Ecological efficiency – Definition, Factors, Calculation, Applications

What is Ecological efficiency?

• Ecological efficiency, also known as Lindman’s efficiency, is a measure that quantifies the effectiveness with which energy is transferred between different trophic levels in an ecosystem. It accounts for the combined efficiencies of resource acquisition and assimilation by organisms within the ecosystem.
• In any trophic structure, there is a noticeable decrease in the amount of energy available at each successive trophic level. This decline can be attributed to two main factors. Firstly, as energy is passed from one level to another, a portion of it is lost through respiration and metabolic processes within organisms. Secondly, energy is also lost as heat during the transformation from lower to higher trophic levels.
• Ecological efficiency is calculated by comparing the amount of energy acquired from the lower trophic level with the amount of energy transferred to the higher trophic level. Lindman, who first defined these ecological efficiencies in 1942, proposed the 10% rule. According to this rule, if autotrophs produce 100 calories of energy, herbivores will only be able to store 10 calories, and carnivores will obtain 1 calorie. It is important to note that ecological efficiencies can vary slightly in different ecosystems, ranging from 5% to 35%.
• The concept of ecological efficiency is crucial for understanding the flow of energy through ecosystems and the dynamics of trophic interactions. It highlights the limitations and constraints imposed by energy transfer and transformation within the food web. By quantifying the efficiency of energy transfer, ecologists can better comprehend the overall functioning and stability of ecosystems.

Energy transfer

Energy transfer in an ecosystem is a fundamental process that involves the flow of energy from one trophic level to another. The energy originates from primary production, which occurs in autotrophic organisms such as plants and algae. These photoautotrophs convert solar energy into chemical energy through the process of photosynthesis, which takes place in the chlorophyll of green plants. The energy stored in carbon compounds is then passed on to other organisms as they consume members of lower trophic levels.

Primary production can be divided into gross primary production and net primary production. Gross primary production represents the total energy harvested by photoautotrophs from the sun. For instance, if a blade of grass absorbs x joules of energy from the sun, the portion of that energy converted into glucose reflects the gross productivity of the grass. The energy remaining after accounting for respiration is considered the net primary production. Gross production refers to the energy within an organism before respiration, while net production refers to the energy after respiration. These terms are applicable to both autotrophs and heterotrophs when describing energy transfer.

Energy transfer between trophic levels is characterized by inefficiency. The net production at one trophic level is typically only 10% of the net production at the preceding trophic level, known as the Ten percent law. Various factors contribute to this energy loss, including non-predatory death, egestion (defecation), and cellular respiration. Consequently, a significant amount of energy is lost to the environment instead of being absorbed and utilized by consumers. The fractions in the figure provided approximate the energy available after each stage of energy loss in a typical ecosystem, although these values can vary significantly across ecosystems and trophic levels. It is common for living systems to experience an energy loss by a factor of one half in each step, such as non-predatory death, defecation, and respiration.

To illustrate, let’s consider an example where trophic level 1 produces 500 units of energy. Half of this energy is lost due to non-predatory death, leaving 250 units to be consumed by trophic level 2. Half of the ingested energy is then expelled through defecation, resulting in 125 units available for assimilation by the organism. Of this remaining energy, half is lost through respiration, and the rest (63 units) is utilized for growth and reproduction. The energy expended for growth and reproduction represents the net production of trophic level 1, which is calculated as 500 * (1/2) * (1/2) * (1/2) = 63 units.

Overall, energy transfer in ecosystems involves a gradual decrease in available energy as it moves up the trophic levels, with only a fraction of energy being passed on from one level to the next. Understanding these energy dynamics is crucial for comprehending the functioning and stability of ecosystems.

Ecological efficiency Quantification

Ecological efficiency can be quantified by considering several related efficiencies that capture different aspects of resource utilization and biomass conversion in an ecosystem.

1. Exploitation efficiency: This efficiency measures the amount of food ingested by consumers divided by the amount of prey production. It is represented as Ingestion (In) divided by Prey production (Pn-1): In/Pn-1.
2. Assimilation efficiency: Assimilation efficiency quantifies the amount of assimilated food divided by the amount of food ingested. It is represented as Assimilation (An) divided by Ingestion (In): An/In.
3. Net Production efficiency: Net production efficiency reflects the amount of consumer production (biomass) divided by the amount of assimilation. It is represented as Production (Pn) divided by Assimilation (An): Pn/An.
4. Gross Production efficiency: Gross production efficiency is calculated by multiplying assimilation efficiency by net production efficiency. It represents the amount of consumer production divided by the amount of ingestion. It is represented as Pn/In.
5. Ecological efficiency: Ecological efficiency encompasses exploitation efficiency, assimilation efficiency, and net production efficiency. It is calculated by multiplying exploitation efficiency by assimilation efficiency and net production efficiency. Ecological efficiency represents the amount of consumer production divided by the amount of prey production. It is represented as Pn/Pn-1.

While the mathematical relationships above provide a theoretical basis for calculating ecological efficiency, obtaining accurate measurements of the values involved can be challenging. For example, assessing ingestion requires knowledge of the total amount of food consumed in an ecosystem and its caloric content, which is often difficult to measure precisely. In many cases, ecologists have to rely on educated estimates, particularly for ecosystems that are inaccessible or lack measurement tools. As a result, ecological efficiency is often approximated rather than precisely measured. However, for most ecosystems, an approximation is sufficient to gain a general understanding of how energy flows through trophic levels and the efficiency of resource utilization.

Factors that affect ecological efficiency

Several factors can affect ecological efficiency in an ecosystem. Here are some key factors:

• Trophic structure: The structure of the food web and the number of trophic levels within an ecosystem can influence ecological efficiency. Longer food chains with more trophic levels often result in lower efficiency due to increased energy losses.
• Species interactions: Interactions between species, such as predation, competition, and symbiosis, can affect ecological efficiency. Predation can transfer energy from one trophic level to another, while competition for resources may limit energy acquisition and efficiency.
• Resource availability: The availability of resources, such as food, water, and nutrients, can impact ecological efficiency. Abundant resources can support higher efficiency, while scarcity or fluctuations in resource availability can decrease efficiency.
• Environmental conditions: Environmental factors like temperature, precipitation, and light availability can influence ecological efficiency. Optimal environmental conditions can enhance energy capture and transfer, while extreme or unfavorable conditions can reduce efficiency.
• Energy loss processes: Energy losses through respiration, metabolism, excretion, and heat production can significantly impact ecological efficiency. The efficiency of these processes varies among organisms and can affect the overall efficiency of energy transfer.
• Physiological characteristics: Organisms with different physiological traits and adaptations can have varying efficiencies. For example, species with more efficient digestive systems or higher metabolic rates may have higher ecological efficiency.
• Habitat quality: The quality and productivity of habitats can influence ecological efficiency. Productive and diverse habitats with ample resources and suitable conditions tend to support higher efficiency compared to degraded or impoverished habitats.
• Human activities: Human activities, such as habitat destruction, pollution, and climate change, can disrupt ecosystems and reduce ecological efficiency. Anthropogenic factors can alter trophic interactions, decrease resource availability, and increase energy losses.
• Successional stage: Ecological efficiency can change during ecological succession as the structure and composition of communities change over time. Early successional stages may have lower efficiency due to limited resources and unstable interactions.
• Spatial and temporal dynamics: Ecological efficiency can vary across spatial scales and over time. Factors such as migration, seasonal changes, and natural disturbances can impact energy flow and efficiency in different ways.

It’s important to note that these factors interact and can have complex effects on ecological efficiency. The specific combination of factors operating in an ecosystem determines its overall efficiency and functioning.

What is Ten percent law?

The “ten percent law” is a concept in ecology that describes the transfer of energy from one trophic level to the next in a food chain. While Raymond Lindeman is often attributed to this idea, he did not specifically term it a “law” and reported a range of ecological efficiencies from 0.1% to 37.5%. According to this principle, only about ten percent of the energy transferred from one trophic level to the next is stored as biomass, while the rest is lost through various processes.

When organisms are consumed, approximately ten percent of the energy in their food is fixed into their flesh and becomes available to the next trophic level, which consists of carnivores or omnivores. This pattern continues as each successive consumer in the food chain consumes the previous consumer, with only about ten percent of the energy fixed in their flesh for the higher level.

For instance, if the sun releases 10,000 J of energy, plants would take in only 100 J (1% of energy) from sunlight. Then, a deer consuming the plant would obtain 10 J (10% of energy) from it. If a wolf were to consume the deer, it would acquire only 1 J (10% of energy from the deer). Following this pattern, if a human were to eat the wolf, they would receive 0.1 J (10% of energy from the wolf), and so on.

The ten percent law provides a fundamental understanding of energy flow in food chains and demonstrates the inefficiency of energy capture at each successive trophic level. It suggests that the preservation of energy efficiency is best achieved by obtaining food from lower trophic levels, as closer proximity to the initial energy source allows for greater energy capture.

The formula for calculating energy at a particular trophic level is: Energy at n(th) level = (energy given by the sun)/(10)^(n+1), and, Energy at n(th) level = (energy given by the plant)/(10)^(n-1).

This formula illustrates the exponential decrease in available energy as one moves up the trophic levels in a food chain.

Applications

The concept of ecological efficiency has practical applications in various fields, particularly in agriculture and food production. By understanding and improving ecological efficiency, economic benefits can be realized, and more sustainable practices can be developed. Here are some notable applications:

1. Agricultural Efficiency: In agricultural environments, maximizing energy transfer from food producers (plants) to consumers (livestock) can have significant economic advantages. This has led to the emergence of a sub-field in agricultural science that focuses on monitoring and enhancing ecological and related efficiencies in livestock production.
2. Livestock Selection: Studies comparing the net efficiency of energy utilization in cattle have shown that breeds historically raised for beef production, such as Hereford, outperform breeds raised for dairy production, such as Holstein. Beef cattle have a higher capacity to convert energy from feed into stored energy as tissue (body fat), making them more efficient in utilizing feed resources compared to dairy cattle. These findings suggest that cultivating cattle for slaughter is a more efficient use of feed than raising them for milk production.
3. Energy Efficiency Comparison: When comparing animal husbandry (livestock) with plant agriculture, it is important to consider the differences in energy efficiency. While caloric concentration in fat tissues is higher than in plant tissues, the energy required to cultivate feed for livestock is only partially converted into fat cells, with the rest being respired or egested by the animals. This leads to a lower overall energy efficiency compared to plant agriculture.
4. Energy Use in Food Production: Energy use in food production is a significant contributor to the total energy consumption. In the United States, approximately 10.5% of the total energy usage in 1999 was attributed to food production, considering both the producer and primary consumer trophic levels. Understanding and improving energy efficiency in food production can help reduce energy consumption and environmental impact.
5. Efficiency of Different Food Sources: There is a substantial difference in energy efficiency when comparing the cultivation of animals (livestock) with plants. The conversion of input energy into edible kilocalories is significantly higher in plant-based food sources compared to animal-based sources. For example, potatoes, corn, and soy exhibit higher energy efficiency, converting a larger percentage of input calories into calories that can be utilized by humans, while animal sources like chicken, grass-fed beef, farmed salmon, and shrimp have lower energy conversion rates. This highlights the importance of considering the energy efficiency and ecological impacts of different food choices.

Overall, understanding and improving ecological efficiency in agriculture and food production can help optimize resource utilization, reduce environmental impacts, and contribute to more sustainable and efficient food systems.

FAQ