Evol Ecol Res 14: 627-665 (2012) Full PDF if your library subscribes.
The struggle for existence: how the notion of carrying capacity, K, obscures the links between demography, Darwinian evolution, and speciation
Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts, USA and Department of Genetics, Evolution and Environment, University College London, London, UK
Correspondence: J. Mallet, Department of Organismic and Evolutionary Biology, Harvard University, 16 Divinity Avenue, Cambridge, MA 02138, USA.
Question: Population ecology and population genetics are treated separately in most textbooks. However, Darwin’s term the ‘struggle for existence’ included both natural selection and ecological competition. Using the simplest possible mathematical models, this paper searches for historical reasons for the lack of unity in ecological and evolutionary thought.
Assumptions and methods: Logistic density-dependent population growth and Lotka-Volterra competition models are used throughout. Derivations of the logistic from first principles of resource use, competition for space, and births and deaths of individuals are documented. A full range of possible kinds of natural selection, including constant selection, density- and frequency-dependent selection, as well as hard and soft selection, can emerge cleanly as natural outcomes from the simplest-imaginable haploid models derived from Lotka-Volterra competition. Extensions to incorporate more realism, including non-linear per capita density dependence, Allee effects, complex life histories, discrete generations, diploid Mendelian genetics, sexual populations, and speciation are briefly discussed.
Conclusions: Widespread use of r-K (‘carrying capacity’) models of population growth appears to have catalysed fundamental discords in ecology, and between ecology and evolution. Verhulst’s original polynomial form of the logistic, here termed the r-α model, is both more natural in theory, and accords better with empirical data. The r-α formulation explains apparent paradoxes involving the r-K logistic, including controversial aspects of r- and K-selection. Adoption of first-principles birth–death or r-α modelling clarifies natural selection in density-regulated populations, and leads to an improved understanding of Darwinian evolution and speciation.
Keywords: adaptive dynamics, density-dependent selection, eco-evolutionary dynamics, history of ecology, population genetics, theoretical ecology.
DOWNLOAD A FREE, FULL PDF COPY
IF you are connected using the IP of a subscribing institution (library, laboratory, etc.)
or through its VPN.
© 2012 J. Mallet. All EER articles are copyrighted by their authors. All authors endorse, permit and license Evolutionary Ecology Ltd. to grant its subscribing institutions/libraries the copying privileges specified below without additional consideration or payment to them or to Evolutionary Ecology, Ltd. These endorsements, in writing, are on file in the office of Evolutionary Ecology, Ltd. Consult authors for permission to use any portion of their work in derivative works, compilations or to distribute their work in any commercial manner.
Subscribing institutions/libraries may grant individuals the privilege of making a single copy of an EER article for non-commercial educational or non-commercial research purposes. Subscribing institutions/libraries may also use articles for non-commercial educational purposes by making any number of copies for course packs or course reserve collections. Subscribing institutions/libraries may also loan single copies of articles to non-commercial libraries for educational purposes.
All copies of abstracts and articles must preserve their copyright notice without modification.