DNA – October 4, 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, 30B Community 2: 20A, 10B What is the species richness for community 1 and community 2? What is the relative abundance?

Community Ecology: Trophic Structures Ms. Klinkhachorn October 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