What factor is essential for determining an ecosystem's primary productivity?

The essential factor for determining an ecosystem's primary productivity is the rate of energy conversion by autotrophs. Primary productivity refers to the rate at which energy is converted by photosynthetic and chemosynthetic autotrophs to organic substances. This process is fundamental because it forms the base of the food web, providing energy for all other organisms in that ecosystem, including herbivores, carnivores, and decomposers.

Autotrophs, such as plants and phytoplankton, capture sunlight (in the case of photosynthesis) or utilize chemicals (in chemosynthesis) to produce organic matter, which is then consumed by other organisms. The efficiency of this energy conversion directly affects the biomass produced, which is a critical indicator of the ecosystem's health and productivity.

In contrast, while factors such as invasive species, levels of predation, and the biome's age can influence an ecosystem's dynamics and function, they do not fundamentally determine the primary productivity. Invasive species may disrupt local populations or alter community structures but do not change the inherent efficiency of energy conversion. Similarly, predation affects population dynamics but does not directly influence the amount of energy autotrophs can convert. The age of a biome can provide context for its ecological characteristics,