Ecology is the study of the interaction between living things and their environment. The environment of an organism includes the living and non-living factors. For example, a frog’s environment would include the living parts: the flies it eats, the plants it uses as shelter, it’s fellow frogs, etc, and the non-living parts: the water temperature, the amount of minerals, the sun, the humidity. An ecosystem is a group organisms and their environment, i.e. ecology is the study of ecosystems. The earth itself is a great big ecosystem, although not all of it can sustain life. The parts of the earth where life can grow is called the biosphere. The living part of an ecosystem is called the biotic component. The different organisms within that group can then be organised in an other subsection group. There are
1. Producers, which make their own food, e.g. plants
2. Consumers, they feed on other plants and animals, e.g. fox
3. Decomposers, they feed on dead and decaying plants and animals, e.g. fungi
The term abiotic refers to the non living in an ecosystem.

Example of Grazing Food Chain (taken from New Senior Biology)

Example of Detritus Food Chain (taken from New Senior Biology)

The primary source of energy is the sun. All organisms need energy to live. Organisms pass down energy using feeding relationships. The producers absorbe the sun’s energy to make their food. These producers are then eaten by the primary consumers (herbivores), who in turn are eaten by the secondary consumers (carnivores), who are then eaten by the tertiary consumers (top carnivores). We use food chains to describe the feeding relationship and passing down of energy from one organism to the next. An example of a food chain would be: (Sun–>) Grass–> Rabbit–> Fox . The sun is always the beginning of the food chain, but since it always where the producer gets it’s energy, it is not noted when food chains are written.  There are two types of food chains, a grazing food chain and a detritus food chain. The grazing food chain is when a primary consumer eats a live plant, and a detritus food chain is when the primary consumer eats detritus (dead organisms). In nature, food chains can interconnect, and two or more interconnecting food chains are then called food webs.

When the plant (producer) takes in energy from the sun, it is used for food and new cells. However, most of the energy escapes as heat. This means that the primary consumer does not get all the energy, and after a while, the sun’s energy has been completely used. Out of all the energy absorbed by the plant, only 10% is used for growth and food. And when the plant gets eaten, only 10% of the plant’s absorbed energy gets taken in, i.e. animal gets 10% of the 10% of the sun’s energy the plant used for growth and food. This continues, each animal passing down less energy than what they received, until eventually, no more energy can be passed down. This means that food chains cannot contain more than four or five levels. This flow of energy is called trophic levels. In food chains, the further you get, the less organisms there are in the species. There are less animals as you go up because the energy available to the tertiary consumer is less than that available to the producers, i.e. the tertiary consumer doesn’t have enough energy available to produce more of its species, to sustain it’s self it has to eat a lot of secondary consumers, who ate a lot of primary consumers, who as well ate a lot of producers.

References: New Senior Biology, Wikipedia

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