LESSON 5: The functioning of the biotic Component in the Ecosystem

In the previous lesson we have seen the importance of the non-living components of the ecosystem. In this lesson we will look at the living or biotic part of the environment. The concept “biotic” actually refers to all material that consists of carbon. It therefore also includes organisms that have deceased and those that have not yet even been discovered.

We are attracted to the beautiful colors, shapes and abilities of animals and plants. Even the structure and functioning of micro-organisms are fascinating. These outnumber by far visible plants and animals most of us are familiar with.

Figure 1: Scientists try to group organisms based on certain resemblances

There are different ways to categorize living things. Firstly there is the taxonomy method where organisms are grouped on the basis of their physical characteristics. Scientists use this ranking system to orderly arrange living things according to some scheme of resemblance. The basic classes living things are traditionally ranked into are referred to as “Kingdoms”.

Over the years the number of kingdoms has grown from two kingdoms, namely animals and plants, to
three kingdoms, namely animals, plants and Protista, which are microscopic single-celled organisms. Later scientists found more defining characteristics in single-cell organisms. For example, distinctions were made based on whether micro-organisms have distinct nuclei or displayed more animal or more plant characteristics, or distinction were made based on genetic characteristics.  Finally, the number of kingdoms have increased to six.

Over the ages many individuals contributed to this process. What Carolus Linnaeus, Jean Baptiste de Lamarck and Charles Darwin popularized during their lifetimes was the result of thousands of years of speculation, and who knows their views might still again be challenged as new species and interrelationships are being discovered.

Ecologists on the other hand have an integrated approach towards the natural environment. They are interested in the inter-relationships between different organisms as well as their impact on the habitat as a whole.

Figure 2: Living organisms can be studied at different levels of complexity. From least to most complex, these levels are (in an ecological context): Individual. Population. Community. Ecosystem. Biome. Biosphere. Biosphere. Biome. Ecosystem. Community. Population. Individual.

They classify the terrain of ecological research under five categories where the most inclusive category would be the ecosphere and the smallest category, the organism.

An organism is one single living thing (or species), for example a single wolf.

Populations are groups of the individual organisms belonging to the same species and living together in the same area, such as a pack of wolves.

Communities are where individuals from different populations co-exist in the same habitat, for example a pack of wolves, a population of rabbits, snakes and a population of birds. This also includes the unique vegetation from the area.

Ecosystems include both living and non-living things in an area. So, added to the plant-populations and animal-populations in an area, ecosystems will include non-living elements like water, the sun, clouds, soil, rocks and temperature. In an ecosystem, organisms compete with one another for survival. For example, both the wolf and the snake could be competing for mice; or both a big tree and a smaller shrub growing next to it could compete for sunlight. Each specie is uniquely adapted to the specific niche they occupy. This increases their chances for survival.

Finally, the ecosphere is the whole part of the earth where active life is possible. This, include the atmosphere, the sea and surface water, as well as the soil and the overlapping ecosystems that exist there.

Figure 3: Ecologists study organisms based on the role it fulfills in the ecosystem

One can also group organisms in an ecosystem by looking at the function they fulfill in the food network. In this context biotic components can be divided into producers, consumers or decomposers. The producers in an ecosystem are those organisms that are able to manufacture organic compounds from inorganic substances. Inorganic elements such as calcium, iron, etc. are taken up by the roots of plants and synthesized into organic compounds such as starches and protein. They are green plants or vegetation and they absorb energy from the sun through the process of photosynthesis and make this energy available to animals that consume them.

Green plants are therefore independent from other organisms to function while consumers are heterotrophic as they rely on autotrophic organisms for their energy needs.

Figure 4: Plants make the energy from the sun available to herbivores that consume them

Plants are however responsible for many more functions in the ecosystem. By providing shade, plants support the formation of organic content in soil and by means of their roots they recycle nutrients. Trees transport nutrients from deep under the surface and store it in their stems and leaves and eventually returns it to the surface in the form of dead leaves that fall to the ground where it decomposes and is in this way returned to the soil in the form of nutrients – available to shallower root systems of shrubs and grasses. Furthermore plants cool the surface as they provide shade. The shade further enhances the performance of micro-organisms to break down organic matter. Plant roots bind soil together and prevent erosion by floodwater.

Together with the canopy of leaves and grass cover, vegetation minimizes the erosive effect of heavy rains and wind on the soil surface.

Figure 5: Carnivores consume herbivores to supply in their energy needs.

Consumers are dependent on producers for their energy needs. They can be divided into primary consumers namely herbivores or plant-eaters and secondary consumers or meat-eaters, also known as carnivores. Omnivores are both primary and secondary consumers.

Those carnivores that kill their prey and eat it are called predators and those that eat what is left by the carnivores are called scavengers.

Figure 6: Decomposers obtain their energy by consuming the corpses of animals or dead plant material.

Among decomposers we get macro-decomposers which include for example earthworms and wood lice. The micro-decomposers consist of a large variety of bacteria, fungi and other single-cell organisms. Decomposers obtain their energy by consuming corpses of animals and dead plant material. They break the organic material down into inorganic elements or minerals which are then restored to the soil or water. These could then be taken up by the roots of plants from where it is transformed again into compounds by means of the processes associated with photosynthesis.

Figure 7: Biotic elements are linked together in a dynamic system by means of energy flow.

In this way all biotic components are somehow linked together in a dynamic functioning system by means of energy flow.

Food pyramids help us to visualize the transfer of energy in the food chain.When a herbivore such as a rabbit, cow or giraffe consumes vegetation, only a fraction of the energy that it receives from the green plant becomes new body mass. The rest of the energy is used by the herbivore to carry out its life processes such as movement, digestion and reproduction and some is released as waste. Therefore, when the herbivore is eaten by a carnivore such as a lion, leopard or fish eagle, the herbivore passes only a small amount (not more than 10%) of the total energy that it has received from green plants to the carnivore. The carnivore therefore has to eat many herbivores to get enough energy for its own life processes.

Figure 8: Energy is lost between each link of the food pyramid.

Because of the large amount of energy that is lost at each link, the amount of energy that remains available gets smaller and smaller the further along the food chain it goes. Therefore, if there are too many links in a single food chain the animals at the end of the chain could theoretically not get enough food to stay alive. It is for this reason that most food chains have no more than four or five links. Therefore, many animals are part of more than one food chain and eat more than one kind of food in order to meet their food and energy requirements. These interconnected chains form a food web. The flow of energy in food chains is graphically represented in food pyramids, but more on that in our next lesson.

The fact that energy is lost at every transfer along the food-chain also has implications on human survival.  The shorter the food chain from which humans eat, the more likely they will be be able to provide enough food for the growing world population. The stretches of land that provide fodder for meat-producing animals, could be more effectively utilized to suppoet the production of grain or vegetables to be used for direct human consumption.

The impact that human consumption has on the natural environment is so overwhelming that the very existence of life on earth seems to hinge on human behavior. Industrialization has enabled astronomic human population growth and it has been responsible for turning vast grasslands ecosystems into agricultural landscapes.  Because of deforestation we are not only losing natural habitats and biodiversity, but also natural oxygen producers and CO2 absorbers.

Figure 9: Humans have the ability to protect or destroy ecosystems.

As humans we have the ability to encourage the establishment and protection of ecosystems or to destroy it. If we are able to peacefully coexist with our pets we can also adapt our way of life towards harmonious co-existence with the various elements of nature.

For too long have people acted with apathy and even contempt towards this message of respect for nature as it has not affect their daily lives or pockets directly. But as environmental deterioration accelerates global warming resulting in regular floods, sporadic fires, extreme cold and the melting of ice caps, these are starting to get people’s attention at last.

The longer we wait to learn to adapt to harmonious interaction with nature the harder it will become to turn the downward spiral of environmental decay.