Abstract
Colias myrmidone has suffered a dramatic decline in Europe, and now its occurrence is restricted to just a few countries. We investigated one of the last viable metapopulations (Knyszyn Forest, NE Poland), where the butterfly is almost completely dependent on forestry, inhabiting some clearings and young tree plantations rich in larval food plants (Chamaecytisus ruthenicus) and nectar resources. Intensive mark-recapture studies were performed in 2017 on eight occupied patches separated by 0.5–5 km. The overall population size of imagoes in the second brood was calculated at about 750 individuals. Sex ratio was shown to be well-balanced and average residency was estimated at 5.6 days. Dispersal occurred mostly between neighbouring patches, and isolation of patches contributed to the high mortality of emigrants. The average distance covered during dispersal was significantly higher for males. However, females left small patches much more readily than males. These patches were probably used only as ‘stepping stone’ sites in dispersal. Restricted dispersal could be related to barriers created by forest stands but it is also not excluded that individuals living in an isolated metapopulation become increasingly sedentary and our results are an early warning sign. The most distant local population was clearly isolated, with hardly any immigration from the other populations. To maintain a network of more stable habitat patches some clearings should be left deforested and appropriately managed. However this goal is difficult to achieve under the current forestry rules and therefore (re)creation of habitats on other available open areas should be considered.
Highlights
Many threatened European butterflies have suffered from habitat loss and/or fragmentation (Bubová et al 2015)
Emigration from a habitat patch may be negatively correlated with its size (Hill et al 1996) and positively correlated with local population density (Nowicki and Vrabec 2011), but is affected by weather (Cormont et al 2011), habitat boundaries (Merckx et al 2003), surrounding matrix (Ricketts 2001), isolation
Using the MRR method we aimed to investigate the demography and mobility of this unique metapopulation system to learn the factors affecting its functioning and possibly develop some conservation recommendations which would be important in increasing the chances of its survival in the longer perspective
Summary
Many threatened European butterflies have suffered from habitat loss and/or fragmentation (Bubová et al 2015). Most of them are dependent on seminatural biotopes whose (re)creation and persistence are related to human activities. They frequently thrive in metapopulation systems supported by unstable and scattered patches of habitat. Typical examples of ephemeral biotopes, which are more or less isolated from each other, are forest clearings In the past they could appear naturally as a result of fire or windfall but nowadays they are mostly of anthropogenic origin, i.e. related to logging. New clearings are usually quickly afforestrated and only rarely left for natural succession. Both processes sooner or later lead to the disappearance of open patches. It is worth emphasizing that woodland butterflies are showing a substantial decline across Europe, in contrast to e.g. woodland birds which situation is more or less stable (Van Swaay et al 2006)
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