Chapter Summary

Major ecosystem types called biomes are characterized by similar climates, soil conditions, and biological communities. Among the major terrestrial biomes are deserts, tundra, grasslands, temperate deciduous forests, temperate coniferous forests, tropical moist forests, and tropical seasonal forests. Aquatic ecosystems include oceans and seas, rivers, lakes, estuaries, marshes, swamps, bogs, fens, and reefs. Moisture and temperature are generally the most critical determinants for terrestrial biomes. Periodic natural disturbances, such as fires, play a major role in maintaining some biomes.

Humans have disturbed, preempted, or damaged much—perhaps half or more—of all terrestrial biomes and now dominate about 40 percent of all net primary productivity on the land. Some of this disturbance and domination is permanent, but we have opportunities to apply ecological knowledge and practical experience to restoring and repairing ecosystems.

Biomes shelter the world’s biodiversity. Humans benefit from biodiversity in many ways, but we also threaten biodiversity through land conversion and other activities. Extinctions occur naturally, including ancient mass extinctions and evolutionary replacement. Among the threats from humans are overharvesting of animals and plants for food and commercial products. Millions of live wild plants and animals are collected for pets, houseplants, and medical research. Among the greatest damage we do to biodiversity are habitat destruction, the introduction of exotic species and diseases, pollution of the environment, and genetic assimilation.

The potential value of the species that may be lost if environmental destruction continues could be enormous. It is also possible that the changes we are causing could disrupt vital ecological services on which we all depend for life.

The first hunting and fishing laws in the United States were introduced more than a century ago to restrict overexploitation and to preserve species for future uses. The Endangered Species Act and CITES represent a new attitude toward wildlife in which we protect organisms just because they are rare and endangered. Now we are expanding our concern from individual species to protecting habitat, threatened landscapes, and entire biogeographical regions. Social, cultural, and economic factors must also be considered if we want to protect biological resources on a long-term, sustainable basis.