Question

Use the second law of thermodynamics (Concept 2-3B, p. 35) to help explain why predators are generally less abundant than their prey.

Short answer

Predators are less abundant than prey due to energy loss in trophic transfer, as per the second law of thermodynamics.

Step-by-step solution

Understanding the Second Law of Thermodynamics

The second law of thermodynamics states that energy transfer or transformation increases the entropy of a closed system. In ecological terms, energy transfer between trophic levels is never 100% efficient.

Energy Transfer Efficiency

When energy is transferred from prey (like plants) to predators, a significant portion of the energy is lost as heat. Typically, only about 10% of the energy from one trophic level is passed on to the next level.

Energy Availability for Predators

Since predators occupy a higher trophic level than their prey, they receive much less energy than what is available at the prey's trophic level. As a result, there is less energy available to support large populations of predators.

Resulting Population Dynamics

Due to the diminished energy available at higher trophic levels, there are fewer resources to sustain large numbers of predators, making them less abundant compared to their prey.

Key concepts

Energy Transfer Efficiency

The Second Law of Thermodynamics plays a key role in understanding energy transfer efficiency among different layers of the food chain. This scientific principle highlights that during energy transformation, some energy is inevitably lost, primarily in the form of heat. This loss of energy occurs every time it is transferred from one organism to another within an ecosystem.

In the context of energy transfer between trophic levels—say from plants (primary producers) to herbivores (primary consumers)—only around 10% of the consumed energy is converted into biomass that is available to the next trophic level. This means that if a plant absorbs a certain amount of solar energy, only a small fraction of that energy will be passed on to the herbivores that eat those plants.

This principle helps to explain why there is a steep decline in available energy as it moves up each trophic level, ultimately affecting the abundance and size of predator populations.

Trophic Levels

Trophic levels represent the positions organisms occupy in a food chain. The main trophic levels include producers at the base, followed by primary consumers, secondary consumers, and at the top, tertiary consumers or apex predators. Understanding trophic levels helps to clarify how energy flows through an ecosystem.

Starting from the bottom, primary producers like plants use photosynthesis to create energy, which is then consumed by herbivores, the primary consumers. Predators, or higher-order consumers, will consume these herbivores. However, with each step up the trophic levels, a significant portion of energy is lost, mostly from metabolic processes like respiration, and as discussed, only around 10% of energy is transferred to the next level.

This energy loss results in fewer resources being available for higher trophic levels, making it more challenging to maintain large populations of higher consumers such as predators.

Predator-Prey Dynamics

Predator-prey dynamics illustrate the complex interactions and dependencies within ecosystems. These dynamics are profoundly influenced by the energy transfer process and the structure of trophic levels.

Predators rely heavily on prey populations for sustenance, but since they receive less energy from their food sources than the prey themselves do, they are naturally less abundant. The scarcity of energy directly influences the population size and health of predator species.

This scarcity means that if prey populations decline, predator populations may experience even greater pressures, potentially leading to decreases in numbers.

• Predators need to work harder and spread out more to find enough prey to sustain their energy needs.
• The abundance of prey can lead to more predators surviving and reproducing, creating a balancing effect between predator and prey populations.

In this light, understanding predator-prey relationships also helps in ecosystem management and conservation efforts by maintaining the natural balance.