Biomes

Biomes
The biome is another major biogeographic pattern. It is a
kind of ecosystem, such as a desert, a tropical rain forest, a
grassland. Here's how it worlcs: Similar environments provide similar opportunities for life and similar constraints. As
a result, similar environments lead to the evolution of organisms similar in form and function (but not necessarily in
genetic heritage or internal makeup) and similar ecosystems.
This is lcnown as the rule of climatic n'milarity and leads to
the concept of the biome. The close relationship between '
environment and kinds of life-forms is shown in Figure 8.4.
Plants that grow in deserts of North America and East
Afiicz illustrate the idea of a biome (see Figure 8.5). The
desert euphorbia of South Africa loolzs similar to North
American desert plants, but is not closely related to them.
They belong to different biological families. Geographically
isolated for 180 million years, they have been subjected to
similar climates, which imposed similar stressrs and opened
up similar ecological opportunities. On both continents,
desert plants evolved to adapt to these stresses and potentials, and have come to look alilze and prevail in like habitats.
The ancestral differences between these loolz-alike plants
can be found in their flowers, fruits, and seeds, which
change the least over time and thus provide the best clues
to the genetic history of a species. The Joshua tree and
saguaro cactus of North America and the giant Euphorbia
of East and Southern Africa are td, have succulent green
stems that replace the leaves as the major sites of photosynthesis, and have spiny projections, but these plants are
not closely related. The Joshua tree is a member of the
agave family, the saguaro is a member of the cactus family,
and the Euphorbia is a member of the spurge family.
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Excerpted from Botltin and Keller. 2007. EnvironmentalScience: Earth as a livingplanet. Wiley. Their similar shapes result from evolution in similar desert
&nates, a process lcnown as convergent evolution. The
~uphorbiaand the Joshua tree are in the same biome but
in different biotic provinces. They function similarly and
have the same niche, but they are not closely related.
So here is the difference between a biotic province and
a biome: A biotic province is based on who is related to
whom. A biome is based on niches and habitats. Species
&hin a biotic province, in general, are more closely related to each other than to species in other provinces.
two different biotic provinces, the same ecological niche will be N e d with species that perform
2 specific function and may look very similar to
each other but have quite different genetic an'
Mediterranean
cestries. In this way, a biotic province is an
evolutionary unit.
The strong relationship between climate and life suggests that if we know the climate of an area, we can make a pretty good prediction about what biome will be found there, what its approximate biomass
(amount of living matter) and
lncreasng aridity
production will be, and what
Figure 8.4
SimpEed diagam of the relationship between precipirauon and latitude and Earrh's mathe shapes and forms of d ~ ~ jor land biomes. Here, latimde sew= as an index of average rempeiature, so latitude can be repiaced by
inant organisms will be.l2>l3 average temperature in this diagram. [Some Figwe 274, p. 293, &om Phyncal Geoflaphy ofthe Global
Environment by Harm de Blij, Peter 0.Muller, and Richard S. WJliams, edited by Harm de BLij, capyright 2004 by Oxford University Press, Inc. Uscd by permission of Oxford Univenity Press, Inc.]
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