Species occurrence

The marsh fritillary was present in 129 of the 256 suitable habitat patches. Between the years 2020 and 2021 35 patches have been colonized and in 30 areas local extinction has occurred.

Dynamics between the years 2020 and 2021 for the marsh fritillary. Yellow patches are unoccupied patches and blue are occupied.

The occurrence probability increased with increasing patch area, connectivity and GMI (ground moisture index). The extinction probability decreased with larger patches, high GMI, and an increase in bush cover. None of the variables, patch area, connectivity, GMI, bush cover and tree cover explained colonization. Patch area was the variable with the strongest influence according to the AIC.

Variables influencing occupancy and extinction of patches for the marsh fritillary on Gotland.

Estimation of the population size

In the four areas of capture-mark-release (CMR) survey, site C held the largest population, followed by site D, A and B. Site A was the largest area surveyed and had a larger number of unique individuals -i.e. not recaptured specimen. Site B had also many surveyed grids, however had the smallest number of unique individuals. Even having the largest populations, site C and D were the smallest areas, and held 795 and 620 unique individuals, respectively.

 Estimation of population sizeNumber of grid cellsHabitat area (ha)Density per hectareUnique Individuals
Site A 2683.97     6727.67 ha971141
Site B223.088   4015.38 ha1593
Site C2909.72    1210.16 ha286795
Site D2735.58    1916.79 ha163620
Estimations of the population in the four areas of CMR study.

Nectar survey   

The results showed that nectar use is not opportunistic, so there are species that are present in the area but that were not chosen by marsh fritillary. Here you can see a list o the flowering species present and how much they were used by the butterfly.

The abundance of flowering species in the area and the percentages of used flowers.

Larvae occurrence

In the small-scale analysis, 328 nests were found in a total of 2000 sampled points. The most informative model explaining the occurrence of larvae included (length of the biggest leaf of the) host plant size, vegetation height, presence of tussocks, number of stalks, and vegetation cover. Areas with plants with larger leaves, short vegetation, tussocks, more stalks in the host plant, and less vegetation cover are beneficial for the presence of larvae. The three most important variables were size of the max leaf, number of stalks, and vegetation height based on AIC.

Variables influencing the presence of larvae in small scale.

On a larger scale, the presence of the larvae was influenced positively by habitat area, GMI and bush cover, and negatively by grazing. Habitat area was the variable that had the strongest influence in the final model, followed by grazing, according to AIC.

Variables influencing the larvae on large scale.