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Sustainable Eating Activity

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In caterpillars, egestion (including excretion) is measurable as the frass that is left after feeding (the small pellets laying on top of the food). The amount of production is simply measured as the change in weight of the caterpillar over time. If we weigh the entire system (including food, frass, caterpillar and container) over time, the change in weight of the system is approximately the energy given off during the interval as respiration. By weighing the frass, we can determine the amount of material egested/excreted, and by weighing the caterpillar, we can determine the amount of biomass increase (production). Using these key pieces of data, we can estimate both assimilation efficiency and production efficiency for caterpillars over time. Procedure: 1. Pack butterfly medium tightly at the bottom of the plastic vial. Add 1 caterpillar and a foam plug. Store in a large zip top bag to avoid excessive moisture loss between measurements. 2. On a daily basis: (record your observations in a notebook or other means) a. Remove from storage bag, and weigh the entire system b. Weigh an empty weigh boat c. Using the weigh boat, gently remove and weigh just the caterpillar (remove the weight of the empty boat) d. Place the weigh boat on a hard surface, remove the foam plug from the vial, upend the vial, and gently tap it inside the weigh dish to remove all the frass into the weigh boat (if the frass doesn't fall out, gently remove it using a small brush or pencil) e. Weigh the boat with the frass inside it (remove the weight of the empty boat) f. Weigh the vial without the frass, caterpillar or plug — just the butterfly medium Expected Results: Results may vary based on materials used, setup, procedure, and other factors, however, here is an example on what to expect: All weights should change from day to day. Between recording days: • The change in weight of the entire system represents respiration • The change in weight of the caterpillar represents production • The weight of the frass represents egestion • The change in weight of the vial with food (no frass, caterpillar or plug — just medium) represents ingestion • Assimilation can be calculated two ways: either subtract the frass from the ingestion calculation, or add respiration to the production calculation — or average the two • Calculate assimilation efficiency by dividing assimilation by ingestion weights • Calculate production efficiency by dividing production by assimilation weights. Follow-up/Teaching Notes: • What should happen to the weight between days if the entire system is weighed in a closed container such as a zip top bag? It should remain the same, because the products of respiration are contained (it is a closed system). • Why is there a difference in the weights between the two methods of calculating the assimilation value? Due to error, such as moisture evaporation, etc. • Students should discuss sources of error, such as loss of moisture, or measurement errors. • Students should discuss the relevance of these values to the number of trophic levels in ecological communities (suboptimal efficiencies limit the number of trophic levels). The higher the efficiencies, the more trophic levels can exist — the lower the efficiencies, the fewer trophic levels can exist. • Students should discuss the implications for the human diet: eating higher trophic levels is less sustainable than eating lower trophic levels — as population increases, it will become increasingly difficult/expensive to include meat and meat products in our diets. • By recording the data into Excel, this experiment generates the necessary data to perform additional analyses, such as growth curves, and changes in efficiency over time; model development and curve fitting using different models (linear, logarithmic, etc). • By including several samples, this is an excellent way to introduce basic descriptive statistics (mean, standard deviation, etc). Sustainable Eating Activity (continued) + ward ' s science

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