Organisms and Their Environment in an Ecosystem
An ecosystem forms through interactions between living things and their environment. The environment includes abiotic factors such as light, water, air, and soil, as well as other organisms.
Organisms Interact with Other Organisms and the Abiotic Environment
In a small garden, grass, insects, birds, fungi, and bacteria interact with soil, water, light, and other organisms. All these living and nonliving components form an ecosystem.
Organisms can be grouped by their role in an ecosystem. Producers make organic material, such as plants that photosynthesize. Consumers get food from other organisms. Decomposers break down remains into materials that can return to the environment.
Energy Flow and Matter Cycling
Energy enters many ecosystems as sunlight and eventually dissipates as heat, while chemical elements circulate among organisms, air, water, and soil.
In a garden, producers build organic matter, consumers obtain food from other organisms, and decomposers return materials to the environment.
Trace two pathways through the ecosystem. Follow energy from a food source to its consumers. Follow matter as decomposers return it to the environment for organisms to use again.
Energy Flows from Food Sources
Food-chain arrows follow the transfer of energy. Start from the organism that makes or provides food, then follow the organism that receives that food next. An organism's own movement is separate from this transfer.
Arrows Show Energy and Matter Transfer
Plants use light during photosynthesis to build organic compounds. Chemical energy is stored in those compounds, and consumers obtain some of that energy by eating plants or other organisms.
The arrow in a food chain shows the direction of energy and food-matter transfer. If grass is eaten by a grasshopper, and the grasshopper is eaten by a bird, the arrow points from grass to grasshopper to bird. Read each arrow as "energy moves from this organism to the next".
Less Energy Is Available at Each Level
Only part of the chemical energy at one trophic level becomes new biomass available to the next. Organisms use much of it in metabolism, which dissipates energy as heat, while unconsumed tissue and waste enter decomposer pathways. Consequently, less energy is available at each successive trophic level.
An energy pyramid therefore narrows toward the top. Its width represents available energy, so it does not measure the importance or number of organisms. A pyramid of numbers can have a different shape.
| What to follow | Direction | Example |
|---|---|---|
| Energy | Flows from producers to consumers and eventually leaves as heat | Grass supplies energy to a grasshopper, then part of that energy reaches a bird |
| Matter | Cycles among organisms, air, water, and soil through biological, physical, and chemical processes | Fallen leaves are broken down, and mineral nutrients can become available to plants again |
| Niche | Describes the conditions an organism tolerates, the resources it uses, and its interactions with other organisms | Pollinators, predators, and decomposers may share a habitat but occupy different niches |
Matter Cycles Through Decomposers
Matter behaves differently from energy. The elements that build bodies move among organisms and abiotic reservoirs such as air, water, and soil. Decomposition returns elements from organic remains to these biogeochemical cycles.
Decomposers Return Elements to the Environment
Energy flows, but matter cycles. When leaves fall, animals die, or food remains are left behind, decomposers such as bacteria and fungi break them down. The products return as nutrients in soil or water.
Without decomposers, remains would accumulate and elements needed by producers would stay locked in organic material. Decomposers convert those remains into forms of matter that other organisms can reuse.
A Niche Describes How an Organism Uses Its Environment
A niche describes the range of environmental conditions an organism tolerates, the resources it uses, and its interactions with other organisms. A habitat is the place where an organism lives. Its niche describes how it lives there. Two organisms can share a habitat but occupy different niches.
For example, pollinating insects, small predators, plants, and soil fungi can all be in the same garden. They use different resources and interact with different organisms. Comparing their niches explains why losing one kind of organism can disturb other relationships.
Many plants depend on pollinators. When pollinator numbers fall, plants reproduce less successfully and food supplies can become less stable.
Energy Arrows and Matter Cycles Show Different Pathways
Body remains, waste, and dead organisms enter decomposer pathways, while matter also moves through air, water, soil, and living bodies in other ways. Together, these pathways form a network. Energy eventually dissipates as heat, while matter continues to cycle.
If one organism disappears, food sources, predators, decomposers, and habitats for other organisms can all be affected. An ecosystem consists of these connected organisms and their physical environment.