The butterfly (Lepidoptera: Papilionoidea) diversity of Mt. Mosor in Dalmatia, Croatia

. Mosor is a small mountain massif situated in central Dalmatia, above the cities of Split and Omiš. It was never a target of any systematic butterfly surveys, with its fauna remaining almost completely unknown. During our surveys from 2011 to 2020, we recorded 96 butterfly species at 60 localities. With the literature record of Polyommatus ripartii, a total of 97 species are recorded from Mt. Mosor. The comparison with the published lists of the neighbouring lower Mt. Kozjak and much higher Mt. Biokovo revealed that the butterfly richness of Mt. Mosor is intermediate, with 87 and 116 species recorded from those mountains, respectively. The biogeographical composition of all three mountains is, however, similar, with the dominant Euro-Siberian and Euro-Oriental faunistic elements comprising together about 80% of the species. For some species with scarce information for Croatia or Dalmatia, like Papilio alexanor, Zerynthia polyxena, Parnassius mnemosynae, Aricia anteros, Polyommatus escheri, Melitaea aurelia, Proterebia phegea, and Neptis rivularis, new records are discussed.


Introduction
Mosor is a small mountain located in central Dalmatia (SE Croatia), between Mt.Kozjak in the north-west and Mt.Biokovo in the south-east, between Split and Omiš cities.It stretches from the Klis Pass in the northwest to the Cetina River in the southeast and is about 25 km long.The highest peak of the mountain is Veliki Kabal (1,339 m a.s.l.).Mosor has a typical Mediterranean climate.The mountain is of limestone composition, with a large number of pits and caves (Ministry of Environment and Energy 2012).The southern slopes are mostly barren, steep, covered with sparse vegetation, while the northern slopes are covered with deciduous forests.The vegetation of Mt.Mosor is of entirely Mediterranean character (Šegulja & Bedalov 1984).The prevailing forest community, Querco-Carpinetum orientalis, occupies altitudes from 400 to 900 m, while the Seslerio-Ostryetum community is present from 900 m upwards (Šegulja & Bedalov 1984).Forest fires are common in the area, especially on the southern slopes of Mt.Mosor.Lower parts of the mountains are easily accessible, and several villages can be reached on both the southern and the northern parts of the mountain.Hiking trails to some of the prominent peaks are available, although poorly maintained.
As for many other mountains in Croatia, historical records of butterflies from Mosor are very limited (Stauder 1911(Stauder , 1913(Stauder , 1923)).Among the records worth mentioning is the record of Polyommatus ripartii, a rare species in Croatia (Koren 2010) from the southern slopes of the mountain (Dincă et al. 2013).Only three species have so far been recorded from Mt. Mosor, indicating the need for a more systematic survey of the mountain.The goal of this contribution is to present the butterfly diversity of Mt.Mosor, and compare it to the published lists of the neighbouring Mt.Kozjak (Koren et al., 2019) and Biokovo (Mihoci et al. 2011;Kačírek 2017).
We also discuss distribution and potential threats to the selected species.

Materials and methods
Field surveys, specifically addressing the butterfly fauna of the region, were carried out from 2014 onwards, but we report also some records from 2011 onward.Most data reported here were collated during the 2019 and 2020 seasons, mostly from early May to the beginning of July at altitudes below 800 m a.s.l.Satellite topography and habitat diversity were used to select the potentially suitable localities in the region prior to the field visits, in order to optimize the time spent in the field.The list of localities contains the relevant toponyms, a short description of the habitat, altitude, coordinates, dates of the visits, and the observers' initials.
In order to record butterflies, random walks and general inventories were carried out.Butterflies were observed in flight or netted for identification, using standard field guides (Lafranchis 2004, Tolman & Lewington 2008).Additionally, specimens of the genera Leptidea, Plebejus, Melitaea and Hipparchia were collected and their genitalia examined.Revision of the collected specimens from Pieris napi / balcana aggregate were examined with the aid of wingmarkings (Lorković 1970).The nomenclature follows Wiemers et al. (2018).
Comparisons of the species composition between the three mountains, i.e.Mosor, Kozjak and Biokovo were made using biogeographical affiliations of butterflies according to Kudrna et al. (2015).

Biogeographical comparisons of Mts. Mosor, Kozjak and Biokovo
The comparison of the biogeographical affiliation of butterfly species of the three neighbouring mountains of Kozjak, Mosor and Biokovo revealed great similarities (Fig. 2; Appendix I).The Euro-Oriental and Euro-Siberian elements are dominant on all three mountains, with all other categories falling below 10% in the faunistic composition.On the lowest Mt.Kozjak, no montane or boreo-montane elements were recorded; a single montane species was recorded on Mt.Mosor (Aricia anteros) and one on Mt.Biokovo (Erebia melas), while Mt.Biokovo is also home to one Boreo-montane species, Aricia artaxerxes.

General overview
For Mt. Mosor, only three species have been mentioned in the literature so far: Pieris mannii (Stauder 1913), Coenonympha pamphilus (Stauder 1923) and Polyommatus ripartii (Dincă et al. 2013).Of these, P. ripartii was not confirmed during our survey despite deliberate search.We visited the area mentioned in Dincă et al. ( 2013) on several occasions, but were not able to record the species or its host plant (Onobrychis spp.).However, both Cupido osiris and Polyommatus thersites, which were recorded from the same side of the mountain, share its host plant, indicating that P. ripartii could be present there, although not at the indicated locality.

Biogeographical comparisons of Mt. Mosor with Mts. Kozjak and Biokovo
The three mentioned coastal mountains of central Dalmatia, altogether host 130 butterfly species (Mihoci et al. 2011, Kačírek 2017, Koren et al. 2019, this survey).This is about 66% of all butterfly species present in Croatia.The number of butterfly species of Mt.Mosor with 97 species is higher than in Mt.Kozjak with 87 species (Koren et al. 2019).The latter could be explained by its smaller size, lower altitude, and less diverse habitats.Still, 12 species occurring on Mt.Kozjak were not recorded on Mt.Mosor during our survey: Pyrgus alveus, Pyrgus serratulae, Polyommatus admetus, Charaxes jasius, Fabriciana adippe, Speyeria aglaja, Brenthis daphne, Melitaea phoebe, Coenonympha arcania, Hyponephele lupinus, Hipparchia fagi and Euchloe ausonia.Further surveys of Mt.Mosor will likely yield some of the mentioned species due to presence of suitable habitats and its vicinity to both Kozjak and Biokovo, on which some of those species have been recorded in the past (Mihoci et al. 2011, Kačírek 2017, Koren et al. 2019).
The largest and most diverse is Mt.Biokovo, for which 116 butterfly species have been reported (Mihoci et al. 2011;Kačírek 2017).However, some of these records are possibly erroneous (e.g.N. sappho, M. dryas etc.), as these species were not recorded anywhere else in Dalmatia during recent butterfly surveys, therefore further inventories in particularly on the northern side of the mountain are needed.Nevertheless, the butterfly fauna of Mt.Biokovo is more diverse in comparison with both Mt.Kozjak (Koren et al. 2019) and Mt.Mosor, but still much depleted in comparison with other larger or more inland positioned mountains like Lička Plješevica or Velebit Mts. for which 152 and 153 butterfly species have been reported (Mihoci et al. 2007;Tvrtković et al. 2015;Koren et al. 2020).Apart from difference in altitude, the size of the mountain systems could be the main reason for the observed differences in diversity, as this implies higher habitat diversity and larger number of surveyed localities.
Several interesting or unexpected species were recorded during the surveys on Mt.Mosor.For each of them, additional information on their occurrence and distribution in Croatia is provided.

Comments on the selected species Papilio alexanor (fam. Papilionidae)
The species has been reconfirmed for Croatia only recently (Verovnik & Švara 2016), but soon after that additional records and the confirmation of its presence in other historical localities were made (Rusell & Pateman 2018, Koren et al. 2019).During our surveys, we recorded this elusive species at four localities in the survey area.The species is, however, known from the exact area (Verovnik & Švara 2016).We searched intensively for additional localities of this species, but while its host plant Opopanax chironium W. D. J. Koch was recorded at several localities both on the southern and northern sides of Mt.Mosor, no additional P. alexanor populations were detected.Interestingly, Stauder (1911) also searched for this species in a seemingly suitable habitat on Mt.Mosor, but with no success.In order to protect this rare species from over-collecting, no exact localities and time of observation are disclosed in this NATURA SLOVENIAE 22(2): 43-68 paper, as was the case with the previous publications (Verovnik & Švara 2016, Koren et al. 2019).

Zerynthia polyxena (fam. Papilionidae)
We recorded this species at six localities, mostly on the northern side of the mountain.The habitat of this species includes small valleys called »dolci«, which are nowadays still used as arable land.The edges of these arable areas are usually maintained and regularly mown enabling growth of its host plant, Aristolochia clematitis L., which is common in such areas.Recent surveys of Dalmatia show that Z. polyxena is much more widespread in Dalmatia than previously considered (see Lorković 2009Lorković , Šašić et al. 2015)).

Parnassius mnemosyne (fam. Papilionidae)
This is a widespread species in Croatia with scattered populations usually present in the montane areas (Lorković 2009).In Dalmatia, this species is limited to mid and high elevations in the mountains and has a very patchy distribution.On Mt.Mosor, we recorded this species only on the northern side where only a few individuals were observed at a single locality near Gornji Dolac.As the populations of this species were found also on Mt.Kozjak (Koren et al. 2019) and Mt.Biokovo (Mihoci et al. 2011), further records are expected from other mountain systems along the Dalmatian coastline.

Aricia anteros (fam. Lycaenidae)
This elusive species has a much wider distribution in Croatia than historically known (see Lorković 2009).Aside from Mt. Velebit, the species has been recently recorded on Mt.Sniježnica (Koren 2012) as well as on Mt.Lička Plješevica further north (Koren et al. 2020).During our survey of Mt.Mosor, several specimens were observed along the path on the southern slopes of the highest peak Veliki Kabal.Interestingly, it was recorded neither on Mt.Kozjak (Koren et al. 2019) nor Mt.Biokovo (Mihoci et al. 2011), despite the higher altitude of the latter.The caterpillars of A. anteros feed on Geranium sp. and Erodium sp.(Thikolovets 2011) and are therefore most probably not the limiting factor for the distribution of this species in the country.Targeted surveys of appropriate habitats of this species should be conducted to determine the true range and its conservation status in Croatia.

Polyommatus escheri (fam. Lycaenidae)
The distinct subspecies Polyommatus escheri dalmatica (Speyer, 1882) occurs in the Balkan Peninsula (Tolman & Lewington 2008).It is easily recognizable by the broader marginal black border and brighter blue colouration in the males (Tolman & Lewington 2008).This typical thermophilous species is distributed in Croatia from Istria in the north-west (Koren et al. 2018), along the islands in Kvarner, and the Dalmatian coastline (Lorković 2009).During our surveys, we recorded this species at seven localities (Tab.2).It was numerous at most sites, and both males and females were recorded, indicating strong populations in the areas.Typical habitats in which observed are road verges or patches of barren sandy ground where the larval host plant Astragalus monspessulanus (Linnaeus, 1753) grows (Fig. 3b).This is in line with observed habitats of this species elsewhere in the region (Verovnik 2004, Micevski et al. 2009).While the NATURA SLOVENIAE 22(2): 43-68 species is not considered threatened in Croatia (Šašić et al. 2015), we believe its status should be revised due to its limited distribution, specific habitat preference, and larval monophagy.

Proterebia phegea (fam. Nymphalidae)
In Croatia, it is distributed from Pag Island in the north to the northern slopes of Mt.Biokovo in the south (Zakšek 2005, Koren et al. 2010).As it is listed both in Annexes II and IV of the Habitats Directive, Special Areas of Conservation (SACs) are required to be designated, while Annex IV contains species in need of strict legal protection (Ur. l. EU 1992).In total, 14 Natura 2000 sites were designated for the long-term survival of this species within Croatia (Narodne Novine 2019), which is one of the two EU countries in which the species is present.In Greece, no such areas were designated so far.P. phegea has not been recorded previously on Mt.Mosor.
It inhabits rocky calcareous grasslands with large open areas among bushes and tree groves.Such habitats were historically widespread in large parts of Dalmatia, but are nowadays becoming more and more reduced due to abandonment and subsequent succession.This also applies to Mt. Mosor, especially the northern side which is almost entirely overgrown.A strong population of this species was discovered on the southern slopes in the area that was only recently reopened by forest fires.This possibly benefited the species and could ensure its further survival in the area.Stopping the succession of the grasslands and former pastures to closedcanopy forests should be implemented for the wellbeing of the species.We also suggest it should be added as a target species to the Natura 2000 site Mosor (HR2001352).

Melitaea aurelia (fam. Nymphalidae)
This species is widespread in western and northern Croatia, with the southernmost record at Zrmanja Vrelo (Koren & Jugovic 2012) and Mt.Biokovo (Kačírek 2017).A single male was collected on the banks of the Cetina River during this survey, and the identification was confirmed by the examination of its genitalia (Jakšić 1998).This record expands the known distribution of the species in Croatia and fills a distribution gap between Vrelo Zrmanje in the north and Mt.Biokovo in the south.This is also the second record of this species for the Dalmatia region, as no historical records exist and the species was not recorded during other recent surveys in the region (Verovnik et al. 2015, Koren et al. 2019, Kučinić et al. 2017).

Neptis rivularis (fam. Nymphalidae)
Records of this forest species are very scattered in southern Croatia.Recently it was found in the mountains bordering Bosnia & Herzegovina, including the Dinara Mts.(Tvrtković et al. 2012), Mt.Kamešnica (Koren & Lauš 2013) and Lička Plješevica (Koren et al. 2020).In Dalmatia, it is known also from Mt. Biokovo where it is common in the upper parts of the mountain (Mihoci et al. 2011, Koren, pers. obs.).We recorded this species at five localities on Mt.Mosor (Tab.2).The largest colony was detected in the woods near the Umberto Girometta chalet.This species is likely more common in the mountains of Dalmatia than considered previously, with further surveys possibly revealing additional populations in the region.

Threats and conservation
In the past, livestock breeding with pasturing was the most significant economic activity in the Mt.Mosor area as well in the whole Split region (Samac 1956).Much has changed in half a century and nowadays pastures in the region are mostly abandoned, with many of them already completely overgrown by forests.During our survey, we observed cattle only on rare occasions, and mostly on the northern side of the mountain.The abandonment of pasturing will likely have a negative impact on the butterfly diversity of the area in the future, especially on grassland specialists.This is a common threat in the whole Dalmatia region, and has been observed in many other butterfly rich areas (e.g.Koren et al. 2019Koren et al. , 2020)).
One of the present threats to the open grassland habitats of Mt.Mosor is spreading of the invasive plant Amorpha fruticosa L. This species has become widespread in Croatia, but in the coastal regions it occurs only sporadically with individual plants (Novak & Novak 2018).This, unfortunately, is not true for the Cetina Valley and wider surroundings of Omiš where it is extremely common (Novak & Novak 2018).One of such localities is at Kostanje, along the Cetina River west of the village (Fig. 3c), where some rare butterfly species like Cupido argiades, Melitaea aurelia and Lampides boeticus (Tab.2) were recorded.All efforts should be made to contain the spreading of A. fruticosa L. and, if possible, eradicate it entirely from this region.
The same is true for another invasive species present in the area, Ailanthus altissima (Mill.)Swingle, which commonly occurs on the southern slopes of Mt.Mosor, especially in and around villages.The uncontrolled spreading of this species can greatly affect the natural balance and have a strong negative impact on biodiversity in general (Sladonja et al. 2015).This plant can also invade steep rocky terrain, which is a suitable habitat for Opopanax chironium W. D. J. Koch, a larval host plant of Papilio alexanor.As for A. fruticosa L., containment and eradication are of high priority to conserve the natural habitats in the region.

Conclusions
During the last decade, a large number of faunistic contributions on butterflies of Croatia greatly expanded the knowledge about the distribution of many rare or local species as well added records for some unexplored regions or mountains (e.g.Mihoci et al. 2007, 2011, Koren et al. 2019, 2020, etc.).This, however, is not sufficient to track current changes in the environment which have, across Europe, already been proved to have drastic negative impact on butterfly populations.For example, the index of common grassland butterfly species abundance has declined by 39% since 1990, indicating a dramatic loss of grassland biodiversity within the European Union (Van Swaay et al. 2019).Even more drastic are the comparisons of the larger dataset for the well-studied countries such as the Netherlands, where an 80% decline in butterflies in general was observed (Van Strien et al. 2019).In order to track such changes in the future, appropriate butterfly transects should be implemented across Croatia, particularly at Natura 2000 sites such as Mt.Mosor.As the abandonment of pasturing continues, such monitoring would provide important information on what is happening with the butterfly populations there.Furthermore, there are some extremely rich natural habitats that could also be monitored for the changes in species abundance and composition.We suggest at least two such sites for long-term surveys at Mt. Mosor, one at Donje Sitno, in a small valley above the