Sunday, May 22, 2011

4.5) Food chain, Food Web, and Pyramids

Understand the concepts of food chains, food webs, pyramids of number, pyramids of biomass and pyramids of energy transfer.


Food Chain - show the flow of matter & energy
linked together the relationship between producers and consumers:
producer --> primary consumers --> secondary consumers --> tertiary consumers ---> ...
- can only show one organism at each trophic level
- can't be sure if the organism is omnivore or feeding at 2 or more trophic levels



Food Web
Allow us a better understanding of the ecosystem, which, in this case of interaction, is feeding.
Food web is a combination of different food chains, showing different trophic leves:
- multiple preys
- multiple predators
- linked
eg) An organism can be secondary or tertiary consumer at the same time. 

Pyramids --> quantifying the food chain
1. Pyramid of Number - shows the number of organism at each trophic level (eg. counting)

                        -1 hawk-
                  ---10flycatcher---
       ---------100 carrotflies----------
------------1000 carrot plants--------------

problem: limitation in expression of energy

                            -1 hawk-
                    -----100 birds-----
     ----------------1000 bees--------------
                         -1 plant- 
                                   
(notice the tiny base... energy cannot be represented this way)

2.Pyramid of Biomass - shows the mass (of matter) contains at each trophic level
Because water content varies and took up a large percentage, we only calculate the amount of dry mass in biomass.
*measured in kg/area

3. Pyramid of Energy - shows the flow of energy, therefore it cannot be inverted

                         -1% consumer-
                   -----10% producers---                               *unit = energy = J/ kJ
------------------100% sunlight------------------                          = area = m2
                                                                                                = time = m/s/yr

(notice the decreasing amount of energy at 10% per trophic level)


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