The Energy in Ecosystems (p. 746)
36.1
36.2
Energy Flows Through Ecosystems (p. 746; Figs. 36.1-36.4)
A. What Is an Ecosystem?
1. A community is the group of different living creatures that inhabit an area and interact
with each other.
2. Where the community lives is defined as the habitat.
3. The community together with its habitat comprises an ecosystem.
4. The biosphere is the sum of all of the ecosystems on earth.
B. The Path of Energy: Who Eats Whom in Ecosystems
1. Each member of a community uses energy, the ultimate source of which is sunshine
striking the earth.
2. Photosynthetic organisms, plants and algae, capture the energy in sunlight and
incorporate it into organic compounds and are called the producers of communities.
3. All other organisms are consumers that obtain their energy either by eating plants or by
eating each other.
4. Each organism can be assigned to a feeding level, known as a trophic level.
5. Plants are trophic level 1; consumers eating plants (primary consumers) are in trophic
level 2; and consumers eating plant-eaters (secondary consumers) are in trophic level 3.
6. If these organisms are arranged in a linear fashion, they make up a food chain.
7. In most communities, however, the feeding relationships among organisms are highly
complex, and make up a food web.
C. Producers
1. Plants use energy from the sun to build energy-rich sugar molecules.
2. Plants also remove nitrogen and other nutrients from soil and incorporate them into plant
tissues.
D. Herbivores
1. Herbivores (primary consumers) eat a variety of different kinds of plants.
E. Carnivores
1. Carnivores (secondary consumers) are animals that eat herbivores.
2. Omnivores make food webs even more complex because, like humans, they eat a variety
of plants and animal tissues.
F. Detritivores and Decomposers
1. Detritivores and decomposers eat dead or dying organisms and recycle nutrients back to
the soil.
G. Energy Flows Through Trophic Levels
1. The amount of energy fixed by producers in the ecosystem is the primary productivity.
2. Plants also use much of the energy they store in organic compounds, so net primary
productivity must be calculated to account for that loss of energy.
3. The total weight of all organisms in the ecosystem is the biomass.
4. Some ecosystems, like cattail swamps, have a very high net primary productivity and a
moderate biomass.
5. Others, like a tropical rain forest, have a high net primary productivity and an extremely
high biomass.
6. A food chain cannot be made up of more than four or five lengths because a great deal of
energy, usually around 90%, is lost at each trophic level.
Ecological Pyramids (p. 750; Fig. 36.5)
A. The biomass and numbers of the producers is usually greater than that of the consumers in an
ecosystem.
B. This relationship can be shown using an ecological pyramid of numbers or biomass.
C. Inverted Pyramids
1. Some aquatic pyramids are inverted because they are dominated by a small biomass of
photosynthetic plankton that have a very high rate of turnover.
D. Top Carnivores
1.
2.
The loss of energy that occurs at each trophic level places a limit on the number of toplevel carnivores a community can support.
Top-level carnivores also tend to be larger animals, so the small biomass available at the
top of the pyramid is concentrated into a few individuals.
Materials Cycle Within Ecosystems (p. 751)
36.3
36.4
36.5
The Water Cycle (p. 751; Figs. 36.6, 36.7)
A. Unlike energy, materials within ecosystems are recycled from one component to the next.
B. The paths of water, carbon, and soil nutrients are closed circles, or cycles.
C. Water cycles through ecosystems.
1. The water cycle has an environmental component and an organismic component.
D. The Environmental Water Cycle
1. In the environmental water cycle, water vapor in the atmosphere condenses and falls to
earth as precipitation and returns to the atmosphere by evaporation from lakes, rivers,
and oceans.
E. The Organismic Water Cycle
1. Plants are the primary component of the organismic water cycle.
2. Plants take up water from the soil, and much of it passes through the plant and is given
off at the leaves by transpiration.
F. Breaking the Cycle
1. In tropical rain forests, a great amount of water is moved via transpiration, causing
localized rainfall.
2. When humans deforest areas, they become desertlike because plants are no longer
present to recycle water.
G. Groundwater
1. Groundwater can be found beneath the surface of the earth in aquifers.
2. People in the United States rely on groundwater for drinking and agricultural uses.
3. Unlike surface water that is continually renewed, groundwater recharge rates are slow,
and pollutants remain trapped in groundwater virtually forever.
The Carbon Cycle (p. 753; Fig. 36.8)
A. Carbon is captured from atmospheric carbon dioxide by plants through photosynthesis.
B. Plants take up carbon dioxide and incorporate it into organic compounds.
C. Carbon cycle is returned to the atmosphere through respiration, combustion, and erosion.
D. Respiration
1. Plants and animals give off carbon dioxide as a by-product of cellular respiration, so
carbon is returned to the atmosphere.
E. Combustion
1. When we burn wood or fossil fuels, carbon trapped long ago is released to the
atmosphere.
F. Erosion
1. When marine organisms die, their calcium carbonate shells are deposited, forming
limestone.
2. When limestone deposits are exposed, carbon again is released back to the atmosphere.
Soil Nutrients and Other Chemical Cycles (p. 754; Figs. 36.9, 36.10)
A. The Nitrogen Cycle
1. Much nitrogen gas exists in the atmosphere, but most livings things are unable to use
nitrogen in this form.
2. Nitrogen fixation is one method by which nitrogen can be moved from the atmosphere to
the soil where plants can use it.
3. Several groups of bacteria can fix nitrogen, but they must be protected from oxygen in
order to carry out that process.
4. Bacteria are encased in cysts or in root nodules of certain types of plants to allow them to
carry out nitrogen fixation without the presence of oxygen.
5. Farmers add artificially produced nitrogen to agricultural fields to increase their crop
yields.
6. Industrial fixation of nitrogen now accounts for up to 30% of the nitrogen cycle.
B. The Phosphorus Cycle
1. Available supplies of phosphorus are taken up from soils by plants and passed along the
food chain.
2. When organisms die, the phosphorus they contain is recycled back to the soil.
3. Agricultural fertilizers often contain phosphorus to increase crop yields.
4. Phosphorus is often a limiting nutrient in aquatic ecosystems, so additional phosphorus
from farm runoff or sewage effluent triggers algal blooms in lakes, killing fish from lack
of oxygen when the algae die all at once.
5. Such rapid increases in lake productivity due to excessive nutrient input are called
eutrophication.
C. The Cycling of Other Chemicals
1. Sulfur can harm an ecosystem when large amounts in atmosphere combine with water
vapor and produce acid rain.
2. Heavy metals tend to accumulate in higher trophic levels, a process called biological
magnification.
How Weather Shapes Ecosystems (p. 756)
36.6
36.7
36.8
The Sun and Atmospheric Circulation (p. 756; Figs. 36.11, 36.12)
A. Different types of major ecosystems are located at specific points around the globe, primarily
due to the influence of climate.
B. Latitude affects climate because the sun's rays hit each latitude differently.
1. At the equator, the sun's rays hit nearly straight on, while at higher and lower latitudes,
the sun's rays are at an angle.
2. At the equator, the weather is similar year round, but away from the equator, areas of the
earth experience changing seasons.
3. These are some of the factors to which plants and animals have to adapt.
C. Air circulates around the earth in six large air masses.
1. Where air flows upward and cools, it drops its moisture—enough to support the world's
forests.
2. After it cools, air sinks back to earth, extracting moisture, and dry, desertlike conditions
prevail.
Latitude and Elevation (p. 757; Figs. 36.13, 36.14)
A. More sunlight falls per unit area on tropical latitudes than elsewhere on the globe, increasing
temperatures in these areas.
B. Temperature also varies with elevation, with higher altitudes experiencing cooler
temperatures.
C. Rain Shadows
1. When air blows across the water, the warmth and moisture are carried out onto the land.
2. The locations of mountains affect climate locally.
3. On the windward side of mountains, air cools as it is pushed upward, and water
condenses and falls to the earth.
4. On the leeward side of the mountains, a rain shadow develops where rainfall is scant.
Patterns of Circulation in the Ocean (p. 758; Figs. 36.15, 36.16)
A. Patterns of ocean circulation are determined by the patterns of atmospheric circulation.
B. The world’s oceans circulate in huge gyres deflected by continental landmasses.
C. The manner in which warm ocean currents redistribute heat profoundly affects life not only in
the oceans but also on coastal lands.
1. Western Europe, for example, is much warmer than other locations at the same latitude
because of the Gulf Stream current that brings warmer water to Europe's coastline.
2. In South America, the Humboldt Current carries phosphorus-rich cold water northward
up the western coast that supports an abundance of marine life in this region.
D. El Nino Southern Oscillations and Ocean Ecology
1. Distributions in ocean currents like El Nino can have profound influences on world
climate.
Major Kinds of Ecosystems (p. 760)
36.9
36.10
36.11
Ocean Ecosystems (p. 760; Figs. 36.17, 36.18, 36.19)
A. Nearly three-quarters of the earth’s surface is covered by water; the average depth of the
oceans is 3 kilometers (two miles).
1. Organisms living near the surface can employ photosynthesis, but those in the deep rely
on organic debris that rains downward.
B. Shallow Waters
1. Where the ocean meets the land are some of the most productive ecosystems on earth.
2. Part of the coastal area consists of the intertidal region, which is alternately exposed and
covered with the tides.
3. Estuaries are areas where rivers flow into the ocean, carrying soils and nutrients with
them; freshwater conditions intergrade into salt water, and dense stands of aquatic
plants provide breeding areas for numerous marine fish.
4. Many of the great fisheries of the world are in the shallower areas of the ocean along
the land.
C. Open Sea Surface
1. Open areas of ocean contain abundant plankton, including the photosynthetic
phytoplankton.
D. Deep Sea Waters
1. Deeper areas of the ocean, where light does not penetrate, are home to a bizarre
collection of creatures, many of which live off organic debris trickling down from
above.
2. Many of these organisms have bioluminescent body parts used for communication or
predation.
3. Some organisms gain their energy from hydrothermal vent systems.
4. Frigid and bare, the ocean floor hosts a surprising diversity of sea creatures, possibly
rivaling that of tropic rain forests.
Freshwater Ecosystems (p. 762; Figs. 36.20, 36.22)
A. Freshwater ecosystems cover only about 2% of the earth’s surface and all are strongly tied to
adjacent terrestrial ecosystems.
1. Many unique adaptations are seen in organisms living in fresh water.
2. For example, stream dwellers must be able to hold on tight or be swept downstream.
B. Eutrophic lakes are those with high productivity; they tend to be warm and shallow.
C. Oligotrophic lakes are less productive, deep, and cold.
1. Oligotrophic lakes are more susceptible to organic enrichment.
D. Eutrophic lakes have an abundance of minerals and organic matter, while these nutrients are
scarce in oligotrophic lakes.
E. Thermal Stratification
1. Thermal stratification can be seen in lakes in temperate regions.
2. In the winter, ice is less dense than water, and floats on the lake's surface.
3. During both spring and fall overturn, nutrient-laden deeper waters are brought to the top
and distributed throughout the lake.
Land Ecosystems (p. 764; Fig. 36.23)
A. A biome is a terrestrial ecosystem that occurs over a broad area and is characterized by a
particular combination of climate and organisms.
B. There are seven major biome types on earth: tropical rain forests, savannas, deserts,
grasslands, deciduous forests, taiga, and tundra.
C. Seven minor, or less widespread, types of biomes also are found: polar ice, mountain zone,
temperate evergreen forest, warm/moist evergreen forest, tropical monsoon forest, chaparral,
and semidesert.
D. Lush Tropical Rain Forests
1. Rain forests receive over 250 centimeters of rain per year and have the most diverse
group of organisms found anywhere on earth.
2. At least half of all the described species of terrestrial plants and animals live in the rain
forest, and half of those are threatened with extinction in the next few years.
3. Extensive tropical rain forests are found in South America, Africa, and Southeast Asia.
E. Savannas: Dry Tropical Grasslands
1. Savannas are grasslands bordering the tropical rain forests.
2. They receive less rain, typically 75 to 125 centimeters per year, and are transitional
between rain forests and desert areas.
3. Large numbers of grazing mammals characterize savannas.
4. Many savannas are being converted to agricultural land for human use, to the demise of
the natural inhabitants.
F. Deserts: Burning Hot Sands
1. Deserts are the world's great hot and dry areas, with less than 25 centimeters of rainfall
per year.
2. Vegetation is sparse, and many unique adaptations for water conservation can be found.
3. Desert animals are nocturnal or, like the camel, can store large quantities of water.
G. Grasslands: Seas of Grass
1. Temperate grasslands, or prairies, cover much of inland North America, Eurasia, and
South America.
2. They are found roughly midway between the equator and either pole.
3. In North America, much of the native prairie has been converted to rich agricultural land.
4. Herds of grazing mammals used to roam the area until much land was converted to
agricultural use.
H. Deciduous Forests: Rich Hardwood Forests
1. Deciduous forests are found in areas with mild climates in Eurasia, the northeastern
United States, and eastern Canada.
2. Deciduous, hardwood trees drop their leaves in the winter.
3. Only remnants of the once great forests now remain.
4. Many animals, such as deer, raccoon, and beaver, characterize this biome.
I. Taiga: Trackless Conifer Forests
1. Taiga, or northern coniferous forest, is found in the colder regions of the north.
2. Coniferous trees have needlelike leaves that remain on the tree throughout the year.
3. Marshes and lakes are common in taiga, and most of the precipitation falls during the
short summer months.
4. Large mammals, such as elk, moose, deer, bears, and wolverines, inhabit taiga.
J. Tundra: Cold Boggy Plains
1. Tundra is even further north than taiga, surrounding the poles of the earth.
2. Precipitation is low there, and a layer of permanently frozen soil, called permafrost, is
present year-round.
3. Trees are small and found on lake shores.
4. Large grazing mammals, such as musk oxen, caribou, and reindeer, seem to thrive in the
tundra, and carnivores, such as wolves, foxes, and lynx, manage to survive too.
5. Lemmings experience population cycles, and serve as a predominant food source for
predators.
K. Chaparral
1. Chaparral consists of evergreen, spiny shrubs and low trees.
2. Many plant species can germinate only when they have been exposed to extreme heat
due to fire.
3. Historically, chaparral of California is derived from deciduous forest.
L. Polar Ice Caps
1. Polar ice caps lie over the Arctic Ocean in the north and Antarctica in the south.
2. Life is limited to the coasts.
3. Only prokaryotes, algae, and small insects inhabit the Antarctic interior.
4.
Fresh water is scarce, the sun barely rises in the winter, and there is hardly any
precipitation.
M. Tropical Monsoon Forest
1. It is also known as a tropical upland forest and is found at a slightly higher latitude than
rainforests.
2. Trees are deciduous with a dense layer of shrubs and small trees in the understory.
3. Rainfall is typically very seasonal with several inches daily during the monsoon season.