Transcript net productivity - IBESSROUNDTABLE

TIVI
TY
AND
ENERGY FLOW
ODUC
PR
Ecology Notes 3
Bioaccumulation and
GPP vs. NPP
First, let’s review…What is the
“hierarchy of organization” in
living systems?
1.
2.
3.
4.
5.
Species
Population
Community
Ecosystem
Biosphere
Pyramids…
• We discussed ecological
pyramids…and how energy
flows up the pyramid (and gets
“lost” as heat along the way…)
Pyramids…a strange yet
deadly phenomenon…
• BIOACCUMULATION or
BIOMAGNIFICATION
• Substances that cannot be
metabolized by organisms
(biodegraded) are passed up
the food chain.
• Example: DDT
• dichloro-diphenyl-trichloroethane
Why does it accumulate in the
higher trophic levels?
It has to do with the fact that
certain chemicals are nonsoluble in water (meaning
lower trophic levels see less
of an effect), but they ARE
soluble in FAT (which gets
passed up the food chain…)
Equations for energy flow
We know on ~2% of the sun’s energy
actually gets used for photosynthesis,
and this energy only decreases as it
moves up the pyramid, so what
equations must we know?
Abbreviations to know:
GP; GPP; GSP; NP; NPP; NSP; R
Gross productivity is a measure
of total energy captured
• Measured in joules
(J) or kcal
• Energy captured or
assimilated by an
organism
• For a producer, it is
the sunlight
actually fixed by
the leaves during
photosynthesis
Energy is
stored in
leaves as
sugars and
starches,
which later
are used to
form flowers,
fruits,
seeds,etc.
Net productivity
• Plants (like all organisms) have to use some
of the energy they capture to keep themselves
living and growing. (respiration energy)
– moving water and stored chemicals around
– making hormones and enzymes to control their
metabolism
– making flowers, fruits, new leaves and stems
• Energy left over after they have used what
they need is called the…
net productivity
So how are gross and net
productivity related?
Net productivity =
Gross productivity - Respiration Energy
or using symbols:
NP = GP - R
This equation applies to animals too,
but more on that later…..
The productivity of a plant is called:
PRIMARY PRODUCTIVITY
because plants are the first or primary
organisms in the food web
Primary Productivity
• So if we are talking about the producer
level of the food chain,
NPP = GPP – R
Net Primary Productivity =
Gross Primary Productivity –
Respiration Energy
So what about animal
productivity?
• Animals eat other organisms to
obtain energy, unlike producers
• Animals may eat plants and/or animals
• Not all the energy in food is absorbed
(assimilated) into an animal’s body
• Unassimilated food is ejected as
faeces or droppings
For the 2nd trophic level on up…
Gross Productivity =
food eaten – fecal losses
When discussing consumers, it is
often called Gross Secondary
Productivity
GSP = Food - Fecal
What about net productivity for an
animal (consumer)?
Animals use lots of energy to move and
keep warm .
Plants need rather less energy- but in the
end it, as in plants, it all turns to heat
?
The equation…
Net secondary productivity (NSP ) =
food eaten - feces - respiration energy
so NSP = GSP- R
(just like plants)
You take the gross – respiratory
losses to get the net.
Back to pyramids…
• Factoring in the large respiratory
losses and the fecal losses at
the secondary trophic level on
up, you can see where the
massive energy shortage
comes from as you move up the
pyramid.
Diagram assumptions
?
– energy input into an organism
represents the GP
– the energy output from that
organism to the next trophic level
represents the NP
– the difference between GP and
NP = R (respiration energy )
and/or loss to decomposers
Calculators ready…
and think about how these
examples would be
diagrammed…
NPP Example:
• The producers begin with an initial GPP
of 20,000 kcal m-2 yr-1 (kilocalories per
meter squared per year)
• They lose 86% of that to respiration.
How much is available to the primary
consumers? (this is the NPP)
• 2800 kcal m-2 yr-1
• With this amount of NPP, only 10%
actually gets consumed by the primary
consumers (due to death,
decomposition, and other losses). How
much is that?
• 280 kcal m-2 yr-1
• The primary consumers lose 95% of
THAT through their massive amounts of
respiration and other losses. What is
net secondary productivity then?
• 14 kcal m-2 yr-1