Opener – Wed., Jan. 18th:
Please write these 2 questions, then
I’ll give you the data to use to
answer them. 
(i)
State which nutrient shows the shortest mean
residence time in a temperate forest. (1 mark)
(ii)
Identify the biome in which potassium has the
longest mean residence time. (1 mark)
Ecosystems require an input of energy, water and nutrients to maintain
themselves. Nutrients may be reused through recycling within ecosystems.
Nutrient cycling within an ecosystem has been studied in many biomes.
One factor studied is the mean residence time (MRT), which is the amount of time
needed for one cycle of decomposition (from absorption by organism to release
after death). The table below gives the mean residence time for certain nutrients in
four different biomes. In addition, the plant productivity is also shown. (Plant
productivity gives an indication of the quantity of biomass potentially available to
consumers.)
Mean residence time / years
Biome
Carbon
Nitrogen
Phosphorus
Potassium
Calcium
Magnesium
Plant
productivity
/g Cm–2 yr–1
Sub-arctic
forest
353.0
230.0
324.0
94.0
149.0
455.0
360
Temperate
forest
4.0
5.5
5.8
1.3
3.0
3.4
540
Chaparral
3.8
4.2
3.6
1.4
5.0
2.8
270
Tropical
rainforest
0.4
2.0
1.6
0.7
1.5
1.1
900
And the winners are...
• (i) potassium/K
• (ii) sub-arctic forest
1
1
• On IB markschemes (answer keys)...
• “/” =
• “;” =
“Entangled Bank”
–Origin of Species, C. Darwin
It is interesting to contemplate an entangled
bank, clothed with many plants of many
kinds. With birds singing on the bushes,
with various insects flitting about, and
with worms crawling through the damp
earth, and to reflect that these elaborate
constructed forms, so different from each
other, and dependent on each other in so
complex a manner, have all been
produced by laws acting around us.
“Entangled Bank”
–Origin of Species, C. Darwin
... There is grandeur in this view of life, with
its several powers, having been originally
breathed into a few forms or into one; and
that, whilst this planet has gone cycling
on according to the fixed laws of gravity,
from so simple a beginning endless forms
so beautiful and most wonderful have
been, and are being, evolved'.
(Chapter 14: Recapitulation and
Conclusion) Darwin. C (1859) Origin of
Species
IB “Core” Topics:
Ecology
5.1
5.2
5.3
5.1 Communities
5.1.1
Define species, habitat, population, community, ecosystem and ecology.
5.1.2
Distinguish between autotroph and heterotroph.
5.1.3
Distinguish between consumers, detritivores and saprotrophs.
5.1.4
Describe what is meant by a food chain, giving three examples, each with at least three
linkages (four organisms).
5.1.5
Describe what is meant by a food web.
5.1.6
Define trophic level.
5.1.7
Deduce the trophic level of organisms in a food chain and a food web.
5.1.8
Construct a food web containing up to 10 organisms, using appropriate information.
5.1.9
State that light is the initial energy source for almost all communities.
5.1.10
Explain the energy flow in a food chain.
5.1.11
State that energy transformations are never 100% efficient.
5.1.12
Explain reasons for the shape of pyramids of energy.
5.1.13
Explain that energy enters and leaves ecosystems, but nutrients must be recycled.
5.1.14
State that saprotrophic bacteria and fungi (decomposers) recycle nutrients.
“Infertile Offspring”
• Female horse, male donkey  mule
• Female tiger, male lion  liger
5.1.2 Autotroph
vs.Heterotroph
5.1.3 Consumers, etc.
5.1.14 Decomposers
• Saprotrophic bacteria & fungi recycle
nutrients (organic molecules) of dead
organisms
5.1.14 Decomposition—how’s it work?
• Decomposition: forms soil, recycles
nutrients, reduces high energy C cmpds
• Begins w/secretion of extra-cellular
digestive enzymes produced by sap.
Bacteria, fungi
• Secreted onto dead organism
• Hydrolyze biol. Molecs that made up the
dead organism  soluble, so absorbed by
sap.
• Oxidized, release CO2 & N
• Gives energy to the bact/fungi but also
returns matter to abiotic envt
5.1.4 Food Chains
• Simple linear flow
• Who eats whom
• ARROWS: Energy & matter flowing
through links in chain
• Amt energy captured @ each level
• Energy lost @ each level?
• REAL examples, common names ok
• But more specific than “tree”, “fish”
• Producer, consumers—no decomp.
• Who’s the producer?
• Primary consumer?
• Tertiary consumer?
• Bushgrass  impala  cheetah 
lion
• Who’s the producer?
• Primary consumer?
• Tertiary consumer?
• Buckwheat  gopher  gopher
snake  red tailed kite
• WHY are big predators so rare?
5.1.5 Food Webs
• Diagram, shows how chains linked
• BENEFITS:
• More complex interactions b/w
species and community/ecosystem
• >1 producer supports community
• Consumer can have diff food
sources @ diff trophic levels
5.1.6 Trophic Level
• Defines feeding rel’ship of it to
others in food web/chain
• Consumer can be in different TLs—
depends on who prey is
5.1.8
Construct
Food
Web
Phytoplankton  sea whip  reef
shark
algae  Diadarma  marine omnivores  groupers
Snappers & reef sharks can be either secondary or tertiary consumers
(depending on food source)
5.1.7 TL in food chain/web
Who’s the most important in the
food web??
5.1.9 Light & Food Chains
• Chain/web/community interactions
maintained by energy
• Sunlight = energy source for most aquatic
& terrestrial communities
• Chlorophyll = principle trap of sun’s
energy
• In producers’ chloroplasts
• Other communities—chemical energy
5.1.11 Efficiency not 100%
• ~ 10-20 % energy @ 1 TL will be
assimilated at next higher TL
• Model: typical loss of energy from solar
radiation through various trophic levels
• tapering of the model
• volume of 1 layer is 10% of the layer below
• in part, this loss of energy  makes food
chains ~short
5.1.11 Efficiency not 100%
• Extreme environments (arctic)
• initial trapping of energy by producers is low
• food chains are short
• Tropical rainforest
• trapping of energy is more efficient
• food chains are longer, webs are more
complex
5.1.12 Shape of energy
pyramids
Solar not shown
• Flow of energy
• Units: energy/unit area/unit time
• kJ m-2 yr-1
• Narrowing shape—why?
• Gradual loss along chain
Energy LOSS...WHY?
• Prey’s not 100% eaten  detritivores
• Not all that is eaten is digested
decomposers
• Death before being eaten
• Heat energy from respiration rxns
• ULTIMATELY...all energy lost as heat
5.1.10 Energy flow in food
chain
• Not all solar energy comes in contact
w/chlorophyll
• (not trapped in synthesis of org. cmpds)
• Photosynthesis
• Consumers feed on producers, pass
on energy in food
• Need lots producers in food web
• Fewer & fewer of higher TLs
5.1.13 Energy vs Nutrients
• Energy Flows, Matter Cycles
• Energy lost as heat @ each TL; top
of pyramid tapers b/c ultimately all
lost as heat
• Producers convert inorg molecs into
organic ones; consumers @ diff
levels take it in and use for
growth...C, N, Water cycles
Why are big predators rare?
•
•
•
•
•
Energy, matter lost at each stage
# organisms reduced @ each link in chain
Higher TL organisms  less common
Most chains have 4 TL
Top carnivores must feed over wide
area/territory to find food
• As population decreases, more vulnerable
to ‘catastrophes’ ...
• ‘super’ top predators unlikely b/c evolutionary
disadvantageous