Blues in the Roer Valley habitat selection and behaviour of Maculinea nausithous butterflies

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1 Blues in the Roer Valley habitat selection and behaviour of Maculinea nausithous butterflies S.H.D.R. Jansen 1,2, M. Holmgren 2 & I. Wynhoff 1 1Dutch Butterfly Conservation, PO Box 506, NL-6700 M Wageningen, The Netherlands, irma.wynhoff@vlinderstichting.nl; 2 Resource Ecology Group, Wageningen University, Bornsesteeg 69, NL-6708 PD Wageningen, The Netherlands For the conservation of Maculinea nausithous butterflies in the Roer valley a detailed study has been performed near Posterholt (Limburg). Since this butterfly species is an obligate parasite of Myrmica ant nests, the impact of food resources in terms of vegetation composition, vegetation structure and host ant presence on habitat selection and oviposition behaviour was studied. The phenology of the only host plant Sanguisorba officinalis was found to be of importance but there was no impact of the proposed host ant Myrmica rubra. The displacement of the butterflies, namely the females, was further in low quality habitats. The study resulted in advice for conservation management of this isolated endangered population. Keywords: Maculinea, Myrmica, Roer Valley, habitat selection Maculinea nausithous is a butterfly species which has been listed on the IUCN red list as low risk/near threatened (IUCN 2004). In the seventies this butterfly species had gone extinct in the Netherlands but in 1990 M. nausithous butterflies originating from a population in Poland were reintroduced in the nature reserve De Moerputten, Northern Brabant (Wynhoff 1992). Furthermore, in 2001 the species colonized sites in the Dutch part of the Roer valley (nonymous 2002). These butterflies were probably coming from a population in Germany. The new population close to the village of Posterholt was studied in detail since 2003 (Wynhoff & Peet 2004, King 2004, Van Swaay et al. 2004). Maculinea nausithous butterflies have a complex life cycle in which they engage in a multi-trophic interaction with two other species. In the first larval instars they depend on the only host plant Sanguisorba officinalis. Female butterflies of M. nausithous deposit their eggs only on the flowerheads of this host plant. Here the eggs hatch and the caterpillars feed on the seeds of the flowerhead. In the last instar the caterpillars live in the nests of the host ant Myrmica rubra where they feed on ant grubs (Thomas 1984, Thomas et al. 1989, Elmes & Thomas 1992). PROC. NETH. ENTOMOL. SOC. MEET. - VOLUME

2 BEHVIOURL ECOLOGY This extremely specialized interaction imposes a restriction since oviposition by M. nausithous butterflies should be on host plants within the host ant s limited nest range. Oviposition on host plants outside the host ant s nest range will cause the caterpillars to die. Butterflies are known to select for certain host plant characteristics before depositing eggs (Figurny & Woyciechowski 1998, Wynhoff 2001). The question is whether in parasitic species host ants are also important in this choice. The random oviposition hypothesis states that the eggs will be deposited evenly on both plants acting as sinks, i.e. host plants outside the host ant s nest range, and sources, i.e. host plants within reach of the host ants. The alternative ant-mediated oviposition hypothesis implies that butterflies select for both host plants and host ants, and that they deposit their eggs on host plants growing close to the host ant s nests. This research project tested the ant-mediated oviposition hypothesis. Population size MN-method Method of Jolly 13-jul 14-jul 15-jul 16-jul 17-jul 18-jul 19-jul 20-jul 21-jul 22-jul 23-jul 24-jul 25-jul 26-jul 27-jul 28-jul 29-jul 30-jul 31-jul 1-aug 2-aug 3-aug 4-aug 5-aug Date Figure 1. Estimated minimal daily population size (MN) and total daily population size (Jolly) of M. nausithous butterflies at Posterholt in Proportion plots with oviposition ant absence ant presence M. rubra Figure 2. Proportion of plots with oviposition at locations with and without the host ant M. rubra. There are no significant differences (Mann-Whitney U-test: p = 0.475, α = 0.05). 46

3 S.H.D.R. JNSEN, M. HOLMGREN & I. WYNHOFF In the Netherlands at the edge of their distribution area M. nausithous butterflies occur on small habitat patches and have a limited displacement capacity (Wynhoff 2001). When dispersing the butterflies use corridors like road verges, ditches or streambanks. For a viable population the availability of empty habitat patches and exchange between populations is necessary. The limited displacement is a constraint in the establishment of meta-populations (Wynhoff 2001). It has been suggested that the displacement of the butterflies is constrained by habitat quality and connectivity. Habitat of high quality and high degree of connectivity has a high probability of colonization while suitable habitat at relatively large distance is not easily colonized. It was tested whether the displacement distance of M. nausithous butterflies is shorter at high quality habitats compared to low quality habitats. MTERIL ND METHODS The research was performed in the Roer valley during the summer of 2005 with the main study site being located near the village of Posterholt (Limburg). Butterflies were marked during the whole flight period. On plots within and outside reach of the adult butterflies, vegetation composition, vegetation structure and ant species distribution were studied. These data were related to the habitat selection, oviposition patterns and the displacement of the M. nausithous butterflies. RESULTS The population size of the marked M. nausithous butterflies at the Posterholt location in 2005 was at least 90 individuals. When including an approximation of the unmarked part of the population a total population size of 160 butterflies was calculated. The total population size more than doubled from The res- B Proportion plots with oviposition 0.00 ant absence ant presence M. ruginodis Figure 3. Proportion of plots with oviposition at locations with and without the ant M. ruginodis. Oviposition is significantly higher at places with M. ruginodis (Mann-Whitney U-test: p = 0.001, α = 0.05). 47

4 BEHVIOURL ECOLOGY idence time (i.e. minimal life span) also increased from 2.7 days in 2004 to 4.4 days in The population development during the flight period of 2005 is given in Fig. 1. The number and phenology of the flowerheads are important factors in habitat selection and oviposition of M. nausithous butterflies. In contrast to earlier research, at Posterholt, there seems to be no influence of the host ant M. rubra (Fig. 2). Oviposition by M. nausithous was found to be significantly higher at places where the ant Myrmica ruginodis was present (Fig. 3). The mean displacement distance was about 75 meters, which is rather low compared to other butterfly species. The maximal displacement distance however was 375 meters. Butterflies captured on high quality plots tended to have moved significantly shorter distances until recapture when compared to those marked at low quality plots (Fig. 4). Females seem to be more sensitive for habitat quality than males (Fig. 5). Their propensity to leave a low quality plot is higher compared to the males and they fly longer distances. Nonetheless, habi- Displacement distance (m) B low habitat qualityhigh quality habitat Figure 4. Displacement (m) of M. nausithous in habitat of low quality and high quality. Butterflies fly significantly further away from low quality plots (Mann-Whitney U- test: p = 0.041, α = 0.05). Displacement distance (m) Female Male low habitat qualityhigh quality habitat Figure 5. Displacement (m) of male and female butterflies in habitat of low quality and high quality. No significant differences between high and low quality plots (Mann- Whitney U-test: P(female) = 0.067, P(male) = 0.498, α = 0.05). 48

5 S.H.D.R. JNSEN, M. HOLMGREN & I. WYNHOFF tat patches at relatively large distance, where both resources for the butterflies were present, still had a low probability of colonisation. DISCUSSION The ant mediated oviposition hypothesis is rejected for the host ant M. rubra while it seems to be valid for the closely related ant M. ruginodis. This species could serve as an extra host ant for the butterflies. More research is needed to show this and to get insight into the survival rate of caterpillars being adopted by M. ruginodis compared to those spending the wintertime in a M. rubra nest. Conservation of M. nausithous butterflies should focus on expanding the present flight area and (re)creating potential new habitat patches within the limited displacement range. Establishment of a meta-population can be facilitated by creating stepping stones and corridors between the flight areas of M. nausithous in the Dutch and German part of the Roer valley. Furthermore, nearby nature reserves with potential habitat should be integrated in this meta-population network. cknowledgments We want to thank Mark Grutters for his help with the fieldwork. REFERENCES nonymous Donker pimpernelblauwtje terug in Limburg. Natuurhistorisch Maandblad 91(7): 186. Elmes, G.W. & Thomas, J Complexity of species conservation in managed habitats: interaction between Maculinea butterflies and their ant hosts. Biodiversity and Conservation 1: Figurny, E. & Woyciechowski, M Flowerhead selection for oviposition by females of the sympatric butterfly species Maculinea teleius and M. nausithous (Lepidoptera: Lycaenidae). Entomologia Generalis 23 (3): IUCN IUCN Red List of Threatened Species. < Downloaded on November 1, King, J.P The habitat selection of a butterfly species (Maculinea nausithous) in Roer valley and Moerputten nature reserve, The Netherlands. De Vlinderstichting. Rapportnr. SV Thomas, J The behaviour and habitat requirements of Maculinea nausithous (the Dusky Large Blue) and M. teleius (the Scarce Large Blue) in France. Biological Conservation 28: Thomas, J.., Elmes, G.W., Wardlaw, J.C. & Woyciechowski, M Host specificity among Maculinea butterflies in Myrmica ant nests. Oecologia 79: Van Swaay, C..M., Grutters, M. & Wynhoff, I Het donker pimpernelblauwtje in het Roerdal De Vlinderstichting, Wageningen. Rapportnr. VS Wynhoff, I Herintroductie pimpernelblauwtje (Maculinea teleius) en donker pimpernelblauwtje (Maculinea nausithous) in Nederland in Report Department of Nature 49

6 BEHVIOURL ECOLOGY Conservation, Wageningen gricultural University, and Department of Nature, Forest, Landscape & Fauna, Ministry of griculture, Nature Conservation & Fisheries, The Hague. Wynhoff, I t home on foreign meadows: the reintroduction of two Maculinea butterfly species. Doctoral thesis, Wageningen gricultural University, The Netherlands. Wynhoff, I. & Peet, N.G Het donker pimpernelblauwtje in het Roerdal De Vlinderstichting, Wageningen. Rapportnr. VS