1 Ecological Systems and Energy Flow
Learn how ecosystems are organized, how energy flows through feeding relationships, and how matter cycles between organisms and their environment.
components and interactions
An links organisms to one another and to the nonliving environment in which they live. A tide pool, forest, lake, or grassland can each be studied as an . Its boundaries may be small or large and depend on the question being studied.
An organism is an individual living thing. Members of the same species living in one area form a , and multiple populations form a . A together with its physical environment makes up an .
Ecosystems include , such as plants, animals, fungi, and microorganisms, and , such as light, temperature, water, air, soil, nutrients, and physical features of the land. These components affect one another: water availability and temperature influence which plants can grow, while plants provide food and shelter for other organisms. Organisms may also compete for limited resources, consume one another, or engage in relationships in which one or both benefit. Together, these interactions and environmental conditions help shape structure.
Feeding relationships and energy flow
Most ecosystems receive energy from sunlight. Producers, including plants, algae, and some bacteria, capture light energy through photosynthesis and store it in organic molecules. Some ecosystems, such as those around certain deep-sea vents, instead begin with producers that obtain energy from chemical reactions. Consumers obtain energy by eating organisms or organic matter, while decomposers, including many fungi and bacteria, break down dead organisms and waste.
A food chain shows one route by which energy passes between organisms. For example:
grass → grasshopper → frog → snake
A connects many food chains and better represents the overlapping feeding relationships found in a real . Each position in a feeding sequence is a . Producers are at the base, followed by primary consumers that eat producers, and then consumers at higher levels.
Why energy does not cycle
Energy transfer between trophic levels is not complete. Organisms use much of the energy they take in to carry out life processes, and some is released as heat. Consequently, less energy is available to support organisms at each higher .
Energy flows through an in one direction: from an energy source, through organisms, and eventually out as heat. It does not cycle back for reuse.
Matter and nutrient cycles
Organisms need matter as well as energy. Elements such as carbon, nitrogen, and phosphorus, along with water, form the materials of living things. Producers take up water, carbon, and nutrients from their surroundings and incorporate them into organic molecules. Consumers obtain some of this matter by eating other organisms. Decomposers break down waste and dead material, returning nutrients to the soil, water, or air, where they may be taken up again.
This ongoing movement of matter between organisms and the nonliving environment is called or biogeochemical cycling. For example, carbon may move from atmospheric carbon dioxide into a plant through photosynthesis, pass to an animal when it eats the plant, and return to the atmosphere through respiration or decomposition.
Unlike energy, matter is recycled. It may move among organisms and environmental reservoirs in different forms and at different rates.