CASE 8 BIODIVERSITY HOTSPOTS: RAIN FORESTS AND CORAL REEFS

Before examining how biologists and policy makers are working to conserve biodiversity, it is worth taking a moment to consider what we wish to preserve. At the broadest level, most biologists would hope to sustain our shared heritage of global species richness—a tall order on a planet increasingly marked by human activities. Not all ecosystems are equal in terms of biodiversity, and, following the lead of British conservationist Norman Myers, biologists have identified about two dozen biodiversity hotspots on land (Case 8). Hotspots are relatively small areas that have unusually high numbers of endemic species and that are under threat from human activities. (By definition, hotspots contain at least 1500 plant species found nowhere else and have lost 70% of their original habitat area.) Biodiversity hotspots represent only about 2% of the land surface, but they support more than half of the world’s endemic plant species and nearly 43% of endemic bird, mammal, reptile, and amphibian species. Therefore, biodiversity hotspots are high priorities for conservation efforts.

Biodiversity reflects both species richness within local communities and the variations in species composition from one community to another, and from one biome to the next. Biodiversity hotspots reflect the variety of biomes found on land, but, for many reasons, conservation biologists wish to conserve species richness in local communities and regional ecosystems throughout the world. There is good evidence that biodiversity provides important ecosystem services—that is, benefits to humans—including cleaner air and water, greater primary productivity and improved resilience to environmental disruption, and untapped sources of food and molecular compounds for use in medicine and agriculture.

As discussed in Chapter 15, genetic variation exists within as well as among species, and this variation is likely to play an important role in conserving species in a time of global change. Genetic variants in plants provide the raw materials for breeding crops able to thrive in habitats that may become warmer or drier than at present. And within marine species vulnerable to global change, geneticists are beginning to find local populations with enhanced capacity to evolve tolerance to warmer temperature or decreased pH. Such variants may help to sustain the commercial shellfishing in the 21st century and provide robust coral populations able to sustain tropical reefs.