1. Opener – Wed., Jan. 18th: I’ll give you the data to use to
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)

2. Mean residence time / years
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
Phos-phorus
Potass-ium
Cal-cium
Magn-esium
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

3. And the winners are... (i) potassium/K 1 (ii) sub-arctic forest 1
On IB markschemes (answer keys)...
“/” =
“;” =

4. “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.

5. “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

6. IB “Core” Topics: Ecology 5.1 5.2 5.3

7. 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.

9. “Infertile Offspring”
Female horse, male donkey  mule
Female tiger, male lion  liger

10. 5.1.2 Autotroph vs.Heterotroph
5.1.3 Consumers, etc.

11. Decomposers
Saprotrophic bacteria & fungi recycle nutrients (organic molecules) of dead organisms

12. 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

15. 5.1.4 Food Chains Simple linear flow Who eats whom
ARROWS: Energy & matter flowing through links in chain
Amt energy each level
Energy each level?
REAL examples, common names ok
But more specific than “tree”, “fish”
Producer, consumers—no decomp.

17. Who’s the producer?
Primary consumer?
Tertiary consumer?

18. Bushgrass  impala  cheetah  lion
Who’s the producer?
Primary consumer?
Tertiary consumer?

19. Buckwheat  gopher  gopher snake  red tailed kite
WHY are big predators so rare?

20. 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 diff trophic levels

21. 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

22. 5.1.8 Construct Food Web

24. Phytoplankton  sea whip  reef shark
algae  Diadarma  marine omnivores  groupers
Snappers & reef sharks can be either secondary or tertiary consumers (depending on food source)

26. 5.1.7 TL in food chain/web

27. Who’s the most important in the food web??
Producers or
Decomposers

29. 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

31. Efficiency not 100%
~ % 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

32. 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

33. 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

34. 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

35. 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

36. 5.1.13 Energy vs Nutrients Energy Flows, Matter Cycles
Energy lost as each TL; top of pyramid tapers b/c ultimately all lost as heat
Producers convert inorg molecs into organic ones; diff levels take it in and use for growth...C, N, Water cycles

38. Why are big predators rare?
Energy, matter lost at each stage
# organisms 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