Ecologia (1)

Notas del editor

• #43: Figure: 29-02 Title: The scales of life that concern ecology. Caption: In this chapter, you will consider how organisms of one species are associated in populations, and how populations of different species are associated in communities. In Chapter 30, you will look at ecosystems, which include not only living community members but the nonliving factors that interact with them (such as the rainfall in the ecosystem above). Chapter 30 also reviews the large-scale ecosystems called biomes and the biosphere, which is the interactive collection of all the Earth’s ecosystems.
• #61: Figure: FG30-18.01 Title: Fattening at the feedlot. Caption: About 40,000 head of cattle are fed for meat production at this commercial feedlot in Imperial Valley, California.
• #62: Figure: FG30-10 Title: Trophic levels. Caption: Plants, algae, and some bacteria are called producers because they use the Sun’s energy to produce their own food through photosynthesis. Organisms at all other trophic levels ultimately derive their energy from these photosynthesizers.
• #63: Figure: FG30-11 Title: A river food web. Caption: The diagram indicates who eats whom along a portion of the Eel River in Northern California. The arrows have been color-coded by trophic level. Note that there are up to five trophic levels in the web. (Adapted with permission from an original drawing by Mary E. Power, University of California, Berkeley.)
• #69: Figure: FG30-01 Title: The carbon cycle. Caption: 1. Plants and other photosynthesizing organisms take in atmospheric carbon dioxide (CO2) and convert or “fix” it into molecules that become part of the plant. 2. The physical functioning or respiration of organisms converts the carbon in their tissues back into CO2. 3. Plants and animals die and are decomposed by fungi and bacteria. Some CO2 results, which moves back into the atmosphere. 4. Some of the carbon in the remains of dead organisms becomes locked up in carbon-based compounds such as coal or oil. 5. The burning of these fossil fuels puts this carbon into the atmosphere in the form of CO2.
• #70: Figure: FG30-02 Title: The nitrogen cycle. Caption: Some bacteria “fix” nitrogen, meaning they convert atmospheric nitrogen (N2) into an organic form that can be used by other living things. 1. Nitrogen-fixing bacteria convert N2 into ammonia (NH3), which converts in water into the ammonium ion (NH4+). The latter is a compound that plants can assimilate into tissues. In the diagram, bacteria living symbiotically in plant root nodules have produced NH4+, which their plant partners have taken up and used. Meanwhile, free-standing bacteria living in the soil have likewise produced NH4+. 2. Other plants take up NH4+ that has been produced by soil-dwelling bacteria and assimilate it. Animals eat plants and assimilate the nitrogen from the plants. 3. Animal waste and the tissues of dead animals and plants are decomposed by fungi and by other bacteria, which turn the organic nitrogen back into NH4+. 4. Other “nitrifying” bacteria convert NH4 + into nitrate (NO3–), which likewise can be assimilated by plants. 5. Some nitrate, however, is converted by “denitrifying” bacteria back into atmospheric nitrogen, completing the cycle.
• #71: Figure: FG30-03 Title: Nutrients beyond what nature provides. Caption: A helicopter applies fertilizer to a sugar beet crop in California.
• #72: Figure: FG30-04 Title: The hydrologic cycle. Caption: More than 95 percent of Earth’s water is stored in the oceans. When water evaporates from the ocean, 90 percent returns to the ocean directly by way of precipitation. The other 10 percent falls on land. There, the water either runs back into the ocean, is stored in such structures as glaciers, or is moved by transpiration and evaporation back into the atmosphere.
• #82: Figure: 29-18ab Title: Competition for resources among species. Caption: Laboratory experiments by G. F. Gause showed that competition for resources between two species can have two possible outcomes. a. When two species compete for the same limited, vital resource, one will always drive the other to local extinction--as the paramecium P. aurelia did to the paramecium P. caudatum. This is the competitive exclusion principle at work. b. Conversely, when Gause put P. aurelia together with another paramecium, P. bursaria,the two species divided up the habitat and both survived. This is a demonstration of resource partitioning.
• #87: Figure: FG31-13 Title: What factors produce bird song? Caption: Male white-crowned sparrows are genetically predisposed to sing a certain type of song—the white-crowned sparrow song. However, males will sing varying dialects of their species’ song in accordance with the area in which they were raised.
• #88: Figure: FG31-07 Title: Hormonal inspiration. Caption: The close correlation, visible in the graph, between testosterone levels and singing in the male willow tit suggests that testosterone release is the proximate cause of singing in these birds.
• #89: Figure: 29-20.01 Title: Predator on the loose. Caption: A domestic cat carrying its prey.
• #93: Fig. 38.10
• #97: Title: Mutually beneficial. Caption: a. Several oxpecker birds sit atop a black rhinoceros, ridding the rhino of ticks and other pests while the rhino provides a safe habitat for the birds. This is a demonstration of mutualism--an interaction between two species that is beneficial to both.
• #120: Figure: 29-05 Title: Three models of growth for natural populations. Caption: Three models of growth for natural populations.