Primary & Secondary Productivity Video Lecture | Biology Class 12 - NEET

all right so primary and secondary
production this is something we've
really talked about on in multiple
different occasions but now we're going
to kind of bring it together and define
it and put the concepts together as well
so we're gonna talk about terrestrial
primary production including evapo
transpiration I think we're actually
gonna squid boat skip over aquatic
primary production we'll talk a little
bit about marine primary production and
then we'll talk about consumer
influences and trophic levels and
dynamics so primary production is the
bottom of the food chain right this is
these are the organisms that fix energy
from photosynthesis they are autotrophs
right and they you can measure this in
biomass right because originally you
have nothing so you'd have nothing there
you would just have you know dirt or
rocks or whatever the increase in
biomass is where that carbon dioxide is
trapped in organic molecules and it's
going to add to the bass of plants so
you can measure primary production
through biomass gross primary production
then is the total amount of energy which
is fixed by autotrophs using sunlight
using carbon dioxide and other minerals
and stuff it's going to create this
gross primary production but the net
primary production is how much is
available for autotrophs after they
consume these primary producers so some
of it is lost of course as heat and
inefficiency or as adjustable for
primary consumers secondary production
then is the production of biomass by
heterotrophic consumers over a period of
time
okay so primary production is then given
by autotrophs secondary production is
what's been produced by heterotrophs
all right and of course we have trophic
levels which is the position kind of on
the food chain or on the food web
determined by the number of energy
transfers from primary production to
wherever you are and so that's what we
have here our trophic levels our primary
producers occupy our first level these
are photosynthetic autotrophs primary
consumers occupy this secondary second
level these are heterotrophs and then
secondary consumers then occupy the
third level and they eat those first
level consumers enteric ordinary and so
on and so forth on up the trophic levels
now Astral primary production
Rasen Zweig in 1968 estimated the
influence of moisture and temperature on
rates of primary production by looking
at the relationship between primary
production and annual actual
evapotranspiration so evapotranspiration
of course is the process by which water
moves through plants and so it gets
sucked up by the soil then evaporates
out of their leaves and is an important
indicator of how well plants can do
because they need water to survive and
to grow so when you look at the annual
actual evapotranspiration rate that's
how much water evaporates and transpires
off of a landscape and it is generally
low and cold and dry ecosystem so you
see this on this map here it's low the
low end is the dark green and light
green here are cold polar regions or our
mountainous regions are going to have
low AET where our warm and moist regions
are going to have high a eet
all right generally there's a positive
relationship between primary production
and AET and you can see that in this
sorry in this graph here this figure
when you look at the actual
evapotranspiration and net primary
production the best most productive
areas are the tropical rainforest the
least are the dry creosote bush deserts
there's also an east-west variation in
primary production of grasslands
correlated with rainfall again if you
have water moisture that's going to
increase its primary production alright
there is however other factors to
consider including terrestrial primary
production as a as influenced by
differences in soil fertility or the
nutrients found within soils so shaver
and chapman looked at tundra net primary
production and they found that if they
added fertilizer to tundra it increased
the amount of production Bowen also
suggested that new nitrogen nitrogen is
the most important nutrient which limits
primary production you can do this you
can do this look at this experimentally
by just adding nitrogen to two plots of
soil and looking at the primary
production and across the board that's
shown that really nitrogen is is the
limiting factor in most ecosystems
phosphorus also has a significant effect
and so you can see that in these graphs
here if you add just phosphorus you get
a little bit of increase if you add just
nitrogen you get much more increase
suggesting nitrogen is more of an
limiting factor you got them both then
you get an increase more than both of
those combined a synergistic effect
alright Marine primary production is a
little bit different so the highest
rates of primary production are going to
be at the surface of marine environments
where the Sun can infiltrate that you
know top layer of water but as you go
deeper and deeper in the ocean you're
gonna have a lot less
but so that's the the limiting factor
for some light but nutrients aren't just
floating around in the water at least
not very many so areas where you have
minerals coming up from the bottom of
the ocean and or access you know shallow
waters where you have nutrients there
those are going to be more productive
and have higher higher levels of primary
production so you find these along
coastal margins so really where the land
meets the sea you have currents which
are taking water or taking nutrients up
from the bottom of the ocean as they hit
the hit the coast
you also get nutrient runoff from land
from rivers and those rivers are all
containing you know nutrients and runoff
and soil which is going to add to the
the nutrients available in the water
open ocean however where you don't have
this vertical mixing where the nutrients
are are not very productive so the
middle of the ocean you know not very
productive shallow areas or areas where
you have currents upwelling okay so here
you have two currents meeting in that
you have some boiling here these are
going to be the most productive area so
you get kelp forests along here little
coral reefs in here all these are either
shallow areas where the water or the
sunlight can infiltrate to the bottom of
the ocean or they are areas where you
have currents bringing nutrients up from
the bottom of the ocean and supplying
those top organisms which have access to
light to nutrients as well
all right Tillman looked at plant
functional groups and found similar
physiological and anatomical
characteristics so what'd he do what he
did is he looked at the number of
species and functional groups present in
168 different plots and he found the
higher species richness resulted in
higher primary production so really a
connection between diversity and primary
production so if you have more species
ones with more species had three times
the production of ones with only single
species and what's that what that's
really doing is different groups are a
lot are making available different
nutrients so nitrogen fix fixing legumes
are going to increase the amount of
nitrogen available c4 grasses also help
to increase the overall predict
productivity those were organisms which
have a significant effect on the primary
productivity Cardinal found a similar
relationship between the Kotik aquatic
algae diversity in production so really
the number of algie's which are diverse
because of the different type of types
of nutrients that they can take
advantage of and make available for
other levels are going to increase
overall biodiversity and production now
here's a concept which we've talked
about before bottom-up controls are
those looking at the primary producers
or the nutrients these are things that
can control all the different or many
things of the ecosystem okay and then
top-down controls would be influences of
consumers and predators and heterotrophs
and how they affect things
alright so in lake primary production
carpenter looked at pie savour so things
that eat smaller fish and plankton
versus fish those that eat plankton and
how they can cause significant
deviations in primary production okay
this is a top-down and
an example of top-down control carpenter
and Kitchel proposed the influence of
consumers on lake primary productivity
propagate through food webs
again our top-down control and this is a
graph showing how it can this pie savour
this fish eating organism can have a
negative effect on plankton or as fish
which can have a positive effect on the
small plankton like things such as
rotifers which are gonna have a negative
effect on these phytoplankton because
that's what they eat or negative effect
on these so if you're decreasing these
guys and increasing those guys you'll
decrease these guys and these will also
eat planktonic and vertebrates smaller
Bayreuth zooplankton eat small
phytoplankton so this is an example of
what we call a trophic cascade where
effects of predators can affect prey and
alter the dynamics between all of them
on different trophic levels all right
carpenter and Kitchel also found a
reduction in planktivores fish
populations led to reduced rates of
primary production so if you don't have
these fish which eats eat the plankton
you're going to decrease the overall
problem because they're allowing for
more diversity so what happened in in
absence of these planktivores minnows
minnows that eat the plankton you had
predation and vertebrates more that they
became more numerous in the presence of
these abundant large herbivores ooh
Plains Oh plankton phytoplankton biomass
and rate of primary production declined
okay so the paisa vores reduced plankton
virus fish which overall reduced primary
production again a trophic cascade all
right secondary production
lindeman concluded that ecosystem
concept is fundamental to the study of
energy transfer within an ecosystem so
really he
came up with this idea of trophic
dynamics dynamics looking at trophic
levels each level feeds on the level
immediately below it and each level
loses efficiency as it eats you know so
just because of entropy every time you
eat something you're gonna decrease the
amount that's available for the next
trophic level and it varies from five to
twenty percent usually about 10 percent
what this does is it makes makes it so
you you can have lots of primary
producers and then it gets less and less
than that comes up and really that's all
we're saying here looking at the
individual you have you may have a
hundred one thousand eight hundred
twenty-nine calories ingested some of
that is assimilated some of it has lost
its respiration or feces or excretion so
you don't have everything that you eat
available for growth or for increasing
the biomass and so production is a
function of ingestion
- egestion excretion and respiration and
that's what leads to the inefficiency
between trophic levels so predictions of
the relationship between primary and
secondary production to pin on which
predator prey model is used - so there's
two different predator prey models which
can explain these increase in biomass is
a different level the prey dependent
model predicts that an increase in
primary production will lead to an
increase in secondary consumers or
predators but not in primary consumers
or herbivores and I'll explain what that
means in a second a ratio dependent
model predicts that all levels will
increase so the primary and secondary
consumers with it alright so this is
what what this means this is kind of a
figure or graphic for it
an increase in production primary
production will essentially increase
primary consumers but because predators
eat them you won't see a change in their
abundance you will only see an increase
in the Predators
as more predators will be eating more of
these and so you won't see a change
there
that's the prey dependent model the
ratio dependent model is that all levels
will increase with an increase in
primary production okay and there's
evidence for both all right finally
wanted to revisit what we talked about
before using stable isotopes so this is
an example the main energy source of
energy in a salt marsh in eastern North
America is the marsh grass spartina
alterniflora but the marsh also contains
organic material from upland plants and
phytoplankton so trying to determine
which one which is the source of the
input you can look at these stable
isotopes because they have different
signatures of carbon nitrogen and sulfur
whether they're from upland plants or
phytoplankton or from spartina
alterniflora so you can look at
individual consumers within there for
example the filter feeding mussel gook
in xia demisa
and look at their stable isotope
signatures and what they found was that
spartina and plankton were the primary
nutrients that this species was using
was consuming and the upland plants then
were not a significant part of their
diet
all right now