Geography 140
Introduction to Physical Geography
Lecture: Introduction to the Biosphere
I. Definition of the biosphere: The living part of our planet. It represents
another overlap among the atmosphere, hydrosphere, and lithosphere, as
living things consume substances from each of these three and add them
thereto.
A. We consume:
1. Oxygen by breathing
2. Water by drinking or root uptake
3. C6H12O6 by respiring (using) or photosynthesizing (producing)
4. Other minerals by eating or root and even leaf uptake
B. We contribute:
1. CO2 through respiration
2. Water by breathing, sweating, urinating, excreting, or, in the case
of plants, by transpiration.
3. Our minerals, sugars, waters by excreting, shedding, and dying
II. Components of the biosphere
A. Simplest "lumping" classification of kingdoms:
1. Animals
2. Plants
3. Microörganisms
B. Another common classification:
1. Animals
2. Plants
3. Fungi (not with plants here because they don't photosynthesize)
4. Protists: one-celled (unicellular) organisms based on eukaryotic
cell (cells with internal differentiation into a nucleus,
mitochondria, and other structures), including protozoa
(microscopic "animals") and algae
5. Prokaryotes: unicellular organisms based on the prokaryotic cell
(no separation of genetic material into a nucleus, no internal
differentiation, e.g., bacteria).
III. Community: The group of interacting populations of the species found in
an area (plants, fungi, animals, microörganisms). Their
interactions move energy and matter around among them and include:
A. Predation and parasitism: One preys on (or parasitizes) another.
B. Competition: One needs the same resources as another.
C. Symbiosis: Two interact in a win-win situation of roughly equal
benefit to both parties.
IV. Ecosystem: The relationships among these components and between all of
them and the physical environment with which they interact. We can
divide these into energy relationships and material relationships.
A. Energy Relationships
1. Energy basically flows in one direction through an ecosystem.
a. Its source is that portion of insolation trapped by plants
though photosynthesis (only about 1% of the insolation that
impinges on a plant is trapped by its photosynthesis
activities):
6H2O + 6CO2 + ~680 kcal ----> C6H12O6 + 6O2
(6 water molecules plus 6 carbon dioxide molecules and solar
radiation, are transformed into 1 molecule of glucose (a simple
sugar) and 6 molecules of ordinary oxygen. The approximately
680 kilocalories of energy are fixed in the chemical bonds of
the sugar.
b. Energy eventually leaves the ecosystem (and the earth) by being
re-radiated through an atmospheric window, as heat. It cannot,
then, re-enter.
2. There are a few different ways of describing this one-way energy
flow through an ecosystem.
a. You may have heard of a "food chain." This tracks a particular
packet of energy as it is fixed by green plants and then eaten
by animals, which get eaten by other animals, etc.
b. Another related concept is that of the "food web." This shows
all the different tracks that a packet of energy COULD
potentially use to move through an ecosystem. Each plant
species could be eaten by any number of animals, and each of
them can be eaten by a variety of predators.
c. "Energy pyramid" describes the energy flow through the ecosystem
in terms of how much biomass (weight of living tissue) can be
supported at each link in a food chain. I'll use the "energy
pyramid" or "trophic pyramid" to describe this one-way energy
flux through an ecosystem. "Trophic" is just a fancy way of
saying "feeding."
3. Expanding on the trophic pyramid:
a. The energy pyramid concept divides an ecosystem into "trophic
levels."
i. These have to do with how close an organism typically is to
the ultimate source of energy: insolation.
ii. This closeness has to do with who preys on whom and who
gets preyed on by whom.
b. Trophic levels:
i. Primary producers: these are the green plants, which trap
insolation through photosynthesis. These are sometimes
called "autotrophs," for "feeding themselves." Everyone
else in the ecosystem is a "heterotroph," "feeding on
something else."
ii. Primary consumers: these are the basically vegetarian
species, which consume the primary producers. They are also
called "herbivores."
iii. Secondary consumers: These are the animals, which eat
herbivores (aka "predators" or "primary carnivores").
iv. Tertiary consumers: animals that eat the predators
("secondary carnivores").
v. etc.
vi. Detritus feeders are the organisms that eat dead organic
matter: animals that die by accident, animal parts left
behind by messy predators, plant parts not eaten by
herbivores before falling off, excreta. These are also
called "scavengers" and "detritivores." They're the ones
that clean up the mess left by the rest of us: Hyaenas,
vultures, many fungi, ants, and dung beetles (charming! the
ancient Egyptians called them "scarabs" -- now you know
what all that New Age jewellery symbolizes!)
c. Available energy decreases the higher a species is on the energy
pyramid. This is a very important point! There is less and
less energy available to support biomass the higher up the
trophic pyramid we go. There is very little top predator
biomass compared to herbivore biomass.
i. This is because each trophic level uses up much of the
energy from the level beneath it through respiration. These
uses include:
a. Movement
b. Generating heat to keep warm
c. Catching food
d. Finding mates (cruisin'!)
e. Feeding offspring
f. Growing and repairing tissue
ii. These uses cause energy loss, because the energy is
dissipated as heat, re-radiated out an atmospheric window,
or absorbed and removed by evaporation (sweat, breathing,
transpiring).
iii. The amount of this loss is determined by the kind of
organism at a particular trophic level.
a. It's relatively low in the case of plants, which use up
roughly one third to one half of the energy they fix for
their own respiration, ~.33-.50
b. It amounts to roughly 90 percent in hot-blooded animals
("endotherms," for "heated from the inside") or very
active ones, and this is a conservative estimate for
some extremely active endotherms. Endotherms burn a lot
of food energy in order to maintain an internal
temperature in a narrow range where all their enzymes
and chemical reactions work best. For our species, most
of us maintain an internal temperature of 37.0° C.
c. It's more like 67 percent in cold-blooded animals
("ectotherms," for "heated from the outside," so they're
not really "cold" blooded but their internal temperature
varies a lot depending on outside conditions, and they
maintain their internal thermostat by moving around to
bask in sunshine when they're cold and hiding in shade
when they're overheated).
d. Endothermy and ectothermy have both benefits and costs
to the lineages that have evolved one way or the other.
1. Endotherms enjoy the advantage of having their bodies
constantly at an ideal temperature for the efficient
operation of all their metabolic processes and they
can rely on their bodies to move instantly when they
need them to boogie. The disadvantage is it takes a
LOT of food to maintain that thermostat, which means
endotherms have to eat a LOT. Endothermy is
EXPENSIVE!
2. Ectotherms' big disadvantage is that they're at the
mercy of their external environments to get their
internal temperatures at the right level for
efficient motion and metabolism, and they may not be
able to find the right external surroundings to
create the right internal temperature. The upside of
ectothermy, though, is it takes a lot less food:
You've all seen snakes that swallow some hapless
critter and then they just sit there, vegging
happily, enjoying the meal for DAYS. We endotherms
have to eat constantly, which takes a lot of work.
3. Six of these and half dozen of the other: Endothermy
and ectothermy have their benefits and costs and,
ultimately, both metabolisms have proven their worth
over the last 200,000,000 years or so of competition
for life between the two lifestyles.
e. Because of the difference in respiration heat loss in
ectotherms and endotherms, ecosystems dominated by
ectotherms tend to feature taller energy pyramids (more
links in the food chain) than ecosystems dominated by
endotherms (three or four links in the food chain:
grass --> cow --> human).
f. Terrestrial ecosystems tend to have more endotherms, so
land-based trophic pyramids tend to be pretty short;
aquatic ecosystems are largely dominated by ectotherms,
so they can be much taller (phytoplankton -->
zoöplankton --> shrimp --> small fish --> bigger
fish --> sharks).
iv. Heat loss up a pyramid can be diagrammed as below, in a
very highly idealized manner. All animals in this example
are endotherms, highly wasteful of energy. The table has
four columns of numbers:
a. "% Used..." means the percentage of fixed energy that a
given trophic level uses in respiration, which is
"wasted" (from the point of view of any organism higher
up, of course) in that level's respiration.
b. % Transmitted..." means the percentage of energy in a
given level, which is passed on to the next level
through predation.
c. % Original..." means the percentage of the original
fixed energy still left in the ecosystem after a given
level is "done" with it (by getting itself killed).
d. "Standing biomass..." means the standing mass of living
tissue that can be supported at a given level, in light
of the original energy left in the system.
e. "Number..." means the number of individuals that the
standing biomass represents, given the average weight
for that species.
=============================================================================
Example % Used % Transmitted % Original Standing Number
of organism at a to the next insolation biomass of
at a level level level left in system at a level individuals
-----------------------------------------------------------------------------
Hawks 90 10 0.06 100 kg 100
-----------------------------------------------------------------------------
Weasels 90 10 0.60 1,000 kg 7,000
-----------------------------------------------------------------------------
Mice 90 10 6.00 10,000 kg 500,000
-----------------------------------------------------------------------------
Grass 40 60 60.00 100,000 kg
-----------------------------------------------------------------------------
v. When you look at the number of individuals that a given
biomass represents, you see how really very scarce a high
level predator is. In this example of a trophic pyramid
supported by a hypothetical 100,000 kg of standing grass
biomass, you see that, by the time you get to the tertiary
consumer level, there are only about 100 individuals that
can be supported. One hundred individuals may not be
sufficient to maintain a viable breeding population,
particularly if the species is slow in reproducing
(inbreeding effects, vulnerability to random chance
catastrophes, the accumulation of toxins in the flesh of a
high level predator). In this little ecosystem, the mice
are in no significant danger of local extinction (there are
500,000 of these very rapidly-reproducing creatures), but
the hawks are. Funny, isn't it? Even though we tend to
feel terribly sorry for the victims of predation who often
suffer awful deaths when caught by a predator, in many ways
it is the predator that may deserve as much if not more
sympathy: It is actually the more fragile of the two
species and more subject to extinction!
B. Material Relationships
1. Unlike energy, matter is recycled back through an ecosystem over
and over (energy flows through once, matter recycles).
a. The sources of matter in an ecosystem are the other spheres of
our planet:
i. Atmosphere O2, CO2, even H2O
ii. Hydrosphere H2O
iii. Lithosphere N, P, K, Ca, Fe, Mg, Ma, z, etc.
b. These substances eventually return to their sources, after a
trip through living tissue.
2. Examples:
a. The oxygen cycle
b. The carbon cycle
c. The water cycle
d. The nitrogen cycle
e. The phosphorous cycle
f. The calcium cycle
e. And loads of others
3. The diagram below represents the cycles linking carbon, hydrogen,
and oxygen together through photosynthesis and respiration.
a. You'll notice that photosynthesis inputs carbon dioxide and
water and fixes about 680 kcal of energy in a molecule of sugar
and outputs oxygen.
b. Looking closely, you'll see that respiration is the complement
to photosynthesis, inputting oxygen and combining it with sugar
to release energy and output carbon dioxide and water.
c. Each of these elements, C, O, and H cycle through the other
spheres of our planet in complex biogeochemical cycles, both
gaseous and sedimentary, which I'll just represent by "black
boxes" standing for the atmospheric parts of the cycles, the
lithospheric parts of the cycle, and the hydrospheric parts.
+-------------+
-------------------------------->| atmosphere |<-----------------.
| +-------------+ |
| ^ | |
| +-------------+ | |_______________ |
| | lithosphere |<------------------ | |
| +-------------+ +--------------------------------+ | |
| ^ '------->| 6H2O + 6CO2 ---> C6H12O6 + 6O2 | | |
| v | photosynthesis | | |
| +-------------+ +--------------------------------+ | |
-->| hydrosphere | ^ ____________| | |
+-------------+ | | ___________________| |
'-----------' | | |
v v |
+--------------------------------+ |
| C6H12O6 + 6O2 ---> 6H2O + 6CO2 |___/|
| respiration | |
+--------------------------------+ |
|_______________'
V. Environment
A. Definition: Surroundings of any biological entity (community, species,
population, individual, heck, even organs and cells, for that matter,
or the whole planet even).
B. Components
1. Energy Components
a. Insolation
i. Fixed by primary producers and available for metabolism
ii. Sensible heat
b. Prey or host animals or plants from which primary productivity
can be taken.
c. Predators or parasites to which "your" energy might be given if
you don't use it to escape.
d. Competitors for same energy sources you need.
2. Matter Components
a. Water
i. Enough water to drink or absorb
ii. Sufficient humidity or moisture
a. Desert creatures are very tolerant of low humidity
b. Aquatic animals and many other creatures need to be
actually covered with water (e.g., mangroves,
hippopotamus, salamander).
b. Oxygen sufficient for respiration (rarely a limiting factor)
c. Carbon dioxide sufficient for photosynthesis (if you're of the
plant persuasion).
d. Prey or host animals or plants from which to obtain nutrients
(proteins, fats, minerals, vitamins, etc.).
e. Predators looking to take same from you.
f. Nutrients otherwise variable (including water quality, quality
of the soil medium to support quality primary production).
3. Reproductive components of the environment. Evolution doesn't give
a fig about your unique individuality: It is interested in you only
so far as you live long enough to transmit your genetic message to
the next generation (get lucky and reproduce successfully).
a. All the above are relevant to reproductive success, since you
have to live long enough to reproduce.
b. The social aspect of the reproductive environment provides:
i. Access to suitable mates likely to help you produce viable
offspring (important both to most animals and to sexually-
reproducing plants)
ii. Psychological balance so that, by interacting with others
of your kind, you are kept from becoming so weird that no-
one in their right mind would reproduce with you
(obviously, an animal "thing").
c. There are also social hindrances and competition.
i. Unfortunately for you in your quest for being a breeder,
not all other members of your species belong to the
opposite sex: You have competition for mates.
ii. Sometimes, the social milieu provides more than
psychological balance in your interactions: There are
nasty confrontations that can directly knock you out of the
gene pool:
a. You can get killed by other members of your species.
b. You can get injured badly enough to ruin your ability to
mate (ouch) or your ability to attract a mate.
Okay, this time you have a mercifully short lecture, because this is a good
place to break the subject. Come away from this lecture knowing the
definition of the biosphere, its common components, and the difference between
a community and an ecosystem. Be able to describe the energy and matter
relationships within an ecosystem (energy flows through once; matter recycles
endlessly). Be able to express the difference between an ecosystem and an
environment, too. Know the energy and matter sources and sinks in the
environment and the nature of an individual's, population's, or species'
reproductive environment.
Document and © maintained by Dr.
Rodrigue
First placed on web: 10/27/00
Last revised: 06/26/07