Secondary Production The biomass and energy of plants that accumulates as a result of photosynthesis

1
Secondary ProductionThe biomass (and energy) of
plants that accumulates as a result of
photosynthesis can eventually go in three
directions- herbivores- detritivores-
reserve pools (oil, coal, natural gas)
2
Recall diagram from previous lecture.- Every
animal will obtain some energy (and matter) from
a lower trophic level- Some will not be used
example, beaver fells tree but only eats some of
the bark, rest goes to decomposers- Of the bark
consumed, some energy passes through the
digestive tract and is lost in feces- Of the
energy assimilated, some is lost as urinary
output- The rest is available for metabolic
energy
3
Metabolic energy can be allocated to either
maintenance or reproduction.How can scientists
measure components of secondary productivity?
4
How do scientists measure secondary
productivity?- Focus on one species of animal
in a community- To determine, must measure
feeding rate gross energy intake - For
example, confine herbivore and measure plant
biomass before and after feeding- For some
predators, the number of food items consumed can
be counted by direct observation
5
Secondary productivity can be measured in lab-
regulate gross intake and and collect waste
(urine and feces)- metabolizable energy Gross
Energy Intake Energy lost through egestion and
urination.- Monitor O2 uptake, CO2 production
and/or heat production to measure metabolic
(maintenance) energy consumption- productivity
metabolizable energy used in maintenance-
more difficult to do in nature, but possible
6
The big picture energy transfer efficiencies-
knowledge of transfer efficiencies between
trophic levels allows scientists to predict
patterns of energy flow
7
Consumption efficiency (CE) - of total
productivity available at one trophic level that
is consumed by a trophic level above ( to gross
energy intake in diagram)- for primary
consumers (herbivores), CE is the percentage of
joules produced per unit time as net primary
productivity that finds its way into the guts of
herbivores- for secondary consumers
(carnivores) it is the of herbiroe productivity
eaten by carnivores- the remainder enters the
decomposer system
8
Averages for CE by herbivores about 5 in
forests, 25 in grasslands, and 50 in
phytoplankton dominated aquatic communities-
much less know for carnivores. May be very high
for vertebrate predators that eat vertebrate prey
9
Assimilation efficiency (AE) is the of food
energy that is assimilated across the gut wall
and becomes available for growth or work. -
what about bacteria and fungi? They have no
guts, dont excrete feces or urine. Have close
to 100 assimilation efficiency.- AEs
typically low for herbivores, detritivores, and
and microbivores (20-50), and high for
carnivores (around 80)
10
The way in which plants allocate production to
roots, wood, leaves, seeds, and fruits influences
their usefulness to herbivores- seeds and
fruits may be assimilated with an efficiency of
60-70, leaves about 50, but wood as low as 15.
11
Production efficiency (PE) is the of
assimilated energy that is incorporated into new
biomass the remainder is lost as respiratory
heat- varies mainly according to the taxonomic
class of organism- invertebrates typically have
high efficiencies (30-40 ) losing relatively
little energy to heat- sidebar most are
poikiliothermic ectotherms
12
Among vertebrates, ectotherms have values around
10- endotherms (birds and mammals) only
1-2- microorganisms on the other hand have
very high production efficiencies.
13
Energy (kJ/m2/yr)Elephants of Queen Elizabeth
parkin UgandaNet primary production 3125 (from
harvest method)Secondary production Gross
energy intake 299 (CE 299/3125 9.5) Fecal
energy lost 168 Urinary loss 33
Metabolizable energy 299 168 33 98 AE
98/299 32 Maintenance loss 96 Production
PE 2/98 2
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Trophic level efficiency CE x AE x PEWide
variation in natureAverage about 10
15
Roles of the live-consumer and decomposer
systems- what is the relative importance of the
two pathways?- studies suggest that decomposers
responsible for the majority of secondary
production, and therefore respiratory heat loss,
in almost every community on earth- live
consumers play greatest role in plankton
communitieswhere large amount of NPP is consumed
alive and assimilated at high efficiency
16
Live consumer system plays relatively minor role
in terrestrial communities because of low
herbivore consumption and assimilation
efficiencies- essentially non-existent in small
streams and ponds? Why?- also true for deep
oceans
17
A closer look at decomposition- Immobilization
occurs when an inorganic nutrient element is
incorporated into organic form, primarily during
the growth of green plants- For example, CO2 is
fixed during photosynthesis into the organic form
(carbohydrate)- remember this requires an
input of energy
18
Conversely, decomposition involves the release of
energy and the mineralization of chemical
nutrients conversion from organic to inorganic
formDecomposition is the gradual disintegration
of dead organic matter as a result of both
physical and biological processes- recall laws
of thermodynamics
19
Consider the fate of a dead animal- if
scavengers (vultures, coyotes) do not find it
decomposition starts with colonization by
bacteria and fungi- bacteria and fungal spores
ubiquitous. - early colonists often make use of
soluble materials, such as amino acids and
sugars, that are freely diffusable.
20
Other resources however not diffusible and are
resistant to attack- subsequent decomposition
proceeds more slowly and involves microbial
specialists that can break down structural
carbohydrates (such as cellulose) and complex
proteins.
21
Microbivores and detritivores

• Microbivores specialize on bacteria or fungi
  but able to exclude detritus from their guts
• Detritus dead organic matter
• Some detritivores specialize on plant material
• Major components of plant tissue are cellulose
  and lignin

22

• Pose considerable challenges to animal digestion
• Digestion of cellulose requires cullulase enzymes
• This enzyme has been found in only one or two
  animal species (surprising!)
• Majority of detritivores rely on assistance from
  bacteria, fungi, or protozoans

23
Such interactions are of a range of types

• Obligate mutualisms between a detritivore and
  specific and permanent gut microflora (bacteria)
  or microfauna (gut flagellates of termites).
• Facultative mutualisms in which the animal makes
  use of cellulases produced by a microflora
  ingested with detritus as it passes through an
  unspecialized gut (wood lice)
• External rumens that assimilate the products of
  cellulase-producing microflora associated with
  decomposing plant remains

24
Important point decomposition of plant detritus
results from an interaction between decomposers
and detritivores

• Consider the fate of a leaf
• Focus on a part of the cell wall
• When the leaf first falls to the ground the cell
  wall is protected from microbial attack because
  it is buried within plant tissue
• After being picked up and chewed by a
  detritivore, say a wood louse, the leaf material
  enters its digestive system

25

• Here it comes into contact with a new microbial
  flora and is acted upon by the digestive enzymes
  of the wood louse
• The changed fragment eventually emerges from the
  gut of the louse,

26

• It is now part of the louses feces, and because
  it has been fragmented and partially digested, is
  much more easily attacked by microorganisms.
• Even as it is colonized by this new group of
  microorganisms the feces may be ingested by some
  other animal and so on until nothing remains
  but CO2 and minerals

27
Consumption of feces and carrion

• Feces of carnivorous vertebrates is poor quality
  stuff
• Recall that carnivores assimilate their food with
  high efficiency
• So feces probably degraded almost exclusively by
  fungi and bacteria

28
In contrast herbivore feces still contains an
abundance of organic matter

• Dung of many species, such as elephants, supports
  its own characteristic fauna
• Examples African dung beetles

29
Scavenging vertebrates also very important in
many systems
30
The flux of matter through ecosystemsBig picture
31
Water comprises greatest bulk of matter in any
living community- rest is made up mainly of
carbon compounds- carbon enters
(immobilization) living world as CO2-
incorporated into NPP- follows exactly the same
route as energy- finally released back into
atmosphere as CO2 (mineralization)
32
Here the link between energy and carbon ends-
heat energy lost to biological systems escapes
into the atmosphere, cannot be recycled- carbon
atoms, however, can be used again and again and
again..- Carbon and other nutrients available
to plants as simple inorganic nutrients in air or
water (as dissolved ions)
33
Unlike energy from sunlight, nutrient
availability not unlimited- the incorporation
of nutrients into biomass reduces the amount
available to the rest of the living world- in
the absence of death and decomposition supply
would run out
34
Useful to think of pools of chemical elements
that exist in compartments- some compartments
occur in the atmosphere (CO2, N2)- some in rocks
of the lithosphere (calcium carbonate, potassium
in feldspar)- still others in hydrosphere
(dissolved nitrates, phosphate, carbonic acid)-
in all of these cases nutrients exist in
inorganic form
35
In contrast, organisms (dead or alive) are
compartments containing nutrients in organic form
(cellulose, fat, protein, etc.)-
Biogeochemistry is the study the movement of
elements between compartments
36
Nutrient budgets in terrestrial ecosystems- the
weathering of bedrock and soil is the ultimate
source of nutrients such as calcium, iron,
magnesium, phosphate, and potassium.- taken up
by the roots of plants- atmospheric CO2 is the
source of carbon for terrestrial communities-
gaseous nitrogen, N2, provides most of the
nitrogen content
37
Several species of bacteria and blue-green algae
are capable of fixing nitrogen N2 converted to
NH4- ammonium ions can then be taken up by
plants- all terrestrial systems receive some
nitrogen through this pathway, but some do so
almost exclusively -root nodules on alder trees
38
Other nutrients from the atmosphere become
available through dry fall or wet
fall.Include1.) trace gases such as sulfur
oxides and nitrogen2.) aerosols produced from
evaporation of seawater. Contain sodium,
magnesium, chloride, and sulfates.3.) dust
particles from fires, volcanoes and windstorms,
often rich in calcium, potassium, and
sulfates.- Most taken up by roots of plants but
some absorbed by leaves
39
Nutrients may circulate within a community for
years, or in some cases may pass through the
system in a matter of minutes within being
incorporated at all.- whatever the case, the
atom will eventually be lost through one of a
variety of processes. - these processes
constitute the debt side of the nutrient budget
equation
40
Release to the atmosphere is one pathway to
nutrient loss- In many communities there is an
approximate balance in the carbon budget-
carbon fixed by photosynthesis carbon loss from
respiration- plants may be direct sources of
gaseous and particulate release
41
for example, forest canopies produce volatile
hydrocarbons (terpenes for example)- tropical
forest trees emit aerosols containing phosporous,
potassium, and sulfur- ammonia gas is released
during decomposition of vertebrate waste
42
Other pathways of loss are important in
particular instances- fire, for example, can
turn a very large proportion of a communities
carbon into CO2 in a very short time- the loss
of nitrogen as a volatile gas can be equally
dramatic
43
For many elements, the most important pathway of
loss is through stream flow- water that drains
from soil carries a nutrient load that consists
of both dissolved and particulate matter- with
the exception of iron and phosphorous, which are
not mobile in soils, the loss of plant nutrients
is primarily in solution
44
The nutrient budgets of terrestrial and aquatic
systems are linked through the movement of
water- terrestrial systems lose nutrients into
streams and groundwater- aquatic systems gain
nutrients from stream flow and groundwater
discharge
45
Nutrient budgets in aquatic communities- bulk
comes in from stream flow- in streams, rivers,
and some lakes, export through outgoing flow also
a major source of loss- by contrast, in lakes
without an outflow (or where outflow is low
relative to lake volume) and oceans nutrients
often become locked-up in permanent sediments
46
Lakes in many arid regions lose water only
through evaporation-waters of these lakes have
much higher concentrations of of sodium and other
nutrients-saline lakes are as abundant as
freshwater lakes
47
The largest of such lakes are the oceans- water
loss only by evaporation-remarkable constant
chemical composition- nutrients in surface
waters come from two sources- river input and
upwelling from the deep
48
Global biogeochemical cycles- The hydrological
cycle- oceans are principle source of water on
earth (97.3)- evaporation, winds, and
precipitation result in the movement and
redistribution of water- may be stored
temporarily in soils, lakes, and ice- loss from
land occurs through evaporation and
transpiration, and in liquid flow back to the
oceans
49
Ice caps and glaciers store about 2.06 of
earths water, underground reservoirs 0.67, and
rivers and lakes 0.01.- of water in transit
at any given time very small, about 0.08 of the
total- but this small percentage plays a
crucial role in supplying living organisms and
transporting chemical nutrients- the
hydrological cycle would proceed whether or not
living organisms exist on earth- but
terrestrial vegetation has a big effect on the
fluxes that occur
50
Living vegetation can intercept water at two
points, preventing some from being returned
immediately to the oceans in stream flow1.)
some water caught in foliage from which it may
evaporate2.) some water in soils will be taken
up by the roots of plants, returned to the
atmosphere by transpirationFrom a human
perspective, water is an extremely valuable
commodity.
51
The phosphorous cycle- principle stocks of
phosphorous occur in waters of soil, rivers,
lakes and oceans, and in rocks and ocean
sediments- cycle can be described as
sedimentary because of the general tendency for
mineral phosphorous to be carried from the land
to the oceans, where it is incorporated into
sediments.
52
- Consider a phosporous atom released from
weathering of rock- may enter the terrestrial
community and cycle for years- eventually will
end up in a stream of water and carried to the
ocean- it then makes on average 100 round trips
between the surface and deep waters, each lasting
perhaps 1,000 years
53
- During each trip it is taken up by
surface-dwelling autotrophs before eventually
falling back to the bottom- will eventually
(after about 10 million years) be incorporated
into bottom sediment. - perhaps 100 million
years later the ocean floor is lifted by
geological activity to become dry land- cycle
(biotic uptake and decomposition) within cycle
(ocean mixing) within cycle (continental uplift
and erosion)
54
The nitrogen cycle- the atmosphere is
predominant in the global nitrogen cycle-
nitrogen fixation and denitritification by
microbes is very important- lightning also
responsible for some nitrogen fixation (3-4)
55
- magnitude of nitrogen flux in stream flow from
terrestrial to aquatic communities is relatively
small, but very important for the aquatic systems
involved.- recall that nitrogen and phosphorous
most often limit plant growth- a small amount
of nitrogen is lost to ocean sediments
56
The sulfur cycle- three natural biogeochemical
processes release sulfur to the atmosphere1.)
the formation of sea-spray aerosols2.) anaerobic
respiration by sulfate-reducing bacteria3.)
volcanic activity (relatively minor)
57
- Sulfur bacteria release reduced sulfur
compounds, such as H2S from waterlogged bog and
marsh communities and marine tidal flats- a
reverse flow from atmosphere involves oxidation
of sulfur compounds to sulfate, which returns to
earth in dryfall or wetfall
58
- Weathering of rock provides about half the
sulfur draining off land into lakes and rivers-
remainder comes from atmosphere- on its way to
oceans, some (mainly sulfates) taken up by the
roots of plants enters biological cycle
(production decomposition)
59
- in comparison to phosphorous and nitrogen, much
faller fraction of the flux of sulfur is involved
in cycling in terrestrial and aquatic
communities- finally, continuous loss of sulfur
to ocean sediments
60
The carbon cycle- Photosynthesis and
respiration drive the global carbon cycle-
predominately a gaseous cycle, with CO2 the main
vehicle of flux between the atmosphere,
hydrosphere, and biological systems
61
Historically, lithosphere played only a minor
role- fossil fuel reserves lay dormant until
human intervention- terrestrial plants use CO2,
aquatic plants use dissolved carbonates- the
two sub-cycles are linked between exchanges of
CO2 between the atmosphere and the oceans
62
In addition, carbon finds its way into inland
waters and oceans as bicarbonate resulting from
weathering of calcium-rich rocks such as
limestone and chalk.- respiration releases
carbon locked in photosynthetic products back to
the atmosphere and hydrospheric carbon
compartments