part 1.3 – ecosystems – biomesw3.marietta.edu/~biol/102online/13eco04ol.pdf · hold less water....

Dr. D. McShaffrey Biology 102L - Organisms and Ecosystems May 2, 2004 of 8 Part 1.3 – Ecosystems – Biomes

Part 1.3 – Ecosystems – Biomes

Based on Mader, Sylvia S. 1993. Biology - 4th Ed. WCB and Levine, J.S. and K.R. Miller. Biology: Discovering Life D.C. Heath and Cox, G.W. 1997. Conservation Biology - 2nd ed. WCB and Lewis, Gaffin, Hoefnagels & Parker. 2004. Life - 5th ed. McGraw Hill Reading: Chapters 43 and 44 in Lewis et al.

I. Biomes - Chapter 44 A. Biological Diversity

1. Ecosystem diversity - all of the different types of ecosystems in an area 2. Species diversity - number of species in an area 3. Genetic diversity - variability within a species

B. Components 1. Non-living (abiotic) environment

a) Oxygen b) Sunlight c) Temperature

(1) Fig. 3.5 d) Soil e) Water f) Dissolved salts g) Salinity h) Metabolic wastes i) Nutrients

2. Living (biotic) community

D:\DMC\2CLASSS\102online\13ECO04ol.doc May 2, 2004


C. Biosphere 1. a thin shell of air, land and water around the Earth supporting life.

Biomes are controlled chiefly by climate (precipitation and temperature) – these in turn are controlled by where the biome is on the planet:

Figure 44.1 Figure 44.2 As you go up a mountain or away from the equator, temperature and precipitation decrease (below left). Sunlight strikes the equator straight on, thus the sun’s rays are hottest there. Towards the poles, the sun’s rays strike on a slant, dispersing them from a circle to an oval, and thus spreading out their energy (right). In the summer, the tilt of the Earth brings that hemisphere more directly under the sun, warming it. In the winter, the hemisphere is tilted away from the sun, spreading out its rays and thus leading to cooler temperatures.



Figure 44.3a Figure 44.3b

Don’t worry about figure 44.3a (above) other than to note that these global patterns lead to particular climates in different places. In Figure 44.3b we see the Earth tilted on its side, with the equator pointed “up”. Sun striking the equator directly warms this area and evaporates water. This warm humid air rises (because it’s warm and thus less dense); but as it rises it cools and can hold less water. This forms clouds and rain (which is why there are tropical rain forests at the equator). The now dry air continues to rise because it is pushed up by the rising air below it. At the top of the atmosphere it spreads out away from the equator, falling back to Earth (because it is now cold) at 30o North and South latitude. This falling cold, dry air gives rise to deserts at these latitudes.



Figure 44.4

The figure above shows how the biomes are distributed around the world. Note the tropical rain forests at the equator; drier regions around the equator will have tropical dry forests or savannas (savannas are grasslands with interspersed trees). Deserts are concentrated at 30o N and S latitude and on the far side of mountains where water from the oceans cannot get to (as the moist air comes off the oceans it goes up and over the mountains, but as it goes up it cools and the rain falls out of it – this forms the deserts in Nevada and Utah). In the eastern US, temperate (hot summer, cold winter) deciduous (leaves fall off trees) forests dominate. As you go west, the climate gets too dry for trees and grasslands take over. If you go north, the climate cools and deciduous trees are replaced by the coniferous (pine, firs, spruce) trees of the taiga. Further north, it is too cool even for those trees and tundra takes over. A similar pattern is seen going up mountains.



D. Biomes - a major biotic community having well-recognized life forms and a typical climax species

1. Terrestrial ecosystems

a) Divided into biomes

(1) Biomes distinguished by a distinctive assemblage of plant species (a) (Plants are long-lived and don't hide, making them convenient)

b) Climate and soil - effects on biomes

(1) Biomes largely determined by combination of temperature and rainfall

moist dry

arctic

subarctic

temperate

tropicalrain forest

seasonal forestsavanna

semidesert

desert

forest semidesertdesertgrassland

taiga

tundra

Focus on the figure above right, which is taken from another text. The inset represents the temperature and precipitation from hundreds of locations around the planet. Note the reversed temperature scale; it gets COLDER as you move to the right. The most obvious thing is that there are no cold, wet places on the planet – why? An ecologist named Whittaker looked at what kind of vegetation was growing at each of the places represented by a dot. It turned out that these could be grouped into plant communities or biomes that had already been described. These communities are outlines in the main figure. Thus, a hot wet climate leads to a tropical rain forest; as the climate gets drier this gives way to a tropical seasonal forest or a savanna, and finally to a subtropical desert. If you cool the desert down you get a temperate grassland or desert and eventually a tundra. Warm the temperate grassland up and it gives way to woodland/shrubland, then temperate seasonal (deciduous) forest then temperate rain forest. Cool these forests down and you get taiga.

The figure above left is a simplification. The next set of figures shopws scenes of the major biomes along with maps illustrating where each occurs.



2. Productivity of biomes.




Biomes differ in their productivity (which is measured by the amount of carbon (a building block of all living material) which is taken from the air and incorporated into living plant tissue. The units for this are grams of carbon per meter squared per year. In other words, scientists measure how much carbon is in a given meter-squared plot, and come back a year later to measure it again. The increase is how much carbon is fixed. To be productive, an ecosystem must have light, nutrients and water. The most light is available at the equator. Nutrient and water availability varies greatly. You should be able to look at each of the biomes above and explain why it is or isn’t productive.

a) Estuaries and tropical rain forest b) Temperate forest c) Agricultural land d) Temperate grassland e) Lakes and streams f) Coastal zone g) Tundra h) Open ocean i) Desert

part 1.3 – ecosystems – biomesw3.marietta.edu/~biol/102online/13eco04ol.pdf · hold less water....

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