First data on the Orthoptera diversity of Poštak Mountain and its surroundings (Croatia)

Summary The insect fauna of the Dinarides is not widely studied. In 2013 and 2014, an orthopterological survey was conducted on the Poštak Mountain and its surroundings in the Lika region (Croatia), in order to sample the orthopteran communities of the prominent habitat types of the area. From 24 sampling sites, 80 Orthoptera species (44 Ensifera and 36 Caelifera) were collected, which amounts to almost half the known species in Croatia. One species, Pholidoptera frivaldszkyi, is recorded for the first time in the country.

The Dinaric Alps are considered a hotspot of endemisms regarding the European Orthoptera fauna (Kenyeres et al. 2009). In terms of Orthoptera diversity, this area is among the richest in Europe (Hochkirch et al. 2016b). Despite the remarkable biodiversity, however, our knowledge on the Orthoptera fauna of the different parts of this mountain range is highly variable. Several sites in the Dinaric Mountains in Bosnia and Herzegovina and Montenegro are well studied (Mikšić 1966(Mikšić , 1970(Mikšić , 1977(Mikšić , 1979Ingrisch & Pavićević 2012), or, at least, their species are listed (Mikšić 1978(Mikšić , 1981. On the other hand, most of the Dinaric Alps of Croatia, excepting only some parts of the range near the Kvarner region (Učka Mt., S part of Velika Kapela Mt., N Velebit Mt.), are comparatively understudied. From the Croatian side of the Dinaric Alps, only two recent orthopterological surveys have been published, a comprehensive work about the Dinara Mountain and its surroundings (Rebrina et al. 2015), and a short survey of the Žumberak and Samoborsko gorje Mountains (Nagy 2006). Due to their transitional position between the continental and the Mediterranean climate (Bertović 1975), the Dinaric Alps display an outstanding degree of biodiversity, representing a mixture of Euro-Siberian and Mediterranean elements, and harbouring several endemic taxa (Tvrtković & Veen 2006).
The entomofauna of the Poštak Mountain in the Lika region (on the border area between Velebit Mt. and Dinara Mt.) is still largely unexplored, except for its butterflies (Koren et al. 2015). Prior to our study, no data were available on the Orthoptera inhabiting this mountain. Thus, the main aim of our study was to investigate orthopteran insects in the most important habitat types of the Poštak Mt. and its surroundings, in order to gain insight into the Orthoptera fauna of this area. We expected to find a rich fauna, composed of continental, Mediterranean, and Dinaric elements.

Study area
The Poštak Mt. (Croatian: planina Poštak) is the southernmost, somewhat isolated part of the nearly 100 km long Lička Plješivica Mountain massif in the Lika region of Croatia, north of the town of Knin, in NW Dalmatia. The mountain massif runs from north to south, contrarily to most of the other Dinaric Mountains. The mountain gets its name from its 1421 m high, grassland covered peak, Poštak, surrounded by several other peaks. North-west of the Poštak Mt. lies the Velikopopinsko polje, separating it from the Lisac Mt., in the south-western part of the Lička Plješivica mountain chain. From the west, the Poštak Mt. is surrounded by the Malopopinsko polje, a small karst field (uvala) which, with the gorge of the Zrmanja River, separates it from the neighbouring Velebit Mt. On the north, the Poštak Mt. is bordered by the headwaters of the Una River, while in the east, by the deep valley of the Butižnica River. The bedrock of the mountain consists predominantly of limestone and dolomite, while its foothills and river valleys are partially covered in alluvial sediments. Acidophilic bedrock is hardly present. The area harbours a great variety of natural and semi-natural habitats. The southern and south-western slopes, often steep, are mostly covered by more or less rocky submediterranean dry grasslands and scrubs, or pubescent oak forests. Mediterranean elements, especially on the grasslands, are distributed from the foothills to the highest peaks, particularly in the central and southern parts of the mountain. On the other hand, the northern and north-eastern parts are often forested. Depending on the prevailing environmental conditions (elevation, depth of ground water level, exposition, etc.) and human activities in the past, they are dominated by continental sessile oak groves, or beech or pine forests. On some plateaus, extensive mountain hay meadows can be found, whereas the lowland variety of this habitat type covers large areas at the foothills, at the bottom of stream and river valleys, and in the plain polje. A small central part (2739 ha) of the range forms a site of community importance in the Natura 2000 network of the European Union (name: Poštak SCI; code: HR2001253).

Sampling sites
During the fieldwork in the summer of 2013 and 2014, 22 sampling sites in the Poštak Mt. area, and two further sites in the neighbouring border area to the Velebit and Lisac Mt. were investigated, near the settlements Malovan, Komići, Momići, Nadvrelo, Otrić, Plavno and Vunduci, between 250 and 1350 m asl. Sampling sites covered: Ljubina poljana (1050-1090 m asl), a four-kilometre mountain valley (orientation W-E) covered by grasslands, situated on the northern side of the peak; other localities around the Poštak peak area (670-1350 m asl); Begovac pond (600 m asl), near the mountain pass to the Velebit Mt.; several sites in Plavno polje (and the surrounding slopes, 320-420 m asl), a southern valley with periodical watercourses; and sites on the slopes near the south-eastern Razvršje peak (1070-1140 m asl). Sites were chosen in order to best represent the variety of habitat types occurring in the study area, at different elevations ( Figure 1). Two sampling sites are situated in the border area of the Poštak Mt. (3 -Malopopinsko polje, 18 -Momići). Data from two additional sampling sites  are not representative of the Orthopteran fauna of the Poštak Mt., but they are situated close to it, in the surrounding hills between the Lisac Mt. and the Velebit Mt.
Sampling sites and events are listed in Table 1. Site numbers correspond to the map of Figure 1.

Methods
All fieldwork was carried out in 2013 and 2014. The study area was shortly visited for the first time in June 2013. This visit was followed by the main study period in the second half of July Most of the collecting in grassland habitats was performed by sweep netting, usually completed by visual and acoustic observations, while in bushy and forested habitats, visual and acoustic detection was chiefly applied, and the insects were collected by hand. To maximize the efficiency of the acoustic detection, an ultrasound detector (Mini-3 Bat Detector, NHBS, Totnes, UKfrequency range modified for orthopterological purposes) was used. The calling songs of several species were recorded directly by a ZOOM H1 digital handy sound recorder (Zoom Corporation, San Francisco, CA, USA) and by an Olympus VN-8400PC digital voice recorder (Olympus, Center Valley, PA, USA), using a Shure BG 4.0 condenser microphone (frequency response: 40-18,000 Hz). Specimens were identified using the taxonomic keys by Harz (1969Harz ( , 1975, Ingrisch and Pavićević (2010), Ingrisch (2012), and Massa et al. (2012). The Orthoptera Species File Online (OSF; Cigliano et al. 2018) was consulted for valid taxonomy.
Most of the collected specimens were preserved in 70 or 96% ethanol solution, while some were captured alive and prepared, pinned and dried in the laboratory. Voucher specimens are deposited in the F. Rebrina private Orthoptera collection (Zagreb, Croatia) [FRcoll], the Orthoptera collection of the Split Natural History Museum (Prirodoslovni Muzej -Split, J. Skejo collection) (Split, Croatia) [PMSt], in the G. Szövényi private Orthoptera collection [SGcoll], and in the Orthoptera collection of the Hungarian Natural History Museum (Budapest, Hungary) [HNHM].

Results
Altogether 80 Orthoptera species (44 Ensifera and 36 Caelifera) were detected in the study area, 78 of which were found within the natural boundaries of the Poštak Mountain. The remaining two (Phaneroptera falcata and Pholidoptera littoralis littoralis) were only found in the surrounding hills. The species are listed below in systematic order. Sampling site identifiers (numbers from 1 to 24), grouped by settlement, are indicated for every species in the list. The identifier number denotes site and sampling date. The geographical names, brief habitat descriptions, altitudes, collecting dates, and the names of collectors for all sampling sites are listed in Table 1. Published data (only . This yet undescribed species from the Poecilimon elegans group is relatively widespread in the dry grasslands of the region between 600 and 1350 m asl. This taxon differs considerably both from P. elegans and P. albolineatus Ingrisch & Pavićević, 2010, and its morphology fits Poecilimon sp. (near elegans) type "a", as described in Ingrisch and Pavićević (2010). The calling songs of the Poštak specimens differ considerably both from P. albolineatus and P. elegans songs, as suggested by Ingrisch and Pavićević (2010). A comprehensive revision of this species group in its entire range is in progress. . In forest edge habitats and bushy meadows, often in rocky, dry places, up to the highest peaks is the region. Specimens collected during the fieldwork did not morphologically match any of the geographical races presently regarded as subspecies according to the OSF (Cigliano et al. 2018), as defined in the last comprehensive work on the infraspecific taxonomy of this species (Mařan 1952). The latter paper provides a detailed description and a morphological key to all the currently valid subspecies of P. dalmatica. However, based on the characters used in Mařan's (1952) paper, part of our specimens exhibited a combination of morphological characters of different subspecies. Several characters (i.e. length of pronotum, dentation of male titillator and the shape of male cerci) varied considerably, even between specimens collected at the same site. This raises questions about the validity of the subspecies and suggests that the subspecific taxonomy of P. dalmatica needs a thorough revision in the future.  (Mikhailenko & Polumordvinov 2015;Kaňuch et al. 2017). Considering the known distribution of this species, the Ljubina poljana population seems to be highly isolated. According to the present knowledge, the Poštak Mt. delineates the south-westernmost border of the distribution of P. frivaldszkyi, the closest known population being the one from the Šator Mountain, 40 km eastwards in Western Bosnia (Mikšić 1978). Here, in the south-western border of its distribution, it is restricted to a few suitable plots, similarly to its north-westernmost occurrences in Slovakia (Fabriciusová et al. 2008). The morphology of P. frivaldszkyi from the Poštak population generally fits the morphology of Transylvanian specimens, where this taxon has been described, but their coloration is unusual. Head, pronotum, legs, as well as dorsal and lateral parts of the abdomen were entirely brown in a considerable portion of the observed specimens, while in other specimens, the lateral parts of the abdomen were partly greenish (Figures 2,  3). This mixed coloration seems to be rather common in Dinaric populations (Figure 4), whereas completely brown ( Figure 5) and predominantly green specimens are rarely found. However, green coloration is common in the Carpathian populations of this species (Figure 6). The specific coloration of the Croatian P. frivaldszkyi may be associated with the high level of isolation (Kaňuch et al. 2014), but this should be confirmed by genetic analyses. The morphology of the male stridulatory file (Figure 7, 8), cerci ( Figure 9) and titillators ( Figure 10) in the Poštak population is similar to the morphology of these traits in Transylvanian populations. However, male calling song exhibits some variability in syllable structure between the populations from different parts of its distribution in the Balkans and the Carpathians (Figures 11-13). In addition, our sound recordings show high temperature dependence of syllable repetition rate, already described in this species by Heller (1988). Due to its small size and possible long-term isolation, the Ljubina poljana population of P. frivaldszkyi may be threatened by extinction, and should therefore be considered a conservation priority. Pholidoptera griseoaptera (De Geer, 1773) Chobanov et al. 2014). The specimens of Tettigonia balcanica collected in the scrubs and forest edges in the eastern part of the Ljubina poljana in July 2013 were designated as paratypes of this species in its description paper (Chobanov et al. 2014). This species is widely distributed in the Balkans, and this is the first population found in Croatia. According to our present knowledge, the Poštak Mt. delineates the north-westernmost border of the species' distribution, and the specimens collected in this area exhibit some slight morphological differences from its other known populations. Most likely widely distributed in mountain forest edges and humid bushy meadows of the study area. Tettigonia viridissima (Linnaeus, 1758): Komići: 19; Malovan: 1; Momici: 18 (song recording on the field); Otrić: 5b,6,7,9,11,13,14;Plavno: 16,17,23 Otrić: 3,4,5b,7,8,9,11,13;Plavno: 16 [1♂ 1♀ SGcoll], 21, 22, 23. Locally common grassland and scrub inhabiting species, occurring in the whole study area.  (Croatia, Poštak Mt.). 7, Stridulatory file; 8, detail of the apical part of the stridulatory file; 9, male left cercus; 10, titillators.

Discussion
The present study provides the first comprehensive orthopterological dataset for the Poštak Mountain, notwithstanding two already published sets of data (Chobanov et al. 2014;Kaya et al. 2015). The outstandingly rich orthopteran fauna of the Poštak Mt. and its surroundings was dominated by species of wider Mediterranean, European or Palearctic distributions. Out of 16 Mediterranean taxa (Acrometopa servillea macropoda, Barbitistes yersini, Leptophyes laticauda, Poecilimon sp./elegans group/, Tylopsis lilifolia, Decticus albifrons, Eupholidoptera schmidti, Pholidoptera dalmatica, P. femorata, Modestana modesta, Ephippiger discoidalis, Anacridium aegyptium, Prionotropis hystrix, Oedipodasp./germanica group/, Arcyptera brevipennis and Chorthippus bornhalmi), three are distributed all the way from the foothills to the mountain peaks, namely Poecilimon sp./elegans group/, E. discoidalis and C. bornhalmi. Six species (Poecilimon sp./elegans group/, Pholidoptera dalmatica, Modestana modesta, Psorodonotus illyricus, Prionotropis hystrix and Paracaloptenus cristatus) and a subspecies (Arcyptera brevipennis brevipennis) occurring in the study area are endemic to the Dinaric Alps. All of these Dinaric taxa are restricted to different types of dry or mesic, well-preserved natural and semi-natural submediterranean grassland habitats, which have recently been declining for various reasons in the entire range of the Dinaric Alps, especially in its northern parts (Kaligarić & Ivajnšić 2014). Four of these species are globally endangered to different degrees (P. illyricus -Near Threatened, P. hystrix -Vulnerable, P. cristatus -Near Threatened and A. brevipennis -Vulnerable), according to the IUCN Red List (Hochkirch et al. 2016b). Another widely distributed Eurasian steppic grasshopper species, Euchorthippus pulvinatus, considered Vulnerable in the European Union (Hochkirch et al. 2016b), also occurs here. Altogether five species fall into one of the endangered categories of the IUCN in the European Red List, which represents 6.3% of the species detected in the study area. Psorodonotus illyricus is restricted to a few large mountain grasslands (Nardetum) in the central part of the Poštak Mt. (parts of the Ljubina poljana and the Poštak peak area), E. pulvinatus has been detected only in a single south-facing dry grassland in the southern edge of the Poštak group, while P. hystrix, P. cristatus and A. brevipennis have been found in several sampling sites with open, rocky, submediterranean grasslands throughout the study area. The presence of these endangered taxa, and their locally wide distribution, underlines the high conservation value of the study area. This is especially true for the large grasslands of the Ljubina poljana, which are highly liable to succession, while harbouring altogether 44 orthopteran species, including some rare ones.
A recent overview of the Orthoptera fauna from the Dinara Mt. (Rebrina et al. 2015) provides an opportunity for the faunistic comparison of these two neighbouring mountains. The Dinara is the highest mountain in Croatia (1831 m asl) and its 100 km long north-west-south-east ridge stretches along the Croatian-Bosnian border, east of the town of Knin. The two ranges are divided by the deep valleys of the Butižnica and Una rivers. Although the Dinara mountain chain is much higher and larger than Poštak, species richness here (78 species) proved to be only slightly lower than that of the Dinara Mt. (86 species). Furthermore, the overlap of the already explored Orthoptera fauna of the two mountains is only 62 of 102 species (61%). In the case of two adjoining mountains of similar bedrock and a rather similar range of habitat types, this suggests that most of the differences are merely apparent, since the detailed investigation of both areas has only just started. Several species, which have formerly been found in the Dinara Mt. [e.g. Acrida ungarica (Herbst, 1786), Acheta domestica (Linnaeus, 1758), Aiolopus thalassinus (Fabricius, 1781), Chorthippus oschei Helversen, 1986, Dociostaurus maroccanus (Thunberg, 1815), Meconema thalassinum (De Geer, 1773), Saga pedo (Pallas, 1771), Sepiana sepium (Yersin, 1854), Tetrix subulata (Linnaeus, 1758)], are common in Southern or South-Eastern Europe. Their apparent absence from our study area is probably caused by the relatively low number of sampling plots, compared to the high habitat diversity of the region. Therefore, it is reasonable to suggest that, with further research, the actual orthopteran species richness in the Poštak Mountain could approach 100.
The surprisingly rich Orthoptera fauna of the Poštak mountain range, recorded in our preliminary survey, shows that even a geographically restricted area with a high variety of natural and semi-natural habitats may harbour high biodiversity and maintain considerable populations of several endangered species. Our results confirm the suggestion, based on the rich butterfly fauna found on the Poštak Mt. (Koren et al. 2015), that the area might be considered a hotspot of insect diversity in Croatia, which underlines the necessity of further research and conservation of its fauna.