Authors: Dustin J Marshall, Hayley E Cameron, and Michel Loreau

Published in: The ISME (International Society for Microbial Ecology) Journal

Introduction

In their simplest form, the dynamics of populations are described in terms of two parameters: r, the intrinsic rate of increase; and K, the carrying capacity of the population. These two parameters are fundamental to population ecology and have a long history of empirical and theoretical study. From an evolutionary perspective, r and K were used to define and describe different modes of life: r-strategists were thought to have fast population growth rates at the expense of poor competitive abilities; K-strategists were thought to have slow-growing populations but be superior competitors, or at least more efficient with regards to resources.

These concepts have strongly influenced microbial ecologists and evolutionary biologists — r and K are often expected to trade off against each other across genotypes, strains or species. Since then, the classification of r– and K-strategists has been adapted by microbiologists to describe copiotrophic and oligotrophic species of microorganisms, respectively.

The idea that it is difficult to have both fast growth and be efficient in the use of resources has intuitive appeal: multiple mechanistic models attempt to explain how and why we might observe trade-offs between r and K. However, empirical studies struggle to detect trade-offs between r and K at multiple levels of biological organisation and instead sometimes even detect ‘trade-ups’ where r and K positively covary. Even within the same microbial strains, different r-K relationships can be observed depending on environmental quality. Similarly, comparisons across species fail to reveal simple oligotrophy and copiotrophy (or r-K strategist) dichotomies — instead species often fall on a continuum between these two extremes. In fact, expectations about how r and K covary with each other are based on an unfortunate quirk of scientific fate…

Marshall DJ, Cameron HE, Loreau M (2023) Relationships between intrinsic population growth rate, carrying capacity and metabolism in microbial populations. The ISME Journal PDF DOI