Understanding Energy Flow in Ecosystems

1. National 5 Energy in Ecosystems Mr G Davidson

2. Food Chains • All organisms require energy. • This energy comes, initially, from the sun. • It is trapped by green plants by photosynthesis. • This energy is then passed from organism to organism along the food chain. Mr G Davidson

3. Food Chains • Food chains always begin with the producer (green plant). • The producer is eaten by animals which are herbivores. • These are called primary consumers. • This animal is then eaten by the next animal in the food chain and this is called the secondary consumer. Mr G Davidson

4. Food Chains • Each time an organism is eaten, energy passes along the food chain. • The arrows indicate the direction of the energy flow. • This passing of energy is represented by arrows, e.g. Fox Grass Rabbit Mr G Davidson

5. Food Chains • Energy is being passed from the grass to the rabbit to the fox. • As energy is passed along the food chain, about 90% of it is lost. • Therefore, the next organism only gains about 10% of the energy of the previous organism. Mr G Davidson

6. Food Chains • The lost energy is lost as: • Heat • Movement • Undigested materials. • Food chains are not as simple as they first appear because they usually involve other organisms. Mr G Davidson

7. OWL FOX WEASEL HEDGEHOG RABBIT VOLE FROG SNAIL PRIMROSE PLANT OAK Food Webs A combination of a number of food chains leads to the formation of a food web. Mr G Davidson

8. Pyramid of Numbers • Food chains give us the feeding relationships between the different organisms, but they don’t provide any information about numbers. • As we move along a food chain the numbers should start high and decrease. • If we take our food chain and look at the numbers, the grass should be the most numerous. Mr G Davidson

9. Pyramid of Numbers Numbers decrease Size of organism increases Mr G Davidson

10. Pyramid of Numbers • Each level of the pyramid represents the total population of this organism. • As we travel up the pyramid, these numbers decrease as energy is lost. • There are, however, exceptions to the true pyramid shape and these pyramids are said to be irregular. Mr G Davidson

11. Irregular Pyramids of Numbers Fleas Fox Rabbit Grass Mr G Davidson

12. Irregular Pyramids of Numbers Sparrow hawk Blue tit Greenfly Oak Tree Mr G Davidson

13. Pyramid of Biomass • Due to the irregular pyramids of numbers, they are not always the best way to represent feeding relationships. • Instead, we use something called a pyramid of biomass. • In this way, each level is represented by the total mass of the organisms. Mr G Davidson

14. Pyramid of Biomass Fox – 4kg Rabbit – 40kg Grass – 400kg Mr G Davidson

15. Pyramid of Energy • The most reliable way of showing feeding relationships is to use a pyramid of energy. • It is measured as kilojoules per square metre per year (kJ/m2/year). • Since energy is lost at each stage, the pyramid formed must be true. Mr G Davidson

16. Pyramid of Energy Seal – 60kJ Squid – 600kJ Zooplankton – 6 000kJ Phytoplankton – 60 000kJ Mr G Davidson

17. Nutrient Cycles • All organisms are made of chemical elements. • These elements come from the environment. • There is a limited supply of these elements and so they need to be recycled. • Nitrogen is one such element. Mr G Davidson

18. Nutrient Cycles • Organisms require nitrogen to make proteins. • They cannot use the nitrogen directly from the air. • Plants get their nitrogen from the soil in the form of nitrates. • Animals get their nitrogen from eating plant or animal protein. Mr G Davidson

19. Nutrient Cycles • Nitrogen is an element which is recycled. • It is very much dependent on bacteria converting compounds into other compounds. • There are different types of bacteria involved in the nitrogen cycle. Mr G Davidson

20. Nitrogen Cycle Nitrates in the Soil Denitrification Nitrogen fixating bacteria in plant roots Converted to Nitrates Plants Nitrogen (in air) Nitrification Decomposer Bacteria Converted to Nitrites Animals Decomposer Bacteria Nitrogen in ammonium compounds Death (products are turned to ammonium compounds) Nitrification Mr G Davidson

21. Nitrogen Cycle • Decomposer bacteria are responsible for breaking down dead plants and animals into ammonium compounds. • Nitrifying bacteria are responsible for the process of nitrification, which is the conversion of ammonium compounds into nitrites and then nitrates. Mr G Davidson

22. Nitrogen Cycle • Denitrifying bacteria are responsible for breaking down nitrates and releasing nitrogen back into the atmosphere. • Nitrogen-fixing bacteria are responsible for converting atmospheric nitrogen back into nitrates. Mr G Davidson

23. Nitrogen Cycle • There are other bacteria which live in plant root nodules of legumes, which also convert nitrogen to nitrates. • Legumes grow well in soil that is nitrogen deficient. • Many modern day fertilisers contain nitrates to allow the crops to produce higher yields. Mr G Davidson

24. Competition in Ecosystems • All organisms require basic resources to stay alive. • If these resources are in short supply then competition will occur. • There are two types of competition: • Interspecific Competition • Intraspecific Competition Mr G Davidson

25. Interspecific Competition • Interspecific competition happens when members of a different species are competing for similar resources. • This type of competition is generally not as fierce because they are not competing for the exact same resources, but it may result in one species having to move away from the ecosystem. Mr G Davidson

26. Intraspecific Competition • Intraspecific competition occurs between members of the same species. • This type of competition is usually very fierce as the organisms will be competing for the same resources. • Intraspecific competition also helps to regulate the size of a population by weeding out the weaker members by natural selection. Mr G Davidson