Environmental Problems, Their Causes, and Sustainability 1

NoorganismsLower limitof toleranceFeworganismsAbundance of organismsFeworganismsUpper limitof toleranceNoorganismsPopulation sizeZone ofintoleranceZone ofphysiological stressOptimum rangeZone ofphysiological stressZone ofintoleranceLowTemperatureHighFigure 4-13 Range of tolerance for a population of organisms, such as fish, to an abiotic environmentalfactor—in this case, temperature.Sugar Mapleoxygen gas dissolved in a given volume of water at aparticular temperature and pressure. Another limitingfactor in aquatic ecosystems is salinity—the amountsof various inorganic minerals or salts dissolved in agiven volume of water.Figure 4-14 The physical conditions of the environment can limitthe distribution of a species. The green area shows the currentrange of sugar maple trees in eastern North America. (Data fromU.S. Department of Agriculture).Too much of an abiotic factor can also be limiting.For example, too much water or too much fertilizercan kill plants, a common mistake of many beginninggardeners.Important limiting factors for aquatic ecosystemsinclude temperature, sunlight, nutrient availability,and dissolved oxygen (DO) content—the amount ofWhat Are the Major Biological Componentsof Ecosystems? Producers andConsumersSome organisms in ecosystems produce food andothers consume food.The earth’s organisms either produce or consumefood. Producers, sometimes called autotrophs (selffeeders),make their own food from compounds obtainedfrom their environment.On land, most producers are green plants. Infreshwater and marine ecosystems, algae and plantsare the major producers near shorelines. In open water,the dominant producers are phytoplankton—mostly microscopicorganisms that float or drift in the water.Most producers capture sunlight to make carbohydrates(such as glucose, C 6 H 12 O 6 )byphotosynthesis.Although hundreds of chemical changes take placeduring photosynthesis, the overall chemical reactioncan be summarized as follows:carbon dioxide water solar energy glucose oxygen6 CO 2 6 H 2 O solar energy C 6 H 12 O 6 6 O 264 CHAPTER 4 Ecosystems: What Are They and How Do They Work?