Opener – Wed., Jan. 18th: Please write these 2 questions, thenI’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 / yearsBiome Carbon Nitrogen Phos-

phorusPotass-

iumCal-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

And the winners are...• (i) potassium/K 1• (ii) sub-arctic forest 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 5.25.3

5.1 Communities5.1.1 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

• Flow of energy• Units: energy/unit area/unit time

• kJ m-2 yr-1 • Narrowing shape—why?• Gradual loss along chain

Solar not shown

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