Energy Budgets

Ecological energetics examines the transformations of fixed, biological energy within communities and ecosystems, in particular, the manner in which biologically fixed energy is passed through the food web.

For example, studies of a natural oak-pine forest in New York found that the vegetation fixed solar energy equivalent to 11,500 kilocalories per hectare per year (10³ Kcal/ha/yr). However, plant respiration utilized 6.5 × 10³ Kcal/ha/yr, so that the actual net accumulation of energy in the ecosystem was 5.0 × 10³ Kcal/ha/yr. The various types of heterotrophic organisms in the forest utilized another 3.0 × 10³ Kcal/ha/yr to support their respiration, so the net accumulation of biomass by all of the organisms of the ecosystem was equivalent to 2.0 x 10³ Kcal/ha/yr.

The preceding is an example of a fixed-energy budget at the ecosystem level. Sometimes, ecologists develop budgets of energy at the levels of population, and even for individuals. For example, depending on environmental circumstances and opportunities, individual plants or animals can optimize their fitness by allocating their energy resources into various activities, most simply, into growth of the individual or into reproduction.

However, biological energy budgets are typically much more complicated than this. For example, a plant can variously allocate its energy into the production of longer stems and more leaves to improve its access to sunlight, or it could grow longer and more roots to increase its access to soil nutrients, or more flowers and seeds to increase the probability of successful reproduction. There are other possible allocation strategies, including some combination of the preceding.

Similarly, a bear must makes decisions about the allocation of its time and energy into activities associated with resting, either during the day or longer-term hibernation, hunting for plant or animal foods, seeking a mate, taking care of the cubs.