Ecology - Food Webs and Trophic Levels

Food Chains and Webs: A food chain shows the linear flow of energy, whereas a food web represents the complex, interconnected feeding relationships within an ecosystem. Energy is transferred when one organism eats another, denoted by arrows pointing in the direction of energy flow (from the eaten to the eater).

Trophic Levels: These are the hierarchical levels in an ecosystem. $T_1$ (Producers/Autotrophs) convert light energy via photosynthesis: $6CO_2 + 6H_2O \xrightarrow{light} C_6H_{12}O_6 + 6O_2$. $T_2$ (Primary Consumers) are herbivores, $T_3$ (Secondary Consumers) are carnivores, and $T_4$ (Tertiary Consumers) are apex predators.

The 10% Rule: On average, only $10\%$ of the energy available at one trophic level is passed on to the next. The remaining $90\%$ is lost to the environment as heat through cellular respiration, movement, and undigested waste.

Ecological Pyramids: These include Pyramids of Numbers (count of individuals), Pyramids of Biomass (total dry mass of organic matter, usually in $g \cdot m^{-2}$), and Pyramids of Energy (rate of energy flow, usually in $kJ \cdot m^{-2} \cdot yr^{-1}$). Pyramids of energy are always upright, unlike the others which can be inverted.

Bioaccumulation and Biomagnification: Bioaccumulation refers to the buildup of toxins within a single organism. Biomagnification is the increase in concentration of persistent toxins (like $DDT$ or Mercury $Hg^{2+}$) as they move up the food chain, reaching the highest concentrations in $T_4$ or $T_5$ organisms.

Decomposers and Detritivores: Organisms like fungi and bacteria that break down dead organic matter, recycling essential nutrients ($N$, $P$, $K$) back into the soil for producers, though they do not recycle energy.