Topic 10 - Ecosystems

Plan Discuss pictures on slide 3 – and develop idea that there are different ecosystems. Hand out and stick in definitions. Complete food chain activity and go over key words, draw out pyramid of number and discuss advantages and disadvantages Complete biomass activity and discuss advantages and disadvantages do the same for pyramids of productivity.

The nature of ecosystems Understand what is meant by the term ecosystem and that they range in size Understand what is meant by trophic levels Understand the advantages and disadvantages of pyramids of numbers, biomass (dry) and energy as useful representations of ecosystem structure and how biomass and energy are transferred within them.

Trophic levels GrassGrasshopperFrogSnakeKestrel Annotate the food chain… Producer, Primary consumer, secondary consumer, tertiary consumer, quaternary consumer, predator, omnivore, carnivore, herbivore, autotroph Now sketch out a pyramid of numbers for the above food chain.

Definitions Species – A group of organisms that interbreed and produce FERTILE offspring. Population – A group of organisms of the SAME SPECIES living in the same area at the same time, and which are capable of interbreeding Habitat – The environment in which a species normally lives Niche – Where, when and how an organism lives. An organism’s niche depends not only on where it lives but also what it does. Community – A group of populations living and INTERACTING with each other in a common habitat. Ecosystems – An ecosystem is a community of DIFFERENT organisms and the physical environment

Definitions Species – A group of organisms that interbreed and produce FERTILE offspring. Population – A group of organisms of the SAME SPECIES living in the same area at the same time, and which are capable of interbreeding Habitat – The environment in which a species normally lives Niche – Where, when and how an organism lives. An organism’s niche depends not only on where it lives but also what it does. Community – A group of populations living and INTERACTING with each other in a common habitat. Ecosystems – An ecosystem is a community of DIFFERENT organisms and the physical environment

Pyramid of number Will it always be pyramid shaped? Show only the NUMBER of organisms at each trophic level Will it always be pyramid shaped? Can you think of an example where this is not the case?

How many do they need to eat?

We can draw this as a Pyramid of Numbers. However the number of organisms at each level does not accurately reflect what is happening to the Biomass. In pairs, on the white boards draw out all the advantages and disadvantages of pyramids of number

Pyramids of Biomass A pyramid of biomass is a chart, drawn to scale, showing the biomass at each stage in a food chain. The bars become narrower as you reach the top. This pyramid of biomass is for the food chain: oak tree → caterpillar → blue tit → sparrowhawk Each bar should be labelled with the name of the organism.

Construct your own pyramid of biomass Organism Numbers Biomass Leaves Aphids Ladybirds Plot a bar chart in your notes that shows the biomass of each organism. What percentage of biomass is passed on at each trophic level? Will a pyramid of biomass always be a pyramid? What are the problems with taking dry biomass?

Construct your own Pyramid of Biomass: Count up the number of leaves. Each leaf weighs 5g.

Construct your own Pyramid of Biomass: Now count the number of aphids that can eat that amount of leaves in one day. Each Aphid weighs 1g

Now count the number of lady birds that can eat that amount of aphids in one day. Each Ladybird weighs 10g

Pyramids of productivity Pyramids of productivity take into account the rate of production over a period of time because each level represents energy per unit time. Biomass is measured in unit of mass (g m-2) or energy (J m-2). Productivity incorporates a unit of time e.g. g m-2 yr-1

On the white boards What are the advantages and disadvantages of pyramids of biomass? What are the advantages and disadvantages of pyramids of energy?

Gross primary productivity, net primary productivity and secondary productivity Primary productivity – The gain by producers (autotrophs) in energy or biomass per unit area per unit time. Secondary productivity – The biomass gained heterotrophic organisms, through feeding and absorption, measured in units of mass or energy per unit time. Primary is conversion of solar energy Secondary depends on amount of food present and the efficiency of consumers turning this into new biomass.

GPP – (Gross primary productivity) – The total energy gained through photosynthesis Net primary productivity (NPP) – Gain in energy thorugh photosynthesis or biomass per unit time remaining after allowing for respiratory losses (R).

Farmers find it helpful to know the productivity of their land. The diagram below shows the relationship between GPP (gross primary productivity), NPP (net primary productivity) and R (plant respiration) for an area of grassland. (a)  The efficiency of the transfer of energy from GPP to NPP for this grassland is 45%. (i)  Calculate the values for NPP and R. Write your answers in the diagram above.(2) (ii)  Using the information given, explain the relationship between GPP and NPP.(3) (b)  Suggest why NPP values would be of use to a farmer who wanted to use this land for cattle. (3) (c)  The units (kJ m−2 year−1) used in the diagram show a rate of energy production. Suggest why this is more useful than measurements of biomass in the grassland on a particular day. (2)

Biotic and abiotic components Biotic refers to the living components within an ecosystem (the community). Abiotic refers to the non-living factors of the ecosystem (the environment) Biotic – animals, plants, algae, fungi Abiotic – light, air, water, temperature, minerals, soil and climatic aspects