Energy Flow in Food Chains

Study Notes

Energy Flow in Food Chains

Energy decreases as you move up the food chain, with only 10% being transferred to each subsequent trophic level (10% Rule).
This is because energy is lost through processes like metabolism, respiration, and heat production at each trophic level.

Trophic Levels

Producers are organisms that produce their own food through photosynthesis (e.g., grass).
Consumers are organisms that obtain energy by consuming other organisms.
Herbivores are consumers that eat plants (e.g., grasshopper, frog).
Carnivores are consumers that eat other animals (e.g., snake, hawk).
Decomposers break down dead organisms and waste products, returning nutrients to the ecosystem (e.g., bacteria, fungi).

Pyramids of Numbers

Upright Pyramid of Numbers: The number of organisms decreases at each higher trophic level. (e.g., Trees → Birds → Parasites → Hyperparasites)
Inverted Pyramid of Numbers: The number of organisms in higher trophic levels is greater than in lower levels. (e.g., Tree → Frugivorous birds → Hawk). This is common in scenarios where the producer is large, like a tree, supporting numerous smaller herbivores.

Photosynthesis and Respiration

Compensation Point: The point at which the rates of photosynthesis and respiration are equal.
This means that the plant is producing the same amount of energy as it is consuming.

Net Primary Productivity (NPP)

NPP is the amount of energy that is stored in plant tissues after accounting for respiration losses.
It is calculated as NPP = APAR × LUE, where APAR is the amount of light energy absorbed by the plant (Absorbed Photosynthetically Active Radiation), and LUE is the plant's Light Use Efficiency (the proportion of absorbed light that is converted into biomass).

Eutrophication

Eutrophic Lakes: High levels of nutrients, leading to excessive algal blooms.
Oligotrophic Lakes: Low levels of nutrients, generally very clear water.
Mesotrophic Lakes: Moderate levels of nutrients, a balance between clear water and algal growth.
Hypereutrophic Lakes: Extremely high levels of nutrients, leading to severe water quality issues.

Trophic Cascades

The indirect effects of top predators on lower trophic levels in a food chain. For example, a decrease in the number of predators can have a cascading effect, increasing the number of herbivores and leading to overgrazing impacts on plants.

Energy Flow Through Food Chains

Energy decreases as you move up a food chain. This is due to the 10% rule, where only about 10% of energy from one trophic level is passed on to the next. The rest is lost as heat.

Trophic Levels

A hawk is a consumer and carnivore. It occupies the top trophic level and consumes other animals.

Ecological Pyramids

Trees → Birds → Parasites → Hyperparasites represents an inverted pyramid of numbers. This is because there are fewer organisms at each higher trophic level.
Tree → Frugivorous birds → Hawk represents an upright pyramid of numbers. This implies a higher number of producers at the base, followed by a decrease in each subsequent trophic level.

Photosynthesis and Respiration

At the compensation point, photosynthesis = respiration. This means the rate of photosynthesis is equal to the rate of respiration, resulting in no net production of organic matter.

Lake Types

Glacial lakes are typical examples of oligotrophic lakes. These lakes are nutrient-poor and have clear, cold water.

Population Dynamics and Food Chains

More number of grasshoppers than hawks can be supported. This reflects the concept of energy flow and the 10% rule, where a larger number of organisms at lower trophic levels can be sustained compared to higher levels.

Vegetarianism and Population

The 10% rule supports the idea that we can support a larger population if we all became vegetarians. This is because there's greater energy available in the food chain lower down, which can be used by humans if they consume plants rather than animals.

Net Primary Productivity

Net primary productivity (NPP) is calculated by subtracting the energy used for respiration (LUE) from the gross primary productivity (APAR): NPP = APAR - LUE. NPP represents the amount of organic matter created by plants that is available for other consumers in the ecosystem.

Description

Explore the dynamics of energy flow within food chains through various trophic levels. Understand the different roles of producers, consumers, and decomposers, as well as the significance of the 10% Rule and pyramid structures. This quiz will test your knowledge on these essential ecological concepts.