POLISH JOURNAL OF ECOLOGY 54 1 151–157 2006 (Pol. J. Ecol.)

Short researchresearch contribution

Kamil Bartoń1, Jan Rafiński2

1 Department of Comparative Anatomy, Institute of Zoology, Jagiellonian University, Ingardena 6, 30-060 Kraków, Poland (present address: Mammal Research Institute, Polish Academy of Sciences, 17-230 Białowieża, Poland; e-mail: [email protected]) 2 Department of Comparative Anatomy, Institute of Zoology, Jagiellonian University, Ingardena 6, 30-060 Kraków, Poland

CO-OCCURRENCE OF AGILE FROG (RANA DALMATINA FITZ. IN BONAPARTE) WITH COMMON FROG (RANA TEMPORARIA L.) IN BREEDING SITES IN SOUTHERN POLAND

ABSTRACT: A location (area 10 km2) of the Rana arvalis (Nilsson), and the agile frog agile frog (Rana dalmatina Fitz. in Bonaparte) in (Rana dalmatina Fitz. in Bonaparte). All of a southwest part of the Sandomierz Valley (south- them reproduce in early spring, immediate- ern Poland), was surveyed during 4 breeding ly following spring thaw, and they differ in seasons (1999–2002). Eighteen breeding sites of their habitat preferences. The common frog brown frogs were inspected for their character- istics, presence and numbers of egg-batches, and is among them the most ubiquitous species, time of egg deposition. Breeding sites were typi- occurring in a range of habitats throughout cally temporary, small, and shallow waters (area the whole country, whereas agile frog is the 5–30 m2, depth <50 cm). The agile frog was found rarest amphibian in Poland, and its occur- to co-occur only with the common frog (Rana rence is still poorly known (e.g. Juszczyk temporaria L.) in most of the sites. Based on the 1987). Mature individuals of agile frog were number of egg-batches, the agile frog was more recorded from southeastern regions: several numerous (total of 315 batches in year 2002) than locations in Carpathian Foothills, and one the common frog (163). Over the four years of lowland location in the edge of Sandomierz the study, there were no significant fluctuations Valley (20°43´E, 50°00´N; Błachuta and in the numbers of eggs. The two species did not Jabłoński 1986, Rafiński et al. 1987, differ significantly in their choice of the habitats, except for the sites with low water pH, used pre- Szymura 1994, Szymura and Rafiński dominantly by the agile frog. Habitat niche over- 1997). The species has been classified as lap was high (Pianka’s O = 0.86). In the acid peat endangered (Polish Red List of Vertebrates; bogs (water pH about 4.5) most of the eggs de- Rafiński and Szymura 2001). generated. Among European anurans, the agile frog exhibits a most disjunctive distribu- tion (Grossenbacher 1997). The species’ KEY WORDS: agile frog, common frog, main range covers large areas of southern brown frogs, breeding sites, acidification Europe. Isolated populations exist in central and northern parts of Europe (Germany, Po- Three species belonging to the brown land, Denmark, and Sweden). The northern- frog group occur in Poland: the common most location is the Swedish island of Öland frog Rana temporaria (L.), the moor frog (Grossenbacher 1997). 152 Kamil Bartoń, Jan Rafiński

Fig. 1. Location and schematic map of the study site (southwest part of the Sandomierz Valley, southern Poland), with locations of the breeding sites of brown frogs. Numbers correspond to Table 2.

Until now, there were no records of watercourses. Open habitats include wet breeding sites of the agile frog from Poland. meadows, peat bogs, and cultivated fields. Therefore, its local breeding preferences, The study area covered about 10 km, forests which vary considerably throughout the and woodlots made 33% of that area (Fig. 1). species range (Grossenbacher 1997), re- In the north, the study site was adjacent to mained unknown. Thus, the first aim of our a large managed forest (Radłów Forests, ca study was to characterize breeding sites of 80 km2). The climate of the area is moderate the agile frog in south-eastern Poland. The with the mean temperature of January aver- second was to assess its co-occurrence with aging –4.7°C, and that in July 19.3°C. Mean two other species of brown frogs in sympat- annual precipitation is about 650 mm. Am- ric populations. phibian community includes also the other The study was conducted in the south- two species of brown frogs occurring in Po- western part of the Sandomierz Valley land (i.e. common frog and moor frog), the (20°43´E, 50°00´N). It is a lowland region green frogs (R. esculenta L. and R. lessonae (200 m a.s.l.), characterised by a mosaic, Camerano), tree frog Hyla arborea L., com- human-transformed landscape. The area mon toad Bufo bufo L., and the smooth newt is covered by fragmented forests composed Triturus vulgaris L. mainly of pine (Pinus silvestris) and birch Study area was visited several times a year, (Betula verrucosa), with admixtures of oak in March and April 1999–2002. Water bodies (Quercus robur) and alder (Alnus sp.) along were located with the use of a map, informa- Co-occurrence of Rana dalmatina with Rana temporaria in breeding sites 153 tion from earlier studies (Szymura 1994), a-th habitat in the numbers of batches of j-th and that obtained from local people. In total, species in all habitats. Value of O ranges from 18 breeding sites were found, and surveyed 0 (exclusive niches) to 1 (complete overlap). for the presence of egg-batches of brown Majority of the breeding sites, consisted frogs, but only 7 of them were surveyed each of temporary, small (5–30 m2) and shallow year. As a breeding site, we considered either pools (<50 cm). Egg-batches or tadpoles of a single water body, or a group of adjacent, the agile frog were found in 17 breeding sites, usually small pools, often surrounding larger and those of the common frog in 11 breeding central pond. The following characteristics of sites. Thus, the two species co-occurred in water bodies within the breeding sites were 10 breeding sites, in 8 of them the agile frog described: size, surroundings, distance from bred solely, and in one breeding site only the the nearest forest, type of vegetation in the common frog was found. In 7 sites surveyed pond, type of bottom, water pH. Egg-batches throughout the whole study period, the of brown frogs were counted in each breed- mean total numbers of egg-batches were 45.5 ing site. Batches were characterized by their (range 24–62) and 24.3 (range 18–36) for the distribution (separately or in groups), verti- agile frog and the common frog, respectively. cal placement (surface, mid-water, bottom), Overall batch numbers throughout 4 breed- type of placement (free floating or attached ing seasons did not show significant changes to submersed objects), and appearance of (chi square test, χ² = 5.57, df = 3, P = 0.13), egg-capsules. Developmental stages of em- although they sometimes varied consider- bryos (according to Gosner 1960) were ably in individual breeding sites (Table 1). determined with a hand lens magnification, The agile frog bred recurrently each year in in some of the eggs from a group of adjacent all the 17 sites, where this species occurred, batches. From selected batches, samples of and the common frog only in old riverbeds. 10–20 eggs were collected and transported In 2002, in all 18 located breeding sites, agile in plastic bags, to the tanks (filled with water frog was significantly more abundant than with neutral pH) in laboratory. Shortly after common frog (χ² = 48.33, df = 1, P = 0.00), hatching, larvae were observed under a bin- 315 egg-batches of the agile frog and 163 of ocular microscope, and their features noted. the common frog were found. Grown up tadpoles were identified according Among the breeding sites, six habitat to the key of Günther (1996). types were distinguished (Table 2). The two Breadth and overlap of the habitat niches species differed in the choice of breeding of the two species were calculated. Habitat sites (Wilcoxon test, Z = 2.20, P = 0.03), bbutut niche breadth was calculated using index less in the choice of habitats (Z = 1.89, P = B (Levins 1968): 0.06). However, ditches, forest pools, peat ponds, and bogs were used predominantly by B = 1 / (n∑pipi2) the agile frog (comparisons for each habitat, (1) χ² = 11.0 – 63.6, df =1, P <<0.003 withwith Holm’sHolm’s correction applied). Using batch numbers in

where pi is the number of batches in 2002, calculated habitat niche breadth of the habitat i expressed as a fraction of summed agile frog (B = 0.50) (equation 1) was wider batch numbers in all n habitats. Value of B than that of the common frog (B = 0.27). can range from 1/n (use of a single habitat) Overlap of habitat niches (O) (equation 2) of to 1 (equal usage of habitats). the two species was 0.86. Overlap of habitat niches was calculated The pH of waters, where the frogs bred, according to Pianka (1973): ranged from 4.6 to 7.5 for the agile frog, and ½ 6.4–7.5 for the common frog. Mortality of O = (∑p p ) [(∑p 2) (∑p 2)] – ij ia jaja ia jaja eggs and embryos occurred in dystrophic peat (2) bogs. This breeding site held acid waters with

where Oij is the overlap between species pH 4.6–6.2. Agile frog bred there throughout i and j, pia iiss tthehe ffractionraction ooff a-th habitat in 4 seasons of the study, while common frog the summed numbers of batches of i-th spe- only in one season. Most of the egg-batches cies in all habitats, and pjaja is the fraction of observed in that site degenerated. The egg- 154 Kamil Bartoń, Jan Rafiński

Table 1. Numbers of egg batches of the agile frog Rana dalmatina (R. d.) and the common frog Rana temporaria (R. t.) found in various habitats (Table 2) during 4 seasons of the study. Qualitative data only are available for peat bogs before 2002. Sand excavation site was found in 2002.

Number of egg batches found

1999 2000 2001 2002 Breeding sites R.d. R.t. R.d. R.t. R.d. R.t. R.d. R.t.

Old riverbeds 14 12 12 10 13 14 5 13

Peat ponds 28 4 6 1 39 22 39 8

Peat bogs + – + – + – 103 16

Sand excavations — — — — — — 144 126

Forest pools 13 0 16 8 12 0 13 0

Ditches 7 10 30 2 9 0 11 0

Total number 62 26 64 21 73 36 315 163 masses were milky-green, infested by fungi, (Szymura and Rafiński 1997). In Ger- and the batches usually lied on the bottom many, the species usually occurs also with (properly developing eggs float under water the common frog, and rarely with the moor surface). However, mortality affected main- frog (Günther et al. 1996). Egg-batches of ly outer eggs of the batch, so often those in the common frog and the agile frog are of- the middle developed normally. Despite that ten found together, but if the populations are mortality, transformed froglets from those large, the species exclude each other (Rohr- ponds were observed (J. M. Szymura, pers. bach and Kuhn 1997). In contrast, there comm.). is a pronounced lack of sympatry of the two The agile frog started breeding in the species in northern Europe (Andrén and first half of March, whereas the common frog Nilson 1988). In sites where both species about a week later (end of March, beginning are present, they seem to segregate in their of April). Egg deposition took place typically choice of breeding ponds (Riis 1997). Riis after the snow had melted permanently, but (1988) explained such a distribution by com- in a few cases, egg-batches were found fro- petitive exclusion at the tadpole stage. zen. Single new batches of both species were Most of the breeding sites in the study found up to the end of April. Hatching took area were situated within forest, but also far place in the first half of April. The larvae of from the forest border. This distance was the common frog often started to hatch ear- larger than in Denmark, where frogs mostly lier than those of the agile frog, which were at used water bodies located 200 m from the that time in stages 19–20 (visible heart beat forest (Wederkinch 1988). Also in France and gill circulation, Gosner 1960). and south Germany this distance was small- In the study area, the agile frog shares er: 50–100 m, never exceeding 250 m (Rohr- breeding sites only with the common frog, bach and Kuhn 1997, Ponsero and Joly even though adult moor frogs were also ob- 1998). The agile frog is strongly connected served (Szymura 1994, K. Bartoń pers. with deciduous forests, in Denmark, num- obs.). In the Carpathian Foothill, the agile bers of egg-batches declined exponentially frog co-occurs only with the common frog with increasing distance of a breeding pond Co-occurrence of Rana dalmatina with Rana temporaria in breeding sites 155 from the forest (Wederkinch 1988). Over Szymura and Rafiński 1997), and this the whole range of the agile frog, its habitats species was not found in strictly agricultural consist of forests and wet meadows. In Swe- vicinities of the study site, with scarce wood- den, the species inhabits scrublands and mo- lots (K. Bartoń unpubl. data). saic of deciduous forest, wetlands, and pas- We observed an evident difference in use tures, the breeding sites were usually found of peat bogs by the two species. While agile in the wooded areas (Ahlén 1997, Riis frog was abundant, common frog avoided 1997). In central Europe, it is found mainly that breeding site. Increased mortality and in deciduous and mixed forests (Grossen- degeneration of eggs was likely to be caused bacher 1997). In north Germany (Lower by acidification, a negative factor for eggs Saxony, Podloucky 1997), breeding sites and larvae (Andrén et al. 1988). Among are most often located in mixed oak or beech brown frogs, the agile frog appears to be least forests, and varied from small to several- tolerant to acidity (Andrén et al. 1988). Ex- hectare water bodies. In central Europe, the periments by Andrén and Nilson (1988) agile frog bred in open, sunny moors, or old showed that all eggs died at pH 4.0, but at pH riverbeds within forests (Grossenbacher 5–6, the hatching success was almost 100%. 1997). Likewise, all locations in Poland were Low pH exerts a strong harmful effect, caus- found in wooded areas (Szymura 1994, ing high mortality of eggs and embryos, la-

Table 2. Description of the breeding sites of the agile frog (Rana dalmatina), surveyed in 1999–2002 in the southwest part of the Sandomierz Valley (southern Poland). Number Size of wa- Depth No. Habitat Location of breed- ter bodies Characteristics pH (cm) ing sites (m2) Former meanders of regu- Meadows, lated river, bottom covered arable Old river- with grass and submerse 1 fields, close 2 20–30 20–40 7.2–7.5 beds vegetation, surface par- to forest tially covered by LemnaLemna border minor. Wet Peat meadow, 20–30, Shallows covered by grass. 2 2 50, 10 5.2–6.2 ponds ca. 100 m <100 Brown water. from edge Group of bogs, former Edge of for- 20–30, sand excavation. Bottom 3a Peat bogs est and wet 2 1–80 4.6–5.5 <50 covered by Sphagnum meadows moss and sedge. Partially covered by sedges, 3c “ “ 1 5 “ 6.5 filamentous algae. Layer of dead leaves on 3b “ “ 1 5 “ 6.2 bottom. Over 100 m Sand ex- 4 within 5 1–20 10–30 Reeds and sedges. 6.5 cavation forest Over 100 m Forest within No vegetation, leaves on 5 2 10 <50 6.0 pools pine-birch bottom. forest Arable land, > 200 m over 400 m Overgrown by filamentous long, 6a Ditches from 2 <30 algae and Lemna minor, 7.5 1–2 m wooded partly by reeds and willow. wide area 50 cm Slowly flowing water, 6b “ Arable land 1 “ 6.4 wide growth of grass. 156 Kamil Bartoń, Jan Rafiński tent embryonic development, deformations REFERENCES and abnormal behaviour of larvae, affecting size and age at the metamorphosis (Pahkala Ahlén I. 1997 – Distribution and habitats of et al. 2001, Räsänen et al. 2002). Tolerance Rana dalmatina in Sweden – Rana, 2: 189– to acidification, however, might be higher 202. in populations exposed naturally to low pH Andrén C., Nilson G. 1988 – Effects of acidi- (Glos et al. 2003). fication on Swedish brown frogs – Mem. Soc. Fauna Flora Fenn. 64: 139–141. 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