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48.1 Solar radiation, wind and ocean currents, and topography determine the distribution of major climactic zones on Earth.
Equatorial climates are warm and polar climates are cold because of the angle at which solar radiation strikes Earth’s curved surface. page 1046
The tilt of Earth on its axis means that solar radiation strikes the Northern and Southern Hemispheres unevenly at different parts of Earth’s orbit, causing seasonality. page 1046
Wind and ocean currents transport heat from the equator toward the poles. page 1047
Topographical features, like mountains, regionally modify global circulation patterns. page 1049
48.2 Biomes are broad, ecologically uniform areas whose characteristic species reflect regional climate.
The distribution of the plants that characterize terrestrial biomes reflects in large part abiotic factors such as climate and soil. page 1050
Regional climate determines the ratio of potential evapotranspiration to precipitation, a key determinant of vegetation type, primary production, and biodiversity. page 1050
Aquatic biomes also reflect abiotic factors, especially the spatial distribution of nutrients and the depth to which sunlight penetrates water. page 1052
48.3 Biologically driven cycles of carbon and other essential elements shape ecology and reflect evolution.
The evolved metabolisms of organisms cycle carbon through the environment and give structure to the food webs characteristics of biomes. page 1060
Nitrogen and phosphorus limit primary production in most biomes. page 1062
Nitrogen in the atmosphere is fixed by bacteria and archaeons, and then cycles through primary consumers, consumers, and decomposers, so is closely linked to the carbon cycle. page 1062
Phosphorus is found mostly in rocks, enters the food web as phosphate ion by chemical weathering, and cycles through ecosystems, supporting primary production. page 1062
Nutrient levels and climate determine global patterns of primary production. page 1063
48.4 Global patterns of biological diversity reflect climate, history, and ecological interactions among species.
Species diversity generally declines from the equator toward the poles, a pattern known as a latitudinal diversity gradient. page 1066
Earth’s biomes are the historical outcome of environmental change through time and natural selection. page 1068
Explain how incoming solar radiation exerts a direct influence on the distribution of temperature across Earth’s surface.
Solar energy striking the equator does so at a direct angle. Because of Earth’s curvature, however, the same amount of solar energy striking Earth at higher latitudes gets distributed over a larger area. In consequence, temperatures decline with increasing latitude.
Why are equatorial latitudes generally wet, but land masses at about 23 to 30 degrees north and south latitude generally dry?
At the equator, where incoming solar energy results in high surface temperatures, air warms, which causes it to rise. As the air rises, it cools. Cooler air can carry less water vapor than warm air, and so as the air cools, the water vapor it contains condenses, resulting in rain. The opposite pattern explains the belt of arid climates around 23‒30 degrees latitude. As air moving northward from the equator cools, it becomes denser and eventually descends, warming as it goes. The warming air takes up water vapor, with the result that rainfall is low.
Why are the sides of tall mountains that face oncoming wind generally wetter than their opposite slopes?
This phenomenon, known as a rain shadow, occurs because air masses rise as they move upward and over mountain ranges, cooling as they ascend. As the air cools, the water vapor it contains condenses, resulting in rain. Air masses on the opposite slopes of mountains warm as they descend, taking up moisture, resulting in low rainfall.
Choose five terrestrial biomes, describe their climate and vegetation, and explain why they differ from one another.
Biomes include: (1) rain forests—
Interestingly, the vegetation that exists in these five different biomes is constrained, in part, by evaporation and transpiration rates (which are dependent on factors such as temperature and annual precipitation). Consider the Sahara Desert in Africa. The high temperature of this desert, paired with the limited amount of rainfall, means that most water in the Sahara will evaporate fairly quickly. Any plants in the Sahara should be able to survive in an environment where water is scarce, and must maintain low transpiration rates (thus conserving precious water). These conditions limit which plants can inhabit the Sahara Desert. In other terms, since the Sahara Desert has a high potential evapotranspiration ratio (the comparison of the rate of evapotranspiration possible given temperature, wind, and humidity, to precipitation, the rate at which water is supplied to the biome), only certain types of vegetation can survive in this environment.
How do marine biomes differ between the surface ocean and the deep seafloor?
In the oceans, surface waters are bathed in sunlight, supporting photosynthesis and, commonly, relatively abundant biomass throughout the various trophic levels in communities. Sunlight does not penetrate to the deep sea floor, so most deep sea life is supported by the slow rain of organic remains from surface waters. In consequence, the biomass of deep sea biomes is generally low. Locally, at hydrothermal vents, high fluxes of hydrogen, methane, and hydrogen sulfide support high rates of chemosynthesis, and thus high densities of consumer organisms.
Describe two ways that the biological nitrogen cycle interacts with the biological carbon cycle.
All primary producers require nitrogen and other nutrients as well as carbon, so the uptake of biologically available nitrogen, provided by nitrogen fixation, ammonification, and nitrification, plays a major role in governing rates of primary production. Bacteria and Archaea can also use nitrate to respire organic molecules in anoxic environments, converting the nitrogen to N2, which returns to the atmosphere. Also, some microbes can derive the energy needed for chemosynthetic carbon fixation by the oxidation of nitrogen compounds. As a result, the carbon and nitrogen cycles are closely intertwined.
Compare and contrast biomes on land and in the sea in terms of their global patterns of primary production.
Terrestrial biomes show a first-
Describe the general pattern of diversity from the equator to the poles. Provide two hypotheses to explain this pattern of diversity.
Generally, greater species diversity is observed at latitudes close to the equator. This is particularly evident if we compare the species observed in rain forests (with latitudes of 0–10 degrees) to those seen in tundra (latitudes at 65 degrees or higher). Rain forests demonstrate a huge array of life, with hundreds of species of trees, insects, and other animals observed in a small area. Conversely, the tundra can only support a limited number of plants capable of surviving in a few inches of topsoil (that is, shrubs). Animal diversity is also low at high latitudes.
Two hypotheses have been proposed to explain this difference in species diversity. At higher latitudes, plants and animals must survive sometimes extreme seasonal changes in temperature. Few species can survive in these climates, effectively limiting species diversity. Higher latitudes have also been considered relatively “new” habitats compared to those observed at the equator. The covering of northern latitudes by glaciers during the ice ages, and the subsequent recession of these glaciers, have only recently opened up these environments to colonization by new species. Regions near the equator, however, have experienced the same environmental conditions for longer periods, allowing for more species to evolve and thrive.