• Pyramid diagrams give information about the Pyramid diagrams give information about the organisms in a food chain. There are three organisms in a food chain. There are three types of pyramids:types of pyramids:

– Pyramid of numbersPyramid of numbers– Pyramid of biomassPyramid of biomass– Pyramid of productivityPyramid of productivity

• Taken from K:\General Education\IB\Science\Environmental ystems\Taken from K:\General Education\IB\Science\Environmental ystems\ecosystems\pyramids.pptecosystems\pyramids.ppt

ECOLOGICAL PYRAMIDSECOLOGICAL PYRAMIDS

There is a There is a one-way flow of energy of energy from the sun from the sun to the earth to the earth and through and through its its ecosystems. ecosystems. (Nutrients are (Nutrients are cycled through cycled through biota to biota to sustain life.sustain life.))

THE SUN IS THE SOURCE THE SUN IS THE SOURCE OF ENERGYOF ENERGY

Energy transfers and “loss”Energy transfers and “loss”

• Energy is never created nor Energy is never created nor

destroyed.destroyed.

• Energy can be converted from one Energy can be converted from one

form to another.form to another.

• During an energy conversion, some During an energy conversion, some

energy is wasted (lost in an energy is wasted (lost in an

unusable form).unusable form).

All energy ingested does not All energy ingested does not become part of the organismbecome part of the organism

• Energy is Energy is converted for converted for an organism’s an organism’s own own respiration, respiration, metabolism, metabolism, digestion and digestion and predation.predation.

Ecological Pyramids Ecological Pyramids

• ““The Rule of Ten” The Rule of Ten” – Only about 10% of the energy available within Only about 10% of the energy available within

one trophic level is transferred to organisms at one trophic level is transferred to organisms at the next trophic level. the next trophic level.

– 90% of an organism’s energy is used for: 90% of an organism’s energy is used for: •MovementMovement•RespirationRespiration•Reproduction Reproduction •Lost as heatLost as heat

Three types of pyramidsThree types of pyramids

PyramidPyramid Pyramid of Pyramid of Pyramid Pyramid

of of BIOMASSBIOMASS of of PRODUCTIVITYPRODUCTIVITY of of NUMBERSNUMBERS

Pyramid diagramsPyramid diagrams• are drawn to scaleare drawn to scale

• the width of each rectangle is the width of each rectangle is proportional to:proportional to:– the number of organisms per square the number of organisms per square

metremetre– oror the biomass in grams per square the biomass in grams per square

metremetre– oror the productivity in joules per square the productivity in joules per square

metre per month/yearmetre per month/year

PYRAMIDS OF NUMBERSPYRAMIDS OF NUMBERS

• These show These show numbersnumbers of organisms at of organisms at different trophic levels, which depend on:different trophic levels, which depend on:

– the size of individual organismsthe size of individual organisms– the standing crop at the trophic levelthe standing crop at the trophic level

• Number pyramid diagrams may be:Number pyramid diagrams may be:– upright pyramidsupright pyramids– inverted pyramidsinverted pyramids

PYRAMIDS OF BIOMASSPYRAMIDS OF BIOMASS

• These show the These show the total biomasstotal biomass of of organisms at different trophic levels, organisms at different trophic levels, which depends on:which depends on:– the energy available at each trophic levelthe energy available at each trophic level– the standing crop at each trophic levelthe standing crop at each trophic level

• Biomass pyramid diagrams may be:Biomass pyramid diagrams may be:– upright pyramidsupright pyramids– inverted pyramidsinverted pyramids

How can a pyramid of How can a pyramid of biomass be inverted?biomass be inverted?

• Pyramids of biomass measure standing crop at a Pyramids of biomass measure standing crop at a particular moment in time.particular moment in time.

• If you collected the all the cuttings from a garden If you collected the all the cuttings from a garden lawn, mown twice a week during the summer, it lawn, mown twice a week during the summer, it would make a huge pile of biomasswould make a huge pile of biomass

• But just after cutting, the biomass stored in the But just after cutting, the biomass stored in the lawn would be quite smalllawn would be quite small

• Exchange your lawn mower for a rabbit and you Exchange your lawn mower for a rabbit and you can see how an inverted biomass pyramid could can see how an inverted biomass pyramid could be producedbe produced

• if you measured biomass over the whole summer if you measured biomass over the whole summer for lawn and rabbit, the pyramid would look quite for lawn and rabbit, the pyramid would look quite differentdifferent

Some data forSome data forthe English Channelthe English Channel

Organism Biomass-dry mass in gm-2

phytoplankton 4.0

zooplankton 21.0

Draw a pyramid of biomass for this data.

Why is the pyramid inverted?

PYRAMIDS OF PRODUCTIVITYPYRAMIDS OF PRODUCTIVITY

These show These show productivity productivity of of organisms at different trophic organisms at different trophic levels, which depends on:levels, which depends on:

• the energy available from the the energy available from the previous trophic levelprevious trophic level

• the efficiency of the organismsthe efficiency of the organisms

Productivity pyramid diagrams are Productivity pyramid diagrams are always:always:– upright pyramidsupright pyramids

WHAT IS PRODUCTIVITY?WHAT IS PRODUCTIVITY?Productivity is the amount of energy converted into biomass by at each trophic level, per unit of time. (Joules per year)

GROSS PRODUCTIVITY is the actual total before the needs of the trophic level are accounted for.

NET PRODUCTIVITY is what is left for growth (and for the next trophic level to consume).

Some Consequences of Some Consequences of pyramidspyramids

Persistent chemicals bio-accumulate in the tissues of the top carnivores? Why?

Biomass decreases; population decreases; size increases as you go up a food chain. Why?

Major Terrestrial BiomesMajor Terrestrial Biomes

Productivity around the worldProductivity around the world

So which are the most So which are the most productive bio-systems?productive bio-systems?

Based on average NPP:Based on average NPP:• EstuariesEstuaries• Swamps, marshesSwamps, marshes• Tropical rainforestsTropical rainforests

Based on total NPP:Based on total NPP:• Open ocean (because it covers Open ocean (because it covers

so much of the earth)so much of the earth)

Productivity as a function of rainfall

Productivity as a function of temperature

What is net primary What is net primary production (npp)production (npp)The sum of ALL the light energy, hydrogen The sum of ALL the light energy, hydrogen (from water) and carbon dioxide which is (from water) and carbon dioxide which is converted by green plants into glucose converted by green plants into glucose and other organic compounds is called and other organic compounds is called GROSS PRIMARY PRODUCTION (GPP).GROSS PRIMARY PRODUCTION (GPP).

The plants themselves use much of these The plants themselves use much of these organic compounds. What is left is called organic compounds. What is left is called NET PRIMARY PRODUCTION (NPP) and can NET PRIMARY PRODUCTION (NPP) and can be consumed by other organisms.be consumed by other organisms.

Significance of nppSignificance of npp

““The planet’s NPP ultimately limits the The planet’s NPP ultimately limits the number of consumers (including number of consumers (including humans) that can survive on earth.”humans) that can survive on earth.”

NPP limits biodiversity.NPP limits biodiversity.

How can we feed more people with How can we feed more people with the land we have?the land we have?

A TUNA FISH SANDWICHA TUNA FISH SANDWICH

Agricultural land: Super Agricultural land: Super productive?productive?

Despite the addition of nutrients, Despite the addition of nutrients, agricultural land has a NPP of agricultural land has a NPP of about 14,000 kJ/mabout 14,000 kJ/m22/yr/yr

Compare this to estuaries at Compare this to estuaries at over 37,000 kJ/mover 37,000 kJ/m22/yr/yr

Solution 1Solution 1: harvest : harvest plants from naturally plants from naturally productive areas, such productive areas, such as estuaries, swamps as estuaries, swamps and marshesand marshes

ProblemProblem: Humans : Humans cannot survive on cannot survive on these foods and using these foods and using them for food would them for food would disrupt the natural disrupt the natural spawning grounds that spawning grounds that provide us with other provide us with other high-protein foods high-protein foods (e.g., shrimp)(e.g., shrimp)

solutionssolutions

Solution 2Solution 2: Clear : Clear areas with areas with demonstrated high demonstrated high NPP, such as tropical NPP, such as tropical rainforest, and use rainforest, and use the land for cropsthe land for crops

ProblemProblem: Soil is : Soil is very poor, nutrients very poor, nutrients are tied up in plants, are tied up in plants, can’t support crops can’t support crops for long. for long. Deforestation.Deforestation.

solutionssolutions

Solution 3Solution 3: harvest : harvest food (phytoplankton) food (phytoplankton) from open oceanfrom open ocean

ProblemProblem: : Phytoplankton are so Phytoplankton are so widely dispersed that widely dispersed that it would take too much it would take too much energy to collect energy to collect them; it would also them; it would also disrupt marine food disrupt marine food webswebs

solutionssolutions

Solution 4Solution 4: Eat : Eat at a lower at a lower trophic leveltrophic level

ProblemsProblems: ???: ???

solutionssolutions

Solution 5Solution 5: Waste : Waste lessless

(humans waste (humans waste 27% of the earth’s 27% of the earth’s total NPP and 40% total NPP and 40% of the earth’s of the earth’s terrestrial terrestrial ecosystems’ NPP)ecosystems’ NPP)

ProblemsProblems: ???: ???

solutionssolutions