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Termite Nest : The gut of termites is filled with large numbers of bacteria, and this helps them digest the cellulose-based materials (eg wood) that they feed on. © Günther Eichhorn

Rainforest Ecology - The word comes from the Greek oikos meaning house and logos meaning study. Ecology is the scientific study of the interaction and relationship between living organisms and their environment. The rainforest is an ecosystem. Animals, plants, arthropods (eg insects and spiders), fungi, bacteria, Archaea, protists and viruses form a complex network of organisms, that use the local resources of their environment to survive. Most plants produce their own food through photosynthesis, animals and insects eat plants and each other. In the soil and humus, micro-organisms dominate and many feed on dead organisms.

Algae, superior plants, and some bacteria use photosynthesis, which is the conversion of the carbon-dioxide and water in carbohydrates and oxygen, using light as the energy source for the chemical process. This is the primary food-making process that sustains the rainforest (and in fact most life on Earth). Some Bacteria and Archaea, however, are able to produce their own food using energy entirely from chemical reactions, instead of solar energy. This is known as chemosynthesis.

Organisms that are able to produce their own food occupy what is called the first trophic level and are known as autotrophs. Organisms unable to produce their own food are known as heterotrophs.

Animals that feed exclusively on plants are known as herbivores, or primary consumers, and form the second trophic level. Animals that feed on herbivores are called carnivores, or secondary consumers, and
are the third trophic level. The fourth level is occupied by tertiary consumers, consisting of carnivores that live on other carnivores.

Fungi and bacteria fall into a category of consumer known as Decomposers. They obtain their energy by degrading or absorbing dead matter, or waste organic matter such as feces.

In ecosystems trophic levels are always the same, but the organisms that occupy each ecological niche may vary. For instance, on land - trees, shrubs and grasses are the autotrophs; while in the water - rivers, streams, lakes and ponds - this position is taken by algae (phytoplankton) and aquatic plants such as water lilies.

The rainforest canopy © Günther Eichhorn

Primary consumers in the forest can vary from small invertebrates such as caterpillars, to great mammals such as gorillas. In rivers and ponds fish, mollusks such as water snails, crustaceans such as shrimps, occupy this slot along with various types of protists. Many plants and algae act as the food source - from phytoplankton to fruit, seeds, and aquatic plants.

Typical secondary and tertiary consumers in the forest are carnivorous mammals, reptiles, birds, amphibians and insects; while in the rivers and lakes secondary and tertiary consumers are represented by fish, mollusks, arthropods (eg crabs), amphibians and reptiles.

Some consumers, for instance some of the great apes, are omnivorous and eat both animals and plants. They are considered, simultaneously, to be both primary/secondary or secondary/tertiary consumers.

The sequence of trophic levels represents the route by which energy is transferred in an ecosystem. This operates in a series of cycles. In each trophic level, energy is used in various activities and is dissipated largely in form of low-grade heat. Energy therefore never returns to the producers, because photosynthesis uses light and not heat. No simple energy cycle exists: the energy flow is through, rather than around, the system. Most life on Earth depends on a continuous supply of solar energy which is "fixed" in the first instance by photosynthesis and stored for use by other organisms. The energy passes through the ecosystem and is eventually re-radiated to space, mainly in the form of very low-grade infrared energy.

The transfer of energy through a series of living organisms is known as a Food or Trophic Chain. Food chains are not isolated and may be superposed, to become a Food or Trophic Web. The amount of energy stored at a particular trophic level is always higher than the amount transferred to the next level up. The reasons are that energy obtained by organisms is used in metabolism, a great part of which is dissipated as heat and can't be transferred to another trophic level. Also, part of the ingested food will not be assimilated, but will become feces.

This "leaking" of energy at each level is why a given habitat, in terms of biomass (the amount of living matter in a given environment), can maintain far fewer herbivores than it can plants, and far fewer carnivores than it can herbivores.

Mankind, however, through various practices such as farming and hunting can modify this natural balance. Usually with undesirable and often far-reaching consequences.