Two species of sea urchins live practically side by side on sandy bottoms. The two species appear to have the same diet: drift seaweedsand other bits of organic matter. They are able to live in the sameenvironment with minimal competition. How might they be able toshare their habitat and food resources?

1. Examine the food webs for Lake Victoria, East Africa (fig 31.2 a,b) before and after the introduction of the Nile perch (Leveque 1995). Calculate the mean food chain length, percent of trophic groups at various levels, and connectance for each food web. Oreochromis Insectivorous Fish Chironomids Chaoborous Man Piscivorous Fish Zooplanktivorous Haplochromines Rastrineobola Zooplankton Detritus/Phytoplankton Lake Victoria in the 1970s Detritivorous Phytoplanktivorous Haplochromines Figure 31.2. (a) Food web structure of Lake Victoria before introduction of the Nile Perch. [continued on next page) Molluscivorous Fish Molluscs

One approach to conservation of fish populations is to releaseunwanted fish accidentally caught in trawling nets. Such fishoften have very high concentrations of lactic acid in their bodies.Why do you think they have these high concentrations of lacticacid, and how might their survival after release be affected bytheir condition?

Consider a trophiccascade with 4 levels:  1) predatory fish that consume planktivorous fish, 2) planktivorous fish that consume zooplankton,3)  herbivorous zoplankton that consume phytoplankton, and 4) phytoplankton. True or False: A reduction in predatory fish will increase the level of phytoplankton.  True  False

Great white shark Clown fish Sea turtle Blue regal Small invértebrates Zoo plankton algae 1. Why does this picture illustrate a food web? 2. Identify organisms that are both predator and prey? 3. Which organisms convert radiant energy into chemical energy? Explain?

The feeding rosette in the sediment is characteristic of the acorn worm in the pic above. Which of the follwing is/are true: