A food chain illustrates a linear sequence of organisms where nutrients and energy move as one organism consumes another. A food web is a more intricate network, showcasing complex feeding relationships and interconnected food chains within an environment. Both are fundamental to understanding how organisms rely on each other and how substances flow through natural communities.
Energy Transfer
Energy enters most ecosystems from the sun, captured by producers like plants, algae, or cyanobacteria through photosynthesis. These producers form the base of the food chain, converting light energy into chemical energy stored in organic molecules. Organisms that consume these producers are known as primary consumers, typically herbivores.
The energy then transfers to secondary consumers, which eat primary consumers, and further to tertiary consumers that prey on secondary consumers. At each step, or trophic level, a significant portion of energy is lost. On average, only about 10% of the energy from one trophic level transfers to the next.
The remaining 90% of energy is lost as heat during metabolic processes, movement, and maintaining bodily functions. This inefficiency explains why food chains are short, rarely extending beyond four or five trophic levels. The diminishing energy availability at higher levels means a much larger biomass of producers is required to support a smaller biomass of top predators.
The Cycling of Matter
Unlike energy, which flows in one direction and is lost as heat, matter, or nutrients, is continuously recycled within an ecosystem. Essential elements like carbon, nitrogen, and phosphorus move through food chains and webs; they are transformed and reused.
Decomposers, primarily bacteria and fungi, play an important role in this recycling process. When organisms die or produce waste, decomposers break down complex organic matter into simpler inorganic substances. This decomposition releases nutrients back into the soil, water, or atmosphere.
These released nutrients become available for producers to absorb and incorporate into organic compounds, restarting the cycle. This continuous process ensures ecosystems do not run out of the building blocks for life. Without decomposers, nutrients would remain locked in dead organisms, making them inaccessible for growth and disrupting the ecosystem.
Accumulation of Toxins
Beyond energy and nutrients, persistent substances, such as pollutants and heavy metals, also travel through food chains and webs. These substances accumulate in organisms, posing risks to health. Two processes describe this phenomenon: bioaccumulation and biomagnification.
Bioaccumulation refers to the buildup of a substance, a persistent chemical, within an individual organism’s tissues over its lifetime. This occurs when an organism absorbs a substance faster than it can excrete or break it down. For instance, microscopic organisms at the base of a food web might absorb trace amounts of a pollutant directly from their environment.
Biomagnification is the process where concentration of a persistent toxin increases at higher trophic levels in food chains. As one organism consumes many contaminated prey, the toxin becomes more concentrated in the predator’s body. For example, small fish eating many contaminated plankton will accumulate higher levels of a toxin, and larger fish eating many small fish will have even higher concentrations.
Apex predators, including some fish and birds, accumulate higher concentrations of these substances than organisms lower in the food chain. Examples include mercury in large predatory fish or DDT in birds of prey, which can lead to reproductive problems or other health issues for these animals and potentially for humans who consume them.