5.2.1.4.1.2. Aquatic Ecosystems

Pyramid of Number:

•They show the relationship between producers, herbivores, and carnivores at successive trophic levels in terms of their number. •In case of pond ecosystem, the producers are mainly phytoplankton and are always maximum in number. This number then shows a decrease towards apex as primary consumers are zooplanktons, which are lesser in number than phytoplankton. The secondary consumers, which are large fish, are even lesser in number than the phytoplankton. Thus the shape of pyramid is upright. But in case of forest ecosystem, the pyramid is always inverted because the producers are mainly large trees, which are lesser in number than the herbivores, such as fruit-eating birds, that are more in number. There is then a gradual decrease in the number of secondary consumers, thus making the pyramid upright again. Therefore, the pyramid of number does not give a true picture of the food chain and is not very functional.

The Pyramid of Number illustrates how many organisms are present at each trophic level of an ecosystem. In a pond ecosystem, for example, phytoplankton (the producers) are abundant, resulting in a pyramid shape that is upright. In contrast, in a forest ecosystem, large trees represent a lower number of producers, leading to an inverted pyramid shape because there are more herbivores. This means that while each ecosystem has a unique structure, the pyramid of number can be misleading regarding the actual functioning of the ecosystem and food chains.

Think of an office where the owner (the producer) has only one manager (herbivore), and this manager has many employees (secondary consumers). This setup resembles a forest’s food chain, while a park filled with flowers (many producers) and fewer bees (primary consumers) resembles a pond ecosystem. In both cases, the pyramid shows that a few large trees can support many more smaller creatures, but this doesn’t reveal the complex interactions within the office or park.

Pyramid of Biomass:

•The pyramid of biomass represents the relationship between different trophic levels in terms of biomass. •There is generally a gradual decrease in biomass of organisms at successive levels from the producers to the top carnivores. Thus, the pyramid of biomass is upright for the grassland ecosystem. •However, in case of a pond, as the producers are algae, which are least in number, this value gradually shows an increase towards the apex of the pyramid, thus making the pyramid inverted in shape.

The Pyramid of Biomass shows how the total mass of living organisms decreases as you move up trophic levels from producers to top consumers. In ecosystems like grasslands, there is a clear decrease in biomass, making the pyramid upright. However, in a pond ecosystem, the producers (algae) have less biomass compared to larger consumers such as fish, resulting in an inverted shape. This highlights that energy availability and storage varies greatly among different ecosystems.

Imagine a layer cake. The largest layer represents the biomass of producers; in a grassland, it’s thick, resembling an upright pyramid. In a pond, the cake has a narrow bottom layer (the algae) but a huge creamy top (larger fish), flipping our cake upside down. This layers analogy helps understand how energy and mass change from producers to consumers.

Pyramid of Energy:

•Of the 3 types of ecological pyramids, the energy pyramid gives the best picture of the overall nature of the ecosystem. In this type of pyramid, the trophic levels are decided based on the rate at which food is being produced. •In shape, it is always upright as, in most cases, there is always a gradual decrease in the energy content at successive trophic levels from producers to various consumers.

The Pyramid of Energy provides the most accurate representation of an ecosystem because it quantifies the energy available at each trophic level. Producers generate energy through photosynthesis, which decreases as this energy is consumed by herbivores (primary consumers) and then by carnivores (secondary and tertiary consumers). This consistent decrease in energy availability ensures that the pyramid maintains an upright shape, illustrating how energy is lost at each level.

Consider a campfire where the flames represent energy. Initially, there is a big blaze (producers) that elders use to cook food (herbivores), but as more food is prepared and shared (energy transfer), the flames dwindle. The pyramid of energy is like watching the campfire—over time, the flames (energy) decrease, just like the energy at each level of the food chain.

--