Ecology topic #22, p. 1 of 8
is the process by which unrelated organisms evolve a resemblance to
each other in response to common environmental conditions. E.g. mangroves worldwide
typically have thick, leathery leaves, root projections, vivipary
B. Biome: a type of ecological community characterized by distinctive plant assemblages
covering major parts of the earth’s surface
I. Geographic distributions of biomes correspond closely to major climate zones
because no single type of plant can endure the entire range of conditions on earth
III. Biome types can be very uniform wherever they occur on the globe, even though
they may possess different species.
E.g. Rain forests or deserts in different parts of the
3. Climatic and physical conditions are the major determinants of plant distributions
A. Because heat influences moisture stress, temperature and precipitation together are the
determinants of boundaries of major biomes.
B. A widely adopted climatic classification is that of Heinrich Walter based on the annual
course of temperature and precipitation (see text Figure 5.8)
I. Recognizes 9 climate zones, from Equatorial (Tropical rain forest) to Polar
C. A different approach: Whittaker started with vegetation structure and related it to
average precipitation and temperature (see text Figure 5.9)
Ecology topic #22, p. 2 of 8
I. The biomes fall in a triangular area with corners representing following warm-
moist, warm-dry, or cool-dry conditions.
A. Other Considerations
I. Soils provide the foundation for terrestrial biomes and influence local plant
a. Profile provides a snapshot of soil structure in a constant state of flux.
: Organic Layer freshly fallen organic material - most superficial layer.
: Mixture of minerals, clay, silt and sand.
: Clay, humus, and other materials leached from A horizon - often
contains plant roots.
: Weathered parent material.
II. Fire shapes vegetation toward drier end of spectrum, typically in grassland and
shrub biomes where moisture is intermediate (sufficient productivity for fuels to
accumulate) and seasonal droughts occur (fuels dry out sufficiently to burn).
4. Terrestrial Biomes
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