Chapter 18 questions
1. Which environmental factor exerts the stronger influence on terrestrial NPP, climate
(actual evapotranspiration, precipitation) OR nutrient availability? See Figs. 18.2-4.
2. Jepsen and Winemiller (1990) used stable isotopes to study food webs of tropical fish
assemblages in Venezuelan streams. What additional information was obtained from
stable isotopes over stomach analyses?
3. Most of the energy that flows through a forest ecosystem flows through detritus-based
food chains, and the detritus consists mainly of dead plant tissues (e.g., leaves, roots and
wood). In contrast, most of the energy flowing through a pelagic or freshwater
ecosystem flows through grazing food chains, with phytoplankton as the major primary
producer. Ecologists have determined that on average, a calorie or joule of energy takes
only several days to pass through the pelagic ecosystem (from the atmosphere through
the food web and back to the atmosphere), but 25 years to pass through the forest
ecosystem. Explain this large difference in the rate of energy flow.
4. Americans eat a wide range of fish species. Some, like anchovies and herring, are
relatively small and eat plankton. Others, like swordfish and bluefin tuna are large and
are the top predators in their food web, eating other medium to large fish. In the context
of an expanding human population placing ever increasing harvesting pressure on marine
fisheries, which of these two groups of fish are most likely to be a sustainable food
resource for human consumption. Explain your answer based on what you’ve learned
about energy flow in chapter 18.