Biology ECOLOGICAL PYRAMIDS

KEY TOPICS

star Type of the pyramids
star Shape of the Pyramids
star Limitations of Ecological Pyramids

TYPES OF PYRAMIDS

● We are familiar with the color{violet}("shape of a pyramid.")

● The base of a color{violet}("pyramid") is broad and it narrows down at the color{violet}("apex.")

● One gets a similar shape, whether it is the color{violet}("food or energy relationship") between organisms at different trophic level that is expressed.

● Thus, relationship is expressed in terms of number, color{violet}("biomass or energy.")

● The base of each color{violet}("pyramid") represents the producers or the color{violet}("first trophic level") while the color{violet}("apex") represents color{violet}("tertiary") or top level consumer.

● The three color{brown}("ecological pyramids") that are usually studied are:

(a) color{brown}("Pyramid of number")

(b) color{brown}("Pyramid of biomass")

(c) color{brown}("Pyramid of energy")

● Any calculations of energy content, color{violet}("biomass,") or numbers has to include color{violet}("all organisms") at that trophic level.

● color{violet}("No generalisations") we make will be true if we take only a few individuals at any color{violet}("trophic level") into
account.

● Also a given organism may occupy more than one color{violet}("trophic level") simultaneously.

SHAPE OF THE PYRAMIDS

● One must remember that the color{violet}("trophic level") represents a color{violet}("functional level"), not a species as such.

● A given species may occupy more than one color{violet}("trophic level") in the same color{violet}("ecosystem") at the same time; for example, a sparrow is a primary consumer when it eats seeds, fruits, peas, and a secondary consumer when it eats insects and worms.

● In most color{violet}("ecosystems"), all the color{violet}("pyramids,") of color{brown}("number"), of color{brown}("energy") and color{brown}("biomass") are color{brown}("upright"), i.e., producers are more in number and color{violet}("biomass") than the color{violet}("herbivores,") and color{violet}("herbivores") are more in number and biomass than the color{violet}("carnivores.")

● Also energy at a color{violet}("lower trophic level") is always more than at a color{violet}("higher level.")

● There are exceptions to this color{violet}("generalisation"): In case we were to count the number of insects feeding on a big tree, the color{violet}("pyramid ")wouldn’t be color{violet}("upright.")

● The pyramid of color{brown}("biomass in sea") is also generally color{brown}("inverted") because the color{violet}("biomass") of fishes far exceeds that of color{violet}("phytoplankton.")

● color{violet}("Pyramid") of energy is color{brown}("always upright "), can never be inverted, because when color{violet}("energy flows") from a color{violet}("particular trophic level") to the color{violet}("next trophic level,") some energy is always lost as heat at each step.

● Each bar in the color{violet}("energy pyramid") indicates the amount of energy present at each color{violet}("trophic level") in a given time or annually per unit area.

LIMITATIONS OF ECOLOGICAL PYRAMIDS

● However, there are certain color{violet}("limitations") of color{violet}("ecological pyramids") such as it does not take into account the same species belonging to two or more color{violet}("trophic levels.")

● It assumes a simple color{violet}("food chain,") something that almost never exists in nature; it does not accommodate a color{violet}("food web. ")

● Moreover,color{violet}(" saprophytes") are not given any place in color{violet}("ecological pyramids") even though they play a vital role in the color{violet}("ecosystem.")