Lecture Outline - Chapter 23

23.1 The Nature of Ecosystems (p. 470, Table 23.1)
	1.	A community is made up of the populations of organisms interacting and inhabiting the same area at the same time. An ecosystem is the community plus its physical environment.
	2.	Succession: Change Over Time (p. 470, Figs. 23.2, 23.3)
		a.	Succession refers to the sequential change in dominant species in an area over time until a climax community is reached.
		b.	Primary succession begins on areas never before having soil. Lichens and mosses contribute to the buildup of soil.
		c.	Secondary succession takes place on areas with soil, such as abandoned agricultural fields. It begins with herbaceous plants, then shrubs, and then trees, until the climax community is reached.
		d.	As succession proceeds, species variety increases, and the community becomes more adept at recycling nutrients and using energy efficiently.
		e.	Climax communities have difficulty recovering from disturbance.
	3.	Components of an Ecosystem (p. 472)
		a.	An ecosystem has both biotic (living) components and abiotic (nonliving) components.
		b.	Biotic Components of an Ecosystem (p. 472, Figs. 23.4, 23.5)
			i.	Each organism within the community has its role to fulfill, which is referred to as its niche.
			ii.	The photosynthetic organisms of a community are the producers.
			iii.	The consumers are heterotrophs that consume food that is already formed. Primary consumers (herbivores) eat producers. Secondary consumers (carnivores) eat primary consumers. Omnivores eat both plants and animals. Decomposers consume dead or decaying matter.
			iv.	Energy flow within an ecosystem begins with energy from sunlight. Producers capture that energy and pass it along to consumers. The energy flow is one-way.
			v.	Nutrients cycle through communities.
			vi.	Ecosystems can perpetuate through time because they cycle nutrients, partition resources, and keep their populations stable. Humans harm ecosystems by replacing them with agricultural fields or cities, by introducing pollutants, by hunting and harvesting to the brink of extinction, and by introducing alien species.
23.2 Energy Flow in an Ecosystem (p. 475)
	1.	Energy cannot be created or destroyed, and energy is always lost as heat when energy is transformed from one form to another. 
	2.	Food Chains Become Food Webs (p. 475, Figs. 23.6, 23.7, 23.8)
		a.	A food chain indicates who eats whom within a community. Natural ecosystems have numerous food chains, complexly interconnected to form food webs.
		b.	Grazing food chains are made up of the producer, primary consumer, and so forth in a community.
		c.	Detritus food chains are based on decomposers.
	3.	Ecosystems Respond to Disturbances (p. 475)
		a.	In natural ecosystems, there is a dynamic balance of populations caused by a limited inorganic nutrient supply and by interactions such as competition, predation, and parasitivism.
		b.	A disturbance in the food chains within a food web can have diverse, unpredictable consequences.
	4.	Populations Form a Pyramid (p. 476, Fig. 23.9)
		a.	The trophic components of an ecosystem can be grouped into an ecological pyramid.
		b.	A pyramid of numbers is based on counting the organisms in each trophic level. A pyramid of biomass uses the combined weight of the organisms in each trophic level.
		c.	A pyramid of energy shows that there is a decreasing amount of energy available at each trophic level. This explains why food chains are relatively short.
		d.	Only about 10% of the energy contained in a trophic level is incorporated into the next level. The rest (90%) is energy lost. 
23.3 Chemical Cycling in an Ecosystem (p. 477, Fig. 23.10)
	1.	Unlike energy, chemicals cycle within ecosystems. Chemical cycles are called biogeochemical cycles.
	2.	In the hydrologic cycle, fresh water evaporates from large bodies of water, condenses over land, and falls back to earth. Water falling on land drains into surface waters and underground aquifers. Water in rivers returns to the ocean, where the cycle begins again.
	3.	In chemical cycles, the process involves a reservoir for the chemical--either in the atmosphere or in the soil--and an exchange pool from which the producers gather their nutrients.
	4.	Phosphorus Cycle (p. 478, Fig. 23.11)
		a.	The weathering of rocks makes phosphate ions available to plants. As soil erodes, phosphorus makes its way to surface waters and the ocean, and algae take up the phosphorus. Phosphorus makes its way through food chains and ends up back in soils and sediments. The phosphorus cycle is a sedimentary cycle.
		b.	Humans Influence the Phosphorus Cycle (p. 478)
			Humans mine phosphorus for fertilizer, applying it to yards and agricultural land, and the excess makes its way to surface waters, causing an overabundance of algae.
	5.	Nitrogen Cycle (p. 479, Fig. 23.12)
		a.	The nitrogen cycle is an atmospheric cycle and depends on the activities of bacteria.
		b.	Nitrogen Gas Becomes Fixed (p. 479)
		Nitrogen fixation occurs when nitrogen gas is reduced and nitrogen added to an organic compound. Bacteria in root nodules and cyanobacteria are able to do this and make nitrogen available to plants.
		c.	Nitrogen Gas Becomes Nitrates (p. 479)
			i.	Nitrates are produced through nitrification. Nitrogen gas can be converted to nitrate with lightning; humans do this artificially when producing fertilizers. Soil bacteria convert ammonium to nitrite. Another group of soil bacteria convert nitrite to nitrate.
			ii.	Denitrification is the conversion of nitrate back to nitrogen gas, which reenters the atmosphere. Denitrifying bacteria perform this step. 
	6.	Carbon Cycle (p. 480, Fig. 23.13)
		a.	Plants take up carbon in the form of carbon dioxide from the atmosphere during photosynthesis. Carbon is passed through the food chain. Cellular respiration releases carbon dioxide as a waste product of this metabolic pathway. 
		b.	Reservoirs Hold Carbon (p. 481)
			Living and dead organisms, especially trees, are carbon reservoirs. Fossil fuels formed because of millions of years of transformation of plant remains.
		c.	Humans Alter the Balances (p. 481)
			By clear-cutting tropical rain forests and by burning fossil fuels, humans have increased the carbon dioxide in the atmosphere, which leads to the greenhouse effect.
23.4 Human-Impacted Ecosystems (p. 481, Fig. 23.14)
	1.	Mature natural ecosystems can perpetuate themselves through time. Human activities alter such ecosystems by many means, including pollution.
	2.	The Country (p. 482, Fig. 23.15)
		U.S. agriculture is characterized by very high yields, but this is due to: planting few genetic varieties; heavy use of fertilizers, pesticides, and herbicides; generous irrigation; and excessive fuel consumption. These have led to environmental degradation.
	3.	The City (p. 483, Fig. 23.16)
		a.	The city is highly dependent on the country to supply its food, but as city populations increase, more land is used to house people.
		b.	The city does not conserve and reuse resources, and generates great quantities of pollutants.
	4.	The Solution (p. 484, Fig. 23.17)
		a.	Conservation of natural resources and natural ecosystems can be achieved through wise use of only what is needed, recycling, and use of renewable energy sources.
		b.	Working with nature to achieve a sustained yield in managed ecosystems will solve the problem of continual ecosystem degradation.
			ECOLOGY FOCUS: Preservation of the Everglades (p. 485, Fig. 23A)
			i.	At the turn of the century, much of the Everglades was drained to grow crops. This interrupted the natural cycle of this aquatic ecosystem and led to the downfall of many natural populations.
			ii.	The usefulness of the Everglades region to grow crops will be over, due to soil erosion, by the year 2000.