Ecological Pyramids

Ecological PyramidsPyramids of numbers, biomass and productivitySTARTER: Plot these values on a bar graphPosition in food chainNumber of organismsProducers100Primary consumers50Secondary consumers25Tertiary consumers10Colour the bars using the key below

Producer GreenPrimary consumer YellowSecondary consumer BlueTertiary consumer - RedEcological PyramidsThese are graphical models of the quantitative differences between the amounts of living material stored at each trophic level of a food chain.

They allow us to easily examine energy transfers and losses

There are three types which measure:NumberBiomass Productivity (Energy)

Pyramid of NumbersA pyramid of numbers shows the number of organisms at each trophic level of the food chain

NowCut out each of the bars and place them onto a separate piece of paper

Which bar will go at the bottom?Which bar will go at the top?

Stick them downLabel!Label each side of the pyramid with the following terms:

Left SideRight SideProducersPlantsPrimary consumersHerbivoresSecondary consumersCarnivoresTertiary consumersTop carnivoresPyramid of numbersThe length of each bar gives a measure of the relative numbersPyramids have producers at the bottom, usually in the greatest number

Pyramid of numbersBut some may have a large single plant, a tree, as the producer so the base is one individual

Pyramids of numbersAdvantagesDisadvantagesSimple easy method of giving an overview

Good for comparing changes in population numbers over times or seasonAll organisms are included regardless of their size therefore some pyramids are inverted

They do not allow for juveniles or immature forms

Numbers can be too great to represent accurately

GROUP ACTIVITY

Pyramids of number

lettuce12A food chain is introduced

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snail14

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hedgehog16

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flea18

If we start to think about how many of each organism there are, we can start to build a pyramid of numbers...19A pyramid of numbers is built up visually

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2728Is it really fair that 1 lettuce counts for the same size box as 1 flea?29The idea of biomass is introducedIs it really fair that 1 lettuce counts for the same size box as 1 flea?

30Pyramids of biomassSTARTER:Is it really fair that 1 lettuce counts for the same size box as 1 flea in a pyramid of number? Explain your reasoning?

A better way is to look at the quantity of living material (biomass) at each feeding (trophic) level...32

lettucessnailshedgehogsfleasPyramids of biomass are always pyramid-shaped as at each stage of a food chain energy (biomass) is lost through respiration and body waste.34Pyramids of biomassA pyramid of biomass contains the biomass (mass of each individual x number of individuals) at each trophic level.

The units of a pyramid of biomass are units of mass per unit area, often grams per square metre (g m -2) or volume of water (g m -3) or sometimes as energy content (joules, J)

A pyramid of biomass is more likely to be a pyramid shape

Pyramids of biomass

Pyramids of biomassAdvantagesDisadvantagesOvercomes the problems of pyramids of numbersOnly uses samples from populations so its impossible to measure biomass exactly

Organisms must be killed to measure dry mass

The time of year affects the results

Two organisms with the same mass do not have the same energy content

GROUP THOUGHT: What is wrong with this pyramid of biomass?

STARTERWhy are biomass and numbers SMALL at HIGHER trophic levels?

Now try building a pyramid of biomass

STARTER: Energy loss in a food chain

Pyramids of productivity show That the amount of available energy decreases down the food chain

It takes a large number of producers to support a small number of primary consumers

It takes a large number of primary consumers to support a small number of secondary consumers

PYRAMIDS OF PRODUCTIVITY show the flow of energy between tropic levels

Pyramids of productivityAdvantagesDisadvantagesShows the actual energy transfers and allows for rate of production

Allows for comparison of ecosystems based on relative energy flow

Pyramids are not inverted

Energy from solar radiation can be addedIt is very difficult to collect energy data as the rate of biomass production over time is required

It is difficult to assign some species to a particular trophic level when they may be omnivorous

Group ActivityMake a poster with the information given in the handout

Things to include:Units for the different pyramidsExplanations for the shape of each pyramid of numberExplanation for why a pyramid of biomass is always pyramid shapedDescription of how a pyramid of energy shows energy flow through a food chain