carrying capacity: one construct, many systems

In population ecology, carrying capacity (K) is the ceiling a given environment sets on a population: growth is fast when numbers are low and resources ample, slows as the population approaches K, and halts at K, tracing the S-shaped logistic curve. Raymond Pearl and Lowell Reed's 1920 On the Rate of Growth of the Population of the United States since 1790 rediscovered and popularised the logistic law, fitting the saturating curve with K as its asymptote. The referent is a saturation ceiling that a growing quantity approaches but does not exceed. It is the identical construct that marketing embeds in diffusion models as the ultimate market potential and that human ecology debates as Earth's carrying capacity for people.[1]

Unit

The asymptotic maximum population an environment can sustain

Recovery means

Not applicable

Measured by

Estimated as the asymptote (K) of a fitted logistic growth curve

In marketing, the diffusion of a new product follows an S-curve toward a fixed ceiling (the ultimate market potential, the total number of eventual adopters), with early growth driven by innovators and later growth by imitators until the untapped market is exhausted. Frank Bass's 1969 A New Product Growth for Model Consumer Durables made this precise, and its parameter m, the market potential, plays exactly the role of the ecological carrying capacity: the saturation level the adoption curve approaches. The referent is the same saturation ceiling on a growing quantity, here the size of the eventual market rather than a sustainable population, approached along a logistic-type diffusion path.[2]

Unit

The ultimate market potential (m): the total number of eventual adopters

Recovery means

Not applicable

Measured by

Estimated as the ceiling parameter m of a fitted diffusion (Bass) model

In human ecology and demography, Earth's carrying capacity is the maximum human population the planet can sustain, a ceiling set jointly by resources, technology, consumption, and values rather than by biology alone, which is why published estimates span orders of magnitude. Joel Cohen's 1995 Population Growth and Earth's Human Carrying Capacity reviewed centuries of such estimates and showed that the ceiling is not a fixed number but depends on the choices that define it. The referent is the same saturation ceiling as the ecological K and the marketing market potential, applied to the human population of the planet and made contingent on human institutions and technology.[3]

Unit

The maximum sustainable human population of a region or the planet

Recovery means

Not applicable

Measured by

Estimated from resource limits, technology, and consumption assumptions, with wide-ranging results