Chapter 18

Marine algae along the west coast of North America do not increase in species richness toward the tropics but peak at about 70 species per $100\mathrm{km}$ of coastline around ${40}^{\circ }\mathrm{N}$ latitude (Gaines and Lubchenco 1982 ). Along the east coast of North America, species richness gradually increases as you move toward the tropics. Discuss why these patterns might hold.

In analyzing the role of fire as a disturbance in tallgrass prairie, Collins et al. (1995) found that the intermediate disturbance hypothesis was supported if, instead of plotting fire frequency as in Figure $25\mathrm{b},$ they plotted time since the last fire on the $x$ -axis. Why should they get different results for these two plots of the same data?

Would you expect to have latitudinal gradients in the species richness of macroparasites of mammals and birds? What factors might control species richness in macro-and microparasites?

In Antarctica, species richness in soft-bottom invertebrates (sponges, bryozoans, polychaetes, and amphipods) is higher than that of almost all other tropical- and temperate-zone soft-bottom communities (Clarke 1990 ). What observations or experiments would you perform to find out why this high biodiversity occurs in Antarctica?