This is the lecture covering ecology and biosphere
Before we get started I wanted to emphasize
... that while we're already covering this topic in a couple of lectures
that this topic really is a very  detailed topic and one could spend a whole semester, bachelors degree, or even Phd studying it
so what is ecology ecology is the study
of living organisms and how living
organisms interact with their
environment and one of the first
questions that one might ask is how are
living organisms distributed on the
planet
what are the features that govern them
the primary factors that govern the distribution of organisms on Planet
include temperature water availability
of light and type of substrate so if
temperature is a primary factor governing
which organisms are found where then
what determines the distribution of
temperatures well it turns out that the
distribution of temperature on the
planet is strongly correlated with  latitude
lines of latitude are horizontal marker
lines that give us one of the two pieces
of information that we need in order to
precisely locate any place on the planet so
for example in Arizona you use a line of
latitude that's approximately 32 degrees
north and then you would have a line of
longitude and those are vertical lines that tell
you how farr east or west you are
well so how is annual mean temperature correlated with latitude
we find the hottest temperatures
approximately 0 degrees at the equator and
those hot temperatures extend about 30
degrees north 30 degrees south
fundamentally the tropics those are the
warmest part of the planet and the
coolest parts of the planet are those
locations that are 40 50 60 degrees
north and 40 50 60 degrees south so what causes this pattern?
this  pattern is caused by the
variation in the sunlights intensity with latitude
the earth is far enough away
from the Sun the sun's beams by the time
they reach the earth are traveling
parallel to one another at the equator
sunlight is directly overhead and so the
number of incoming particles of sunlight
which are  called photons are most
concentrated
further north and south
there's a low angle of incoming light
and that spreads the photons over a much
larger area so close to the equator you
have concentrated light and close to
the poles you have  much more diffused light
and each photon or packet of light
energy can be used to transform that
from light energy to heat energy so you
can have more heat energy at the equator
than you do at the polls
And this amount of heat energy changes and shifts
through the seasons as the earth moves
around the Sun the Earth's axis is not
straight up and down
instead the earth is tilted at an angle
of 23 and a half degrees and every day
the earth spins once on its axis when
you're facing what if you are on the
part of the earth is facing sun it's
daytime if you're on the part of the
earth that is facing away
from the Sun it's nighttime but while
you're constantly every day you're
spinning around the axis the earth
itself also moves all the way around the
Sun and it takes one year to move all
the way around the Sun now there are two
days of the year where the 
the sun and the earth are in a position so
that as the Earth spins on its axis
every place on the planet has precisely
12 hours of daylight 12 hours of
darkness
the first of those events is in the
March equinox “Equi” means same and “nox” means night.
so equal day and night. There's a  March
equinox and then there's a September
equinox so we are heading towards September
equinox right now as i'm recording because i'm
recording beginning august so once you
have passed one of the equinoxes  you
get your heading towards the solstice so
if we start the September equinox where
half of the earth getting 12 hours of day
in 12 hours a night other half of the
earth is also getting 12 hours of night and 12
hours of day we're moving towards the
December solstice what's happening here?
well the earth is tilted on axis and as
it moves towards its position for the
December solstice the northern
hemisphere is tilted away from the Sun
and the southern hemisphere is tilted
towards the Sun so the part of the earth
that is tilted toward the Sun gets more solar
energy and becomes warmer so towards
December the southern hemisphere gets
warmer and has a summer and the northern
hemisphere is tilted away from the Sun
becomes colder so we have a winter in
the Northern Hemisphere after the
December solstice which is the day which
you have the longest night in the
northern hemisphere and the longest day
time in the southern hemisphere you move
once again towards
the equinox where you've got
equivalent night and day and then from
the march equinox you move towards the June
 solstice and so on and so forth
now the variation in sunlight intensity
is going to be much much stronger the
further north in the further south you
are so for example at the equator you're
very close to 12 hours of daylight and 12
hours of darkness
almost all the year round whereas if
you're living in northern Canada or
close to the South poll what you'll
notice is at certain times of year you
have lots of sunlight another time for
you have hardly any and example is in
Scandinavia they sometimes call it the
land of the Midnight Sun in the middle
of summer time in Scandinavia the sun
sometimes doesn't actually set or it
will only set for two or three hours at
night and that's in the summertime in
the wintertime on the other hand they'll
have weeks at a time where the Sun will
only rise hours and they're in darkness
this variation in the heating of the air
and land on a planet sets up a pattern
of global air circulation and
precipitation precipitation includes
rainfall and snow and hail and the path
of starts at the equator so this picture
over here with sunshine over 0 degrees is
showing you at the equator you get a lot of
sunshine lot of heat when you heat up
air it expands and rises and as the air
expands and rises the air releases its
moisture and you have precipitation or
rainfall  so at the equator at zero
degrees you have
both steady hot temperatures and plenty of
rainfall  a little bit north and a  little bit south
about 30 degrees you have an arid Zone a dry zone
 where air is descending and it's
dry and absorbs moisture in Arizona we
live approximately 30 degrees north and
that is one of the reasons for the
Sonoran Desert so the changes in
intensity of sunlight corresponding with
latitude setup global air circulation
patterns and they determine bands of dry
and wet habitats now these bands of
habitats can be altered by the local
geography and I'll get into that in a
second but already with just the small
amount of information we can describe
some important levels of variation in
living organisms across the planet the
first level of variation is where do you
find tropical forests tropical forests are
lush green have huge trees high biological
diversity these are found close to the
equator  and between the tropics on the other
hand you might ask where are the deserts
of the world found  the deserts of the
world are found in subtropical high pressure
belts that are north and south of the
Equator approximately 30 degrees now
onto how local geography can alter your
climate this illustration is showing you
the changes in vegetation structure as
you increase in elevation will go up a
mountain side and for those of us living
in Arizona who have driven from the
phoenix or tucson area all the way to
the mountains will be very familiar with
this picture close to the city you'll be
in the desert where you'll see saguaro
cacti and barrel cactus and as you go up
you'll reach an area where there's a lot
of grass and so if you recall driving up
to flagstaff from Phoenix there's a stop
called sunset stop and it's got
beautiful gold and green grass you go a
little bit further north and you go a
little higher in elevation and hit you'll
oakwood land and pine trees and if you
go all the way up to the top of the San
Francisco Peaks you'll get to spruce and
fir forests and actually get all the way
up to alpine types of habitats
so why is this as you go up in elevation
you experience cooling of the air and
different organisms have evolved to cope
within different temperature and
rainfall conditions and so for example
at 3,000 to 4,000 feet its too dry and too hot
for oak trees to live naturally and so
their seeds will not germinate on the
other hand at 6,000 feet its too moist and
two cool for saguaro  cacti to be able to
survive and so you don't find them
living there another factor that
influences local habitats are the
presence of mountains and the direction
of wind
this image is showing you the overall
wind direction across the coastal and
Cascade Range in California the Pacific
Ocean has a lot of water in it and that
evaporates so you have moist air above
the Pacific Ocean the landmass heats up
faster than the water because water has
got hydrogen bonds between the molecules
and those can absorb a lot more heat
energy before you actually start to
manifest and temperature changes as the
land heats up faster and so what that
does is close to the coast you end up
with winds that blow from the water to
the coast and that moist air goes over
the Coastal Range it i will start to
deposit water and then the wind will
continue to move inland towards the
Cascade Range now the Cascade Range is
much much taller so as those clouds and
as that wind with moisture move up
towards the Cascade Range the clouds
will be forced upwards and cooled and
and then they will get cooler and drop their
rain so on the side of the mountains
that's closest to the oceans you're
going to be getting rainfall  and as those
winds cross over the top of the mountain
range you'll find that they are dry and
you have a rain shadow and the desert
