Ecological Knowledge and Environmental Problem-Solving Concepts and Case Studies (1986) / Chapter Skim
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2. Population Interactions
2. Population Interactions
Pages 38-46
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From page 38... ...
If disruption of mutualisms lowers seed set or dispersal, the energy content of the lost seeds is only a small component of the significance of those changes. The overall unit for expressing these effects is fitness (relative reproductive success)
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From page 39... ...
Green plants account for about 97% of all the carbon fixed in terrestrial and aquatic ecosystems, and their photosynthetic activity supports almost all other components of those systems. Plants carry out photosynthesis by only three different mechanisms, which differ in a variety of ways, including optimal temperature and amount of carbon that can be fixed per unit of water lost (Berry, 1975; Bjorkman and Berry, 19731.
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From page 40... ...
Like animals, microorganisms are diverse in their modes of obtaining energy. They use various substrates for their synthetic abilities, use various photosynthetic pigments, and derive energy by oxidizing many simple substrates, such as gaseous hydrogen, inorganic nitrogen, sulfur, and iron.
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From page 41... ...
A major advantage of using natural defenses is that effects on nontarget organisms are minimized and the plant itself synthesizes and distributes the defenses. Breeding of pestresistant crop plants has a long tradition, but improved knowledge of the chemical bases of resistance now enables managers to search for specific kinds of chemical and physical defenses in plants to deal with particular herbivores, rather than relying simply on randomized field trials to see what happens to work (Maxwell and Jennings, 19801.
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From page 42... ...
Moreover, damaged plants might release volatile materials that induce neighboring plants to increase their defenses (Baldwin and Schultz, 1983; Rhoades, 19821; if so, that opens up still other possibilities to manipulate plant defenses against herbivores to reduce reliance on toxic substances. COMPETITIVE INTERACTIONS Competition occurs when a number of individuals use common resources for which the demand exceeds the supply or when resources are not scarce and organisms harm one another in the process of seeking those resources (Birch, 19571.
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From page 43... ...
The literature is biased, owing to underrepresentation of negative results, and, not surprisingly, there is much controversy among ecologists about the importance of competition in nature and about the extent to which patterns observed in ecological communities can be attributed to it (Cody, 1974; Diamond and Gilpin, 1982; Gilpin and Diamond, 1982; Strong et al., 1979, 1984; Tilman, 19821. All observers do agree, however, that competition occurs and that it must be understood better if we are to understand ecological communities.
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From page 44... ...
Indeed, many cases are so asymmetrical that the effects on one of the species are almost undetectable. Such a situation was predicted by theoretical considerations: a slight difference in competitive abilities between two species can lead to the elimination of one of them in simple environments (Gause, 1934; Park, 19481; therefore, in nature, even a slightly subordinate species might be much less common and found in many fewer habitat types than if the dominant species were not present.
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From page 45... ...
(Agriculture, however, depends heavily on the honey bee, Apis mellifera, which has a catholic diet and ready access to the flowers of most cultivated plants. The loss of bees, as sometimes occurs when pesticides are used extensively in a region, can cause serious losses of fruits and seeds, even when plant growth remains normal and the harvesting activity of the bees is a rather minor component of the total energy flux in the plant community.)
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From page 46... ...
, by preying on competitively dominant mussels in rocky intertidal environments, make possible the presence of many species of animals that they do not eat or otherwise directly affect (Paine, 19801. Such indirect effects are less well documented than are direct effects of interactions among species, because more careful experimentation would be needed; and such effects are likely to be missed, simply because investigators do not think to monitor the relevant species in the system likely to be affected by indirect interaction.
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