Transcript III. Ecosystem Def. - the combination of biotic and abiotic components through which energy flows and materials cycle (usually a self-contained unit, such as.

III. Ecosystem
Def. - the combination of biotic and abiotic
components through which energy flows and
materials cycle (usually a self-contained unit, such
as a pond, swamp, meadow, or woods)
A. Energy Flow
1. Ultimate source - SUN
- 50% of suns energy reaches surface of earth
- 0.1 % of that ends up in living organisms
Primary Productivity
Synthesis of organic material from inorganic
substances.
Primary productivity is measured in grams of
carbon bound into organic material per square
meter of ocean surface per year, or, more simply:
gC/m2/yr
2. Trophic levels (food chain or web)
a. Producers - first trophic level , primarily
plants on the land and algae in the water
(99% of all organic matter is at this level)
Gross primary productivity (light energy converted)
- Cost of metabolic activity (cell respiration by plant)
Net primary productivity* (energy stored in chemical
compounds)
*when positive, there is an increase in
biomass (total dry weight of all organisms
being measured)
b. Primary consumer (herbivores)
c. Secondary consumer (carnivores), eat
herbivores
[There a four levels of consumer in most food
chains]
d. Detritovores - live on the refuse of the
ecosystem, i.e. dead leaves, branches,
carcasses, feces, etc.
i. Scavengers - consumers of dead prey
- vultures, jackals, crabs, earthworms
ii. Decomposers - specialized organisms that
get at the trapped chemical energy
- fungi, bacteria
3. Efficiency of energy transfer
a. In Cayuga Lake in New York
1000 calories of light yields
150 calories of algae, which yields
30 calories of smelt, which yields
6 calories of trout, which yields
1.2 calories of human
b. Energy flow pyramid (“10% rule”)
GPP & NPP
An ecosystem's gross primary productivity (GPP) is the total
amount of organic matter that it produces through
photosynthesis. Net primary productivity (NPP) describes
the amount of energy that remains available for plant
growth after subtracting the fraction that plants use for
respiration. Productivity in land ecosystems generally rises
with temperature up to about 30°C, after which it declines,
and is positively correlated with moisture.
In the oceans, light and nutrients are important controlling
factors for productivity. As noted in Unit 3, "Oceans," light
penetrates only into the uppermost level of the oceans, so
photosynthesis occurs in surface and near-surface waters.
Marine primary productivity is high near coastlines and
other areas where upwelling brings nutrients to the surface,
promoting plankton blooms. Runoff from land is also a
source of nutrients in estuaries and along the continental
shelves. Among aquatic ecosystems, algal beds and coral
reefs have the highest net primary production, while the
lowest rates occur in the open due to a lack of nutrients in
the illuminated surface layers
If tropical rainforests produce 200 times as much NPP
than the open ocean, why do we get more than twice
as much carbon from the open ocean each year?
B. Biological magnification - increase in the
concentration of toxins as those toxins move
through the food chain (DDT, PCB’s)
C. Ecological succession- the succession of
communities that follows the disturbing of
and area (plowing, landslide, volcano, fire)
Characteristics
1. Increase in total biomass
2. Gradual decrease in net productivity
3. Mature systems have a greater capacity to
entrap and hold nutrients
4. Number of species increase
5. r-species early
K-species late
[Climax community = final stable stage]
[Current thinking is that this model is simplistic
and incomplete, that disturbances themselves
drive succession throughout the process.]
1
10
2
20
5
D. Biogeochemical cycles - the cycling of
chemicals through the biotic and abiotic
portions of the ecosystem
1. Water cycle
2. Carbon cycle
3. Nitrogen cycle
4. Phosphorus cycle
IV. Terrestrial Biomes (life zones)
A. Def. - geographical areas distinguished by
particular dominant plant types
B. Characteristics
1. Not a place, but a class of plants
2. Determined by climate
3. Boundaries are indistinct
4. Convergent evolution common between
similar biomes
V. Aquatic Biomes (life zones)
A. Primary ecological subdivisions of organisms
1. Plankton - at mercy of currents, weak or
nonswimmers (small or microscopic)
a. Phytoplankton - primary producers,
(cyanobacteria or diatoms)
b. Zooplankton - protists and small animals
(larval stages)
2. Benthos - bottom dwellers (sessile, walking,
or burrowing)
3. Nekton - larger, strong swimmers (top of the
food chains)
B. Freshwater
1. Zones
a. Littoral zone - near shoreline, richest in life
b. Limnetic zone - open water, sparse life
c. Profundal zone - deep. anaerobic, no light,
detritovores, mineral rich
2. Lake stratification and seasonal turnover
3. Types of lakes
a. Oligotrophic - nutrient-poor, deep, sandy
or rocky bottom, clear
b. Eutrophic - nutrient-rich, phytoplankton
very productive, shallow, murky
Oligotrophic lake Eutrophication
(lake aging)
Eutrophic lake
C. Marine life zones
1. Estuaries and salt marshes - where rivers
(freshwater) meets saltwater of ocean
- most fertile water in the world, breeding
grounds for many fish, nutrients from
rivers meets constant mixing of tides (plants)
2.Intertidal zone - between high and low tides, rich in
life forms (barnacles, clams, crabs), tidal pools
3.Subtidal zone - sea stars, sea urchins, worms, crabs,
flounder
4.Neritic zone - over continental shelf (nekton and
most benthic organisms are here (food is here)
[photosynthetic limit - 200 meters]
5. Pelagic zone – includes neritic and open ocean
6. Benthic zone - deep waters, mostly predators
= Neritic zone
(Neritic zone)
Pelagic
Zone