Introduction to Ecology: Ecological Pyramids

Relevance of the Theme

Ecological Pyramid is one of the central tools for understanding interactions and energy flow in ecosystems. It is a visual reflection of the thermodynamic laws that govern energy transfer, highlighting how different species interact and depend on each other. Understanding ecological pyramids is essential to unravel the secrets of biodiversity, ecosystem stability, and ultimately, it is crucial for the survival and maintenance of life on Earth.

Contextualization

• Ecology: Ecological Pyramids are strongly situated in the field of Biology, specifically in the area of Ecology and Ecosystems. This section naturally follows the study of energy and matter flows.
• The theme constitutes an important stage in the study of trophic levels, food chains, and webs, representing a visual way to understand the energy flow and trophic structure of an ecosystem.
• The ability to interpret and construct ecological pyramids not only deepens the understanding of ecological processes but also serves as a basis for subsequent themes, such as biogeochemical cycles, ecological succession, and biodiversity conservation.
• By understanding this topic, we will be in a better position to understand how human actions can affect ecosystems and, by extension, ourselves.

Theoretical Development

Components:

• Energy Pyramid: Represents the amount of energy available at each trophic level in an ecosystem. Energy decreases as it passes through trophic levels, due to heat loss during organism metabolism.

• Biomass Pyramid: Shows the amount of biomass (total mass of living organisms) present at each trophic level of an ecosystem. Biomass also decreases as we move to higher trophic levels, due to metabolic energy losses.

• Number Pyramid: Indicates the number of individuals at each trophic level of an ecosystem. Unlike energy and biomass pyramids, the number pyramid can be inverted in certain ecosystems, such as where there is a presence of parasites.

• Trophic Levels: Classify the organisms of an ecosystem based on their main food source. Producers occupy the first trophic level, primary consumers the second, secondary consumers the third, and so on.

Key Terms:

• Ecosystem: System formed by a community of organisms interacting with the physical environment that surrounds it.

• Primary and Secondary Development: The development of an ecosystem from scratch is called primary development, while subsequent development after a disturbance, such as a fire, is called secondary development.

• Biomass: The total amount of living organisms in a specific area or volume.

Examples and Cases:

• Food Chain of an Aquatic Ecosystem: We can build ecological pyramids to represent the food chains of a lake. Phytoplankton (producers) form the base of the energy and biomass pyramid, providing energy and food for zooplankton (primary consumers). These, in turn, serve as food for small fish (secondary consumers), which are then preyed upon by larger fish (tertiary consumers).

• Ecological Pyramid of a Forest: This pyramid would show that the highest amount of energy and biomass is in the lower trophic levels (producers and primary consumers), while the higher trophic levels contain less energy and biomass (secondary and tertiary consumers).

Detailed Summary

Key Points:

• Ecological Pyramids: They are graphical representations that demonstrate the relationship between organisms at different trophic levels within an ecosystem. There are three main types of ecological pyramids: energy, biomass, and number.

• Energy Pyramid: Shows the amount of energy flowing through the different trophic levels of an ecosystem. Each trophic level has less energy available than the previous trophic level, due to energy losses in the form of heat during organism metabolism.

• Biomass Pyramid: Represents the total mass of organisms at each trophic level. Like energy, biomass decreases as it moves to higher trophic levels, as the consumed energy is used for metabolism and lost as heat.

• Number Pyramid: Reflects the number of individuals at each trophic level of an ecosystem. It can be direct or inverted, depending on the proportion of organisms at each level.

• Trophic Levels: Classify the organisms of an ecosystem according to their position in the food chain. Producers are at the lowest trophic level, followed by primary, secondary, tertiary, quaternary consumers, and so on.

• Biomass Concept: Refers to the total amount of living organisms in a specific area or volume of an ecosystem.

Conclusions:

• Ecological pyramids provide a visual and intuitive way to understand energy flow and trophic structure in an ecosystem. They help us understand how energy and biomass decrease as they pass from one trophic level to the next, due to metabolic energy losses.

• Although ecological pyramids generally follow a pattern with energy and biomass decreasing as we move to higher trophic levels, the number pyramid can be inverted in certain situations, such as in ecosystems with many producers and few consumers.

• In the study of ecological pyramids, the concept of trophic levels and biomass is fundamental. Trophic levels help organize organisms within an ecosystem, while biomass provides a measure of the total number of organisms present.

Exercises:

1. Build an ecological pyramid for an ecosystem of your choice. Be sure to include producers, primary, secondary, and tertiary consumers.

2. Describe why the energy pyramid in an ecosystem is always a pyramid and never inverted.

3. Explain why the number pyramid can be both direct and inverted in different ecosystems. Give examples of each type.