BIOL 2060 Lecture Notes - Lecture 2: Evapotranspiration, Vapor Pressure, Drought Deciduous

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6 Dec 2014
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Effect of the Abiotic Environment on the Distribution of Organisms September 15, 2014
1. Climate and biome distributions.
Biomes (Details will not be tested, but a basic understanding will be [where is it located etc.])
A way of categorizing the dominant plant life in an area
Why do biomes occur at certain latitudes? CLIMATE
oMean annual temperature is higher at the equator
oMean annual precipitation is higher at the equator
Why do temperature and precipitation vary latitudinally? CURVATURE OF THE EARTH
oMore solar energy/m2 hits the earth at low latitudes than at high latitudes
Sun’s rays hit higher latitudes at a more oblique angle, and it strikes near the
equator at a 90 angle
More solar energy/m2 means higher temperature
oWarm air can hold more moisture than cold air
oTemperature affects air circulation patterns
Add/draw diagram!!!
Hadley cells
At equator, we have highest amount of moisture in the air
Warm air rises
At equator, warm moist air rises, cools, forms clouds, and drops a lot of moisture
– why we get a heavy band of precipitation at equator
Once air loses moisture, it moves north and south and at 30 degrees north and
south that air starts to drop back down at the surface of the earth and this creates
warm air that drops down and it is very dry so this creates deserts at 30 degrees
north and south – this is known as Hedley cells
There are two other cells: Ferrel Cell (north) and Ferrel Cell (South)
**draw another diagram**
This explains why Canada gets a lot of precipitation
Hadley Cells are the strongest ones
The effect of temp on these cells causes air circulation patterns
Seasonality in temperature is lower at the equator, and higher at the poles
oYou have a smaller temperature range at the equator, and it is most pronounced the
further you get away towards the poles
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What causes seasonal variation in temperature? THE TILT OF THE EARTH’S AXIS
o**draw another diagram**
Tilt of the earth’s axis also causes seasonal variation in precipitation
oInter-tropical convergence zone (ITCZ)
Location where two Hadley Cells come together is the ITCZ (where those two
cells converge together) and where you get a lot of precipitation
oThe ITCZ is at the equator only during autumn and spring
oDuring the northern hemisphere’s summer, it is closer to equator, so the thermal equator
(place where you get the most direct sunlight) moves north, so the Hadley shells move
further north, so biomes between the equator and tropic of cancer tend to have a wet
season during the summer – so they have a very pronounced wet season during this
summer
oDuring the southern hemisphere’s summer, the sun shines on the tropic of Capricorn, the
thermal equator moves south, which causes a wet season during this time
If the Earth’s axis of rotation was not tilted but instead were perfectly perpendicular to the plane
of its orbit around the sun, seasons would be less pronounced
oThe circuit of the earth is not a perfect circle, so sometime in the year the earth is closer
to the sun than other times
oNot as important as the tilt, but it does have an effect
oTherefore we would still have seasons but they would be a lot less pronounced
If the distribution of biomes is determined by latitudinal variation in temperature and precipitation, why
do different biomes occur at the same latitude?
Ocean currents: warm ocean currents cause biomes to occur at higher latitudes than they would
otherwise
oIn diagram: red is warm, blue is cold
oGolf stream – it’s a very major ocean current that is warm and end up in Northern Europe
It is one of the reasons why the UK has a relatively warm climate even though it
are further north
Reason why North Europe has temperate forests further north, while in North
America we have boreal forests at that same latitude
oThese warm and cold oceans currents are moving heat around the globe
oOcean currents form in variation and different solar energy reaching the globe
What does this mean in light of global warming?
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Hypothesis that golf stream will become weaker, and Northern Europe may
become colder and the biome may change, and consequently cause rapid climate
changes
Mountains:
oRain shadow effect causes drier biomes to occur on the east side of mountain ranges
Moist air comes in from west to east, so when it goes up the mountain, it gets
cooler and holds less moisture and drops a lot of rain. Once it gets over the
mountain, it already dropped the moisture on the other side of the mountain, so
the east side becomes dry and warm
oTemperature is lower at high altitudes because the air is less dense and can hold less
energy
Reason why mountains often have snow at the peaks
At high altitudes, you see biomes characteristic of higher latitudes
i.g. you see Spruce-fir Forests and Alpine Tundras on the mountains in
San Francisco, which is at a southern latitude than where these biomes
are expected to occur
oThis is limited to mountain ranges – biome differences occur only on the mountains, not
on the sea level surrounding them
oLatitude and altitude interact; the temperature at the top of the mountain (altitude) may
change depending the latitude of the mountain
Question: The San Francisco Peaks occur at 35degrees N latitude. If they instead occurred at 5degrees N,
how would the altitudinal distribution of biomes change?
a. The same biome would occur at all altitudes
b. The tundra biome might be absent –if the peaks were moved south, the top of the mountain
would not be as cold, so the tundra would not be there
c. The altitudinal distribution of biomes would not change – they wouldn’t change much, but
the tundra biome would not be there
2. The physical environment and species distribution
The Mean Precipitation and Temperature of a Location Can be Summarized Using a Climate Diagram
This is a graph that plots both temperature and precipitation on the y-axis (one on the left and one
on the right), and the months of the year on the x-axis
The Distribution of Biomes can be Predicted from Mean Precipitation and Temperature –WHY??
**You can plot a graph with temperature as x-axis and precipitation as y-axis, and this gives you the
different biomes that depend on both temperature and precipitation
**How come there are no biomes that are cold and wet? Cold air cannot hold that much water (why skin
dries). Therefore, if the cold air can’t hold water, there is no precipitation. Therefore, a cold and wet
climate cannot exist on Earth.
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