Ecosystems have trophic levels that describe the movement of energy. Trophic levels are the successive levels of organisms consuming one another that includes 4 levels; producers, primary consumers, secondary consumers, and tertiary consumers. Although not all organisms neatly fit into anyone level it gives a general overview of movement of energy through consumption.
Energy flow begins with sunlight that is absorbed by producers through photosynthesis. Producers are eaten by primary consumers. Next is secondary consumers who eat primary consumers. Lastly is tertiary consumers who eat secondary consumers.
A food chain is the sequence of consumption from producers through tertiary consumers.
A food web is a complex model of how energy and matter move between tropic levels.
An autotroph or producer, is an organism that produces complex organic compounds from simple substances present in its surroundings, generally using energy from light or inorganic chemical reactions. Autotrophs typically use photosynthesis which changes solar energy into oxygen and glucose.
Other organisms such as herbivores eat producers to fuel cellular respiration which is a process by which the chemical energy of "food" molecules is released and partially captured in the form of ATP. Carbohydrates, fats, and proteins can all be used as fuels in cellular respiration, but glucose is most commonly used as an example. Carbon dioxide is a byproduct of cellular respiration. Anaerobic respiration is the process of producing cellular energy without oxygen. Whereas aerobic uses oxygen.
Consumers or heterotrophs are organisms that derive its nutritional requirements from complex organic substances. Types of consumers include carnivores, omnivores, and herbivores. Carnivores eat other consumers. Omnivores eat both consumers and producers. Herbivores eat producers. Producers are organisms that use energy from the Sun to produce usable forms of energy.
Each trophic level eventually produces dead individuals and waste products. Three groups of organisms feed on this dead organic matter: scavengers, detritivores, and decomposers. Scavengers are organisms that eat dead animals. Detritivores, such as dung beetles, specialize in breaking down dead or waste tissues into smaller particles that can be processed by decomposers.
Environmental scientists measure the ecosystem's productivity using the gross primary productivity (GPP) and net primary productivity (NPP). GPP is the total amount of solar energy that producers in an ecosystem capture via photosynthesis over a given amount of time. NPP is the energy captured by producers in an ecosystem minus the energy producers respire.
net primary productivity = gross primary productivity - respiration by producers
Measurement of NPP allows us to compare productivity of different ecosystems. Producers grow best in environments with ample sunlight, water and nutrients, and warm weather.
Ecological efficiency is the proportion of consumed energy that can be passed from one trophic level to another. Ecological efficiency ranges from 5 to 20 percent averaging around 10 percent.