Problem 1
The species-area curve rises continually as area is increased, implying that there is no limit to the number of species in any community. Is this a correct interpretation? What hypotheses can you suggest to explain why the number of species rises as area increases?
Problem 4
Can nonequilibrium models of community organization be stable? Read Chesson and Case (1986) and DeAngelis and Waterhouse (1987) and discuss the relationship between stability and equilibrium/nonequilibrium concepts.
Problem 6
In western North American grasslands, bison (Bison bison ) and prairie dogs (Cynomys ludovicianus) are considered keystone herbivores. What changes would you predict in the plant community of these grasslands if you set up an experiment in which bison were excluded from some plots, prairie dogs from other plots, and both species from a third set of plots. Fahnestock and Detling (2002) did this experiment for three years and got no vegetation changes in any of the plots. Is this sufficient information to reject the idea that these herbivores are keystone species?
Problem 7
Freshwater lakes have been suggested to have two alternate stable states, one of clear water dominated by macrophytes and one of murky water with high phytoplankton levels. If this is correct, would you predict that measurement of the clarity of lake water for many lakes would be bimodal with a peak of lakes at the clear end of the spectrum and another peak of lakes at the murky end, with few lakes in between? Why might this prediction be incorrect? Peckham et al. (2006) did this analysis for Wisconsin lakes and discuss the results obtained from satellite measurement of lake transparency.
Problem 8
Trophic cascades are weaker in terrestrial systems compared with aquatic ones (Hall et al. 2007 ). One suggested explanation for this difference is that differences in body size between plants and their herbivores could be responsible (Shurin et al. 2006 ). Discuss the relative size of plants and their herbivores in aquatic ecosystems and in terrestrial ecosystems, and speculate how these differences might affect trophic cascades.
