ECOLOGICAL PYRAMIDS Pyramid diagrams give information about the organisms in a food chain. There are three types of pyramids: Pyramid of numbers Pyramid of biomass Pyramid of productivity Taken from K:\General Education\IB\Science\Environmental ystems\ecosystems\pyramids.ppt Taken from K:\General Education\IB\Science\Environmental systems\ecosystems\pyramids.ppt

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

Energy transfers and “loss” Energy is never created nor destroyed. Energy can be converted from one form to another. During an energy conversion, some energy is wasted (lost in an unusable form).

All energy ingested does not become part of the organism Energy is converted for an organism’s own respiration, metabolism, digestion and predation.

Ecological Pyramids “The Rule of Ten” Only about 10% of the energy available within one trophic level is transferred to organisms at the next trophic level. 90% of an organism’s energy is used for: Movement Respiration Reproduction Lost as heat Energy efficiency ranges from 0.05% to 20% The advantages are  It takes account of the rate of production over a period of time because each rectangle represents energy per unit area / vol per unit time. An example of units might be kJ/m2/yr  Two species weight for weight may not have the same energy content therefore the biomass is misleading but energy is directly comparable.  The relative energy flow within an ecosystem can be compared using pyramids of energy, also different ecosystems can be compared.  There are no inverted pyramids.  The input of solar energy can be added. The disadvantages are  The energy value for a given mass of organism is required, which involves complete combustion of a sample. There is still the difficulty of assigning the organisms to a specific trophic level. As well as the organism in the food chains there is the problem of assigning the decomposers and detritivores to a particular trophic level.

Three types of pyramids Pyramid Pyramid of Pyramid of BIOMASS of PRODUCTIVITY of NUMBERS

Pyramid diagrams are drawn to scale the width of each rectangle is proportional to: the number of organisms per square metre or the biomass in grams per square metre or the productivity in joules per square metre per month/year

PYRAMIDS OF NUMBERS These show numbers of organisms at different trophic levels, which depend on: the size of individual organisms the standing crop at the trophic level Number pyramid diagrams may be: upright pyramids inverted pyramids

PYRAMIDS OF BIOMASS These show the total biomass of organisms at different trophic levels, which depends on: the energy available at each trophic level the standing crop at each trophic level Biomass pyramid diagrams may be: upright pyramids inverted pyramids

How can a pyramid of biomass be inverted? Pyramids of biomass measure standing crop at a particular moment in time. If you collected the all the cuttings from a garden lawn, mown twice a week during the summer, it would make a huge pile of biomass But just after cutting, the biomass stored in the lawn would be quite small Exchange your lawn mower for a rabbit and you can see how an inverted biomass pyramid could be produced if you measured biomass over the whole summer for lawn and rabbit, the pyramid would look quite different

Some data for the English Channel Draw a pyramid of biomass for this data. Why is the pyramid inverted?

PYRAMIDS OF PRODUCTIVITY These show productivity of organisms at different trophic levels, which depends on: the energy available from the previous trophic level the efficiency of the organisms Productivity pyramid diagrams are always: upright pyramids

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 pyramids 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?

Productivity around the world Major Terrestrial Biomes

So which are the most productive bio-systems? Based on average NPP: Estuaries Swamps, marshes Tropical rainforests Based on total NPP: Open ocean (because it covers so much of the earth)

Productivity as a function of rainfall

Productivity as a function of temperature

What is net primary production (npp) The sum of ALL the light energy, hydrogen (from water) and carbon dioxide which is converted by green plants into glucose and other organic compounds is called GROSS PRIMARY PRODUCTION (GPP). The plants themselves use much of these organic compounds. What is left is called NET PRIMARY PRODUCTION (NPP) and can be consumed by other organisms.

Significance of npp “The planet’s NPP ultimately limits the number of consumers (including humans) that can survive on earth.” NPP limits biodiversity. How can we feed more people with the land we have?

A TUNA FISH SANDWICH

Agricultural land: Super productive? Despite the addition of nutrients, agricultural land has a NPP of about 14,000 kJ/m2/yr Compare this to estuaries at over 37,000 kJ/m2/yr

solutions Solution 1: harvest plants from naturally productive areas, such as estuaries, swamps and marshes Problem: Humans cannot survive on these foods and using them for food would disrupt the natural spawning grounds that provide us with other high-protein foods (e.g., shrimp)

solutions Solution 2: Clear areas with demonstrated high NPP, such as tropical rainforest, and use the land for crops Problem: Soil is very poor, nutrients are tied up in plants, can’t support crops for long. Deforestation.

solutions Solution 3: harvest food (phytoplankton) from open ocean Problem: Phytoplankton are so widely dispersed that it would take too much energy to collect them; it would also disrupt marine food webs

solutions Solution 4: Eat at a lower trophic level Problems: ???

solutions Solution 5: Waste less (humans waste 27% of the earth’s total NPP and 40% of the earth’s terrestrial ecosystems’ NPP) Problems: ???