Think-Pair-Share Activity s1

Think-Pair-Share Activity Intraspecific variation in response to toxins

Mercury concentrations vs. length in walleye from South Manistique Lake From: Fish contaminant monitoring program: review and recommendations. 2003. Report prepared by Exponent (Bellevue, WA) for the Michigan Department of Environmental Quality, Lansing, Michigan, Doc. no. 8601969.001 0501 0103 BH29.

Think about your answers to these questions, then turn to your neighbor and share your answers

1. Describe the overall trend, if any, of mercury concentration with fish length. 2. If you saw a trend in the data, what could explain the trend? 3. How much mercury is there in a walleye fish that is 18 inches long? 4. Why might different fish of the same size have different mercury concentrations? Minute paper topics 1. Compare the graph above to the one in the Pretest. How do these data fit into the pattern you saw in the Pretest graph?

2. If you worked for the Environmental Protection Agency and you had to tell people how much walleye they could safely eat, how would you decide what size of fish is safe?

3. Would you get a very different dose of mercury if you ate the same mass of fish from a lower trophic level than walleye? Explain your reasoning?

Examples of topics students should cover in their minute papers

1. They should identify the difference between this graph, which shows data for only one species, and the Pretest graph which shows many trophic levels. They should discuss variability within a species, and should be able to say that despite intraspecific variation, the pattern of biomagnification across trophic levels is strong enough to be evident despite this variability.

2. This question should elicit answers that discuss skepticism in specific “safe” levels of mercury as measured by a size or weight of fish one can eat. The conservative answer would state that if limits are to be set, one should err on the side of caution and suggest that people eat less, or smaller, fish. An observant student would notice that the scatter in the data are sufficient to warrant skepticism about setting limits based on fish size. Looking at the walleye graph, fish between about 16 and 22 inches can have any of a number of mercury concentrations. It’s not clear that a 16” fish is any more likely to have less mercury than a 22” fish.

3. For this question, students would need to think back to the Pretest graph and put this graph into that context. They would have to recall trophic levels and how biomagnification works from that exercise. What should be different in their answer, now that they’ve seen the walleye graph, is a discussion of intraspecific variation and how that can “blur” the otherwise clear pattern of biomagnification with trophic level. Asking this question at this point allows the instructor to make sure students don’t see this intraspecific variability and think it translates into NO pattern with trophic level. This gives the instructor the chance to point out how biomagnification is a strong enough process that it’s clearly visible despite variability at the level of the species or population.