Different ecological demands shape differences in population structure and behaviour among the two generations of the small pearl-bordered fritillary

Abstract

The population structure and behaviour of univoltine butterfly species have been studied intensively. However, much less is known about bivoltine species. In particular, in-depth studies of the differences in population structure, behaviour, and ecology between these two generations are largely lacking. Therefore, we here present a mark-release-recapture study of two successive generations of the fritillary butterfly Boloria selene performed in eastern Brandenburg (Germany). We revealed intersexual and intergenerational differences regarding behaviour, dispersal, population characteristics, and protandry. The observed population densities were higher in the second generation. The flight activity of females decreased in the second generation, but remained unchanged in males. This was further supported by the rate of wing decay. The first generation displayed a linear correlation between wing decay and passed time in both sexes, whereas the linear correlation was lost in second-generation females. The proportion of resting individuals in both sexes increased in the second generation, as well as the number of nectaring females. The choice of plant genera used for nectaring seems to be more specialised in the first and more opportunistic in the second generation. The average flight distances were generally higher for females than for males and overall higher in the first generation. Predictions of long-distance movements based on the inverse power function were also generally higher in females than in males but lower in the first generation. Additionally, we found protandry only in the first but not in the second generation, which might correlate with the different developmental pathways of the two generations. These remarkable differences between both generations might reflect an adaptation to the different ecological demands during the flight season and the different tasks they have, i.e., growth in the spring season; dispersal and colonisation of new habitats during the summer season.

Keywords: Boloria selene; Butterflies; Ecological interaction; Mark-release-recature; Nature conservation; Resource use; Trait-off.

Figure 1. Map of the study area “Gumnitzwiesen” in Müncheberg, eastern Brandenburg.

Map data ©2024 GeoBasis-DE/BKG (©2009); small map: ©2018–2022 GADM.

Figure 2. Estimated population size of the (A) first and (B) second generation of Boloria selene for every sampling day.

Black: males; red: females. Standard errors are given for all values.

Figure 3. Behaviour [%] observed during the first capture event of Boloria selene for males (left) and females (right) in the first (A) and second (B) generation.

Figure 4. Percentages of visited plant genera by Boloria selene males (left) and females (right) of the first (A) and the second (B) generation.

Figure 5. Daily average wing condition of males (black) and females (red) of Boloria selene in the first (A) and second (B) generation.

Linear regression with formula as black line for males and red line for females; days with less than five individuals were excluded for the respective sex.

Figure 6. Inverse proportion of individuals reaching certain distance classes in 50 m intervals for Boloria selene with the fitted NEF (grey lines) and IPF (black line).

Males (A, B; blue) and females (C, D; red) in the first (A, C) and second (B, D) generation.