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Biomass and Ecological Pyramids

The combined weight of all species of plants and animals that may exist within an ecosystem make up what ecologists refer to as the biomass. Biomass is usually measured in dry weight per unit area, and ecologists use it to discover and compare the level of animal and plant activity and energy exchange in an ecosystem. Biomass is usually the highest at the bottom of the food web, with the producers, and decreases through herbivores and carnivores. Ecosystems have four basic trophic levels.

As shown in the accompanying diagram, the biomass of primary consumers is much less than the primary producers. Potentially, herbivores could eat all of the available biomass of plants in an ecosystem. The plant biomass that herbivores do consume, however, does not become part of the primary consumer biomass. 

Secondary consumers depend on the biomass of primary consumers or herbivores for their energy and nutrition requirements. Like the diagram shows, in an ecosystem there are much fewer secondary consumers than primary consumers. This is due to the fact that herbivores have, over time, developed many defences to prevent them from being eaten by carnivores. These defences include things like porcupine quills, and the ability of a snowshoe hare to change colours with the seasons.

Finally, tertiary consumers consume the biomass of primary carnivores and herbivores. Primary carnivores have also developed defense mechanisms such as sharp claws and the ability to run fast.

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