Course handout Degradation and conservation of ecosystems (DCE) : Ineeded for master 2 of Applied Microbiology students
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Date
2025
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Faculty of Sciences
Abstract
The structure of ecosystems can be visualized with ecological pyramids, which were first
described by the pioneering studies of Charles Elton in the 1920s. Ecological pyramids show
the relative amounts of various parameters (such as number of organisms, energy, and biomass)
across trophic levels.
Pyramids of numbers can be either upright or inverted, depending on the ecosystem. As
shown in Figure 7, typical grassland during the summer has a base of many plants and the
numbers of organisms decrease at each trophic level. However, during the summer in a
temperate forest, the base of the pyramid consists of few trees compared with the number of
primary consumers, mostly insects. Because trees are large, they have great photosynthetic
capability, and dominate other plants in this ecosystem to obtain sunlight. Even in smaller
numbers, primary producers in forests are still capable of supporting other trophic levels.
Another way to visualize ecosystem structure is with pyramids of biomass. This pyramid
measures the amount of energy converted into living tissue at the different trophic levels. Using
the Silver Springs ecosystem example, this data exhibits an upright biomass pyramid (Figure 8),
whereas the pyramid from the English Channel example is inverted. The plants (primary
producers) of the Silver Springs ecosystem make up a large percentage of the biomass found
there. However, the phytoplankton in the English Channel example make up less biomass than
the primary consumers, the zooplankton. As with inverted pyramids of numbers, this inverted
pyramid is not due to a lack of productivity from the primary producers, but results from the
high turnover rate of the phytoplankton. The phytoplankton are consumed rapidly by the
primary consumers, thus, minimizing their biomass at any particular point in time. However,
phytoplankton reproduce quickly, thus they are able to support the rest of the ecosystem.
Pyramid ecosystem modeling can also be used to show energy flow through the trophic
levels. Notice that these numbers are the same as those used in the energy flow compartment
diagram in Figure 8. Pyramids of energy are always upright, and an ecosystem without
sufficient primary productivity cannot be supported. All types of ecological pyramids are useful
for characterizing ecosystem structure. However, in the study of energy flow through the
ecosystem, pyramids of energy are the most consistent and representative models of ecosystem
structure (Figure 8).