Environmental Problems, Their Causes, and Sustainability 1

HeatDecomposers(bacteria, fungi)Abiotic chemicals(carbon dioxide,oxygen, nitrogen,minerals)HeatHeatProducers(plants)Solarenergythe fertility of soils, dispose of wastes, and control populationsof pests that attack crops and forests.Biodiversity is a renewable resource as long welive off the biological income it provides instead of thenatural capital that supplies this income.Some scientists say that the loss and degradationof biodiversity is the most important environmentalproblem we face. This is why understanding, protecting,and sustaining biodiversity is a major theme ofecology and of this book.4-4 ENERGY FLOW IN ECOSYSTEMSHeatConsumers(herbivores,carnivores)HeatFigure 4-17 Natural capital: the main structural componentsof an ecosystem (energy, chemicals, and organisms).Matter recycling and the flow of energy from the sun, throughorganisms, and then into the environment as low-quality heat,link these components.Biological diversity, or biodiversity, is one of theearth’s most important renewable resources. Kinds ofbiodiversity include the following:■ Genetic diversity: the variety of genetic materialwithin a species or a population■ Species diversity: the number of species present indifferent habitats■ Ecological diversity: the variety of terrestrialand aquatic ecosystems found in an area or on theearth■ Functional diversity: the biological and chemicalprocesses such as energy flow and matter cyclingneeded for the survival of species, communities, andecosystems (Figure 4-17)Some people also include human cultural diversityas part of the earth’s biodiversity. Each human culturehas developed various ways to deal with changing environmentalconditions.The earth’s biodiversity is the biological wealth orcapital that helps keep us alive and supports oureconomies. Biologist Edward O. Wilson describes theearth’s biodiversity as a “natural or biological Internet”that all living things are part of.The earth’s biodiversity supplies us with food,wood, fibers, energy, raw materials, industrial chemicals,and medicines—all of which pour hundreds of billionsof dollars into the world economy each year. It alsohelps preserve the quality of the air and water, maintainWhat Are Food Chains and FoodWebs? Maps of Ecological InterdependenceFood chains and webs show how eaters, the eaten,and the decomposed are connected to one anotherin an ecosystem.All organisms, whether dead or alive, are potentialsources of food for other organisms. A caterpillar eats aleaf, a robin eats the caterpillar, and a hawk eats therobin. Decomposers consume the leaf, caterpillar, robin,and hawk after they die. As a result, there is little matterwaste in natural ecosystems.The sequence of organisms, each of which is asource of food for the next, is called a food chain. It determineshow energy and nutrients move from one organismto another through an ecosystem (Figure 4-18,p. 68).Ecologists assign each organism in an ecosystemto a feeding level, also called a trophic level, dependingon whether it is a producer or a consumer and onwhat it eats or decomposes. Producers belong to thefirst trophic level, primary consumers to the secondtrophic level, secondary consumers to the third, and soon. Detritivores and decomposers process detritusfrom all trophic levels.Real ecosystems are more complex than this. Mostconsumers feed on more than one type of organism,and most organisms are eaten or decomposed by morethan one type of consumer. Because most species participatein several different food chains, the organisms inmost ecosystems form a complex network of interconnectedfood chains called a food web. Trace the flows ofmatter and energy within the simplified food web inFigure 4-19 (p. 69). Trophic levels can be assigned infood webs just as in food chains. Afood web shows howeaters, the eaten, and the decomposed are connected toone another. It is a map of life’s interdependence.How Can We Represent the Energy Flowin an Ecosystem? Think PyramidThere is a decrease in the amount of energy availableto each succeeding organism in a food chain or web.http://biology.brookscole.com/miller1467