1. Ecology is the study of the relationships of organisms and their environment. It is a vast field with many facets.
2. The environment of a plant’s habitat is determined by both living and nonliving factors. Plants reflect and respond to their environment.
3. Populations vary in numbers, density, and in the total mass of individuals. Populations of one community may also occur in another community, and ecotypes may be specifically adapted to a single community.
4. Precipitation, temperature, soils, and biotic factors play roles in determining the distributions of plant species in an ecosystem.
5. Xerophytes and hydrophytes have modifications of leaves and other organs.
6. Species distribution is influenced by soil mineral content and biotic factors, such as competition for light, nutrients, and water.
7. Ecosystems sustain themselves through photosynthetic activity, energy flow through food chains, and the recycling of nutrients. Producers carry on photosynthesis; consumers feed on producers. Primary consumers feed directly on producers, and secondary consumers feed on primary consumers.
8. Decomposers break down organic materials to forms that can be reassimilated by the producers. In any ecosystem, the producers and consumers comprise food chains that determine the flow of energy through the different levels. Food chains vary in length and intricacy and, because of their interconnections, form food webs.
9. Energy itself is not recycled in an ecosystem; it escapes in the form of heat as it passes from one level to another. In a long food chain, the final consumer gains only a tiny fraction of the energy originally captured by the producer at the bottom of the chain.
10. When producers increase the amount of food available, consumers may increase correspondingly and compete for food; this reduces what is available, resulting in a self-maintaining ecosystem. The composition of an ecosystem may be influenced by its living components through the secretion of growth-inhibiting and growth-promoting substances.
11. Annual plants complete their life cycle in one year, while biennials require two years. Perennial plants live for more than two years.
12. Some nitrogen from the air is fixed by the nitrogen-fixing bacteria found in legumes and other plants. In the nitrogen cycle, there is a constant flow of nitrogen from dead plant and animal tissues into the soil and from the soil back to the plants.
13. Water leaches nitrogen from the soil and carries it away when erosion occurs. Other nitrogen is lost from harvesting crops, but the loss can be reduced if wastes are decomposed and annually returned to the soil. Fire also causes nitrogen loss.
14. Replacement of nitrogen loss by the application of chemical fertilizers may eventually create hardpan by altering the soil structure.
15. Bacteria also recycle carbon and other substances, such as water and phosphorus.
16. Succession occurs whenever there has been a disturbance of natural areas on land or in water.
17. Primary succession involves the formation of soil in the beginning stages, while secondary succession takes place in areas previously covered with vegetation. When a primary succession begins with bare rock or lava, the activities of lichens, plants, and physical forces convert the rock or lava to soil in an orderly progression of events over a period of time.
18. A climax community becomes established at the conclusion of succession and remains until or unless a disturbance disrupts it.
19. A primary succession can be initiated in a wet habitat and culminates in a climax community. As a lake or other body of water is filled in with silt and debris, eutrophication facilitating the growth of algae and other organisms occurs.
20. Secondary succession, which proceeds more rapidly than primary succession, may take place if soil is present. It may occur after fires.
21. Impacts of humans on plant communities occur at both global and regional levels.
22. A global rise in temperature due to carbon dioxide, methane, and other gases preventing the sun's radiant heat from escaping back into space is referred to as the greenhouse effect.
23. The carbon dioxide and methane levels in the earth's atmosphere and the earth's temperature have been rising. It is predicted that polar ice will, as a result, melt, and flooding of low-lying coastal areas will occur.
24. In the stratosphere, sunlight converts methane, chlorofluorocarbons, and halons into active compounds that destroy the ozone shield that protects us from intense ultraviolet radiation.
25. Beach and soil erosion are increasingly serious environmental problems with no simple solutions.
26. The depletion of aquifers may lead to serious water shortages in the near future.
27. Loss of biodiversity has serious consequences, including the potential loss of means with which to combat crop diseases.
28. Regional ecological issues include acid deposition, water contamination, wetlands, hazardous waste, and invasion of foreign species.
29. Acid deposition damages or kills living organisms; it is produced when sulfur and nitrogen compounds released by the burning of fossil fuels are converted to nitric acid and sulfur dioxide by sunlight and rain.
30. Water contamination occurs when toxic wastes, pesticides, septic tanks, and fertilizers wash or leach into surface and ground water. Bacteria may in the future be used to break down various contaminants.
31. Wetlands were once considered wastelands. They have been drained but now increasingly are being protected.
32. Hazardous waste sites are gradually being detoxified, but progress is slow.
33. Foreign invasive species may crowd out or destroy native vegetation.
