Primary producers make up a very large portion of the total biomass in terrestri
ID: 274741 • Letter: P
Question
Primary producers make up a very large portion of the total biomass in terrestrial systems, but only a very small fraction in aquatic systems. Which
one of the following statements is an incorrect†explanation for this observation?
a. Terrestrial net primary productivity (NPP) far exceeds the rate of herbivory.
b. Predators cannot constrain population densities of terrestrial herbivores to a low level.
c. Most longlived land plants defend themselves against herbivory, but aquatic producers do not.
d. Terrestrial plants contain nutrient poor structural materials such as stems and wood, which are unattractive to herbivores.
e. Inorganic nutrients become available from decomposition much more slowly in terrestrial systems, but on average remain locally more
available to land plants than such nutrients do to aquatic producers after decomposition in aquatic systems has run its course.
Community structure depends to a large degree on the digestive efficiencies of the organisms involved? unless a threshold amount of energy makes it
out of a trophic level, there will be no further trophic level above, so the efficiencies often determine how many trophic levels will be present and thus set the foodweb associations and possibility for topdown influences such as keystone effects. Which one of the following statements about efficiencies is correct?
a. on land consumption efficiency is higher for herbivores than for carnivores, because plants cannot run away.
b. in terrestrial systems production efficiencies are low, because animals always expend a great deal of energy chasing after and wrestling down their fooditems.
c. in aquatic systems production efficiencies must be low, because none of the organisms are warmblooded.
d. assimilation efficiency is much better for carnivores than for herbivores, because all animal tissue is of similar composition.
e. there is necessarily an inverse relationship between consumption efficiency and assimilation efficiency.
Interactions in a food web are: (choose the correct answer)
a. of consistent impact over time for any given pair of species present.
b. important to evaluate only for species with multiple prey types.
c. cannot be estimated for any links involving omnivorous species which may be present.
d. measurable only where the organisms involved all have specialized diets.
e. best estimated through demonstrated fitness influences from experimental removals of organisms.
Explanation / Answer
B.Predators cannot constrain population densities of terrestrial herbivores to a low level
A.on land consumption efficiency is higher for herbivores than for carnivores, because plants cannot run away
B.important to evaluate only for species with multiple prey types.
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