Energy is Linear: Energy enters an ecosystem as light, is converted to chemical energy, and eventually dissipates as heat. It cannot be reused by the ecosystem, necessitating a constant input from the sun.
Matter is Cyclic: Unlike energy, chemical nutrients (carbon, nitrogen, phosphorus) are finite. They cycle through the biotic and abiotic components in biogeochemical cycles, moving from the soil/atmosphere into organisms and back again through decomposition.
Sustainability: The sustainability of an ecosystem depends on the efficient recycling of these nutrients. If the cycle is broken (e.g., through the removal of decomposers), the producers will eventually run out of the raw materials needed for growth.
Habitat: This is the physical environment where an organism lives, characterized by specific abiotic conditions like moisture, light, and shelter. It can be thought of as the organism's "address."
Ecological Niche: This is the functional role or "profession" of an organism within its ecosystem. It includes what the organism eats, how it interacts with others, and its effect on the environment.
Competitive Exclusion: Two species cannot occupy the exact same niche in the same habitat for long. One will eventually outcompete the other for resources, leading to the extinction of the weaker competitor or a shift in its niche.
| Feature | Food Chain | Food Web |
|---|---|---|
| Structure | Linear, single path | Interconnected, multiple paths |
| Complexity | Simple and easy to follow | Complex and realistic |
| Resilience | Low; one break affects all | High; alternative paths exist |
| Representation | Shows one energy pathway | Shows all feeding relationships |
Arrow Direction: In food chains and webs, arrows MUST point in the direction of energy flow (from the food to the eater). A common mistake is drawing arrows from the predator to the prey.
Energy Calculations: When asked to calculate energy at a specific level, apply the rule cumulatively. For example, if producers have units, secondary consumers have units.
Identify the Role: If a question asks for the role of an organism, look for its feeding habits. If it eats plants, it is a primary consumer; if it eats animals that eat plants, it is a secondary consumer.
Sanity Check: Always ensure your energy values decrease as you move up the trophic levels. If your tertiary consumer has more energy than your producer, your calculation is incorrect.
