Aphantopus Hyperantus As a Response to Microhabitat Structures in and Around a Natura-2000 Site in Upper Austria
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Investigations on population dynamics of Phengaris teleius, P. nausithous, & Aphantopus hyperantus as a response to microhabitat structures in and around a Natura-2000 site in Upper Austria Masterarbeit Zur Erlangung des Mastergrades – MSc An der Naturwissenschaftlichen Fakultät der Paris- Lodron-Universität Salzburg Eingereicht von Anna Sommer, BSc GutachterIn: Univ.-Doz. Dr. Andrea Grill Univ.-Prof. Dr. Jan Christian Habel Fachbereich: Biowissenschaften Salzburg, September 2020 Abstract Biodiversity is declining worldwide. Insects are among the most threatened groups. Specialist species are in particular negatively affected by habitat loss and deterioration of habitat quality. The occurrence of the two endangered and often sympatrically existing butterfly species Phengaris nausithous and P. teleius is strongly limited by the availability of their host ants (Myrmica) and host plant (Sanguisorba officinalis). Using a mark release recapture approach, this study investigated the dispersal behaviour of these two rare specialist species and one abundant generalist butterfly Aphantopus hyperantus across five meadows from July to August 2019. Based on the obtained data, the following research questions were answered: (1) Does daily abundance of butterflies in the three species differ between the five meadow patches, (2) Is flight distance explained by habitat quality measured in abundance of flowerheads and Myrmica ants, and (3) Does border structure (road, path, forest, bushes, fertilized grassland) as well as the availability of Sanguisorba officinalis flowerheads and nectar beyond the border affect the crossing probability of the butterflies? Statistical analyses revealed that daily abundance of butterflies differed significantly between the five meadows and between species. Flight distances, on the other hand, were most significantly affected by species-membership. Border structure and nectar availability beyond the border affected the crossing probability. Conclusively, the results allow insights into what is hindering or promoting the dispersal of the two endangered lycaenid species between patches. Biodiversität ist weltweit im Rückgang, wobei Insekten zu den am meistgefährdetsten Tieren zählen. Besonders Spezialisten sind durch Lebensraumverlust und -degradierung stark betroffen. Phengaris teleius und P. nausithous, zwei gefährdete, oft sympatrisch vorkommende Schmetterlinge, sind durch das Vorkommen ihrer Wirtspflanze (Sanguisorba officinalis) und ihrer Wirtsameisen (Myrmica) limitiert. Mittels Fang-Wiederfang Methode untersucht diese Studie das Flugverhalten und die Ausbreitung der zwei spezialisierten Bläulings-Arten und einer generalistischen Art (Aphantopus hyperantus) in fünf Flächen. Im Rahmen dieser Studie werden folgende Fragen beantwortet: (1) Unterscheidet sich die tägliche Abundanz der drei Arten in den fünf untersuchten Flächen?, (2) Ist die Flugdistanz der Schmetterlinge von der Habitatsqualität (gemessen an der Anzahl von S. officinalis Blütenköpfen und Myrmica-Ameisen) abhängig?, (3) Haben verschiedene Grenzstrukturen (Straße, Schotterweg, Wald, Gebüsch, Fettwiese) sowie Nektar- und Wirtspflanzenangebot jenseits der Habitatsgrenze Einfluss auf das Überqueren und somit auf die Ausbreitung der Schmetterlinge in andere Wiesenflächen. Statistische Analysen ergaben signifikante Unterschiede in der täglichen Schmetterlingsabundanz zwischen den fünf Flächen, außerdem unterschieden sich die Arten untereinander in deren Abundanz. Unterschiede in der Flugdistanz wurden nicht durch die Habitatsqualität sondern durch die Artzugehörigkeit erklärt. A. hyperantus legte weitere Strecken zurück als die beiden Bläulings-Arten. Die Art der Grenzstruktur und die Verfügbarkeit von Nektar jenseits der Habitatsgrenze beeinflusste das Überqueren der Grenzen. Basierend auf diesen Ergebnissen bietet diese Studie Einsicht in förderliche und hinderliche Faktoren in Bezug auf das Flugverhalten und somit auf die Ausbreitung der Schmetterlinge. 1. Introduction During the last 50 years, the earth's biodiversity has declined profoundly; furthermore, biodiversity crisis is occurring worldwide (IPBES report on biodiversity and ecosystem services (Díaz et al. 2020)). Further, besides of direct exploitation, climate change, pollution and the invasion of alien species, the authors include land use change into the direct drivers of global biodiversity loss. Moreover, this IPBES report reveals that 75 % of global land surface has been altered due to rapid increase of human population followed by rising human necessities, consumption- and production patterns and an expanding agriculture. Intensified agriculture often leads to monocultures, habitat deterioration and - fragmentation (Crews et al. 2018 and references theirein) mainly affecting terrestrial organisms like insects. Insects are relatively well studied when compared to other invertebrates and heavy declines in both, species richness and abundance have been documented (Wagner 2020, Simmons et al. 2019). Among insects, butterflies belong to the most threatened groups (Habel et al. 2019 and references theirein) being strongly negatively affected by habitat loss and deterioration as a consequence of intensive agriculture (Thomas 2016). They can be divided into two main functional groups: generalists (polyphagous) and specialists (oligo- or monophagous), the latter often are highly specialized feeding and breeding on few or single plant species (Slansky 1976). While generalists can persist and sometimes thrive in homogenous landscapes, specialists mostly are directly negatively affected by habitat homogenisation and the subsequent loss of biodiversity (Melero et al. 2016). Besides habitat loss and -deterioration, habitat fragmentation is a severe threat for butterflies as it bears the risk of genetic isolation. In both, urban and rural areas, high quality habitats (species rich patches, high in biodiversity) often are isolated patches, cut through by buildings, roads etc., or they are embedded into a matrix of intensified agricultural landscape, which may lead to lower dispersal rates and a subsequent decrease of genetic diversity (Rochat et al. 2017 and references theirein, Schtickzelle et al. 2006). Dispersal leads to higher population and metapopulation size, thus to more stability (Hansson 1991) and is therefore detrimental for the persistence of metapopulations (Hanski 1999, Hanski et al. 2000). Although butterflies are highly mobile species, even certain generalist butterflies (e.g. Maniola jurtina) tend to stay within a confined space of 100 m in a non-fragmented area (Grill et al. 2006). The study species Both large blue butterflies, the dusky large blue (Phengaris nausithous, Bergsträsser 1779) and the scarce large blue (Phengaris teleius, Bergsträsser 1779) (former genus Maculinea), are highly specialized. They often occur sympatrically, inhabiting wetland like fen meadows or heathland, where Sanguisorba officinalis (great burnet) and their host ants of the genus Myrmica occur. P. nausithous is restricted to M. rubra as host ant (Thomas et al. 1989) while P. teleius mainly is confined to M. scabrinodis and M. rubra but also has been reported to parasitize successfully in nests of Aphaenogaster japonica, M. gallienii, M. salina, M. specioides and M. vandeli (Hymenoptera: Formicidae) (Tartally and Varga 2008). For oviposition, females exclusively use the capitulum (flower head) of the great burnet, where the larvae feed on Sanguisorba officinalis inside the flower head until their fourth instar. After these 3-4 weeks (Bubová et al. 2018), once the larva have completed their third molt the caterpillars leave their host plant and drop down onto the ground surface. Using mimicry by imitating certain sounds and pheromones, they lure their host ants, which pick them up and bring them actively into the ant nest, where they live parasitically (Thomas 1984). P. nausithous caterpillars are immediately attractive to Myrmica ants and adopted in less than 6 minutes (on average); in contrast, to become attractive to the host ants, larvae of P. teleius need to perform a certain adoption behaviour by offering secretion droplets from the dorsal nectary organ, which results in an average adoption time of 44 minutes (Fiedler 1990). Inside the nest, P. nausithous lives predatory feeding on ant brood but also is fed actively by worker ants (Thomas and Settele 2004), whereas P. teleius lives predatory only, depleting the ant brood. As a result, several caterpillars of P. nausithous can survive in one ant nest, while only one larva of P. teleius survives per nest (Weidemann 1986). Having finished the metamorphosis, the butterflies fly from July to mid of August and live on average for three days (Bubová et al. 2016, Nowicki et al. 2005). Due to this high level of specialization, both species are regarded as flagship species for insect conservation, they have a high conservation status in Europe (Bubová et al. 2018 and references theirein). The World Conservation Monitoring Centre (IUCN 1996a, IUCN 1996b) lists both species as “Near threatened”. Additionally, they are cited in various red lists of many European countries (Grill et al. 2008). In the red list of Austria both are declared as “Vulnerable” (Höttinger and Pennerstorfer 2005). Moreover, they are listed in Annex II and IV of the European Habitats Directive, which means that conservation areas must be established, and that the species are strictly protected EU wide, inside and outside of Natura 2000 sites (Council of the European Union, EU 1992).