Biotic Factors Definition
The biotic factors of an ecosystem are the living organisms and the molecules they produce. Living things contain DNA, which code for proteins. These proteins carry out important biological chemical reactions, which create wide range of biomolecules, like fats, carbohydrates, and other cellular components. All of these products of DNA, and the organisms themselves are biotic factors.
Biotic Factors and the Ecosystem
Within every ecosystem, there are two types of factors, biotic factors and abiotic factors. The abiotic factors are all of the non-living things within the environment. This can be things like the minerals within the soil, the climate, and natural disasters. The biotic factors react to and influence the abiotic factors of any given environment.
In the following examples, look for interactions between biotic factors and abiotic factors. Sometimes the biotic factors are influenced by things like weather, pH, and the general conditions of their environment. In other cases, the biotic factors change and morph the environment, changing the general conditions as they do so. Biotic factors, unlike abiotic ones, interact in the environment in a way which tends to keep the system in flux.
Examples of Biotic Factors
A Grassy Hillside
Though it might not look like much, a simple grassy hillside is a perfect example of biotic factors altering what changes take place in an environment. If you are lucky enough to live next to a beautiful grassy hillside, look out your window. If not, check out the one below.
The easiest way to imagine the effects of the biotic factors is by taking them away. In this picture, there are only a few easily visible biotic factors. Imagine first that all of the trees were gone. These biotic factors take up nutrients from the ground, but they also provide shade and shelter for other organisms. Their high canopies collect water, directing it to plants below. Without the trees, the biotic factors below them disappear as well. Take away the grass, and you are left with nothing but dirt.
Using your microscope, you could see many more biotic factors in the soil itself. Small insects, bacteria, and a whole underground ecosystem. These biotic factors are harbored and supplied by the roots of the plants. Without the grass, the other organisms would not survive, and only barren minerals would be left. Without the roots, the topsoil would also blow away in the wind, turning the ground into hard rocks and compacted dirt. Any rain would quickly wash away remaining minerals and nutrients, carrying them eventually to the ocean.
As you can see, the abiotic factors of this environment (soil, water, etc.) are quickly changed as the biotic factors disappear. The biotic factors are therefore influencing the distribution, use, and arrangement of the other factors, and changing their environment to better suit life.
Under the waves of the ocean, things are very similar. The non-living factors most important in the open ocean are sunlight, nutrients, and oxygen. The biotic factors of the open ocean require all three for communities to survive. In this case, it is even easier to see how active the biotic factors are in changing the environment.
In the ocean, the food web is mainly based on algae. These small photosynthesizing autotrophs use energy from the sun to produce sugars and other biologically important molecules. In doing so, they create a small amount of oxygen but use many nutrients. Sometimes, if the nutrients like nitrogen and phosphorous are heavy, these algae will form dense algal blooms. These blooms can be a boon for other species, which come to feed on the massively expanding algae.
However, these blooms can sometimes turn deadly. If all the conditions are just right, the biotic factors can completely change the non-living factors within the environment. When algal blooms are thick, the algae become densely clustered together, in an attempt to capture the sun’s rays. Eventually, the top layer of dense algae completely blocks out the sun. The algae below start to die and drop to the bottom.
Here, a number of small organisms and bacteria rapidly consume the decaying algae. They gather in such numbers and reproduce so fast, they start to deplete the oxygen of water. If the algal bloom is large enough, these biotic factors can create vast zones completely depleted of oxygen. Many organisms, even large sharks and fish, will die if they try to pass through it. This is an extreme case of how the biotic factors of an environment change the abiotic factors.
Biotic Factors throughout Evolutionary History
Life (a.k.a. biotic factors) has been present on this planet for roughly 4,000,000,000 years. The planet before this had no biotic factors. It was essentially a barren rock, with vast oceans, and a slight atmosphere, barely capable of deflecting the sun’s most harmful rays. Then, life happened. The biotic factors started to expand. With them, they brought drastic changes to the environment.
Above is a graph of the oxygen content of the atmosphere, since life first evolved nearly 4 billion years ago. As you can see, for nearly 1.5 billion years, the oxygen content on Earth remained at zero. However, as Earth entered Stage 2 (see graph), something profound happened. Some of the organisms evolved the ability to photosynthesize. During Stages 2 and 3, the oxygen produced by these organisms is rapidly absorbed into the oceans, rock, and atmosphere. An Ozone layer is created, which greatly protects the Earth’s surface from harmful UV radiation.
By the end of stage 3, the oxygen has completely saturated everything it can and begins to fill the atmosphere. This leads to mass extinction, and many of the anaerobic biotic factors are killed off. However, oxygen-based metabolisms are also very efficient. This massive change in the atmosphere and the quality of sunlight leads to an explosion of lifeforms. Around this time, many multicellular lifeforms were taking shape. These biotic factors eventually exploded onto land, gradually transforming the rocky landscape into productive ecosystems with layers of nutrient-rich topsoil.