The correct option is Consumers.
Explanation
Productivity in an ecosystem refers to the rate at which biomass (organic matter) is produced. It is classified into primary and secondary productivity based on the trophic level at which the generation of organic matter occurs.
- Primary Productivity: This is defined as the amount of biomass or organic matter produced per unit area over a time period by plants (producers) during photosynthesis. It is associated with autotrophs (e.g., plants, algae, phytoplankton).
- Secondary Productivity: This is defined as the rate of formation of new organic matter by consumers (heterotrophs). It represents the assimilation of food energy into the biomass of herbivores, carnivores, and decomposers.
Analysis of Options:
- Consumers Consumers: Correct. Secondary productivity specifically refers to the biomass generation by organisms that depend on producers for nutrition.
- Producers Producers: Incorrect. Producers are responsible for primary productivity.
- Algae Algae: Incorrect. Algae are photosynthetic organisms (autotrophs) and are responsible for primary productivity, particularly in aquatic ecosystems.
- Lichens Lichens: Incorrect. Lichens are symbiotic associations between fungi and algae (or cyanobacteria). The algal component performs photosynthesis, contributing to primary productivity.
Key Takeaway:
Primary Productivity is the rate of biomass production by producers (solar energy to chemical energy), whereas Secondary Productivity is the rate of biomass formation by consumers (assimilation of ingested food).