Chapter 20 Key Terms
o The input of energy and nutrients from outside the ecosystem. Compare
x assimilation efficiency
o The proportion of ingested food that is assimilated by an organism.
o Energy and nutrients produced within the ecosystem. Compare allochthonous.
o An increase in the tissue concentrations of a substance at higher trophic levels that
results as animals at each trophic level consume prey with increasing
concentrations of the substance.
x consumption efficiency
o The proportion of the biomass available in an ecosystem that is ingested.
x food web
o A diagram showing the connections between organisms and the food they
x interaction strength
x keystone species
o A strongly interacting species that has a large effect on energy flow and on
community structure and composition disproportionate to its abundance or
x production efficiency
o The proportion of assimilated food that is used to produce new consumer
x trophic cascade
o A change in the rate of consumption at one trophic level that results in a series of
changes in species abundances and species compositions at lower trophic levels.
x trophic efficiency
o A measure of the transfer of energy between trophic levels, consisting of the
amount of energy at one trophic level divided by the amount of energy at the
trophic level immediately below it.
x trophic level
o A group of species in a community that obtain energy in similar ways, classified
by the number of feeding steps by which the group is removed from auto-trophs,
which are the first trophic level.
x trophic pyramid