Climatic warming increases voltinism in European butterflies and moths

Abstract

Climate change is altering geographical ranges, population dynamics and phenologies of many organisms. For ectotherms, increased ambient temperatures frequently have direct consequences for metabolic rates, activity patterns and developmental rates. Consequently, in many insect species both an earlier beginning and prolongation of seasonal duration occurred in parallel with recent global warming. However, from an ecological and evolutionary perspective, the number of generations (voltinism) and investment into each generation may be even more important than seasonality, since an additional generation per unit time may accelerate population growth or adaptation. Using a dataset extending back to the mid-nineteenth century, I report changes in the voltinism of butterfly and moth species of Central Europe. A significant proportion of 263 multi-voltine species showed augmented frequency of second and subsequent generations relative to the first generation in a warm period since 1980, and 44 species even increased the number of generations after 1980. Expected ecological consequences are diverse. Since multi-voltinism has been linked to insect outbreaks they include an increase in the abundance of herbivorous pests of agriculture and forestry. However, disruption of the developmental synchrony associated with multi-voltinism and host plant phenology may also reduce fitness, potentially having unexpected consequences for species of conservation concern. The ability of species to adapt evolutionarily to a changing environment may be facilitated by increased voltinism.

Figure 1.

Mean summer temperature anomalies in the study region in Central Europe. Annual summer temperature anomalies above the long-term average are given in black, while anomalies below the long-term average are given in dark grey. The light grey line is the symmetric normalized smoothing kernel with a moving average of 10 years.

Figure 2.

Species-specific proportion of records belonging to the second or subsequent generations before and after 1980. Boxplots depict the median and the range of the relative proportion of the second and subsequent generations for in total 263 bi- and multi-voltine butterfly and moth species from Central Europe. On average, there was a highly significant shift in the voltinism in favour of the second and subsequent generations after 1980 (paired Wilcoxon signed-rank test, n = 263 species, V = 26 121, p < 0.00001).

Figure 3.

Four examples of species that showed a pronounced change in favour of the second generation after 1980 compared with before 1980. The species belong to four different families of butterflies and moths: (a) Leptidea sinapis (Pieridae), (b) Plagodis dolabraria (Geometridae), (c) Hypena proboscidalis (Noctuidae) and (d) Lithosia quadra (Arctiidae). All species are known to be at least partially bi-voltine. The second generation, however, was more expressed after 1980 compared with before 1980. The frequency distribution and rugs (depicting individual records with tick marks) are shown in dashed grey for records before 1980 and in solid black for records after 1980.