CHAPTER 4: The functioning of the ecosystem and the role of a-biotic components

In the previous Chapter we have seen the importance of the non-living components of the environment. 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.

Figure 4.1: The organizational structure of living things

Since the time of the Greek philosopher and scientist Aristotle, born 384 BCE, animals and plants were classified according to their complexity. The science of classification is called Taxonomy, from the Greek word ‘taxis’ which means arrangement and the word ‘nomos’ which means law. In this hierarchical system, the broadest classification of life is domain and kingdom, and the most specific classification is genus and species. The hierarchical groupings in between include phylum, class, family and order.

The father of modern classification is Carl von Linne (1707-1778), was a Swedish professor of Botany at the University of Uppsala. He set up what has become known as the binomial system of classification, which involves the naming of individual organisms by two names, one for the genus and one for the species (the singular and plural are also species). The genus name is always a single word beginning with a capital letter e.g. Acacia. 

The species name can be a single or compound word, always beginning with a small letter e.g. Acacia karoo. If a few references are made one after the other to species from the same genus, such as Acacia in our example above, the genus name is not written out fully every time but represented by the initial only, such as A. karoo. Such names are written in italics. 

But 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. They classify the terrain of ecological research under six categories where the most inclusive category would be the biosphere and the smallest category, the individual organism.

The next level, that of Population, consists of all individuals within a species living in the same area (e.g., heard of antelope).

Communities are where individuals from different populations co-exist in the same habitat, for example (e.g., various antelope species and predators such as a pack of wolves as well as a population of rabbits, snakes, and a population of birds).

An Ecosystem includes the study of the interactions between communities and their entire environment in a specific locality (e.g., a riverine stretch inclusive of all its bio-physical components). Added to the animal and animal populations in an area, an ecosystem will include non-living elements like water, the clouds, soil, and rocks.

An Ecosystem includes the study of the interactions between communities and their entire environment in a specific locality (e.g., a riverine stretch inclusive of all its bio-physical components). Added to the animal and animal populations in an area, an ecosystem will include non-living elements like water, the clouds, soil, and rocks.

Figure 4.2: Classification of living things

Biomes consist of several related (associated) ecosystems, for example, the rivers, hills, and plains of the Savannah of Africa and their biotic communities; or the cold Tundra landscapes with their differently adapted vegetation and animal populations in the Northern hemisphere bordering the polar regions. 

Finally, the Ecosphere (or Biosphere) is the entire part of the earth where active life is found. This, include the atmosphere, the sea and surface water, as well as the land surface with its biota.

As stated before, the components of the Biosphere and all its ecosystems, communities, populations and species are not loose standing elements, but all are connected in a reciprocal dynamic way. Individual organisms are all connected with each other by a food chain.One can group organisms within an ecosystem by looking at the function they fulfil in the food network. In this context biotic components can be divided into producers, consumers, and decomposers.

Figure 4.3: Ecologists study organisms based on the role it fulfills in the ecosystem

The producers in an ecosystem are those organisms thatcan manufacture organic compounds from inorganic substances. These are green plants.Inorganic elements such as calcium, iron, etc. are taken up by the roots of plants and are synthesized into organic compounds such as starches and protein. It absorbs energy from the sun and through the process of  photosynthesis makes this energy available to animals in the form of fruits,seeds, leaves and other vegetative products.

Figure 4.4: The process of photosynthesis: Plants make the energy from the sun available to

Green plants are called autotrophs as they can function independentlyfrom other organisms. 

Figure 4.5: Biotic elements are linked together in a dynamic system by means of energy flow

They fill the position of the primary feeding level, the so-called Trophic level 1. Consumers are called heterotrophs and they rely on autotrophic organisms for their energy needs. They form subsequent feeding levels called Trophic levels 2, 3 and 4.

Plants are however responsible for many more functions in the ecosystem.By means of their roots they recycle nutrients. The roots of trees can transport nutrients from under the surface and store it in their stems and leaves.

Plants also release nutrients to the soil in the form of dead leaves that fall to the ground where it decomposes. 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 minimize the erosive effect of heavy rains and wind on the soil surface.

Consumers are thus dependent on producers for their energy needs. They can be divided into primary consumersand secondary consumers.Primary consumers are herbivores or plant-eaterslike rabbits and cattle, and secondary consumers are carnivores or meat-eaters like lions. Omnivores are both primary and secondary consumers like humans, baboons, and pigs.

Figure 4.6: Carnivores consume herbivores to supply in their energy needs.

Figure 4.7: Decomposers obtain their energy by consuming the corpses of animals or dead plant material

Those carnivores that kill their prey and eat it are called predators and those that eat the body-parts what is left by the carnivores are called scavengers like vultures and hyenas and can be named Trophic  level  4. 

Among decomposers in the soil there are macro-decomposers and micro-decomposers. Macro-decomposers 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 mineralswhich 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 organic compounds by means of the processes associated with photosynthesis.

 

In this way all biotic components are 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 an herbivore such as a rabbit, cow, or giraffe consumes vegetation, only a fraction of the energy that it receives from the green plant becomes part of his 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 and heat. 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 must eat many herbivores to get enough energy for its own life processes.

Figure 4.8:”The Rule of 10” – Energy is lost between each link of the food pyramid

Figure 4.9 In a Food Network individuals from various trophic levels may feed on the same prey.

Within each Trophic level there can obviously be a variety of populations e.g. worms, mice, many buck species of various populations, etc. The amount of energy is spread amongst all herbivores and its availability gets smaller and smaller. The same is true for carnivores due to the diversity of links in subsequent Trophic levels. The further up along the food chain there are many links in the food chain so that the animals at the end of the chain may 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. 

This is also why many animals are part of more than one food chain and eat more than one kind of food in order to meet their nutritional needs and energy requirements. This emphasises the importance of keeping the biodiversity of all ecosystems intact. These interconnected chains form a food web and become immensely complicated.

The fact that energy is lost at every transfer along the food-chain also has implications for human survival.  The shorter the food chain from which humans eat, the more likely there will be enough food (energy) to provide for the growing world population. The land that is used for meat-producing animals could be more effectively used to produce grain and vegetables to be directly used for human consumption.

Farmland already takes up half the habitable land on Earth. More and more land isbeing ploughed and deforested to grow fodder for cattle. If we are able to change our dietary habits to consume mostly plant-based rather than meat-based foods deforestation will stop, and biodiversity will have a chance to recover.

For too long have people acted with apathy and even contempt towards this message of respect for nature as it has not affected their daily lives or pockets directly.But as environmental deterioration accelerates and global warming leads to catastrophes such as floods, sporadic fires, extreme cold, and droughts, food production is hampered, and the cost of living isgoing up. These extreme events are eventually starting to get people’s serious attention.

Figure 4.10 Humans have the ability to appreciate and protect ecosystems or destroy it due to ignorance.

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 degradation that will lead to our demise.