As you prepare for the TASC Test Assessing Secondary Completion™ Science subtest, understanding the interactions, energy, and dynamics of an ecosystem is designated as a high emphasis topic.
An ecosystem is the interactions between living and non-living things in a particular environment. Ecology is the study of the relationship between living organisms and their ecosystem. Ecologists are scientists who study the relationships between the organisms and their ecosystems.
Interaction within an Ecosystem
Ecosystems have a host of living and non-living organisms within them. There are many different types of ecosystems on Earth:
- Sea and rocky shores
- Ponds and wetlands
- Arctic and alpine tundra
- Forests, and forests of coniferous and/or deciduous trees
- Tropical rain forests
Living organisms are always interacting with each other and non-living organisms in these ecosystems. On our planet, nothing can truly live on its own. All living things are connected and depend on each other and non-living things for survival.
For example, as humans, we depend on oxygen and water to survive. Both entities are non-living. Along with several other organisms, we use non-living things to build shelter.
Energy within an Ecosystem
Ecosystems maintain themselves by cycling energy and nutrients obtained from external sources, according to Annenberg Learner.
Within an ecosystem, there are several trophic levels (a feeding level within a food web). According to Annenberg Learner, “at the first trophic level, primary producers (such as plants, algae, and some bacteria) use solar energy to produce organic plant material through photosynthesis.”
Herbivores, animals that feed entirely on plants, make up the second trophic level. The third trophic level consists of predators that eat herbivores. This web continues if larger predators are present, as they represent the higher trophic levels.
Within certain ecosystems, there can be organisms that feed at several trophic levels. Bears are a good example as they eat salmon and berries. These organisms are in the highest trophic level.
Bacteria, fungi, molds, worms, and insects are all classified as decomposers. These organisms break down waste and dead organisms and return nutrients to the soil.
A visual representation of an energy flow within an ecosystem can be seen at Annenberg Learner.
At each trophic level, about 90% of the energy is lost. Shmoop.com gives us a good example that if a plant captures 1,000 calories of solar energy, a bug that eats the plant will only obtain 100 calories of energy. A chicken that eats the bug will only obtain 10 calories, and a human that eats the chicken will only obtain 1 calorie of the original 1,000 calories of solar energy captured by the plant.
In essence, it would take 100 1,000-calorie plants to produce a single 100-calorie piece of free-range chicken. Visit Shmoop.com for more on Earth’s ecosystem’s energy flow.
Ecosystems are dynamic in nature and always in a constant state of change. Ecosystems are subject to occasional disturbances, or could be in the process of recovering from past disturbances.
The tendency of a system to remain close to its equilibrium state, despite a particular disturbance, is called its resistance. Alternatively, the speed with which it returns to its initial state after a disturbance is called its resilience.
The frequency and severity of a particular disturbance determines the way it impacts an ecosystem. Examples of minor ecological disturbances are fires, flooding, windstorms, insect outbreaks and trampling.
Earthquakes, volcanic eruptions, tsunami, and the devastating effects of human impact on the environment like clearcutting, forest clearing, and poaching (leading to decreased or extinct animal populations) are examples of major ecological disturbances.