Lecture Outline - Chapter 33

33.1. The Nature of Ecosystems (p. 656)

1. Ecology is a study of interactions of organisms with each other and with physical environment; see terms in Table 33.1.
2. Study of ecosystem includes living community plus physical environment.
   • a. Living (biotic) components include habitats and niches.
   • b. Nonliving (abiotic) components: soil, water, light, inorganic nutrients, and weather.
3. Habitat is organism's place of residence, where it can be found, such as under a log.
4. Niche is profession or role of that organism in the community, factors limiting its life, and how it acquires food.
5. Producers are autotrophic photosynthetic organisms.
   • a. In terrestrial ecosystems, producers are predominantly green plants.
   • b. In freshwater and marine ecosystems, dominant producers are algae.
6. Consumers are heterotrophic organisms that eat preformed food.
   • a. Herbivores feed directly on green plants; are primary consumers.
   • b. Carnivores feed on other animals and are secondary or tertiary consumers.
   • c. Omnivores feed on both plants and animals; for example, humans eat both leafy vegetables and beef.
   • d. Decomposers are organisms of decay.
     • i. Mostly are bacteria and fungi.
     • ii. Break down detritus, nonliving organic matter, into inorganic matter.
     • iii. Small soil organisms are critical in helping bacteria and fungi shred leaf litter and form rich soil.
7. Energy Flow and Chemical Cycling (Fig. 33.2)
   • a. Diagram of components of ecosystem reveal energy flows through system once.
     • i. Producers absorb solar energy; convert it to chemical bonds from inorganic nutrients taken from environment.
     • ii. Energy content of organic food passes up food chain; eventually all energy is lost as heat, therefore requiring continual input.
     • iii. Original inorganic elements are mostly returned to soil and producers; can be used again by producers and no new input is required.

1. Energy flow in ecosystems based on two laws of thermodynamics:
   • a. First law states energy cannot be created or destroyed.
   • b. Second law asserts that when energy is transformed from one form to another, some usable energy is lost as heat.
   • c. Therefore, in any food chain, as consumers feed on producers, etc., some energy must be lost.
2. Ultimate source of energy for nearly all life is sun; exception is unique community of organisms around ocean vents where food chain begins with chemosynthetic bacteria that oxidize hydrogen sulfide.
3. Food Chains Become Food Webs (p. 659)
   • a. Food chains indicate who eats whom in an ecosystem.
     • i. Represent one path of energy flow through an ecosystem.
     • ii. Natural ecosystems have numerous interconnected food chains.
     • iii. Each level of producer and consumers is a trophic level.
     • iv. Some primary consumers feed on plants and make grazing food chains; others feed on detritus. (Figs. 33.3-5)
4. Populations Maintain Their Size
   • a. In undisturbed ecosystems, population size is limited by limited food supply and competition, predation and parasitism.
   • b. Food webs help determine consequences of perturbations: if titmice and vireos fed on beetles and earthworms, insecticides that killed beetles would increase competition between birds and probably increase predation of earthworms, etc.
5. Populations Form a Pyramid
   • a. Trophic structure of an ecosystem forms an ecological pyramid.
   • b. Base of pyramid represents producer trophic level, apex is highest level consumer or the top predator.
   • c. Pyramid of numbers is based on number of organisms at each trophic level.
   • d. Pyramid of biomass is calculated by multiplying the average weight for organisms times the number of organisms at each trophic level.
   • e. Pyramid of energy calculates amounts of energy available at each successive trophic level. (Fig. 33.6)
   • f. The food energy pyramid always shows a decrease moving up trophic levels because:
     • i. Only a certain amount of food is captured and eaten by organisms on the next trophic level.
     • ii. Some of food that is eaten cannot be digested and exits digestive tract as undigested waste.
     • iii. Only a portion of digested food becomes part of the organism's body; rest is used as source of energy.
     • iv. Substantial portion of food energy goes to build up temporary ATP in mitochondria; ATP energy is then used to synthesize proteins, lipids, carbohydrates, and fuel contraction of muscles, nerve conduction, etc.
   • g. Only about 10% of energy available at a particular trophic level is incorporated into tissues at the next level. Example: a larger population can be sustained by eating grain than by eating grain-fed animals since 100 kg of grain would result in 10 human kgs but if fed to cattle, the result is 1 human kg.

1. Inorganic nutrients are cycled through natural ecosystems repeatedly.
2. Biogeochemical cycles are the pathways by which chemicals circulate.
3. Water Cycle
   • a. Saltwater evaporates from sun's energy producing fresh water in clouds; leaves salts in ocean.
   • b. Water vapor cools and condenses to precipitation over oceans and land.
   • c. Runoff forms fresh water lakes, streams, ponds, groundwater, and is held in plants and transpired.
   • d. Gravity returns water to oceans but some moves slowly through water table and porous aquifers between rock layers.
   • e. Although the water cycle shows water to be a renewable resource, the 3% of water that is fresh may be polluted or inadequate for human populations concentrated in specific areas.
4. Cycling processes for other elements involve:
   • a. Reservoir or portion of earth that acts as storehouse for element.
   • b. Exchange pool or part of environment from which producers take nutrients.
   • c. Biotic community where elements move along food chains to and from the exchange pool. (Fig. 33.7)
5. Phosphorus Cycle
   • a. Weathering of rocks makes phosphate ions (PO₄⁼ and HPO₄⁼) available to plants through soil. (Fig. 33.8)
   • b. Runoff returns phosphates to aquatic systems and sediment; called a sedimentary cycle.
   • c. Widely used in organisms for: phospholipids, ATP, teeth, bones, etc.
   • d. Phosphate is a limiting nutrient because available amount is in organisms.
   • e. Humans Influence the Phosphorus Cycle
     • i. We mine phosphate ores for fertilizer, animal feed supplement, detergents.
     • ii. Detergents, untreated human and animal wastes, fertilizers from cropland, etc., all add excess phosphate to water often causing algal blooms.
6. Nitrogen Cycle (p. 663)
   • a. Atmospheric nitrogen gas (N₂) is unavailable to plants.
   • b. Plants therefore depend on various types of bacteria to take up nitrogen gas and make it available to them. (Fig. 33.9)
   • c. Nitrogen Gas Becomes Fixed
     • i. Nitrogen fixation occurs when nitrogen gas is reduced and nitrogen is added to organic compounds.
     • ii. Atmospheric nitrogen is converted to ammonium (NH₄⁺) by some cyanobacteria in aquatic ecosystems and by nitrogen-fixing bacteria in the nodules on roots of legume plants in terrestrial ecosystems. (Fig. 33.9)
     • iii. Plants take up both NH₄⁺ and nitrate (NO₃^-) from soil; (NO₃^-) is enzymatically reduced to NH₄⁺ and used to produce amino acids and nucleic acids.
   • d. Nitrogen Gas Becomes Nitrates
     • i. Nitrification is production of nitrates.
     • ii. Nitrogen gas (N₂) is converted to nitrate (NO₃^-) by:
       - cosmic radiation, meteor trails, and lightning in atmosphere.
       - human manufacture of nitrates for use in fertilizers.

       iii. In soil, bacteria convert ammonium (NH₄⁺) to nitrate in a two-step process.

       - First, nitrite-producing bacteria convert ammonia to nitrite (NO₂^-).

       - Then nitrate-producing bacteria convert nitrite to nitrate.

       - These two groups of bacteria are called nitrifying bacteria.

       iv. Subcycle of nitrogen cycle involving ammonium, nitrates, and nitrites does not depend on nitrogen gas. (Fig. 33.9)
   • e. Denitrification is conversion of nitrate to nitrous oxide and nitrogen gas back to atmosphere.
     • i. Accomplished by denitrifying bacteria in both aquatic and terrestrial ecosystems.
     • ii. Almost but not completely counterbalances nitrogen fixation.
7. The Carbon Cycle
   • a. Relationship exists between photosynthesis and respiration.
     • i. Respiration releases carbon dioxide, which is used in photosynthesis.
     • ii. Photosynthesis releases oxygen used in respiration.
     • iii. Therefore animals depend on green organisms for organic food, energy and oxygen.
   • b. In the carbon cycle, organisms exchange carbon dioxide with the atmosphere. (Fig. 33.10)
     • i. On land, plants take up carbon dioxide; via photosynthesis incorporate it into food used by themselves and heterotrophs.
     • ii. When organisms respire, a portion of this carbon is returned to the atmosphere as carbon dioxide.
     • iii. In aquatic ecosystems, carbon dioxide from air combines with water to give carbonic acid, which breaks down to bicarbonate ions.
     • iv. Bicarbonate ions are a source of carbon for algae.
     • v. When aquatic organisms respire, released carbon dioxide becomes bicarbonate (HCO₃).
     • vi. Amount of bicarbonate in water is in equilibrium with amount of carbon dioxide in air.
   • c. Reservoirs Hold Carbon
     • i. Living and dead organisms are reservoirs of carbon in carbon cycle.
       -800 billion tons of carbon are in world's biota, mainly trees.
       -additional 1,000 - 3,000 billion tons in plant and animal remains in soil.

       ii. Fossil fuels, such as coal, oil, and natural gas were formed during the Carboniferous period when exceptional amount of organic matter was buried.

       iii. Inorganic carbonate accumulates in limestone and calcium carbonate shells.
   • d. Humans Alter the Balances (p. 665)
     • i. Human burning of fossil fuels and wood has increased amount of carbon dioxide released into atmosphere of 42 billion metric tons in 22 years.
     • ii. Since human activity in 22 years probably released 78 billion metric tons, 36 billion metric tons were probably absorbed in oceans.
     • iii. Increased CO₂ may increase the greenhouse effect, where such gases allow sun's rays to pass through to earth where it is absorbed and reradiated as heat, but heat is then reradiated back to earth, perhaps causing global warming.

1. Natural ecosystems tend to be stable.
   • a. Sizes of populations are held in check by competition, predation, etc.
   • b. Energy input-output is balanced; cycles are sustainable.
   • c. Pollution, any undesirable change in environment harmful to humans and life, does not normally occur. (Fig. 33.11a)
2. Human beings replace natural ecosystems with their own. (Fig. 33.11b)
   • a. Rural country with agriculture and animal husbandry.
   • b. Cities where most people live and build industries.
3. Human-impacted ecosystems have two major inputs: fuel energy and raw materials; use of these results in pollution and waste as outputs.
4. The Country-U.S. agriculture produces exceptionally high yields because of five factors.
   • a. Planting of a few high-production genetic varieties. (Fig. 33.12)
     • i. Monoculture agriculture produces uniform crops susceptible to attack by single well-adapted parasite.
     • ii. Examples: single molds reduced 1970 corn crop by 15%; 80% was susceptible.
   • b. Heavy use of fertilizers, pesticides, and herbicides.
     • i. Fertilizer production requires large energy input and runoff contributes to water pollution.
     • ii. Pesticides kill off beneficial organisms; some may pose medical risks.
     • iii. Some herbicides may cause adverse reproductive effects and cancer.
   • c. Generous irrigation.
     • i. River waters diverted for irrigation return to rivers with a heavy load of salt.
     • ii. Underground aquifers can be drastically lowered when pumped for irrigation water.
   • d. Excessive fuel consumption.
     • i. Use of heavy farm equipment, beyond irrigation, to spread fertilizers and sow and harvest crops consume much fossil fuel; modern farming therefore transforms fossil fuel into food energy.
     • ii. Cattle are fed grain in feedlots and other animals are fed supplements.
   • e. Loss of land quality.
     • i. Salination is increased saltiness of irrigated lands.
     • ii. Soil erosion causes loss of topsoil and contributes to decreased productivity; more fertilizers, pesticides, and energy is required to maintain yield.
5. Organic Farming
   • a. Organic farming involves:
     • i. Not using fertilizers, pesticides or herbicides.
     • ii. Return to cultivation of row crops to control weeds.
     • iii. Standard practice of crop rotation to reduce crop pest build up, and use of legumes to supply nitrogen are increased.
     • iv. Natural predators and parasites are used to reduce pest insects.
   • b. Results of limited organic farming:
     • i. Requires about two-fifths fossil energy to produce one dollar of crop.
     • ii. Reduces soil erosion by one-third.
     • iii. Crop yields were lower but so were operating costs; profit is about same.
     • iv. However, protein content was low without use of fertilizers.
   • c. If biotechnology succeeds in producing resistant strains, organic farming may increase.
6. The City (p. 667)
   • a. Dependent upon the country to meet its needs. (Fig. 33.13)
   • b. Each person requires several acres for food production.
   • c. Overcrowding in city encroaches on agricultural areas.
   • d. Cities rely heavily on fossil fuels to continuously provide light, heat and cool without windows, and transport people, usually inefficiently.
   • e. Concentration of people and fossil fuel use also concentrates pollution.
   • f. Most human products generate pollution in their production, use and disposal; humans also generate sewage wastes.
7. The Solution
   • a. Natural ecosystems can absorb some pollutants and compensate for aspects of human-impacted system.
   • b. Both higher human population and higher standard of living per person contribute to overloading environment.
   • c. Deterioration can be halted if we achieve zero population growth and . . .
   • d. Conserve energy and raw materials; conservation can be achieved by:
     • i. Wise use of only what is actually needed.
     • ii. Recycling nonfuel minerals (iron, lead, aluminum, and copper).
     • iii. Use of renewable energy resources and increase in efficiency.
   • e. Example includes: Lamar, Colorado plant produces methane from feed lot animal's wastes to burn for city electrical power and produce feed supplement. (Fig. 33.14b)