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Summary of topic 2.1


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  • 1. Topic 2.1 Ecosystem Structure
  • 2. Ecological Pyramids • There are 3 types of ecological pyramid: – Pyramid of number – Pyramid of biomass – Pyramid of productivity
  • 3. Pyramid of Number • Either you count each individual, or if this is not possible make a collection over a specific limited area and multiply up • They are not always pyramid shaped • The first level may be smaller than the second if the individual primary producers are very large (eg. trees)
  • 4. Pyramid of Biomass • Units of g m-2 or J m-2 (if you use joules it is technically a pyramid of energy) • A limitation is that they don’t represent changes over time (they are just a ‘snap-shot’ or a representation of ‘standing stock’) • For this reason they are not always pyramid shaped. Eg if a field has been extensively grazed, its biomass at one moment in time may be very low (even though its productivity may be high)
  • 5. Pyramid of Productivity • Possibly the most useful type of pyramid • Units of g m-2 yr-1 or J m-2 yr-1 • Represent the flow of biomass or energy over time. Therefore not just a snapshot like the other pyramids • Represent the flow of energy or biomass through a food chain, and therefore are always pyramid shaped
  • 6. Pyramid of Numbers Pyramid of Biomass Pyramid of Productivity
  • 7. Bioaccumulation and Biomagnification • Which trophic level is most at risk to toxic pollutants in the environment and why? • The top predators • This is due to 2 processes: – Bioaccumulation – the retention of non-polar compounds in body tissues (usually fat) – Biomagnification – the increase in these compounds in organisms as you move up the food chain. Each animal retains the compounds from all of those in the preceding trophic levels Video clip - biomagnification
  • 8. Case Study: DDT • • • • • • • • • • Dichlorodiphenyltrichloroethane An organochlorine insecticide Very non-polar Similar in structure to oestrogen and therefore has ´feminising’ effects on animals In birds it weakens egg shells so that the parents break them as they try to incubate the eggs The birds at highest risk are those close to the top of the food chain DDT was one of the main subjects of Rachel Carson’s 1962 book ‘Silent Spring’ which helped to kickstart modern environmentalism It was banned in most developed countries in the 1970s and 1980s It is now known to cause birth defects, damage to the nervous system and cancers It is still used in many poorer countries to control insect problems – why?
  • 9. Case Study: Minimata Disease • Caused by the heavy metal mercury • First documented In Minimata, Japan in 1957 • A chemical factory was releasing methyl mercury into Minimata Bay between 1932 and 1968 • This biaccumulated in shellfish and was biomagnified in fish • Both were the staple diet of the local human population • Mercury causes severe damage to the nervous system and Minimata Disease was first identified due to the high incidence of cerebral palsy in children in the area
  • 10. Population Interactions • Make sure you have definitions of: – Species – Habitat – Niche – Community – Ecosystem
  • 11. Population Interactions • Population Interactions occur due to: 1. 2. 3. 4. Competition Predation Parasitism Mutualism • They are examples of biotic factors
  • 12. 1. Competition • This may be interspecific and/or intraspecific • Interspecific competition occurs when niches overlap (this is called competitive exclusion or Gause’s Principle) • Intraspecific competition drives natural selection • G.F. Gause (Russian ecologist) demonstrated his theorem by putting two species of Paramecium in the same Petri dish • They can survive separately, but when together P. aurelia outcompetes and eliminates P. caudatem
  • 13. 2. Predation • Simply the hunting of one animal by another for food • Controlled by negative feedback loops to create a steady-state equilibrium
  • 14. 3. Parasitism • A relationship in which one organism benefits at the expense of another – Ectoparasites – on the surface of a host (eg lice) – Endoparasites – inside a host (eg tapeworm)
  • 15. 4. Mutualism • A relationship in which two organisms live together and both benefit (often refered to as a symbiotic relationship)