Physical Setting
Living organisms are found in virtually every habitat on the
planet.
However, no single type of
organism is found
EVERYWHERE.
Each has its own, restricted,
geographic range.
The most significant factor
controlling distribution is
the physical environment.
In terrestrial organisms,
distributions may be
affected by temperature,
precipitation, or soil type.
In aquatic organisms,
temperature, salinity, light,
and pressure are
significant.
It is well documented that environmental variables vary in
a nonrandom manner. It is also well established that more
distant sites tend to be more different than closer sites.
This relates to distributions in that, as the distance
between locations grows, we might expect the
environmental conditions to differ.
A model for understanding the
diversity of geographic patterns.
A key factor in
determining climate
zones and, therefore,
the distribution of habitat
types is the angle of
incident radiation.
This is a function of
latitude.
As the earth
moves around
the sun, the
angle of
incidence
varies at
different
latitudes.
Because this tilted angle of rotation is maintained as the
earth revolves around the sun, the amount of sunlight
received by the Northern and Southern Hemispheres varies
seasonally.
Further
complicating
matters is the
fact that the
earth’s axis is
tilted at an angle
of 23.5 to the
plane of the
ecliptic.
Summer solstice
Autumnal equinox
Winter solstice
Vernal equinox
June 21
Sun over Tropic of
Cancer
September
23
Sun over Equator
December 21 Sun over Tropic of
Capricorn
March
Sun over Equator
The unequal heating of
the earth’s surface sets up
a series of “cells” of rising
and falling air as one
moves from the equator to
the poles.
Solar-driven, latitude and atmospheric circulation
Superimposed on this pattern of air movement is the Coriolis
Effect, which causes moving objects in the Northern Hemisphere
to have an apparent curve to the right, while causing a curve to the
left in the Southern Hemisphere.
Expanding gases
undergo adiabatic
cooling.
So, rising airs cools.
As it does, the water
vapor it contains
condenses.
Rain shadows may
result when air
moving over a
mountain cools and
loses its moisture.
The leeward side of
the mountain
experiences dry
winds.
Dry air cools with
elevation faster than
humid air. Therefore
the air on the
leeward side of a
mountain range is
warmer and drier
than the same
elevation on the
windward side.
A precipitation
map of Oregon
illustrates the rain
shadow effect of
the Coast Range
and the
Cascades.
Small-Scale Spatial and Temporal Variation
Great variation can be created on a local
scale.
Mountains can have a particularly strong
effect.
Examine the effect of
elevation on climate.
A high elevation site
in Arizona is more
similar to one 1500
km away in Oregon
than a low elevation
site 15 miles away in
Arizona.
The spruce forests high on the slopes
of the Great Smoky Mountains
National Park are similar to those of
boreal forests of Canada.
Puerto Rico has a high,
mountainous “backbone”.
Lowlands on the northern
and eastern sides of the
island are lush and tropical.
As the northeast trade winds
move across high backbone
of the island, they lose much
of the moisture they contain.
As a result, the southwestern
corner of the island is extremely
dry, with flora similar to that of
western Mexico.
The cold Humboldt current, flowing
north along the Pacific coast of
South America, along with the rain
shadow cast by the Andes
Mountains, leads to a dramatic
difference over a rather short
distance.
As much as 10 m of rain falls
annually on the tropical rain
forests on the eastern slope of the
Andes.
The Atacama Desert to the west
may go years without rain.
There are also year-to-year and longer
term variations in climate.
The entire global system of moving
fluids fluctuates on a 5-7 year cycle.
These fluctuations seem to be
linked to events in the tropical
Pacific Ocean known as the El Niňo
Southern Oscillation.
The trigger is uncertain, but ENSO
leads to a change in the pattern of
circulation in the tropical ocean.
The warm equatorial countercurrent
may become stronger and push
water up the coasts of North and
South America. Westerly winds
may carry moisture inland causing
heavy precipitation in the winter
when the air temperature is colder
than the offshore waters.
ENSO is also associated with
reduced coastal upwellling,
which may impact the entire
marine food chain and greatly
impact fisheries.
Ocean currents are driven by prevailing winds.
Continents block the flow, and create a northern and southern gyre in the
Atlantic and Pacific.
The global pattern of winds leads to global patterns of oceanic
circulation.
The earth’s major climatic regions. Note the
pattern with respect to latitude. Other factors
influencing climatic patterns are continents,
oceans, mountain ranges.
Soils
The type of vegetation fouind in a region dependings primarily on three
factors:
1. Climate.
2. History of disturbance.
3. Soils.
Soil formation is a chemical
and biological process
resulting from the
weathering of rock and the
accumulation of organic
material from dead and
decaying organisms.
Four characteristic processes produce the primary soil types:
1. Podzolization – characteristic of temperate deciduous and coniferous forests.
2. Lateralization – characteristic of tropical forests.
3. Calcification – typical of arid grasslands and shrublands.
4. Gleization – typical of waterlogged tundra.
Climate is the
primary
determinant of soil
type.
Two primary
climatological
factors that figure
in soil type are
temperature and
aridity.
Lake Zonation
Stratification is a characteristic feature of lakes.
Vertical temperature stratification of Lake Mendota, WI from summer
through winter showing the loss of stratification with cooling.
Summer Stratification
In summer, solar radiation heats the surface water. It becomes lighter,
and floats on the colder, denser water beneath.
The warm upper water is not easily mixed with the water beneath it,
creating a barrier.
The warm surface water is called the epilimnion, and grows progressively
deeper during the summer.
Beneath the thermal barrier is a middle mass of water known as the
metalimnion. This mass is characterized by a steep and rapid decline in
temperature known as the thermocline.
Beneath the metalimnion is the cold, dense hypolimnion.
The warming of the surface water during the summer months leads to
summer stratification.
As the temperature drops in the fall, the depth of the epilimnion
decreases.
Fall Overturn
Eventually, the temperature of the water is uniform from top to bottom,
the waters of the lake circulate, and oxygen and nutrients are
recharged throughout the lake.
This seasonal mixing is called overturn.
Stirred by the wind, it may last until ice forms.
Winter Stratification
As the surface water cools below 4C., it becomes lighter and remains
on the surface.
If the climate is cold enough, the surface water freezes. If not, it
remains close to 0C.
A slight inverse stratification may develop in which the water becomes
warmed up to 4C. with depth.
During the summer,
oxygen may also
become stratified in
lakes and ponds.
The amount of oxygen
is usually greatest at
the surface, due
primarily to interchange
with the atmosphere.
Typically, the amount of
oxygen decreases with
depth because of
decomposition in
bottom sediments.
Tides
The action of centrifugal force on
the earth and the gravitational
pull of the moon to produce tides.
On the side of the earth facing
the moon, the pull of the moon’s
gravity is greater than centrifugal
force and the net tidal force pulls
water toward the moon.
On the side opposite the moon,
centrifugal force outweights
gravitational pull, and the net
force draws water away from the
moon.
While the Gulf of Mexico has
diurnal tides, most locations
show semidiurnal fluctuations.
Tide calendar for the
northern Gulf of
California.
June - Horn Island, Mississippi Sound
06/09/2008 Mon 12:30AM LDT 0.1 L
01:57PM LDT 1.2 H
06/10/2008 Tue 12:19AM LDT
11:07AM LDT 1.0 H 10:30PM LDT 0.6 L
0.4 L
06/11/2008 Wed 08:10AM LDT 1.0 H
2008 Horn Island Pass Tides
06:00PM LDT 0.4 L
Microclimatic
variation can result
in dramatically
different conditions
over very small
spatial scales.
We can see similar microclimatic differences in aquatic habitats.
Alamuchee Creek – Sumter County, AL
Longear
sunfish
Rock darter