Energy flow (ecology)

[4][5] Trophic dynamics relates to thermodynamics because it deals with the transfer and transformation of energy (originating externally from the sun via solar radiation) to and among organisms.

[1] The first step in energetics is photosynthesis, where in water and carbon dioxide from the air are taken in with energy from the sun, and are converted into oxygen and glucose.

[7] Cellular respiration is the reverse reaction, wherein oxygen and sugar are taken in and release energy as they are converted back into carbon dioxide and water.

[10] Chemosynthetic bacteria can use the energy in the bonds of the hydrogen sulfide and oxygen to convert carbon dioxide to glucose, releasing water and sulfur in the process.

[13] Another factor controlling primary production is organic/inorganic nutrient levels in the water or soil that the producer is living in.

There is also a large amount of energy that is in primary production and ends up being waste or litter, referred to as detritus.

The detrital food chain includes a large amount of microbes, macroinvertebrates, meiofauna, fungi, and bacteria.

[16] Primarily herbivores and decomposers consume all the carbon from two main organic sources in aquatic ecosystems, autochthonous and allochthonous.

[17] Secondary production is often described in terms of trophic levels, and while this can be useful in explaining relationships it overemphasizes the rarer interactions.

[18] In an aquatic ecosystem, leaf matter that falls into streams gets wet and begins to leech organic material.

The leaves can be broken down into large pieces called coarse particulate organic matter (CPOM).

The detritovores make the leaf matter more edible by releasing compounds from the tissues; it ultimately helps soften them.

[20] Research has demonstrated that primary producers fix carbon at similar rates across ecosystems.

Among aquatic and terrestrial ecosystems, patterns have been identified that can account for this variation and have been divided into two main pathways of control: top-down and bottom-up.

[22][23] The acting mechanisms within each pathway ultimately regulate community and trophic level structure within an ecosystem to varying degrees.

[23] The strength of bottom-up controls on energy flow are determined by the nutritional quality, size, and growth rates of primary producers in an ecosystem.

[14][22] Photosynthetic material is typically rich in nitrogen (N) and phosphorus (P) and supplements the high herbivore demand for N and P across all ecosystems.

[26] Aquatic primary production is dominated by small, single-celled phytoplankton that are mostly composed of photosynthetic material, providing an efficient source of these nutrients for herbivores.

[22] In contrast, multi-cellular terrestrial plants contain many large supporting cellulose structures of high carbon but low nutrient value.

[22] As phytoplankton are consumed by herbivores, their enhanced growth and reproduction rates sufficiently replace lost biomass and, in conjunction with their nutrient dense quality, support greater secondary production.

[22] Additional factors impacting primary production includes inputs of N and P, which occurs at a greater magnitude in aquatic ecosystems.

[24] Allochthonous material washed into an aquatic ecosystem introduces N and P as well as energy in the form of carbon molecules that are readily taken up by primary producers.

[27] Access to nutritious food sources enhances herbivore metabolism and energy demands, leading to greater removal of primary producers.

[27] This results in greater top-down control because consumed plant matter is quickly released back into the system as labile organic waste.

[27] Herbivore avoidance of low-quality plant matter may be why terrestrial systems exhibit weaker top-down control on the flow of energy.