Plant Adaptations
Plant adaptations refer to the unique traits and characteristics that evolve in plants, enabling them to survive and reproduce in varying environmental conditions. These adaptations arise through a process called natural selection, where beneficial mutations in a plant's genetic material enhance its ability to cope with specific challenges in its habitat. Over time, plants that possess advantageous adaptations, such as resistance to heavy metals or specialized photosynthesis mechanisms, like CAM in cacti, become more prevalent in a population.
Adaptations can be structural—like the protective spines of cacti—or physiological, which include changes in metabolism that help plants conserve water in arid conditions. Additionally, adaptations can vary in specificity; some plants may develop highly specialized traits suited for stable environments, while others may exhibit general adaptations that allow for flexibility in harsher or unpredictable climates. Understanding plant adaptations sheds light on the intricate relationships between species, as many plants and their pollinators have evolved together in a process known as coevolution. Through this lens, one can appreciate the diverse strategies plants use to thrive in their ecosystems, contributing to the richness of biodiversity on Earth.
Plant Adaptations
Categories: Evolution; genetics
Adaptations ensure that individuals in populations will reproduce and leave well-adapted offspring, thus ensuring the survival of the species. Adaptations arise through mutations—inheritable changes in an organism’s genetic material. These rare events are usually harmful, but occasionally they give specific survival advantages to the mutated organism and its offspring. When certain individuals in a population possess advantageous mutations, they are better able to cope with their specific environmental conditions and, as a result, will contribute more offspring to future generations than those individuals that lack the mutation. Over time, the number of individuals that have the advantageous mutation will increase in the population at the expense of those that do not have it. Individuals with an advantageous mutation are said to have a higher fitness than those without it, because they tend to have comparatively higher survival and reproductive rates. This is natural selection.
Natural Selection
Over very long periods of time, evolution by natural selection results in increasingly better adaptations to environmental circumstances. Natural selection is the primary mechanism of evolutionary change, and it is the force that either favors or selects against mutations. Although natural selection acts on individuals, a population gradually changes as those with adaptations become better represented in the total population. Most flowering plants, for example, are unable to grow in soil containing high concentrations of certain elements (for example, heavy metals) commonly found in mine tailings. Therefore, an adaptation that conferred resistance to these elements would open up a whole new habitat where competition with other plants would be minimal. Natural selection would favor the mutations, which confer specific survival advantages to those that carry them and impose limitations on individuals lacking these advantages. Thus, plants with special adaptations for resistance to the poisonous effects of heavy metals would have a competitive advantage over those that find heavy metals toxic. These attributes would be passed to their more numerous offspring and, in evolutionary time, resistance to heavy metals would increase in the population.
Types of Adaptations
Although natural selection serves as the instrument of change in shaping organisms to very specific environmental features, highly specific adaptations may ultimately be a disadvantage. Adaptations that are specialized may not allow sufficient flexibility (generalization) for survival in changing environmental conditions. The degree of adaptative specialization is ultimately controlled by the nature of the environment. Environments, such as the tropics, that have predictable, uniform climates and have had long, uninterrupted periods of climatic stability are biologically complex and have high species diversity. Scientists generally believe that this diversity results, in part, from complex competition for resources and from intense predator-prey relationships. Because of these factors, many narrowly specialized adaptations have evolved when environmental stability and predictability prevail. By contrast, harsh physical environments with unpredictable or erratic climates seem to favor organisms with general adaptations, or adaptations that allow flexibility. Regardless of the environment type, organisms with both general and specific adaptations exist because both types of adaptation enhance survival under different environmental circumstances.
Structural adaptations are parts of organisms that enhance their survival ability. Camouflage that enables organisms to hide from predators or their prey; protective spines on cacti that inhibit organisms that might feed on them; color, scent, or shape of flowers that promotes seed production—these are all structural adaptations. These adaptations enhance survival because they assist individuals in dealing with the rigors of the physical environment, obtaining nourishment, competing with others, or attracting pollinators.
Metabolism is the sum of all chemical reactions taking place in an organism, whereas physiology consists of the processes involved in an organism carrying out its function. Physiological adaptations are changes in the metabolism or physiology of organisms, giving them specific advantages for a given set of environmental circumstances. Because organisms must cope with the rigors of their physical environments, physiological adaptations for temperature regulation, water conservation, varying metabolic rate, and dormancy allow organisms to adjust to the physical environment or respond to changing environmental conditions.
Adaptations and Environment
Desert environments, for example, pose a special set of problems for organisms. Hot, dry environments require physiological mechanisms that enable organisms to conserve water and resist prolonged periods of high temperature. Evolution has favored a specialized form of photosynthesis in cacti and other succulents inhabiting arid regions. Crassulacean acid metabolism (CAM) photosynthesis allows plants with this physiological adaptation to absorb carbon dioxide at night, when relative humidity is comparatively high and air temperatures relatively low. Taking in carbon dioxide during the day would dehydrate plants, because opening the pores through which gas exchange takes place allows water to escape from the plant. CAM photosynthesis, therefore, allows these plants to exchange the atmospheric gases essential for their metabolism at night, when the danger of dehydration is minimized.
Because organisms must also respond and adapt to an environment filled with other organisms—including potential predators and competitors—adaptations that minimize the negative effects of biological interactions are favored by natural selection. Often the interaction among species is so close that each species strongly influences the others and serves as the selective force causing change. Under these circumstances, species evolve together in a process called coevolution. The adaptations resulting from coevolution have a common survival value to all the species involved in the interaction. The coevolution of flowers and their pollinators is a classic example of these tight associations and their resulting adaptations.
Speciation
Adaptations can be general or highly specific. General adaptations define broad groups of organisms whose lifestyles are similar. At the species level, however, adaptations are more specific and give narrow definition to those organisms that are more closely related to one another. Slight variations in a single characteristic, such as bill size in the seed-eating Galapágos finches, are adaptive in that they enhance the survival of several closely related species. An understanding of how adaptations function to make species distinct also furthers the knowledge of how species are related to one another.
Why so many species exist is one of the most intriguing questions of biology. The study of adaptations offers biologists an explanation. Because there are many ways to cope with the environment, and because natural selection has guided the course of evolutionary change for billions of years, the vast variety of species existing on the earth today is simply an extremely complicated variation on the theme of survival.
Bibliography
Arms, Karen, and Pamela Camp. Biology: Journey into Life. 3d ed. Fort Worth, Texas: Saunders, 1994. This college-level text is well written and easily understandable because the authors use nontechnical language. Gives an excellent overview of evolution and natural selection. Several good examples of adaptations.
Brandon, Robert N. Adaptation and Environment. Princeton, N.J.: Princeton University Press, 1990. Explains the concept of selective environment and its influence on adaptation.
Futuyma, Douglas. Science on Trial. Reprint. Sunderland, Mass.: Sinauer Associates, 1995. Written for readers with little background in science; gives evidence for the theory of evolution. In presenting this evidence, Futuyma also shows how the views of creationists contrast with those of evolutionists. The illustrations and examples of adaptations are excellent.
Gould, Stephen J. Ever Since Darwin. Reprint. New York: W. W. Norton, 1992. Gould is well known for his ability to write humorous, slightly irreverent biological literature that the nonscientist can enjoy. No exception, this book gives an interesting view of evolution.
Ricklefs, Robert E. Ecology . 4th ed. New York: W. H. Freeman, 2000. The section on evolutionary ecology offers the reader an excellent but technical description of adaptations in their ecological context. Although this is an advanced college text, the material is accessible with little difficulty. The introduction gives the current views in evolutionary ecology, and the chapter summaries are excellent.
Rose, Michael R., and George V. Lauder, eds. Adaptation. San Diego: Academic Press, 1996. A discussion of new developments in adaptation, with new methods and new theoretical foundations and achievements. Rose provides an insightful reintroduction to the themes that Charles Darwin and his successors regarded as central to any profound understanding of biology.
Whitfield, Philip. From So Simple a Beginning: The Book of Evolution. New York: Maxwell Macmillan, 1993. A well-organized and well-written introduction to the concepts of evolution, written for the general reader. Illustrated.
Wickler, Wolfgang. Mimicry in Plants and Animals. New York: McGraw-Hill, 1968. This intriguing, small book takes up the fascinating subject of mimicry, the resemblance of one organism to another or to some object that gives the mimic a specific offensive or defensive advantage. Highly adaptive forms are beautifully illustrated in color; most examples are from the insect world.