Free response · Unit 8 Beta

Energy available at each trophic level of a grassland

Analyze Model or Visual Representation · 4 points

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The question

Name: ______________________   Date: ____________   Energy available at each trophic level of a grassland (4 points)

Model

A grassland food web with energy values

The model shows part of a grassland food web. Each box gives the energy stored in new biomass at that population each year, in kJ per m² per year. Arrows point from the food to the organism that eats it. Hawks and mice are endotherms; grasshoppers, frogs and snakes are ectotherms.

Grassland food web with energy stored per yearGrasses store 8,000 kilojoules per square meter per year. Grasshoppers eat grass and store 720. Mice eat grass and store 160. Frogs eat grasshoppers and store 60. Snakes eat frogs and mice and store 18. Hawks eat snakes and mice and store 1.2.Grasses8,000Grasshoppers720Mice160Frogs60Snakes18Hawks1.2kJ per m² per year

  1. (a) Calculate the percentage of the energy stored by the grasshoppers that is stored by the frogs. Show your work. [1 point]

  2. (b) Explain why the energy stored by the frogs is so much less than the energy stored by the grasshoppers. [1 point]

  3. (c) A disease kills most of the mice. Predict how the frog population will change over the next year, and justify your prediction using the model. [1 point]

  4. (d) The hawks store 1.2 kJ per m² per year, about 0.7% of the 178 kJ stored by the snakes and mice they eat. Predict the energy the hawks could store if they ate only snakes, keeping the same 0.7%, and justify your prediction using the trophic levels in the model. [1 point]