Summary: Meta‐analysis has become a standard way of summarizing empirical studies in many fields, including ecology and evolution. In ecology and evolution, meta‐analyses comparing two groups (usually experimental and control groups) have almost exclusively focused on comparing the means, using standardized metrics such as Cohen's / Hedges’ d or the response ratio. However, an experimental treatment may not only affect the mean but also the variance. Investigating differences in the variance between two groups may be informative, especially when a treatment influences the variance in addition to or instead of the mean. In this paper, we propose the effect size statistic lnCVR (the natural logarithm of the ratio between the coefficients of variation, CV, from two groups), which enables us to meta‐analytically compare differences between the variability of two groups. We illustrate the use of lnCVR with examples from ecology and evolution. Further, as an alternative approach to the use of lnCVR, we propose the combined use of ln s (the log standard deviation) and (the log mean) in a hierarchical (linear mixed) model. The use of ln s with overcomes potential limitations of lnCVR and it provides a more flexible, albeit more complex, way to examine variation beyond two‐group comparisons. Relevantly, we also refer to the potential use of ln s and lnCV (the log CV) in the context of comparative analysis. Our approaches to compare variability could be applied to already published meta‐analytic data sets that compare two‐group means to uncover potentially overlooked effects on the variance. Additionally, our approaches should be applied to future meta‐analyses, especially when one suspects a treatment has an effect not only on the mean, but also on the variance. Notably, the application of the proposed methods extends beyond the fields of ecology and evolution.

We examined evolutionary stable sperm allocation and included stochastic variation in male mating frequency, not included in previous models examining sperm allocation strategies. We assumed sperm mixing and variation in female quality and used a genetic algorithm to analyse the evolution of male sperm allocation. Our results show that males should invest more sperm in initial copulations than in subsequent copulations as a male might fail to mate again. The inclusion of variation in female fecundity had no influence on the evolutionary stable sperm allocation strategy if males were unable to recognize female quality. If males were assumed to allocate sperm in response to female quality, the proportion of sperm allocated was positively correlated with female quality. Moreover, with increasing variance in female quality, males conserved more sperm for later copulations. Literature data on sperm allocation from diverse taxa show a good fit with the predictions given by our model.

In animal species with high male mating effort, males often find themselves in a dilemma: by increasing their mating effort, the gain from each copulation increases but simultaneously reduces available resources and, thus, the opportunity for future copulations. Therefore, we expect males to spend less reproductive resources on matings that provide low reproductive potential, thereby saving resources for future copulations, possibly with high–quality females, a sort of cryptic male choice. However, the strength of the trade–off between investment in a current mating and resources available for future matings must not be the same for all males. Males with relatively high mating costs should allocate their limited resources more cautiously than males with more plentiful resources. Here, we examine this prediction in the scorpionfly Panorpa cognata. Prior to copulation, males produce a large salivary mass on which females feed during copulation. We show that the production of larger salivary masses leads to longer copulations. Moreover, the size of the salivary gland and salivary mass increases with increasing male condition. However, males in poor condition make a relatively higher mating investment than males in good condition. We therefore expect male condition to influence cryptic male choice. In accordance with our hypothesis, only males in poor condition choose cryptically, producing larger salivary masses in copulations with females of high fecundity.