56.1 Climate shapes the character of ecosystems.
Effects of the Sun and Atmospheric Circulation
• The tropics are warmer than temperate regions because the sun's rays arrive almost perpendicular to equatorial regions. (p. 1204)
• High temperatures near the equator encourage evaporation and create warm, moist air, causing large amounts of precipitation near the equator. (p. 1205)
• When the air masses reach about 30° north and south latitude, the cool, dry air sinks, forming areas of low precipitation (deserts). (p. 1205)
Atmospheric Circulation, Precipitation, and Climate
• The rain shadow effect helps create deserts at places other than 30° north and south latitude, as mountain ranges intercept moisture-laden winds and cause most of the precipitation to fall on the windward side of the range, blocking moisture from the leeward side. (p. 1206)
• Unique regional climates are also formed due to prevailing winds such as the westerlies and the trade winds. (p. 1206)
• Temperature tends to vary according to latitude -- warm in the tropics, and cooler as you move away -- and according to elevation, with temperature decreasing as elevation increases. (p. 1207)
56.2 Biomes are widespread terrestrial ecosystems.
The Major Biomes
• Biomes are major communities of organisms with a characteristic appearance that are distributed over areas defined by temperature and precipitation differences. (p. 1208)
• Eight of the major biomes are tropical rain forest, savanna, desert, temperate grassland, temperate deciduous forest, temperate evergreen forest, taiga, and tundra. (p. 1208)
56.3 Aquatic ecosystems cover much of the earth.
Patterns of Circulation in the Oceans
• Ocean circulation patterns are determined by patterns of atmospheric circulation, but are also modified by the location of landmasses. (p. 1212)
• When the east-west trade winds in the Pacific Ocean slacken, warm water begins to move back across the ocean from the coast of South America, causing a phenomenon called El Niño, which widely influences the world's weather systems. (p. 1213)
Marine Ecosystems
• The marine environment consists of three major habitats: the neritic zone (shallow water containing most of the world's major fisheries), the pelagic zone (water above the ocean floor), and the benthic zone (ocean floor). (p. 1214)
• Approximately 40% of all photosynthesis on earth takes place in the oceans. (p. 1215)
Freshwater Habitats
• Freshwater habitats are much more limited in area than marine habitats. (p. 1216)
• Photosynthetic organisms are limited to the upper photic zone of ponds and lakes. (p. 1216)
• Ponds and lakes have three zones where organisms are found, which are distributed according to the distance from shore: the littoral, limnetic, and profundal zones. (p. 1216)
• Thermal stratification is characteristic of larger lakes in temperate regions. (p. 1216)
• Eutrophic lakes contain an abundant supply of organic matter, while organic matter and nutrients are relatively scarce in oligotrophic lakes. (p. 1217)
• Human activities can lead to the eutrophication of oligotrophic waters. (p. 1217)
• Wetlands are often very productive ecosystems that also serve as water storage basins helping to moderate flooding. (p. 1217)
56.4 Human activity is placing the biosphere under increasing stress.
Pollution
• Widespread modern agriculture introduces large amounts of new chemicals into the global ecosystem, including pesticides, herbicides, and fertilizers. (p. 1218)
• Stable, long-lasting chlorinated hydrocarbons such as DDT can become increasingly concentrated in an ecosystem due to biological magnification. (p. 1218)
Acid Precipitation
• Industrial pollution contains many chemicals. For example, sulfur, when introduced into the upper atmosphere, can combine with water vapor to produce sulfuric acid, which can fall to the ground in many forms, including snow and rain. (p. 1219)
• Precipitation with an acidic pH can cause many environmental problems, including lake acidification, groundwater contamination, and forest damage. (p. 1219)
Destruction of the Tropical Forests
• More than half of the world's human population lives in the tropics, and this percentage is increasing. (p. 1220)
• Rain forests grow on poor soil, thus they can become hard to regenerate once they are cleared. (p. 1220)
• Increasingly, larger numbers of people moving into tropical areas are clearing larger areas of rain forest. (p. 1220)
The Ozone Hole
• Industrial chlorofluorocarbons (CFCs) released into the atmosphere for many decades have led to a thinning of the earth's stratospheric ozone layer, which shields the planet from harmful ultraviolet radiation. (p. 1221)
Carbon Dioxide and Global Warming
• The greenhouse effect is caused when carbon dioxide and other gases allow short-wavelength solar radiation into the atmosphere, but trap longer-wavelength heat radiation from escaping, thus warming the earth's atmosphere. (p. 1222)
• In the 1990s, the scientific community reached a consensus that the earth's average temperature is increasing, and human-related greenhouse gases are the major cause of the increase. (p. 1222)
• The effects of global warming on natural ecosystems may include the shifting of the geographic distribution of organisms tracking environmental conditions, as well as life cycle changes to adapt to changing environmental conditions. (p. 1223)
• Continued global warming may also influence human conditions due to rising sea levels, effects on agriculture, and human health issues. (p. 1224)