The 10% rule in energy transfer is a key concept in ecology, indicating that in an ecosystem, approximately 10% of the energy from one trophic level is transferred to the next.

To elaborate, the 10% rule describes the flow of energy within a food chain. It posits that when energy is transferred from one trophic level to another, only about 10% of that energy is successfully passed along, while the remaining energy is lost, primarily as heat. This phenomenon is rooted in the second law of thermodynamics, which states that during any energy transfer or transformation, a considerable amount of energy is dissipated as heat.

For instance, if a plant captures $1000$ units of sunlight energy, it manages to convert roughly $100$ units into chemical energy through the process of photosynthesis. When a herbivore consumes this plant, it can assimilate only about $10$ units of that energy. Subsequently, if a carnivore feeds on the herbivore, it receives merely $1$ unit of energy. This energy loss at each trophic level explains why food chains typically consist of only four or five trophic levels; there is insufficient energy to sustain additional levels.

Additionally, the 10% rule clarifies why there tend to be fewer organisms at higher trophic levels. With diminishing energy availability at each successive level, the number of organisms that can be supported decreases. For example, a field may sustain thousands of plants, but only hundreds of herbivores, and just tens of carnivores.

Overall, the 10% rule is a fundamental principle for understanding energy flow within ecosystems. It has significant implications for the structure and function of ecological communities and is crucial for wildlife management and conservation efforts, as it aids in determining the carrying capacity of various habitats.