Biomes are often given local names. For example, a temperate grassland or shrubland biome is known as steppe in central Asia, prairie in North America, and pampas in South America. Tropical grasslands are known as savanna or veldt in southern Africa and outback or scrub in Australia.
Terrestrial Biomes
Terrestrial biomes are defined based on factors such as plant structures (such as trees, shrubs, and grasses), leaf types (such as broadleaf and needleleaf), and plant spacing (forest, woodland, savanna). Climate is also a major factor determining the distribution of terrestrial biomes. Among the important climatic factors are latitude, from the poles to the equator (Arctic, boreal, temperate, subtropical, tropical); humidity (humid, semi-humid, semi-arid, and arid), with seasonal variation in rainfall; and elevation (increasing elevation causes a distribution of habitat types similar to that of increasing latitude) (Table (below)). Terrestrial biomes (Figure below) that lie within the Arctic and Antarctic Circles are relatively barren of plant and animal life, while most of the more populous biomes lie near the equator (Figure below).
Figure 23.22
One of the terrestrial biomes, a taiga, a coniferous evergreen forest of the subarctic, covering extensive areas of northern North America and Eurasia. This taiga is along the Denali Highway in Alaska. The Alaska Range is in the background.
Figure 23.23
A terrestrial biome, a tropical rainforest, located in the Amazon basin north of Manaus, Brazil. The image was taken 30 minutes after a rain event, and a few white clouds above the canopy are indicative of rapid evaporation from wet leaves after the rain.
Characteristics of Terrestrial Biome Description of Characteristics
Plant structures Trees, shrubs, grasses
Leaf types Broadleaf, needleleaf
Plant spacing Forest, woodland, savanna
Latitude from poles to the equator Arctic, boreal, temperate, subtropical, tropical
Humidity Humid, semi-humid, semi-arid, arid
Elevation Increasing elevation causes habitat changes similar to that of increasing latitude
Aquatic Biomes
Aquatic biomes (which also can be classified into freshwater and marine biomes) can be defined according to:
size
depth, such as the continental shelf
vegetation, such as a kelp forest
animal communities
other physical characteristics, including pack ice or hydrothermal vents
According to the WWF scheme, freshwater biomes can be classified according to:
large lakes
large river deltas
polar freshwaters
montane freshwaters (in mountain areas)
temperate coastal rivers
temperate floodplain rivers and wetlands
temperate upland rivers
tropical and subtropical coastal rivers
tropical and subtropical floodplain rivers and wetlands
tropical and subtropical upland rivers
xeric (dry habitat) freshwaters and endorheic (interior drainage) basins
oceanic islands
The WWF classifies marine biomes according to:
polar habitat types
temperate shelves and seas
temperate upwelling
tropical upwelling
tropical coral
Other marine habitat types include:
continental shelf
littoral/intertidal zone
coral reef
kelp forest (Figure below)
pack ice (Figure below)
hydrothermal vents
cold seeps
benthic zone
pelagic zone
neritic zone
Figure 23.24
An example of an aquatic marine biome, a kelp forest, located near Santa Cruz Island, Channel Islands. National Park, California.
Figure 23.25
An example of an aquatic marine biome, pack ice.
The Biosphere
The most inclusive level of organization in ecology is the biosphere. It is the part of the Earth, including air, land, surface rocks, and water, within which life occurs, and which biotic processes in turn alter or change. It is the global ecological system integrating all life forms and their relationships, including their interactions with the outer layer of the earth: the lithosphere (or sphere of soils and rocks), hydrosphere (or sphere of water) and atmosphere (or sphere of the air). The biosphere occurs in a very thin layer of the planet, extending from about 11,000 meters below sea level to 15,000 meters above sea level and reaches well into the other three spheres.
The concept that the biosphere is itself a living organism, either actually or metaphorically, is known as the GAIA hypothesis. The hypothesis explains how biotic and abiotic factors interact in the biosphere. It considers Earth itself a kind of living organism. Its atmosphere, heliosphere, and hydrosphere are cooperating systems that yield a biosphere full of life. Lynn Margulis, a microbiologist, added to the hypothesis, by noting the ties between the biosphere and other Earth systems. For example, when carbon dioxide levels increase in the atmosphere, plants grow more quickly. As their growth continues, they remove more carbon dioxide from the atmosphere. Many scientists are now devoting their careers to organizing new fields of study, such as geobiology and geomicrobiology, to examine such relationships.
For a better understanding of how the biosphere works and various dysfunctions related to human activity, scientists have simulated the biosphere in small-scale models. Biosphere 2 (Figure below) is a laboratory in Arizona which contains 3.15 acres of closed ecosystem BIOS-3 was a closed ecosystem in Siberia; and Biosphere J is located in Japan.
Figure 23.26
Biosphere 2, in Arizona, contains 3.15 acres of closed ecosystem and is a small-scale model of the biosphere.
Direct human interactions with ecosystems, including agriculture, human settlements, urbanization, forestry, and other uses of land, have fundamentally altered global patterns of biodiversity and ecosystem processes. As a result, vegetation patterns predicted by conventional biome systems are rarely observed across most of the planet’s land surface. In terms of the human impact on biomes and ecosystems, the study of ecology is now more important than ever. Scientists that study ecology will move us toward an understanding of how best to live in and manage our biosphere.
Lesson Summary
A biome is a climatically and geographically defined area of ecologically similar communities of plants and animals
Biomes are classified in different ways, sometimes according to patterns of ecological succession and climax vegetation, other times according to differences in the physical environment, and in other situations according to latitude and humidity
Biodiversity of each biome is a function of abiotic factors, such as moisture availability and temperature, and the biomass productivity of the dominant vegetation
Terrestrial biomes are defined based on various plant factors and on climate
Aquatic biomes are classified according to various factors and further subdivided into freshwater and marine biomes
The most inclusive level of organization in ecology is the biosphere and it is a global ecological system
The biosphere is itself a living organism, as explained by the GAIA hypothesis
Humans have fundamentally altered global patterns of biodiversity and ecosystem processes
Review Questions
Define a biome.
Name a type of biome based on the physical environment.
Where would you expect to find more biodiversity, in an equatorial rainforest, or in a southwestern desert? Explain why.
Which classification scheme is used to define ecoregions as priorities for conservation?
As you climb a mountain, you will see the vegetation and habitat type change. How could you see a similar change of habitat types if you were traveling geographically?
Name the aquatic biomes classified according to depth.
Water is exchanged between the hydrosphere, lithosphere, atmosphere, and biosphere in regular cycles. What role do the oceans play in the biosphere?
Further Reading / Supplemental Links
Unabridged Dictionary, Second Edition. Random House, New York, 1998.
http://www.kidsconnect.com/content/view/62/27
http://library.thinkquest.org/11353/ecosystems.htm
http://lsb.syr.edu/projects/cyberzoo/biome.html
http://earthobservatory.nasa.gov/Laboratory/Biome
http://www.worldbiomes.com/biomes_map.htm
http://www.mbgnet.net/sets/index.htm
http://www.mbgnet.net/fresh/index.htm
http://www.mbgnet.net/salt/index.htm
http://www.kidsgeo.com/geography-for-kids/0153-biosphere.php
http://www.geography4kids.com/files/land_intro.html
en.wikipedia.org/wiki
Vocabulary
aquatic biomes
Biomes divided into freshwater and marine biomes and defined according to different physical and ecological factors.
biome
A climatically and geographically defined area of ecologically similar communities of plants and animals.
biosphere
The part of the Earth within which life occurs.
GAIA hypothesis
The concept that the biosphere is itself a living organism.
terrestrial biomes
Biomes defined based on plant and climatic factors.
Points to Consider
You now have a general idea of what a biome is and how the diversity of a biome is related to other factors; the next chapter, on ecosystem dynamics, will give you a greater understanding of how energy flow, cycling of matter, and succession vary from one biome to another
One of the aquatic biomes, the hydrothermal vents, mentioned previously in this chapter, is not dependent on sunlight but on bacteria, which utilize the chemistry of the hot volcanic vents. See if you can guess where these bacteria fit into the flow of energy in an ecosystem.
Chapter 24: Ecosystem Dynamics
Lesson 24.1: Flow of Energy
Lesson Objectives
Explain where all the energy in an ecosystem ultimately comes from.
Classify organisms on the basis of how they obtain energy (producers, consumers, and decomposers) and describe examples of each.
Be able to draw and interpret a food web.
Explain the flow of energy through an ecosystem using an energy pyramid.
Check Your Understanding
What is photosynthesis?
What are some examples of organisms that can photosynthesize?
What is a community?
Introduction
Energy is defined as the ability to do work. In organisms, this work can involve not only physical work like walking or jumping, but also carrying out the essential chemical reactions of our bodies. Therefore, all organisms need a supply of energy to stay alive. Some organisms can capture the energy of the sun, while others obtain energy from the bodies of other organisms. Through predator-prey relationships, the energy of one organism is passed on to another. Therefore, energy is constantly flowing through a community. Understanding how this energy moves through the ecosystem is an important part of the study of ecology.
Energy and Producers
With just a few exceptions, all life on Earth depends on the sun’s energy for survival. The energy of the sun is first captured by producers (Figure below), organisms that can make their own food. Many producers make their own food through the process of photosynthesis. Producers make or “produce” food for the rest of the ecosystem. Therefore the survival of every ecosystem is highly dependent on the stability of the producers. Without producers capturing the energy from the sun and turning it into "food," an ecosystem could not exist. In addition, there are bacteria that use chemical processes to produce food, getting their energy from sources other than the sun, and these are also considered producers.
There are many types of photosynthetic organisms that produce food for ecosystems. On land, plants are the dominant photosynthetic organisms. Algae are common producers in aquatic ecosystems. Single celled algae and tiny multicellular algae that float near the surface of water and that photosynthesize are called phytoplankton.
Figure 24.1
Producers include plants (a), algae (b), and diatoms, which are unicellular algae(c).
Although producers might look quite different from one another, they are similar in that they make food containing complex organic compounds, such as fats or carbohydrates, from simple inorganic ingredients. Recall that the only required ingredients needed for photosynthesis are sunlight, carbon dioxide (CO2), and water (H2O). From these simple inorganic building blocks, photosynthetic organisms can produce glucose (C6H12O6) and other complex organic compounds.
Consumers and Decomposers
Many types of organisms are not producers and cannot make their own food from sunlight, air, and water. The animals that must consume other organisms to get food for energy are called consumers. The consumers can be placed into several groups. Herbivores are animals that eat photosynthetic organisms to obtain energy. For example, rabbits and deer are herbivores that eat plants. The caterpillar in Figure below is a herbivore. Animals that eat phytoplankton in aquatic environments are also herbivores. Carnivores feed on animals, either the herbivores or other carnivores. Snakes that eat mice are carnivores, and hawks that eat the snakes are also carnivores. Omnivores eat both producers and consumers. Most people are omnivores since they eat fruits, vegetables, and grains from plants and also meat and dairy products from animals. Dogs, bears, and raccoons are also omnivores.
Figure 24.2
Examples of consumers are caterpillars (herbivores) and hawks (carnivore).
Decomposers (Figure below) obtain nutrients and energy by breaking down dead organisms and animal wastes. Through this process, decomposers release nutrients, such as carbon and nitrogen, back into the ecosystem so that the producers can use them. Through this process these essential nutrients are recycled, an essential role for the survival of every ecosystem. Therefore, as with the producers, the stability of an ecosystem also depends on the actions of the decomposers. Examples of decomposers include mushrooms on a decaying log and bacteria in the soil. Decomposers are essential for the survival of every ecosystem. Imagine what would happen if there were no decomposers. Wastes and the remains of dead organisms would pile up and the nutrients within the waste and dead organisms would never be released back into the ecosystem!
Figure 24.3
Examples of decomposers are bacteria (a) and fungi (b).
Food Chains and Food Webs
Food chains (Figure below) are a visual representation of the eating patterns in an ecosystem, depicting how food energy flows from one organism to another. Arrows are used to indicate the feeding relationship between the animals. For example, an arrow from the leaves to a grasshopper shows that the grasshopper eats the leaves, so energy and nutrients are moving from the leaves to the grasshopper. Next, a mouse might prey on the grasshopper, a snake may eat the mouse, and then a hawk might eat the snake.
Figure 24.4
Food chain. This figure shows, for example, that the snake gets its energy from the rat, and the rat gets its energy from the insect.
In an ocean ecosystem, one possible food chain might look like this: phytoplankton -> krill -> fish -> shark. The producers are always at the beginning of the food chain, followed by the herbivores, then the carnivores. In this example, phytoplankton are eaten by krill, which are tiny shrimp-like animals. The krill are in turn eaten by fish, which are then eaten by sharks. Each organism can eat and be eaten by many different other types of organisms, so simple food chains are rare in nature. There are also many different species of fish and sharks. Therefore, many food chains exist in each ecosystem
Since feeding relationships are so complicated, we can combine food chains together to create a more accu
rate depiction of the flow of energy within an ecosystem. A food web (Figure below) shows the complex feeding relationships between many organisms in an ecosystem. If you expand our original example of a food chain, you might also include that deer also eat clover and foxes that also hunt chipmunks. A food web shows many more arrows but follows the same principle; the arrows depict the flow of energy (Figure below). A complete food web may show hundreds of different feeding relationships.
Figure 24.5
Food web in the Arctic Ocean.
Figure 24.6
Food web in the Arctic Ocean.
Energy Pyramids
When an herbivore eats a plant, the energy that is stored in the plant tissues is used by the herbivore to power its own life processes and to build more body tissues. Only about 10% of the total energy from the plant gets stored in the herbivore’s body as extra body tissue. The rest of the energy is transformed by the herbivore through metabolic activity and released as heat. The next consumer on the food chain that eats the herbivore will only store about 10% of the total energy from the herbivore in its own body. This means the carnivore will store only about 1% of the total energy that was originally in the plant. In other words, only about 10% of energy of one step in a food chain is stored in the next step in the food chain.
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