Population Density and Characteristics

Population density and characteristics

Our MRR study started at the beginning of the B. ino flight season in 2010. This assumption is supported by (i) the initially low number of males (calculated by our best POPAN Model) with almost all of them showing undamaged wings, (ii) the male’s daily population size increasing over the first two weeks of our survey and (iii) no female records during the first five days of our study. Our study period (22nd of June to 23rd of July) also coincides with other ecological studies on B. ino in Central Europe (21st of June to 4th of August; Zimmermann et al. 2005, Fric et al. 2009) and embraces most of the species' entire flight period given in text book on butterflies (Ebert & Rennwald 1991).

The total population size in our study (Ntot: 2,376 individuals) is in the range of other observations on B. ino Zimmermann et al. (2005): 1,860; Fric et al. (2009): 3,700. However, our population had higher densities (316 individuals per hectare at the day with the highest population density) than all other populations studied (Zimmermann et al. (2005) 66; Cozzi et al. (2008): 31 range: two to 109; Fric et al. (2009): 132). This high population density characterises our study area as a very suitable habitat for B. ino. However, much higher population densities were sometimes recorded for other Nymphalid butterfly species as e.g.

Euphydryas aurinia with 2,220 individuals per hectare (Junker & Schmitt 2010).

The female’s population peak is about two weeks later than the male’s peak. This phenomenon of protandry is typical for the Lesser Marbled Fritillary (Fric et al. 2009) as well as for many other butterfly species (e.g. Kuras et al. (2003); Euphydryas aurinia, Junker &

Schmitt (2010)). Apparently, only extreme habitat conditions as survival in alpine environments with very unpredictable climate are able to rescind this phenomenon (Junker et al. 2010).

Methodological aspects A frequently applied rule of thumb for fieldwork with butterflies assumes that about one third of the total population is on the wing at the population peak (Settele et al. 1999b). In our study, about 42.5% of the total population was present on the 1st of July representing about

1,011 individuals in our study area. This is a relatively high proportion if compared with Fric et al. (2009) calculating 17.6% (Melitaea athalia), 16% (Melitaea diamina) and 27% (B. ino) of the butterflies being present during population peak. This high proportion of the population being present might result from the permanently suitable weather conditions during our study.

Therefore, the assumption of one third of all individuals being present at peak flight has to be applied with care as it might be strongly influenced by the respective weather conditions, but still might be in the order of magnitude.

The higher number of marked males in comparison to marked females is coinciding with other capture-recapture studies in Nymphalidae (Fric et al. 2009, Junker et al. 2010, Junker &

Schmitt 2010). In our study, this might also be an artefact due to the dense stands of

Filipendula ulmaria: as flying individuals were much easier to detect as individuals showing any other behaviour (resting, feeding and mating) and males invested much more time in flight activities than females, they had to be sampled more often. These behavioural differences between sexes are also reflected by quicker wing decay in males.

The majority of butterflies were caught in the areas dominated by Filipendula ulmaria (larval resource) and on the mesophilic fallows with dense stands of nectar plants (resource of imagos). Nevertheless, Filipendula ulmaria areas and the Luzula sylvaticus area were frequented more often than expected at random, following the MCP analysis. This analysis revealed in general similar results as the capture point analysis, but the mesophilic fallows were underrepresented in the MCP´s because of their peripheral distribution in the study area.

Therefore, the MCP analysis might be a useful technique to measure area sizes in the field.

However, the simple method of capture point analysis in our case yielded better results for the distribution of the individuals in the field because this analysis is simply based on the real use of habitat. MCP based analysis are automatically distorted by the distribution of habitats in space so that those habitat types with distribution at the edges of the study area have to be underrepresented.

All cited references' in the online supplementary are also included in the article reference list. Table S 1. Potential nectar plant species of B. ino in our study area, their dominance in the field and the observed and expected amount of butterfly visits.

Reported nectar plant coverage (%) observed visits expected visits under species in our study area (study area) random choice Filipendula ulmaria 37.5 0 41 Bistorta officinalis 20 7 22 Lysimachia vulgaris 20 1 22 Lotus uliginosus 10 6 11 Stachys officinalis 10 1 11 Epilobium montanum 5 2 6 Epilobium hirsutum 5 1 6 Cirsium palustre 5 85 6 Vicia cracca 3 5 3 Knautia arvensis 3 5 3 Centaurea nigra 3 5 3 Rubus fruticosus agg. 3 19 3 Succisa pratensis 0.5 1 1 Lathyrus linifolius 1 1 1

Figure S1. Changes in wing wear of B. ino over the flight period in 2010. At the end of the season, wings of both sexes were heavily damaged, but the advance in males was quicker than in females, for each individual we included only the first capture event. wing wear at first capture event

4 males females

3 r a e w g n i w

1 21.6 28.6 5.7 12.7 19.7 Date