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| Inquiry Questions FIGURE 56.5 Temperature varies with latitude. The blue line represents the annual mean temperature at latitudes from the North Pole to Antarctica. Why is it hotter at low latitudes? Answer: The tropics are warmer than temperate regions because the sun's rays arrive almost perpendicular to regions near the equator. Near the poles, the angle of incidence of the sun's rays spreads them out over a much greater area, providing less energy per unit of area. Figure 56.8 The effects of precipitation and temperature on primary productivity. The net primary productivity of ecosystems at 52 locations around the globe depends significantly upon (a) mean annual precipitation and (b) mean annual temperature. Why does productivity increase with increasing precipitation and temperature? Answer: This is one of the great questions in ecology. Many factors are involved, and scientists are not entirely in agreement. Increasing precipitation is responsible for increased plant growth. Increased temperature is related to many factors, but perhaps the most important is the increased availability of energy from the sun, which plants can convert into plant tissue through photosynthesis. FIGURE 56.25 The greenhouse effect. The concentration of carbon dioxide in the atmosphere has steadily increased since the 1950s (blue line). The red line shows the general increase in average global temperature for the same period of time. Why has temperature change been erratic, even though carbon dioxide levels have risen steadily? Answer: Because other factors beside CO2 concentrations affect global temperatures. For example, in 1991 the eruption of Mount Pinatubo in the Philippines produced much ash that circulated in the atmosphere, blocking the sun and leading to a short-term decrease in temperature. Self Test 1). A rain shadow results in a). extremely wet conditions due to loss of moisture from winds rising over a mountain range. b). dry air moving toward the poles that cools and sinks in regions 15° to 30° north/south latitude. c). global polar regions that rarely receive moisture from the warmer, tropical regions, and are therefore dryer. d). desert conditions on the down-wind side of a mountain due to increased moisture-holding capacity of the winds coming from the seas. Answer: d 2). What two factors are most important in biome distribution? a). temperature and latitude b). rainfall and temperature c). latitude and rainfall d). temperature and soil type Answer: b 3). Savannas are best described as areas with a). extremely dry conditions and sparse vegetation. b). cold, dry conditions with herbs and few trees. c). warm summers, cool winters, and abundant rainfall which promotes tree growth. d). seasonal rainfall, few trees, and abundant grasses. Answer: d 4). The cacti that are found in the deserts of North and South America look very much like the euphorbs that are found in the deserts of Africa. However, these plants are not closely related. The similarities in these plants are due to a). convergent evolution as a result of similar environmental pressures. b). artificial selection for these similar traits. c). differences in rainfall between the two deserts. d). differences in pollinator species in the two deserts. Answer: a 5). Which of the following is not a result of an El Niño event? a). The trade winds relax in the central and western Pacific. b). The sea surface is about a meter higher at the Philippines than at Ecuador. c). A rise in sea surface temperature and a decline in primary productivity adversely affect fisheries in Ecuador and Peru. d). Flooding and strong winter storms occur in California. Answer: b 6). The neritic zone is best described as the a). area of water above the ocean floor where a diversity of plankton species are concentrated. b). ocean floor that is made up of mud and other fine particles that have settled from the water. c). area less than 300 meters below the surface of the oceans along the coasts of continents and islands. d). part of the ocean floor that drops to depths where light does not penetrate. Answer: c 7). The limnetic zone of a lake is best described as the a). shallow area along the shore. b). area below the limits where light can penetrate. c). zone where photosynthesis cannot occur. d). well-illuminated surface waters away from the shore. Answer: d 8). In temperate regions, lakes are thermally stratified, with warm waters at the top and cooler waters at the bottom during the summer. The region of abrupt change between these layers is known as the a). thermocline. b). hypolimnion. c). epilimnion. d). fall overturn. Answer: a 9). Oligotrophic lakes can be turned into eutrophic lakes as a result of human activities such as a). overfishing of sensitive species, which disrupts fish communities. b). introducing nutrients into the water, which stimulates plant and algal growth. c). disrupting terrestrial vegetation near the shore, which causes soil to run into the lake. d). spraying pesticides into the water to control aquatic insect populations. Answer: b 10). The loss of the ozone layer has serious implications for the quality of the environment because a). ozone (O3) protects organisms from ultraviolet radiation that can cause cancer. b). a depleted ozone layer causes rainwater to have a lower pH that kills plant life. c). loss of the ozone layer causes the sun's rays to get trapped in the atmosphere and increase global temperatures. d). a depleted ozone layer can interact with toxic chemicals to increase their effect on organismal health. Answer: a Test Your Visual Knowledge 1). Predict what changes to global climate would occur if the earth's axis were not tilted. Answer: The earth's axis is tilted by 23.5 degrees relative to its plane of orbit around the sun. This results in seasonal variation at the poles as the earth travels around the sun. If the earth were perpendicular relative to its plane of orbit around the sun there would be no seasonal variation at temperate latitudes. Apply Your Knowledge 1). Some vegetarians argue that it is more ethical to eat "lower on the food chain" (eat more grains and vegetables) than to consume meat. Explain this argument in terms of energy conversions in ecosystems. Answer: Energy transformations through trophic levels are not 100% efficient and energy is lost with each transfer. Eating meat instead of grains adds a link to the food chain, which decreases energy efficiency. 2). The Clean Water Act protects wetlands. Under the act, there is to be no net loss of wetlands and any wetland losses should be offset through restoration projects or creation of new wetlands. Why are wetlands given this status? Answer: Wetlands are highly productive systems that are the homes to many different species of plants and animals. In addition, wetlands provide "ecosystem services" such as flood abatement and filtering pollutants from water. 3). The concentration of CO2 in the atmosphere has steadily increased since the 1950s. A general increase in average global temperature has already occurred. How is global climate change predicted to affect the area where you live? Answer: Answer will vary. |