planetary scales.
For all Earth ecosystems (other than volcanic-vent abyssal communities subsisting on chemical energy from the Earth’s internal heat), the basis of energy flow through all living systems is solar photosynthesis. The total amount of photosynthetic energy cap tured by life is known as the Earth’s net primary productivity. This flow of photosynthetic energy sets an aggregate limit on plant biomass, and in turn, upon the biomass of the animals who eat plants and other animals. This is not the only limit, however, for life requires many things to thrive, and the absence of even one of them is a deal- breaker (See Liebig’s Limit, below). If the salinity of water rises too high, it will kill most plants and be undrinkable by most animals. Without sufficient trace elements, animals can’t exist, and so on. The carrying capacity of any environment for any species is dependent on innumerable variables and is thus subject to change. The carrying capacity is also determined by what other life forms exist in the same environment: a pasture which has both grasshoppers and deer competing for the same grass could exist with different proportions of deer and grasshoppers. That environment’s “deer” carrying capacity is also a function of the grasshopper biomass, which in turn may be a function of the grasshopper-eating bird population, which in turn is a function of the carrying capacity for the birds. So, carrying capacity is dynamic with many intertwined components. As a concept, it highlights the “upper limits” to a species’ bi omass potential. And since humans are a species, the concept of carrying
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