b - Food Webs, Trophic Levels, and Biogeochemical Cycles
Food Webs and Trophic Levels
Food webs illustrate trophic interactions and how organisms obtain nutrients. They can be analyzed by functional roles or trophic levels.
Primary Producers: Autotrophic organisms (e.g., plants, algae) that get energy from abiotic factors like the sun and nutrients from the environment (soil for terrestrial, water for aquatic).
Consumers: Heterotrophic organisms that feed on other living organisms.
Primary Consumers: Herbivores that eat primary producers.
Secondary Consumers: Feed on primary consumers.
Tertiary Consumers: Feed on secondary consumers, and so on.
Decomposers and Detritivores: Heterotrophic recyclers that break down dead organisms, returning nutrients to the ecosystem.
Food webs are organized in trophic levels such as primary producers, primary consumers, secondary consumers and tertiary consumers. Consumers may feed from multiple trophic levels, creating complexity (e.g., omnivores).
Energy Transfer and Trophic Pyramids
Energy does not cycle through ecosystems; it must be continuously harvested. Photosynthesis is typically the primary energy source.
Energy is stored in organic molecules, but the transfer is not 100% efficient; some energy is lost as heat.
Biomass and energy decrease from one trophic level to the next, forming a trophic pyramid. Only about 10% of the energy in biomass is transferred to the next level.
Energy transfer is unidirectional, unlike the cycling of carbon and other elements.
Biogeochemical Cycles
Biogeochemical cycles, such as the carbon cycle, link organisms and their environment through the chemical cycling of raw materials. Photosynthetic rate depends on water availability controlling carbon fixation rates.
Terrestrial Example: Vascular plants absorb , herbivores consume plants, predators eat herbivores, and decomposers break down organic waste, releasing through respiration and fermentation.
Ocean Example: Algae and cyanobacteria convert in