Blackwell Publishing, Ltd.
The carrying capacity of ecosystems
Pablo del Monte-Luna1*, Barry W. Brook2, Manuel J. Zetina-Rejón1 and Victor H. Cruz-Escalona1
Centro Interdisciplinario de Ciencias Marinas — Instituto Politécnico Nacional, Departamento de Biología Marina y Pesquerías, ApartadoPostal 592, Código Postal 23000, La Paz, Baja California Sur, México. E-mail: firstname.lastname@example.org, 2Key Centre for Tropical Wildlife Management, Charles Darwin University, Darwin, NT 0909, Australia
*Correspondence: Pablo del Monte-Luna, Centro Interdisciplinario de Ciencias Marinas — Instituto Politécnico Nacional, Departamento de Biología Marina y Pesquerías, Apartado Postal 592,Código Postal 23000, La Paz, Baja California Sur, México. E-mail: email@example.com
We analyse the concept of carrying capacity (CC), from populations to the biosphere, and offer a deﬁnition suitable for any level. For communities and ecosystems, the CC evokes density-dependence assumptions analogous to those of population dynamics. At the biosphere level, human CC is uncertain and dynamic,leading to apprehensive rather than practical conclusions. The term CC is widely used among ecological disciplines but remains vague and elusive. We propose the following deﬁnition: the CC is ‘the limit of growth or development of each and all hierarchical levels of biological integration, beginning with the population, and shaped by processes and interdependent relationships between ﬁnite resourcesand the consumers of those resources’. The restrictions of the concept relate to the hierarchical approach. Emergent properties arise at each level, and environmental heterogeneity restrains the measurement and application of the CC. Because the CC entails a myriad of interrelated, ever-changing biotic and abiotic factors, it must not be assumed constant, if we are to derive more effective andrealistic management schemes. At the ecosystem level, stability and resilience are dynamic components of the CC. Historical processes that help shape global biodiversity (e.g. continental drift, glaciations) are likely drivers of large-scale changes in the earth’s CC. Finally, world population growth and consumption of resources by humanity will necessitate modiﬁcations to the paradigm of sustainabledevelopment, and demand a clear and fundamental understanding of how CC operates across all biological levels. Keywords Biosphere, community, ecosystem, hierarchy theory, population, renewable resource management, resilience, stability, sustainable development.
INTRODUCTION Humans and human impacts on the biosphere continue to expand at an alarming rate. Unchecked, this will eventually lead tounsustainable degradation of the global biosphere. As early as 1798, Malthus raised the spectre of an exponential increase in human population but only arithmetic increase in available food (Fig. 1a). Verhulst (1838) modiﬁed the Malthusian model to include the concept of ‘saturation level’, termed ‘carrying capacity’ (CC), being the maximum population level that a given environment can supportgiven ﬁnite resources (food, space, water, jobs, etc.), often termed ‘logistic growth’ (Fig. 1b). The biological rationale is simple. Theoretically, a new sexually reproducing population begins from two or more individuals. Initial nearexponential growth begins to slow as each new individual or unit of biomass causes a diminution in the environmental resources (food, space, etc.) available.Eventually, this demand provokes a decline in the actual numbers (or biomass) added to the popula© 2004 Blackwell Publishing Ltd www.blackwellpublishing.com/geb
tion. As intraspeciﬁc competition intensiﬁes, overall survival decreases, increasing selection pressure and stabilizing the total number of individuals or the total biomass at some constant maximum level (CC). This idea is the cornerstone of...