By the end of this session I should be able to:(a) define the term ecosystem; (b) state that ecosystems are dynamic systems;(c) define the terms biotic factor and abiotic factor, using named examples; (d) define the terms producer, consumer decomposer and trophic level; (e) describe how energy is transferred though ecosystems; (f) outline how energy transfers between trophic levels can be measured;(g) discuss the efficiency of energy transfers between trophic levels; (h) explain how human activities can manipulate the flow of energy through ecosystems (HSW6b);

On the piece of paper in front of you there are 10 different

ecosystems. Name as many as you can by labelling the pictures

and adding the selection pressure that would have the

biggest effect on the organisms living there.

What is lurking in your eyelashes?

Use your texts to complete the followingKey Word Definition Examples Link across the

spec

Ecosystem

Abiotic factor

Biotic factor

Producer

Consumer

Decomposer

Trophic level

What selection pressures does Zara have to cope with? Think biotic and abiotic factors.

Biotic living / Abiotic non livingBiotic factors that Zara needs to

considerAbiotic factors that Zara needs to

consider

What limits the length of the food chain?

What limits length of food chain?• H1: Energetics • Availability of energy limits to 5-7 levels• Depends on: NPP energy needed by consumers average ecological efficiency

• H2: Dynamic stability Longer chains less stable because: Fluctuations at lower trophic levels magnified at higher levels ---> extinction of top predators.

• A food web is a branching food chain with complex trophic interactions

• Species may play a role at more than one trophic level

• Food webs can be simplified by isolating a portion of a community that interacts very little with the rest of the community

• About one order of magnitude of available energy is lost from one trophic level to the next

How heterotrophs use food energy

Biomass available at the next trophic level

Energy loss in an ecosystem

Cayuga LakeIn NY

– Reason why food chains generally consist of only 3 or 4 steps

How can we calculate the amount of energy? each trophic level?

Producers (autotrophs)

Consumers(heterotrophs)

How is energy lost between trophic level?Lost in the transfer of light energy

into chemical energy in photosynthetic organisms

Lost in the transfer from one consumer the next

• • • • • • •

• • • • • • •

Primary productivity• Gross Primary Productivity (GPP):

– total amount of photosynthetic energy captured in a given period of time.

• Net Primary Productivity (NPP): – the amount of plant biomass (energy) after cell respiration

has occurred in plant tissues.

NPP = GPP – Plant respirationplant growth/ total photosynthesis/ unit area/ unit area/unit timeunit time

Primary productivity – marine ecosystems

Global variation in estimated NPP

Figure 9

Mr Moore set the homework on

‘increasing efficiency in the production of food

by manipulating trophic levels’