Mobility, Habitat Selection and Population Connectivity of the Butterfy Lycaena Helle in Central Sweden

Journal of Insect Conservation (2020) 24:821–831 https://doi.org/10.1007/s10841-020-00254-y ORIGINAL PAPER Mobility, habitat selection and population connectivity of the butterfy Lycaena helle in central Sweden Hanna Modin1 · Erik Öckinger1 Received: 9 January 2020 / Accepted: 13 July 2020 / Published online: 18 July 2020 © The Author(s) 2020 Abstract To be able to predict habitat quality and potential distribution of threatened species is key to developing successful conservation strategies for threatened species with fragmented distributions. The aim of this study was to assess factors that limit the local distribution and density of Lycaena helle, an endangered butterfy, in central Sweden, and to estimate its mobility in order to classify local populations according to their importance for the connectivity on a regional level. An additional aim was to test if L. helle habitat quality could be assessed using remotely-sensed data such as laser scanning (LiDAR). We derived potential predictors of L. helle occurrence from laser scanning data and used a resource selection function to assess their predictive power. We used a mark-recapture approach to study L. helle movement and estimate dispersal distances. The probability of occurrence of L. helle increased with higher solar irradiation and was negatively afected by sloping terrain, but the LiDAR data generally had low predictive power. Population density increased with host plant density, but this efect was weak. The mark-recapture study confrmed that L. helle is very sedentary, with a mean movement distance of only 114 m and a maximum of 600 m. The studied population extends over a large network of interconnected linear habitats, which probably facilitates dispersal and thereby population persistence. Our study highlight the importance of a warm micro-climate and of man-made habitats like road verges and power-line corridors for the conservation of L. helle. Keywords Dispersal · Lepidoptera · Mark-recapture · Metapopulation · Resource selection function · Stepping stone Introduction strategies (Dennis et al. 2003; Fourcade and Öckinger 2017). Both local habitat area and quality and landscape context Loss of biodiversity is a worldwide concern that is driven such as connectivity to other populations can infuence patch mainly by habitat degradation and fragmentation (Pimm occupancy and local population densities (Fleishman et al. et al. 2014; Saunders et al. 1991). Many specialized but- 2002; Thomas et al. 2001). Habitat loss and fragmentation terfies are strongly negatively afected by habitat loss and leads to the disruption of colonization–extinction dynam- fragmentation (Öckinger et al. 2010), making them a use- ics in metapopulations, resulting in an increased risk of ful model group for studies on the efects of habitat loss regional extinction (Hanski 1998). To maintain function- and fragmentation on species persistence (Thomas 2005). ing metapopulations, it is crucial to identify populations For species with fragmented distributions, knowledge about and habitat patches (i.e. stepping stones) that are important the determinants behind patch occupancy and local popula- from a connectivity perspective and to which conservation tion densities is key to developing successful conservation eforts should be directed (Heller and Zavaleta 2009; Saura et al. 2014). Connectivity models based on network analysis (graph theory) are a useful tool to identify such stepping Electronic supplementary material The online version of this stones (Saura and Rubio 2010). article (https ://doi.org/10.1007/s1084 1-020-00254 -y) contains On the local scale, factors such as resource abundance supplementary material, which is available to authorized users. and vegetation structure can be important (Fleishman et al. * Erik Öckinger 2002; Thomas et al. 2001). The abundance of essential [email protected] resources limit the carrying capacity of local populations. Vegetation structure in combination with topography are 1 Department of Ecology, Swedish University of Agricultural important determinants of micro-climate, which is a key Sciences, Box 7044, 75007 Uppsala, Sweden Vol.:(0123456789)1 3 822 Journal of Insect Conservation (2020) 24:821–831 component of habitat quality for many ectothermic animals, and Fig. 1). The observed decrease in Sweden has been such as insects (Bonebrake et al. 2010; Eilers et al. 2013). attributed mainly to habitat degradation and fragmentation Resource selection functions (RSFs) can be used to inves- as a consequence of altered agricultural practices, especially tigate which factors best predict a species’ spatial use of a abandonment of traditionally managed grasslands and inten- habitat (Boyce et al. 2002). sifed management of remaining grasslands (Eliasson 2012; The Violet Copper butterfy Lycaena helle is listed as Ryrholm 2014). Loss and fragmentation of habitats, lead- ‘endangered’ on the European Red List of butterfies (van ing to increasing isolation between remnant populations and Swaay et al. 2010), and also on the national Swedish Red subsequent collapse of metapopulation dynamics (Hanski List (Artdatabanken 2015). Fennoscandian populations of L. 1999) has been suggested as a possible explanation as to helle have been described as a separate subspecies, L. helle why L. helle has disappeared from a number of sites where lapponica, and difer from populations in Central Europe the habitat still appears favourable (Mutanen and Välimäki in e.g. host plant use (Ryrholm 2014). Studies from Central 2014). Understanding dispersal distances is key to prioritize Europe show that micro-climatic conditions are an impor- areas for habitat management and restoration for threatened tant aspect of the habitat of L. helle, and that L. helle is species. favoured by high solar radiation and low vegetation (Skórka This study aimed at increasing the knowledge on the et al. 2007), but also a variable vegetation cover that pro- habitat requirements and dispersal ability of L. helle in vides wind shelter (Sawchik et al. 2003). In Central Europe, Sweden, and to analyse the connectivity of existing popu- L. helle is extremely sedentary and a poor colonizer (Craio- lations. An important question is whether habitat quality veanu et al. 2014; Fischer et al. 1999; Turlure et al. 2014). is mainly determined by host plant availability or by veg- As a consequence, it is highly sensitive to habitat fragmen- etation structure, which in turn infuences micro-climate. tation and isolation of populations (Sawchik et al. 2003). First, we hypothesized that the habitat quality of L. helle However, given the diferences in ecology between Central is strongly determined by microclimatic conditions, and European and Fennoscandian forms of L. helle, it is unclear tested to what extent remotely-sensed variables relating to how informative these fndings are for the conservation of solar radiation, vegetation height, variation in vegetation L. helle in Northern Europe. height, slope and aspect can predict presence and absence In Sweden, the distribution of L. helle has decreased of L. helle. Second, we tested if the population density of signifcantly since the mid-1900s (Ryrholm 2014), and the L. helle is related to the abundance of the larval host plant population size decreased with 20–45% during 2005–2015 Bistorta vivipara and to vegetation height, as measured in (Eliasson 2012). The current population size in Sweden is the feld. Here, we hypothesized that the population density estimated to between 3500 and 10,500 reproductive indi- of L. helle is positively related to the host plant abundance viduals, distributed over ca. 70 populations (Lindeborg 2014 and is highest at an intermediate vegetation height. Third, we Fig. 1 Left: The distribution of Lycaena helle in Sweden. Data from distribution of L. helle and the study area indicated. Right: The area the Swedish LifeWatch Analysis Portal (Leidenberger et al. 2016), all where the feld study was conducted. Background maps: © Lantmä- databases, years 2000–2019. Centre: Jämtland County in central Swe- teriet 2018 den, the region used for the regional connectivity analyses, with the 1 3 Journal of Insect Conservation (2020) 24:821–831 823 used mark-release-recapture data to estimate the dispersal whole area in one day, but if not, the search was resumed the capacity of L. helle and performed a regional connectivity next day with suitable weather conditions. Care was taken to analysis to identify the populations in Jämtland County that vary the time of day that was spent at the diferent locations. are most important from a stepping-stone perspective and to The search efort was the same in the whole area. which conservation eforts should be directed. To investigate the relationship between L. helle density and the abundance of B. vivipara and fne-scaled vegetation height, respectively, we placed 171 quadrats of 1 × 1 m Methods throughout the study area. Care was taken to distribute the quadrats relatively evenly both along the width and length Historically, the primary habitats of L. helle in Scandina- of the area but as the study area expanded continuously and via are fower-rich moist grasslands that are maintained by some inventories were made at the start of the study, the extensive mowing or grazing regimes. With the decrease quadrats were more widely dispersed in some parts than in and fragmentation of traditionally managed grasslands, L. others. Within each quadrat, we counted the total number of helle has become increasingly dependent on naturally

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