i) .012 % = 98.8% lost d) How much energy is lost by primary producers as respiration in this ecosystem? How much is lost as respiration by the insect population? i) 81% ii) 73% e) If all of the detritus leaving the marsh is plant material, what proportion of all net primary production leaves the marsh as detritus (non-living organic material) each year? i) 0.56 Compare with yesterday There are two models of community organization that are common: the bottom-up and the top-down models. The bottom-up model postulates a unidirectional influence from lower to higher trophic levels. In this case, the presence or absence of mineral nutrients control plant numbers, which controls herbivore numbers, which in turn controls predator numbers. In contrast, the top-down model postulates the opposite: Predation mainly controls community organization because predators limit herbivores, herbivores limit plants, and plants limit nutrient levels through nutrient uptake This model is also called the trophic cascade model. Given this information, think back to our original question last class: What is the strongest limiting factor for an herbivore population? Based on the case studies you just looked at, what additional information did this line of evidence provided? How does that influence the way we think about communities?
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