Explain the Productivity of ecology?

When scientists study an ecosystem as a whole, they often examine the relationships between feeding, or trophic, levels. In order to do this, they lump together all of the organisms according to their functions. For example, all of the photosynthetic (producers) species are grouped together, as are all of the herbivore (primary consumers) species, and the carnivore (secondary consumers) species, and so on. Ecologists usually like to add up all of the living mass, or biomass of each group in order to compare relative values. These representations are useful in visualizing relationships, especially when it comes to comparing things like biomass, energy, and numbers.

The information about biomass (weight), numbers of individuals, or amounts of energy can be graphically presented as Ecological Pyramids as seen below (Ecological pyramid information is derived from W. E. Pequegnat, 1961; H.T. Odum, 1957; Harvey, 1950; Teal, 1962).

Pyramid of Numbers :  Note the huge difference in numbers of individual organisms between each step of the food chain. It takes a large number of individuals to support a relatively small number at the top of the food chain. Pyramids of numbers like this one do not consider important factors such as weight or energy.

Pyramids of Biomass : Although ecological pyramids are usually sloping downward in typical pyramidal shapes, sometimes the pyramids of biomass are inverted, as seen below. This happens when the data reflects a specific point in time. Since the life span of plankton in general is very short, a given sample will only reflect what is present at the time of sampling. However, we also know that the reproductive rates of plankton populations are very rapid, and in this way are able to sustain a large population of consumers over long periods of time.