predator – the organisms eating other organisms

24.  Ex.: Cat = Predator Mice = Prey

25.  A food chain is a series of predators and prey  Ex: Coyote  Dog  Cat  Mice  bread crumbs (wheat)

26.  Predators keep the prey population in check.  The prey keep the predators alive by providing food. predator prey

27.  Ex. Pacific Sea otters mainly eat sea urchins and sea urchins eat kelp (form of seaweed) and little fish hide in the kelp

28. EAT HIDE IN

29.  Hunters used to kill sea otters for their fur. As a result, the number of sea urchins rapidly increased. As the number of sea urchins grew, the amount of kelp went down.  The fish that relied on the kelp for shelter and food also decreased in number.  So killing the sea otters for their fur (nearly becoming extinct), affected sea urchins, which affected the kelp, which affected the fish. (DOMINO EFFECT!!)

30. EAT HIDE IN

31. Restoring the Balance Is a Difficult Task  Can the “Domino Effect” be stopped? o Yes! The sea otter was reintroduced (more brought back in) which caused the sea urchin population to get smaller because they are being eaten. o The kelp bed have increased and so the number of fish are increasing too. o This has “restored the natural balance” of the food chain  This is not always easy to do.