Environmental Problems, Their Causes, and Sustainability 1

Figure 4-5 A population ofmonarch butterflies. The geographicdistribution of thisbutterfly coincides with that ofthe milkweed plant, onwhich monarch larvaeand caterpillars feed.Scientists studying ecosystems seek answers toseveral questions. First, how many members of eachspecies are present? Second, how do these organismscapture energy and matter (nutrients) from their environment?Third, how do they transfer energy andmatter among themselves and to other ecosystems?Fourth, how do they release energy into the environmentand return nutrients to the environment forrecycling?4-2 THE EARTH’S LIFE-SUPPORTSYSTEMSFigure 4-6 The geneticdiversity among individualsof onespecies ofCaribbean snail isreflected in thevariations in shellcolor and bandingpatterns.What Are Communities and Ecosystems?Interactions in NatureA community consists of populations of differentspecies living and interacting in an area, and anecosystem is a community interacting with itsphysical environment of matter and energy.A community, or biological community, consists of allthe populations of the different species living and interactingin an area. It is a complex and interacting networkof plants, animals, and microorganisms.An ecosystem is a community of different speciesinteracting with one another and with their physicalenvironment of matter and energy. Ecosystems canrange in size from a puddle of water to a stream, apatch of woods, an entire forest, or a desert. Ecosystemscan be natural or artificial (human created). Examplesof artificial ecosystems are crop fields, farmponds, and reservoirs. All of the earth’s ecosystems togethermake up what we call the biosphere.What Are the Major Parts of the Earth’sLife-Support Systems? The Spheres of LifeThe earth is made up of interconnected sphericallayers that contain air, water, soil, minerals,and life.We can think of the earth as being made up of severalspherical layers, as diagrammed in Figure 4-7 (p. 60).Study this figure carefully. The atmosphere is a thin envelopeor membrane of air around the planet. Its innerlayer, the troposphere, extends only about 17 kilometers(11 miles) above sea level. It contains most of theplanet’s air, mostly nitrogen (78%) and oxygen(21%). The next layer, stretching 17–48 kilometers(11–30 miles) above the earth’s surface, isthe stratosphere. Its lower portion containsenough ozone (O 3 )tofilter out most of thesun’s harmful ultraviolet radiation. This allowslife to exist on land and in the surface layersof bodies of water.The hydrosphere consists of the earth’s water.It is found as liquid water (both surface and underground),ice (polar ice, icebergs, and ice in frozen soillayers called permafrost), and water vapor in the atmosphere.The lithosphere is the earth’s crust and uppermantle; the crust contains nonrenewable fossil fuels(created from ancient fossils that were buried and subjectedto intense pressure and heat) and minerals, andrenewable soil chemicals (nutrients) needed for plantlife.The biosphere is the portion of the earth in whichliving (biotic) organisms exist and interact with oneanother and with their nonliving (abiotic) environment.The biosphere includes most of the hydrosphereand parts of the lower atmosphere and upper lithosphere.It reaches from the deepest ocean floor, 20 kilometers(12 miles) below sea level, to the tops of thehighest mountains.All parts of the biosphere are interconnected. If theearth were an apple, the biosphere would be nothicker than the apple’s skin. The goal of ecology is to understandthe interactions in this thin, life-supporting globalmembrane of air, water, soil, and organisms.http://biology.brookscole.com/miller1459