Ecology (part 2) - Pyramid of numbers, pyramid of biomass and carbon cycle

1. Food chains and food webs

2. Lesson Objectives At the end of the lesson, you should be able to (d) describe and interpret pyramids of numbers and biomass (e) describe how carbon is cycled within an ecosystem

4. Food Chains • Is a series of organisms through which energy is transferred in the form of food • Always begins with a producer • Each arrow means ‘is eaten by’ • Each stage in a food chain is known as a trophic level • Do not have more than 4 trophic levels

5. Food Chains • Producers make up the first trophic level, primary consumers make up the second trophic level, and so on • An animal that feeds on another animal is called a predator • An animal that is eaten by another animal is called the prey Primary Consumer (herbivore) Secondary Consumer (carnivore) TertiaryConsumer (carnivore) Producer (green plant)

6. How energy and nutrients flow through the ecosystem - converts energy from the sun or light energy into chemical energy and store it as food during photosynthesis - mainly green plants, but algae and certain bacteria can photosynthesize are also producers - either directly or indirectly affect the lives of other organisms because they provide energy and O2 Producers Consumers - obtain their energy by feeding on other organisms - Primary consumers (herbivores), secondary consumers (carnivores) and tertiary consumers Decomposers (e.g. fungi, bacteria and earthworms) - obtain energy by breaking down dead organisms, faeces and excretory products - The materials released e.g. inorganic nutrients, carbon and nitrogen compounds return to the physical environment and are used again by green plants

8. Keeping the balance in an ecosystem Water plant Small fish Bear Salmon What would happen if the population of the salmon increased?

9. 3 types of pyramids Pyramid of Energy Shows the relative amount of energy available at each trophic level. Organisms use about 10 percent of this energy for life processes. The rest is lost as heat. Pyramid of Numbers Shows the relative number of individual organisms at each trophic level. Pyramid of Biomass Represents the amount of living organic matter at each trophic level. Typically, the greatest biomass is at the base of the pyramid.

11. Ecological Pyramids of Energy • Energy is lost to the environment: • As heat lost to the environment during respiration at every trophic level • Through undigested matter egested by consumers • Through waste products excreted by consumers e.g. urea from consumers • In uneaten body parts

12. Worksheet on Pyramids of Numbers, Energy and Biomass

14. Difference between parasites and scavengers • Parasites - organisms that live on or in the body of another species and get their nutrients and energy from their hosts - Most parasites cause harm to their hosts - e.g. aphids and mosquitoes • Scavengers - organisms that feed on dead animals - e.g. vultures

15. Variations in Ecological Pyramids Most ecological pyramids are pyramid-shaped, but there are important exceptions • A pyramid of numbers may be upside down or inverted if: i) Organisms of one trophic level are parasitic on organisms of another trophic level ii) Many small organisms of one trophic level feed on a large organism of another trophic level parasitic protozoa aphids tree

16. Variations in Ecological Pyramids • Pyramids of biomass for rapidly reproducing organisms Since the pyramid of biomass is based on standing mass (dry mass of organisms in each trophic level at any one time),it does not take into account the rate of reproduction (productivity) of organisms. This is a disadvantage when considering organisms that reproduce rapidly

17. For Example: Phytoplankton → zooplankton → small fish → large fish The pyramid gives the impression that the biomass of phytoplankton is smaller than that of zooplankton, which is not possible. What happens is that the rate of reproduction of phytoplankton is fast enough to replace the organisms that were eaten by zooplankton (microscopic plant-like organisms that can photosynthesize) (microscopic primary consumers that feed on phytoplankton) large fish small fish zooplankton phytoplankton

19. Nutrient Cycling in an Ecosystem

20. Nutrient Cycling in an Ecosystem • Carbon, oxygen, nitrogen and water are essential nutrients for life • In natural ecosystems, these nutrients are released back into the soil when organisms die • Decomposers break down the dead organisms • The materials locked up in the dead organisms can be returned to the physical environment to be used again by green plants • Hence in a balanced ecosystem, nutrients are never lost but are continually recycled

21. The Carbon Cycle

22. The Carbon Cycle • Carbon is constantly being removed from and released into the environment in the form of CO2 • Hence the CO2 concentration in the environment remains relatively constant • The various processes by which carbon, in the form of CO2 is removed from and released into the environment make up the carbon cycle

23. Carbon cycle Release of CO2 into the atmosphere by i) Respiration ii) Combustion iii) Decay Removal of CO2 from the atmosphere • Photosynthesis • Feeding and assimiliation into carbohydrates, fats, proteins • Preserved as fossil fuels

25. Importance of the carbon cycle • Ensures that there is a continuous supply of inorganic CO2 for plants to carry out photosynthesis. Photosynthesis converts energy from the sun into chemical energy in food, which other non-photosynthetic organisms can use to stay alive • Enables energy to flow through the ecosystem. Carbon compounds carry the trapped solar energy from organism to organism in the food chains in the ecosystem