Desert habitats
In this episode we'll learn:
- What defines a desert?
- Where are deserts found?
- What causes a desert?
- Rainshadow effect.
- Adaptations to life.
Desert Communities
What defines a desert?
A desert is defined simply by the amount of rainfall that falls
in an area in conjunction with the amount of evaporation. In essence,
its any area that receives on average less than 10 inches of rainfall
per year, and where the yearly evaporation is more than 10 inches
of rain a year.
Where are deserts found?
Deserts are found around the globe, generally around a belt of
30 degrees north and south latitude where global wind patterns carry
down dry air from the upper atmosphere.
What causes a desert?
Deserts can be caused by any factor that limits rainfall. I've
come up with three such reasons here:
Rain shadow effect: These deserts are formed on
the leeward side of large mountain ranges. Think of the desert of
Nevada caused by the Sierra Nevadas. As the moisture in the air
goes up and over these ranges, it cools, depositing its moisture
load on the range. By the time the air comes down, it has very little
moisture left ... thus causing a desert. Another good example of
this can be found on island ecosystems where there is a predominant
wind direction. Hawaii is a great example. Waikiki and Diamond Head
receive only about 13 inches of rain a year ... nearly a desert!
Cold Ocean/Warm Land: Around the tropic of cancer
and Capricorn, is an area of world that tends to have dry air coming
down from the upper atmosphere, causing high pressure systems and
dry air. Combine this with the fact that the ocean currents tend
to move cold ocean water down certain sides of the continents (The
western sides in the north and the eastern sides in the south).
Whenever you combine a cold ocean with a warm land, you're not going
to have much rainfall. Cold oceans simply provide very little moisture
content, while the warm land, evaporates heavily. More simply, think
about the mirror in the bathroom when you shower. The reason water
condenses on the mirror is because its much cooler than the rest
of the air. Warm land won't allow that condensing effect.
Interior Basins: The final type of desert can
form when a piece of land is simply too far from a source of moisture.
Take the Sahara or Gobi deserts as examples.
Adaptations to life in a desert
To survive in the desert you need to optimize your water use. Many
plants have come up with a unique type of photosynthesis that allows
them to only open their pores at night (C4 plants). Animals must
also be able to conserve water. Reptiles produce a type of concentrated
urate instead of our normal liquid waste to excrete ammonia.
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