Every spring, when the weather is still yet cool, I like to take our STEM Club outdoors for more in-depth, hands-on ecology lessons. This year, to align with the International Year of Soils, we are focusing on soil ecology.
As I begin each ecology study, we review the cycles of energy and nutrients. Ecosystems are characterized by different cycles that enable organisms to survive. Plants and animals interact with each other and with their environment through these important ecosystem cycles.
- Energy Cycle
- Carbon and Oxygen Cycle
- Nitrogen Cycle
- Water Cycle
- Disturbance Cycle
The Energy Cycle
An ecosystem is a type of community in which all of the plants and animals that live in it either feed off each other or depend upon one another in some way. Just as people interact and depend on each other in our communities. In each ecosystem, there are different feeding levels called trophic levels: primary producers (or plants) that convert energy from the sun through photosynthesis, primary consumers (herbivores), secondary consumers (animals that eat the primary consumers), tertiary consumers (animals that each both primary and secondary consumers), and decomposers that break down dead or dying matter into nutrients that can be used again by producers.
The Carbon and Oxygen Cycle
Another important cycle in an ecosystem is the carbon and oxygen cycle. Each of these elements is needed in order for plants and animals to live. Plants take in carbon dioxide during the process of photosynthesis. They use the carbon from carbon dioxide to make food which provides matter and energy to make new plant cells. During respiration plants take in carbon dioxide, a gas they need to live, and release oxygen. Animals breathe in oxygen, a gas they need to live, and release carbon dioxide. Dead plants and animals release carbon dioxide during the decaying process. The carbon is stored as fossil fuels that include coal, gas, and oil.
The Nitrogen Cycle
Nitrogen is a gas that makes up about 78% of the air we breathe. It is an important part of proteins and other plant and animal matter. Plants and animals cannot use nitrogen directly from the air. The nitrogen must be changed into a form that plant roots can take up and use. Certain bacteria, like lichen, are able to take nitrogen from the air and change it into a form that plants can use. The process of changing nitrogen into a form that plants can use is called nitrogen fixation. The bacteria break down the nitrogen containing tissues of dead plants and animals and change them into nitrates. Plants absorb the nitrates through their roots and release nitrogen gas back into the air.
The Water Cycle
Organisms need water to survive. The water cycle is very important in an ecosystem. The water cycle is the movement of water from the ocean to the atmosphere to land and back to the ocean. An ecosystem, especially a wetland or forest, is essential to the water cycle because it stores, releases, and filters the water as it passes through the system.
There are three steps to the water cycle:
- Evaporation occurs when the sun heats the water in soil, rivers, lakes, and oceans, causing it to evaporate and become water vapor, which is a gas.
- Condensation occurs when water vapor rises, cools, and condenses to form tiny water droplets or ice crystals in clouds.
- Precipitation occurs when the water falls back to earth as rain, snow, or other precipitation. Most water returns to the sea or sinks into underground water sources.
The Disturbance Cycle
A regular cycle of events including fires, floods, landslides, and storms keep every ecosystem in a constant state of change and adaptation. Although the disturbance cycle can cause disruption, some species depend on this cycle for survival and reproduction. For example, some forests depend on fire for reproduction. The cones of the trees are sealed shut around the seed with a resin that will only dissolve under very high temperatures such as those caused by fires. Another example is flooding. Flooding, in some areas like the Nile Delta in Egypt, brings rich nutrients to the soil.
It is a delicate balance within each ecosystem. Competing for food, water, light, and other resources is how plants and animals stay in balance. This balance is called homeostasis.
If a new plant or animal is brought into an ecosystem, where it did not exist before, it competes with the existing organisms for available resources. The new plant or animal can out compete other organisms and cause them to become extinct by breaking the chain and thereby affecting other organisms that depended on the extinct organisms for food.
When an ecosystem functions smoothly, there are many benefits to people including healthy forests, streams, and wetlands which contribute to clean air and water. The survival of healthy ecosystems, however, is sometimes threatened by human activities that include deforestation, filling of wetlands, damming rivers, and polluting the air, soil, and water. Today, there are government agencies and other organizations that work to manage and protect Earth’s natural resources and ecosystems.
Bring it Home
Review the cycles of energy and nutrients with your students and ask that they illustrate each cycle. I’ve put together an interactive Ecosystem Cycles Flip Book specifically for this purpose – print this freebie and get started today!
If you are interested in more in-depth ecology activities, I encourage you to check out my curriculum materials:
Ecology Explorations is one of my favorite hands-on life science curriculum because it provides several opportunities to explore your local ecosystems. What better way to learn about ecology than to get out there, collect data, and experience the physical factors that influence the animal and plant communities first hand.
Estuary Ecology is a fourteen lesson unit study that focuses upon estuaries and salt water marshes. It incorporates a month-long moon observation project as well as a field trip to an estuary or salt marsh.