Environmental Problems, Their Causes, and Sustainability 1

Detritus feedersDecomposersLong-hornedbeetle holesBark beetleengravingCarpenterantgalleriesTermite andcarpenterantworkDry rot fungusWoodreducedto powderMushroomTime progressionPowder broken down by decomposersinto plant nutrients in soilFigure 4-16 Natural capital: Some detritivores, called detritus feeders, directly consume tiny fragments of thislog. Other detritivores, called decomposers (mostly fungi and bacteria), digest complex organic chemicals infragments of the log into simpler inorganic nutrients that can be used again by producers.this energy is released by aerobic respiration, whichuses oxygen to convert organic nutrients back into carbondioxide and water. The net effect of the hundredsof steps in this complex process is represented by thefollowing chemical reaction:glucose oxygencarbon dioxide water energyC 6 H 12 O 6 6 O 2 6 CO 2 6 H 2 O energyAlthough the detailed steps differ, the net chemicalchange for aerobic respiration is the opposite of thatfor photosynthesis (p. 64).Some decomposers get the energy they need bybreaking down glucose (or other organic compounds)in the absence of oxygen. This form of cellular respirationis called anaerobic respiration, or fermentation.Instead of carbon dioxide and water, the end productsof this process are compounds such as methane gas(CH 4 , the main component of natural gas), ethyl alcohol(C 2 H 6 O), acetic acid (C 2 H 4 O 2 , the key componentof vinegar), and hydrogen sulfide (H 2 S, when sulfurcompounds are broken down). This is a plan B way toget a meal.The survival of any individual organism dependson the flow of matter and energy through its body. However,an ecosystem as a whole survives primarilythrough a combination of matter recycling (rather thanone-way flow) and one-way energy flow (Figure 4-17).Figure 4-17 sums up most of what is going on in ourplanetary home.Decomposers complete the cycle of matter bybreaking down detritus into inorganic nutrients thatcan be reused by producers. These waste eaters andnutrient recyclers provide us with this crucial ecologicalservice and never send us a bill. Without decomposers,the entire world would be knee-deep in plantlitter, dead animal bodies, animal wastes, and garbage,and most life as we know it would no longer exist.Have you thanked a decomposer today?What Is Biodiversity? Variety Is the Spiceof LifeA vital renewable resource is the biodiversityfound in the earth’s variety of genes, species,ecosystems, and ecosystem processes.66 CHAPTER 4 Ecosystems: What Are They and How Do They Work?