Field guide training: Ecology – Part 3

A food chain is the linear flow of energy within an ecosystem. This usually starts with the producers (e.g. plants) who can produce their own food. These are first eaten by primary consumers (herbivores) who then serve as food for secondary consumers (carnivores). Tertiary consumers mainly eat secondary consumers, i.e. other carnivores.

The following relationship would be an example of such a food chain: a grasshopper eats the savannah grass and is eaten by a shrew. This serves a snake as prey, which in turn is hunted by the eagle.

This greatly simplified system of food relations can be supplemented by the component of the decomposers whereby the "chain" becomes a "cycle", because all dead organic substances (plant residues, faeces, animal carcasses, dead wood) are degraded by the decomposers and transported back to the beginning of the food chain as inorganic substances.

In general, the term food chain is rather controversial from a biological point of view. It can only be understood as the smallest unit of the food relationships within an ecosystem, but it can never describe the real relationships in nature. The various food chains must rather be linked to form a network that takes into account the innumerable interactions between the individual organisms. Not every organism has exactly one prey animal or one food plant, often there are, depending on specialization, (many) different food sources and different trophic levels depending on the point of view to which an organism belongs. Thus, a primary consumer may also be a secondary consumer at the same time, depending on the food specification it has in a particular habitat.

Typically, the individual linear energy flows intersect in a food web. This allows, for example, a much more realistic representation of what happens when one or more species disappear from an ecosystem or are replaced by other species. Applied ecology deals with simulation models that are supposed to find out more about this. Due to the increasing extinction of species because of climate change and environmental degradation, such models are becoming increasingly important as they can provide information on which animal and plant species are particularly important in a food web. This in turn provides a basis for decisions on species and nature conservation measures, i.e. decisions that every field and nature guide has to make.

As a field guide, it is important to know these relationships as they contribute to a basic understanding of energy flows and food relationships in nature.