Monday, September 15, 2008 HW #6: –Answer “weighing the issues” pg 162 –Answer #2, 3, 5 on pg 179 Review questions for Ch 6 due Friday

Energy Flow and Keystone Species Aim: How does energy move through an ecosystem? 9/15/08

Energy Flow in ecosystems All energy in organisms ultimately comes from the sun via photosynthesis All energy in organisms ultimately comes from the sun via photosynthesis This energy moves through the community as members feed on one another, through each trophic level This energy moves through the community as members feed on one another, through each trophic level

Producers Also called autotrophs Also called autotrophs Plants, cyanobacteria, and algae capture solar energy and use photosynthesis to produce sugars Plants, cyanobacteria, and algae capture solar energy and use photosynthesis to produce sugars

Consumers Primary consumers Primary consumers eat producers Herbivores—only eat plants Ex) deer, grasshoppers

Consumers cont. Secondary consumers Secondary consumers prey on primary consumers Ex) wolves, rodents, birds

Consumers cont. Tertiary consumers Tertiary consumers predators at higher levels Carnivores—only eat meat Hawks, owls

Decomposers and Detritivores Consume nonliving organic matter and recycle the energy and nutrients Consume nonliving organic matter and recycle the energy and nutrients Decomposers Decomposers Break down leaf litter to be reused by plants Break down leaf litter to be reused by plants Ex) fungi and bacteria Ex) fungi and bacteria Detritivores Detritivores Scavenge the waste products or Scavenge the waste products or dead bodies of organisms Ex) millipedes and soil insects Ex) millipedes and soil insects

Food Web

Ecological Pyramids

Ecological Pyramids cont. Rule of 10—each trophic level contains 10% of the energy of the trophic level below it Rule of 10—each trophic level contains 10% of the energy of the trophic level below it This means that there usually are fewer organisms at higher levels of the food chain This means that there usually are fewer organisms at higher levels of the food chain Even though predators are physically larger, the number of prey lead to a greater total biomass Even though predators are physically larger, the number of prey lead to a greater total biomass

Keystone species A species with a strong influence on an ecosystem A species with a strong influence on an ecosystem See figure 6.12 on pg 162

Keystone species cont. If you remove a keystone species, it will alter a large portion of a food web If you remove a keystone species, it will alter a large portion of a food web Often is the large secondary or tertiary consumers Often is the large secondary or tertiary consumers Ex) wolves, mountain lions, starfish, sea otters Ex) wolves, mountain lions, starfish, sea otters

Keystone species

United States History In the mid 20 th century, the US government gave bounties for the hunting of wolves and mountain lions In the mid 20 th century, the US government gave bounties for the hunting of wolves and mountain lions They were largely exterminated They were largely exterminated In their absence, deer populations rose unnaturally and have overgrazed forests In their absence, deer populations rose unnaturally and have overgrazed forests

Another keystone example Predatory starfish Pisaster ochraceus Predatory starfish Pisaster ochraceus When it is present, diversity is high in the tidepools When it is present, diversity is high in the tidepools When it is removed, the mussels that it eats overpopulate and diversity is low When it is removed, the mussels that it eats overpopulate and diversity is low