Wolf spiders ( Araneae : Lycosidae ) on the overgrowing peat bog in Dubravica ( north-western Croatia )

Wolf spiders (Araneae: Lycosidae) on the overgrowing peat bog in Dubravica (north-western Croatia). The peat bog in Dubravica is of spread interest due to its overgrowing by the process of natural succession, causing the habitat to become dryer and shadier. The dominance structure and phenology of wolf spiders on the Dubravica bog was studied. The spiders were collected during the period 09.04.-9.10.1995, using 20 pitfall traps. Altogether 10 lycosid species were found among 723 adult individuals. For six more abundant species phenology graphs are presented. Three species are found to be eudominant: Pardosa lugubris, Trochosa spinipalpis and Hygrolycosa rubrofasciata. The lycosids habitat preferences and dominance structure according the habitat condition and species occurrences on some other European bogs are discussed. 55,2 % caught specimens are hygrophilous species, and only 7,6 % are photophilous. The lycosid fauna and dominance structure does reflect the habitat condition. As overgrowing is not fully progressed yet, the lycosid fauna of this bog is still relatively bog-characteristic.


INTRODUCTION
Bogs, mires and fens are reliets in Croatia, rare and exeeedingly loealised habitats (ILIJANK2 1 996).The peat bog in Dubravica is an endangered and protected landscape, and has carried the status of a botanical reservation since 1 966.During the last 50 years the area of the peat bog has significantly decreased.Surrounding alder and alder buckthorn seedlings have been slowly overgrowing the bog, changing the habitat in the process of natural succession.When communities change, abundance of species, whose demands are in accordance with the newly establishing conditions, increase.
For groups of species whose demands correspond to the previous condition of the habitat decreasing of abundance takes place (RUZKSkA & ANTUS  1989).In accordance, with overgrowth of the bog the proportion of photophiloiis or peat bog species deerease in favour of scotophilous (often forest) ones (SCHIKORA 1994, KUPRYJANOWICZ et al. 1998).
For monitoring the situation and ehanges of bog habitats eomposition and abundanee of dominant spider speeies (often lyeosids) provide useful data (KOPONEN 1979, SCHIKORA 1994).Lyeosidae are one of the dominant group of epigeie aetive Araneae.Light and moisture are two important abiotical faetors limiting their abundance (TRETZEL 1952).The objectives of this paper were to establish the fauna of wolf spiders on this bog, and to investigate in what way the spider species dominanee and abundanee re fleets the habitat eondition.We also wanted to compare oecurrenee of lycosid species on this bog and some other European bogs (concerning the habitat requirements) and to contribute to the knowledge of the phenology and biology of some lycosid species.Furthermore, this is the first contribution to the arthropod fauna of Dubraviea bog.

STUDY SITE
The bog in Dubraviea is one ofthe most southern studied in Europe.The bog is located in sessile oak and hornbeam forest (assoeiation Epimedio- Carpinetum betuli (Ht38) Borh.63) near the village of Dubraviea (45°57' N and 15°45' E) at an altitude of 160 m.The inclination of the bog's surface is 4-5°w ith a north-western exposure.At the loeation where the bog of 1 630 square meters was found by HORVAT (1939), only a small bog of 605 square meters was in 1994 (HRSAK 1996).The purple moor grass (Molinia caerulea) and peat moss {Sphagnum subsecundum) are the most dominant plant species.The alder and the buckthorn bushes are overgrowing the bog, changing the habitat slowly into the bushes, and possibly into the forest (site deseription according to HRSAK 1996).The average monthly temperature and preeipitation are given in Eig.

MATERIAL AND METHODS
The material was collected with 20 pitfalls exposed during 5 months, from 9^^A pril to 9'' October 1995, dates coincident approximately with the growing season.Because of the variability in morphology we did not determine the females of the genus Trochosa to the species level and we have calculated the average number of individuals of both Trochosa species according to the number of males.Data on females of both species are presented together.

RESULTS AND DISCUSION
Altogether 994 adult spiders were caught, within 72,7 % (723) were wolf spiders (Araneae: Lycosidae), among which ten species were found.The dominance oflycosids in the material varied from 3 8, 1 % to 82,8% throughout the season (Fig. 2).The abundance of other spiders did not vary in such extent.Their activity was slightly higher in spring.
H. rubrofasciata has, as eudominant species on Dubravica bog (but not  widely distributed in this region) certainly found suitable ecological parameters in this habitat.
Pirata hygrophilus Thorell, 1872 (4,6%) is a typical species for alder forest (KOPONEN 1979), but it has been found on Sphagnum as well (KOPONEN 1968, CASELIUS & ITÄMIES 1993, KUPRYJANOWICZ   et al. 1998).It prefers habitats with low evaporation, low temperature, and low light values (RENNER 1986).As both H. rubrofasciata and P. hygrophilus are alder forest species, it is not likely that their abundances would be negatively affected by a change of the habitat into an alder forest.
Pirata uliginosus (Thorell, 1 856) (0,2%) is a stenotopic species (THALER 1996), with clear preferences for Sphagnum.It is interesting that this species was subrecedent on Dubravica bog, while it is one ofthe characteristic and often abundant species on some other European peat bogs (DAHL &  DAHL 1927, KOPONEN   KOPONEN et al.  2001).This species prefers habitats with high temperature and high light values (RENNER 1986).Still, it is not certain if the low abundance of this species is connected with the overgrowing of the bog, since it is also found on shady wet habitats as well (BREYMEYER 1 966a, KUPRYJANOWICZ et al. 1 998), and SCHIKORA ( 1 994) founds, uliginosus after overgrowing of a bog even in greater number.BAEHR & EISENBEIS (1985) suggest that P. uliginosus is less hygrophilous than P. hygrophilus, which is far more abundant in our material.This means that possible dryness caused by overgrowing is not the probable cause for its small abundance, either.Also, bogs inhabited by P. uliginosus are geographically widely distributed with different temperature conditions.So it could be thatP.uliginosus is so rare on this bog due to some biotic factors (competition or predatory interaction).This is the third record of P. uliginosus in Croatia.It is already found more southern in Istria and eastern in Slavonija (RUCNER & RUCNER 1995).
It usually lives under the stones on freshwater shores (BUCHAR &   THAEER, 1995) and we assume that one male caught in early summer came from the brook distanced app.fifty meters of the bog, and that this species does not normally inhabit the peat bog.It is not usually reported from European peat bogs either.
Altogether, five of the ten species found commonly inhabit European peat bogs; none of them is bog specific.Additionally, two eurytopic and one xerophilic species occasionally inhabit European peat bogs, one species is characteristic for moist meadows, and one is accidentally caught.The typical European peat bog lycosid species Pardosa sphagnicola was not found on this habitat, probably due to its more northern distribution.
Shady peat bogs are often characterized by a low proportion of peat bog and photophilous species and high proportion of forest species; all peat bogs are characterized by a relatively high proportion of hygrophilous species (KUPRYJANOWICZ et al. 1998).The predominance of photo- philous species is a typical feature of the terrestrial spider fauna on pristine bog biotopes (SCHIKORA 1994).Only 7,6 % of the caught lycosids are photophilous (v4.albimana,A.pulverulenta.P. amentatasLndP.uliginosus).
In accordance with the shadiness of the habitat none of them is among the dominant species.However, it is not sure if the small abundance of photophilous species is caused by the purple moor grass, which certainly decreases the insolation during the period from June to September, or if it is caused strictly by the presence of the alder and alder buckthorn bushes.
Hygrophilous species are T. spinipalpis, H. rubrofasciata, P. hygrophilus, P. amentata, P. uliginosus and A. maculata, comprising 55,2% of all the lycosids.This indicates that the exsiccation of the bog is still not quite progressed.

Phenology
Phenology is presented (Fig 3 .)only for six subdominant to dominant species (over 2 %), when data were substantial for some phenological conclusions.Males were generally active through a shorter period than females, usually with higher peaks, which are considered to be the time of copulation (BREYMEYER 1961).Their activity during summer and autumn was only sporadic.Females are known to lay eggs app.two weeks after copulation; they carry the egg-cocoon for six weeks and than the hatched juveniles for about one week on their backs (EDGAR 1971).For the more abundant species all of these events could be tracked in phenology pattern.
Trochosa spp.and H. rubrofasciata show the same pattern of phenology (Fig. 3.).In one short period (the first half of the May), there was the highest peak in abundance due to increasing activity of males.The onset of activity is surely influenced by the temperature conditions.This results in the same onset ofactivity of Trochosa spp.and//, rubrofasciata, which all overwinter as adults.Eow number of females of all these species in traps in June indicate a period when females carrying the egg sacs decreased their activity.They were spending most of the time in a burrow in the ground (FUHN & NICOLESCU-BURLACU 1971).Their activity increases afterwards, what is probably the period of hatching juveniles, when females leave the burrow.The phenology of two Trochosa species was very similar.These are diplochronus species, but a second copulation period, noticed by some authors (BREYMEYER 1961) was not observed.H. rubrofasciata was the last species found to be active in autumn (October), and this was because of the appearing of a new generation of adults in autumn, which will mate during the next spring (KRONESTEDT 1 984).The phenology pattern of Trochosa spp.and H. rubrofasciata coincide with other data of authors (BREYMEYER 1966b, FREUDENTHALER     KRONESTEDT 1996).¥orP./wgw/?rä another pattern of phenology is shown (Eig.3.).Only for this species an obvious increase of number of females in samples and an overlap of peaks in males and females activity were observed.This is also the only species with more females in the material.This could be because males preferred forest, females meadow like vegetation (ITÄMIES & RUOTSAEAINEN 1985).
According to BUCHAR (1970), females move during June from the forest to the more sunny places for worming their egg sacs.Actually, few weeks after the main peak in activity (indicating copulation), during June, the number of females in traps started to increase (Fig. 3.).This was appro- ximately the period of eggs laying and the activity remained increased for six weeks while females were carrying egg-sacs.
All this, including a border effect (TISCHLER 1958), could explain the greater abundance of females in material as well as the fact that there are probably no real limits between forest and bog populations of this species.
Even when the total number of individuals of one species is smaller, the significant increase of the number of males in a short period indicating copulation is detectable, for A. pulverulenta and P. hygrophilus (Fig 3 ).
Activity ofA.pulverulenta adults started at end of April, with male activity peak in the middle of May what is in coincidence with some other authors' data (KRONESTEDT 1 990).The latest in season was the copulation period of P. hygrophilus, in June.
Similarities of our results with other authors data on the phenology of A. pulverulenta and T. terricola indicate that the pitfall method can give representative phenology patterns for less abundant species too, at least higher peaks could be noticed.

Aggregation
For males of the species T. spinipalpis and T. terricola, H. rubrofasciata and P. hygrophilus we have noticed aggregation during their period of increased activity (indicating copulation period) as statistically significant (p<0,05) higher number of males in certain traps.During other trapping periods no significant differences in number of spiders in some traps were noticed.However, the number of caught specimens was significantly lower, decreasing the possibility of noticing aggregation.
During the peak activity of T. spinipalpis males, most of them (89,8 %- of specimens of T. terricola in a few traps located a few meters of each other, in the border zone between forest and clearing; but they were avoiding places that are too moist or too shady.T. spinipalpis and T. terricola are sibling species with different ecological preferences and it is not likely that the same microhabitat would suite best for both of the species. 77% (47 of 61) //.rubrofasciata males were caught in 5 of 17 operating traps (Standardized Morisita index is 0,53).However, traps in which H. rubrofasciata males were caught, were not situated nearby each other, rather randomly spread on the bog area.KÖHLER & TEMBROCK ( 1 987) found that males of//, rubrofasciata aggregate during the mating period on sunny, dry places, where they find appropriate substrate for drumming on dry leaves.Even though the abundant presence of the purple moor grass and alder and alder buckthorn bushes make this habitat shady during most of the vegetational season, at this time (the end of April, and first half of May ) the ground is still quite insolated.Also, last years purple moor grass dry leaves could probably make a suitable substrate for precopulatory drumming.77, 8 % (14 of 18) of P. hygrophilus males were caught in 1 of 20 operating pitfalls during their peak of activity (Standardized Morisita index is 0, 77).
As this is one of the most hygrophilous species, it is interesting that this trap was not situated in the area of the highest humidity.

CONCEUSIONS
Considering dominance and ecological preferences of all species, the dominance structure of this guild does reflect the habitat condition.It is in accordance with one expected for a shady wet habitat.Although we have no knowledge on the lycosid fauna of this bog before the succession, we can presume that the change of habitat did influence spider species composition and dominance structure.With overgrowth of the peat bog the habitat becomes shadier and dryer which causes photophilous species to become less, and some forest species more abundant.Lycosid fauna of Dubravica bog is still relatively bog-characteristic.Our results confirm that wolf spiders are good ecological indicators of the habitat changes, but the dominance of all species has to be taken in consideration.
Fig. 1: a) Monthly temperature b) Precipitation and number of sunny days number of spiders in pitfalls per dayxlOO

Fig
Fig. 3: Phenology graphs Traps were emptied at28.04., 14.05., 27.05., 17.06., 1 1.07., 05.08., 01.09;, 20.09. and 09.10.Pitfalls were plastic cups (diameter 8,5 cm and 12 cm deep) set randomly across the whole bog area at 4-5 m spacing, each filled with 1,5 dl of mixture of water, formalin and EtOH as a preservative.In this paper we deal only with data on adult spiders.In the estimation of species dominance and seasonal dynamic we present numbers of adults in one pitfall per day (xlOO), as number of days and operating pitfalls were different during each exposure period.Dominance of each lycosid species was calculated as a percentage of all adult spiders.Morisita index of aggregation is calculated after KREBS(1989).
1979, FREUDENTHALER 1989, THALER & BUCHAR 1 996, SCHIKORA 1 997,KAJAK et al. 2000, 1989,KÖHLER & HRSAK 1996)dividuals) were caught in 7 (nearby situated) of 17 working traps (trapping period28.04.-14.05.1995).Standardized Morisita index of dispersion is 0,53.This indicates an aggregated pattern of activity or distribution.It is interesting that 7 1 ,4 % ( 1 5 of 2 1 individuals) of7.terricola males were caught in the same 7 traps.Correlation coefficient of the numbers of T. spinipalpis and T. terricola in traps during this period is 0,78 (p<0,05).Most of the females (88,2 %; 15 of 17 individuals) were caught during the same period in the same 7 traps.It is possible that this was influenced by the microhabitat selection, while on a main part of this bog area is a water filled gully, causing the highest humidity and greater insolation and the floristic composition was a bit different (seeHRSAK 1996).SCHIKORA (1994) also found ihdiiAntistea elegans shows clearly aggregated pattern of activity or distribution on a peat bog, correlated with the wet and open spot.1TÄMIES & RUOTSAEAINEN (1985) caught half