1) (20 pts. total) Estimating trophic efficiencies in terrestrial ecosystems. Yo
ID: 119225 • Letter: 1
Question
1) (20 pts. total) Estimating trophic efficiencies in terrestrial ecosystems. You have collected the following data on aboveground net primary productivity (ANPP) in a coniferous forest and a perennial grassland, along with the average ecological efficiencies of the aboveground herbivores in these two ecosystems onsumption Effici ssimilation Efficiency (%) 40 cosystem ion Efficien 40 950 Coniferous Forest Grassland 540 45 40 (5 pts.) Calculate the trophic efficiency of the herbivores in each ecosystem. Comment briefly on the ecological characteristics of these two ecosystems that result in these differences in ecological efficiencies a) b) (5 pts.) Based on (a), calculate the net secondary production of herbivores (give units) in these two ecosystems. Comment briefly on their relative magnitude and the capacity of each ecosystem to support total secondary production (all trophic levels higher than producers) c) (5 pts.) Using estimates of ecological efficiencies in aquatic ecosystems for herbivory by zooplankton on phytoplankton (see textbook or other sources for values), calculate the trophic efficiency of herbivory in this ecosystem. Comment briefly on the ecological characteristics of this aquatic ecosystem that result in any differences in trophic efficiency d) (5 pts.) Assume this aquatic ecosystem is a nutrient-poor i.e. montane and unpolluted) stream with a NPP of 125 g m2y. Calculate the net secondary production of this ecosystem type using the trophic efficiency value calculated in (c) and compare this aquatic herbivore net secondary production to those from the two terrestrial ecosystems Explain briefly any differences.Explanation / Answer
a) WKT,
Trophic efficiency = Consumption efficiency * assimilation efficiency * Production efficiency
For Coniferous forest, TE = 0.02 *0.4*0.4 = 0.32%
For Grassland, TE = 0.54%
The trophic efficiency of the conifoerous forest is low because of the lower consumer production compared to higher primary production. The tropic efficiency is nothing but the ratio of consumer production to prey production. Since we are talking about the herbivores the prey here refers to the autotrophs. As shown by the data in the table too, the aboveground net primary productivity (ANPP) of the coniferous forest is greater than grassland. Since this value is inversely proportional to the trophic efficiency, the value for grassland is higher. The lower value for coniferous forest simply suggests that the assimilation and production of herbivore biomass are comparatively lower though the ANPPof the ecosystem is high.
b) WKT,
Trophic efficiency = Consumer production / Prey production
Consumer production here refers to the net secondary production of herbivores and prey production is the ANPP.
Therefore, net secondary production of herbivores in coniferous forest = 0.0032 * 950 = 3.04 g/m2/yr
and net secondary production of herbivores in grassland = 0.0054 * 540 = 2.92 g/m2/yr
The magnitude of net secondary production in both the ecosystem is almost similar and thus they possess the similar capacity for supporting secondary production. However, the total secondary production of grassland might exceed slightly because of the higher trophic efficiency.
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