Ecosystem Energetics




BIO226 : Ecosystem : Energy : Ecosystem Energetics

Exercise: Ecosystem Energetics

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DUE: 16-Apr-99. Work sent after this date will receive a grade of zero.

1. In a tropical rainforest, the vegetation fixes 14,000 kcal/m²/yr with a respiration rate of 7000 kcal/m²/yr. An Appalachian forest fixes 6000 kcal/m²/yr with a respiration rate of 1200 kcal/m²/yr. After calculating net primary productivity and net production efficiency for the two forests, which forest comes out ahead? Explain your results and show the calculations.

2. In box 6.2, the textbook gives 4.3 trophic levels for temperate grasslands. If temperate grasslands actually have only 500 kcal/m²/yr instead of 2000, how many trophic levels would you expect to find? If a gram of dry biomass is equivalent to 4 kcal of energy, what habitat would be more consistent with a net production of 500 kcal/m²/yr than a temperate grassland?

3. Jackrabbits from the pinyon-juniper habitat near Flagstaff were found to have a mean respiration rate of 140 kcal/m²/yr. The net primary productivity of the plants they eat was measured at 400 kcal/m²/yr. Because of cellulose and lignin, the rabbits digest only 30% of their food. The population of jackrabbits gained biomass at the rate of 5.0 kcal/m²/yr. The energy of excretion was negligible.

a) What was the assimilation rate and the net production efficiency of the jackrabbits?

b) What was the ecological efficiency of the jackrabbits?

c) At what rate do the jackrabbits need to consume their food to average this rate of production each year?

d) How many grams of dry fecal matter do these rabbits distribute on every square meter each year?

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