Measuring the potential for growth in populations investing in diapause

Abstract

The intrinsic rate of population increase (r) is a common performance measure in many ecological and evolutionary studies. However, in life cycles with diapause investment resources are split into a short-term (current population growth) and a long-term (population survival through periods of unsuitable habitat conditions) component, which complicates the use of r as a single performance measure. Here we propose a new measure that integrates both performance components into a single parameter, the potential intrinsic growth rate, rpot. This is the rate of increase that a population/genotype would have if no investment in diapausing stages would occur. We show that rpot can be computed using standard demographic data from temporal series or life table experiments and demonstrate the use of the rpot for two common life cycles among zooplanktonic organisms: (1) a cyclically parthenogenetic life cycle where investment in diapause happens only during the sexual phase, and (2) an obligate sexual life cycle with a switch from non-investing females to investing females along the lifespan. Using case studies we show that choosing rpot or the standard r affects comparisons between genotypes/populations or environmental factors. We provide clues on how rpot can be estimated in other life cycles with diapause investment if appropriate assumptions are made.