General Ecology, Lecture 2 (2007)
Abiotic Factors that affect the distribution of organisms
I.
Temperature and Moisture
A.
Global scale
1.
The distribution of biomes can be classified on the basis of their temperature
and moisture profiles [Fig. 50.18, 50.19 Campbell/Reece, 7th ed]
2.
What causes the poles to be much colder than equatorial regions?
a.
Key: curvature of the earth angle of the sun’s rays varies with
latitude [Fig. 2.7 and associated text]
3.
Which other factors mediate the distribution of global temperature?
a.
Earth’s rotation wind currents and ocean currents that affect the
distribution of heat energy [Fig. 2.8, 2.10 and associated text—text
goes into much more detail than what we will cover]

Example 1: Air circulation “cells”

Example 2: The Gulf Stream and its climatic effects.

Compare Great Britain to Northern Canada (at the same
latitude.)
b.
Earth’s tilt seasons [Fig. 50.10,Campbell/Reese; Fig. 2.9, text]
c.
Albedo: reflectance of solar radiation (pp. 21-22)

Different surfaces reflect sunlight differently; and this also
affects the global heat distribution

Examples

Snow and ice: high albedo

Forested areas: low albedo

Water: variable depending upon angle.
4.
How is moisture distributed on a global scale? [Fig. 2.12]
a.
Moist areas are centered at the equator, and 60º N and S latitude.
b.
Coastal areas also tend to be moister than inland regions.
5.
What mediates the global distribution of moisture? (Brief explanation for
equatorial band.) [Fig. 50.10, Campbell/Reese]
a.
Key: warm air holds more moisture than cold air
b.
Warm air rises and cools, moisture dropped close to its source.
B.
Regional scale (esp. pp. 31-33, 38-40)
1.
Altitude
a.
All else being equal, air temperature decreases with altitude
(approximately 1º C/100 meter rise)

This also affects moisture content and precipitation
b.
Rain shadows [Fig. 2.15]

Air saturated with water from the ocean (or another body of
water) blows shoreward toward mountain ranges

Air current is directed upward, follows mountain’s slope

As the air rises, it cools, and thus precipitation occurs on the
ocean side of the mountain.

Why no rainfall on leeward side?

What are the effects on plant communities?
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2.
II.
III.
North-facing and south-facing slopes
a.
South-facing slopes have:

Higher temperatures [Fig. 2.16]

Higher rates of evaporation  dryer conditions
b.
Different plant communities at different elevations on N vs. S-facing
slopes [Fig. 2.17]
C.
Local scale: Microclimates
1.
Defined: The specific conditions of climate (i.e. temp, moisture, etc…)
within a much localized area. Microclimate can vary within very small
distances owing to several factors: presence of vegetation, slope/shade,
cracks and crevices, etc…
2.
Vegetation strongly influences the microclimate
a.
Plants intercept solar radiation, reducing the temperature difference
between ground and air [Fig. 2.25]
b.
Vegetation reduces wind (depending on type)
c.
Vegetation traps moisture

Some examples of how this affects distribution of animals.
3.
Local topography also affects microclimates (not mentioned in text)
a.
Examples…
Nutrients (focus on inorganic nutrients) (pp. 54-56)
A.
Previous courses have introduced you to the role of inorganic nutrients for the
survival and growth of primary producers as well as for consumers.
1.
Define macronutrient vs. micronutrient; provide examples [Table 3.1]
2.
What are the initial sources of these nutrients?
3.
Nutrients vs. distribution of primary production in the ocean [Fig. 24.9]
a.
More nutrients and thus higher productivity in coastal regions due to
riverine inputs and upwelling

We will not get into the precise mechanism of upwelling here,
but you should know the “net result” of upwelling.

Note also region of equatorial upwelling
4.
NOTE: The term usually refers to inorganic nutrients.
Light (Ch. 3, pp. 43-48)
A.
Four major characteristics vary with climate/microclimate. These are…?
1.
All four vary with latitude, time of day, season, slope, water and vegetation.
a.
Energy differences as a function of latitude and time of year [Fig. 3.2]
B.
What is PAR? What range of wavelengths is PAR? [Fig. 3.1]
1.
Available wavelengths and light intensity change as light is
absorbed/reflected by vegetation (terrestrial) and water (aquatic)
a.
Attenuation of light as it passes through water [Fig. from Nybakken,
Marine Biology]

Only 40% of light passes beyond 1m depth
b.
Attenuation of light as a function of leaf area index = m2 leaf area/m2
ground area [Figs. 3.5-3.6]

Only 1-5% of light that strikes the canopy of a “typical
deciduous forest” (LAI 3-5) reaches the forest floor

Wavelength shift: red and blues are absorbed most efficiently,
while green and far-red waves are reflected or transmitted.
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IV.
Other key factors
A.
Salinity (Example: Estuarine organisms)
B.
Oxygen concentration
1.
Example 1: Surface waters vs. sediments in an estuary
C.
pH
D.
Substrate (i.e. soil type, rocky vs. muddy river bottom, etc…)
1.
Example: Distribution of macroinvertebrates in streams.
Study questions
1.
Which two abiotic factors, taken together, are well-correlated with the distribution of
biomes?
2.
What is the primary reason that polar regions are much colder than equatorial regions?
3.
Which other factors mediate the distribution of global temperature? List and provide
examples.
4.
Use the Gulf Stream to explain how ocean currents affect the distribution of heat on earth.
5.
Explain why there is a band of relatively moist terrestrial ecosystems (i.e. tropical rain
forests) centered at the equator. (NOTE: I will not ask you to explain similar bands at
60ºN and 60ºS latitudes as this is a bit more complex.)
6.
Explain a rain shadow with diagrams and words.
7.
Climatically speaking, how do north-facing slopes differ from south-facing slopes?
Briefly explain why this is so.
8.
What is a microclimate? Describe several factors that affect microclimate. Provide some
specific examples of how microclimate affects the distribution of organisms.
9.
What are macronutrients? What are micronutrients? Provide examples.
10.
Which abiotic factor appears to be the key determinant of global primary production in the
ocean (and aquatic environments in general?)
11.
List four key characteristics of light that vary with climate/microclimate. What specific
factors cause them to vary?
12.
What does PAR stand for? What is its range of wavelengths?
13.
What happens to PAR when it passes through water? Through vegetation? Describe the
changes in both intensity and wavelength.
14.
What is the leaf area index?
15.
Review: List as many abiotic factors as you can that affect the distribution of organisms,
and provide examples of how they vary in particular environments (or globally, if
discussed).
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