DNA – October 4, 2010

1. What is the difference between parasitism and mutualism? How do we represent those using symbols?

2. What’s the difference between species richness and relative abundance?

3. Community 1: 30A, 30BCommunity 2: 20A, 10B

What is the species richness for community 1 and community 2? What is the relative abundance?

Community Ecology: Trophic Structures

Ms. KlinkhachornOctober 4, 2010

AP Biology

Trophic Structure

• “troph” refers to feeding, nourishment• Feeding relationships within a community

• All energy that we consume can be traced back to the sun

Food Chains

Grass Mouse Hawk

• Show transfer of energy and nutrients up feeding levels (trophic levels)

• When drawing feeding relationships, arrow points toward the organism receiving the nutrients

Food Webs• Food web = visual organizer that represents

possible feeding relationships in a community– Linked food chains

• Give a more accurate picture of what is happening compared to food webs

• Show trophic levels

Bottom of the Food Web• Always start with producers• Then consumers– Primary– Secondary– Tertiary

Decomposers and Detrivores

• Top of the food web – prevention of waste buildup

• Detrivore = organism that eats dead organisms– Example: vulture

• Decomposer = breaks down dead organisms and returns nutrients to the soil– Example: bacteria

Food Web Limits

• Typically no more than 5 links in the chain• 2 Theories– Energy is not transferred efficiently (you lose

energy as you go up the levels)• Energetic hypothesis

– Long food chains aren’t very stable due to population fluctuations• Dynamic stability hypothesis