What Do the Terrestrial Isopods Eaten by Some Frogs from North-Western Romania Have to Say?

North-Western Journal of Zoology Vol. 6, No. 2, 2010, pp.268-274 P-ISSN: 1584-9074, E-ISSN: 1843-5629 Article No.: 061126

What do the terrestrial isopods eaten by some frogs from north-western Romania have to say?

Nicolae TOMESCU1,*, Sára FERENŢI1,2,*, Severus D. COVACIU-MARCOV2, István SAS2 and Anamaria DAVID2

1. “Babes-Bolyai” University, Faculty of Biology and Geology, Department of Biology, Gheorghe Bilascu (Republicii) str. 44; 400015 Cluj-Napoca, Romania. 2. University of Oradea, Faculty of Sciences, Department of Biology, Universitatii str. 1, 410087 Oradea, Romania. * Corresponding authors, N. Tomescu, e-mail: [email protected], S. Ferenţi, e-mail: [email protected]

Abstract. Eight species of terrestrial isopods: Hyloniscus transsylvanicus, Protracheoniscus politus, Porcellium conspersum, Trachelipus wachtleri, T. arcuatus, T. nodulosus, T. rathkei and Armadillidium vulgare have been identified in the stomach contents of four species of frogs (Rana arvalis, R. dalmatina, Phelophylax. lessonae and P. kl. esculentus). The isopods belong to four ecological categories: paludicolous, sylvan, praticolous and euritopes, most species being sylvan. The highest number of individuals belongs to A. vulgare. There are differences between the four species of amphibians concerning the isopods’ consumption, but also within the same species from different habitats. Amphibians from a treeless marsh located far from any forest have preyed upon several sylvan isopods. Perhaps, these have survived in marshes after deforestation due to the colder and moisture climate of the region. It seems that the general ecological conditions of the plain from north-western Romania act upon isopods too, the frogs from plain consuming also isopods generally associated with higher altitudes. The differences concerning the intake of isopods are determined by the overall biodiversity of the frogs foraging habitats and possibly by the behaviour of the isopods, the faster species and those which are often hiding being consumed less frequently.

Key words: terrestrial isopods, unusual records, amphibian food, Romania.

Introduction ton 1970), there are known situations when over 90% of the individuals of some amphibian Terrestrial isopods are consumed by various populations fed on isopods (David et al. 2008). predators (Sutton 1970) including amphibians, Amphibians are important consumers in both a fact pointed out by several studies concern- aquatic and terrestrial habitats, the quantitative ing the feeding of frogs (e.g. Hirai & Matsui information about their role in ecosystems be- 2000, Arroyo et al. 2008, Cicort-Lucaciu 2009, ing important (Whiles et al. 2006) as food is a Ferenţi & Covaciu-Marcov 2009, Sas et al. 2009, primary link between an animal and its envi- Yu et al. 2009, Covaciu-Marcov et al. 2010, ronment (Kennett & Tory 1996). Knowledge of Kovács et al. 2010). However, these studies al- a species diet may provide information about most in all cases stop at this point and do not life history, population fluctuations, effects of assign the species of isopods eaten by the frogs, habitat modification (Anderson et al. 1999) or their ecological requirements or zoogeographi- even about the quality of habitats inhabited by cal history and thus synthesis connections are amphibians (Kovács et al. 2007). At their turn, not made. Although it is considered that pre- isopods are major components of the litter dation is not an important factor in the nu- fauna being among the most important de- merical limitation of isopods populations (Sut- composers (Anderson 1988). Some species of

©NwjZ, Oradea, Romania, 2010 North-West J Zool, 6, 2010 www.herp-or.uv.ro/nwjz Oradea, Romania Terrestrial isopods eaten by frogs from Romania 269 isopods are bioindicators (Paoletti & Hassall The wetland from Andrid has a length of several km 1999), others have narrow ecological require- and a width of few metres, established at the level of a small stream on whose course there is a fishpond. The ments and are bound to certain types of habi- habitat has typical marshy vegetation, exclusively herba- tats. Thus, knowledge of isopods species from ceous, surrounded by agriculture fields. At Livada, the the diet of frogs might help in ascertaining the frogs were found in a highly humid oak forest, located at trophical strategies and the feeding habitats of the bound of Livada Plain and the lowest peaks of Oaş frogs as well as in extending the data about the Mountains. R. arvalis and R. dalmatina were captured from an extremely broad wetland, with short vegetation, ecology and biology of both groups. situated in the neighbourhood of a channel. P. lessonae and P. kl. esculentus proceed from a permanent pond surrounded by marshy zones, located at the edge of the for- Material and Methods est.

The studies about the feeding of amphibians were made in 2003, samples being taken at a monthly frequency and Results a total number of 738 frogs were studied. The diet of four species of frogs were analysed: Rana arvalis, R. dalmatina, The four studied amphibian species consumed Phelophylax. lessonae and P. kl. esculentus (Sas et al. 2003, 2007, Aszalós et al. 2005). The first two are terrestrial spe- isopods belonging to eight species Hyloniscus cies except during the breeding period and the last two transsylvanicus, Protracheoniscus politus, Porcelli- are more aquatic. Terrestrial frogs were captured by um conspersum, Trachelipus wachtleri, T. arcuatus, hand and aquatic ones with the help of some nets assem- T. nodulosus, T. rathkei and Armadillidium vul- bled on long metallic handles. Stomach contents were collected using the stomach flushing method (Solé et al. gare. Not all the isopods from the stomach con- 2005). This method does not harm the animals, which are tents of the frogs could have been identified to later released. The samples were stored in separate air- species level due to fact that they were too tight test tubes in formaldehyde and identified in the strongly digested. laboratory under a binocular microscope. Food composi- The eight species of isopods were not even- tion was evaluated by percentage abundance (%A) and frequency of occurrence (%f). ly consumed by frogs; there were differences The study was carried out in Satu-Mare County, both between habitats and between amphibian north-western Romania, near the border with Hungary species (Table 1). From the ecological point of and Ukraine (Fig. 1). The frogs were captured from two view, the terrestrial isopods eaten by amphi- localities situated at approximately 150 m altitude, at bians belong to four categories: paludicolous Andrid only a single species, Rana arvalis was studied, and at Livada all the four. Frogs inhabited marshy zones, (H. transsylvanicus), sylvan (P. politus, P. cons- but at Andrid they were captured from a treeless swamp persum, T. wachtleri, T. arcuatus), praticolous (T. and at Livada from wooded swamps. nodulosus, A. vulgare) and euritopes (T. rathkei). Overall, the highest number of individuals

consumed by frogs belongs to A. vulgare species, a praticolous form but with synanthrope tendencies. The second place is held by T. arcuatus followed by T. wachtleri, both sylvan species. The paludicolous species H. transsylvanicus was consumed only accidentally. The habitat in which the most terrestrial isopods were consumed and in which the con-

dition of most of them allowed their determi- Figure 1. Map of study area nation, was that from Andrid. The highest (1. Andrid locality, 2. Livada locality) number of identified species and individuals

were intake by frogs belonging to R. arvalis

North-West J Zool, 6, 2010 270 Tomescu, N. et al.

Table 1. The species and number of isopods from the stomach contents of the frogs; the isopods percentage abundance (%A) and their frequency of occurrence (%f) related to the other prey categories.

Locality / Amphibian species Andrid Livada Isopod species R. arvalis R. arvalis R. dalmatina P. lessonae P. kl. esculentus Hyloniscus transsylvanicus - - - - 1 Protracheoniscus politus 1 - 1 - - Porcellium conspersum 3 - - - - Trachelipus wachtleri - - 10 2 3 Trachelipus arcuatus 17 - - - - Trachelipus nodulosus 4 - - - - Trachelipus rathkei 11 1 - - - Armadillidium vulgare 27 - - - 3 Isopods percentage from total 4.5 3.14 3.55 1.4 3.1 preys (%A) Occurrence of isopods (%f) 19.7 9.25 8.83 7.1 19.3

species, followed by P. esculentus. Between the tion in the marshy zones. Ingress of some syl- two studied populations of R. arvalis the differ- van isopods in wet grasslands has been re- ences are great concerning the identified iso- ported before (Tomescu et al. 2000), but in ar- pods species as well as the overall percentage eas where there were forests nearby and only abundance of isopods and their frequency of in the mountains where moisture and low occurrence. temperatures have allowed this (Tomescu et al. 2000, 2005). The reason sylvan isopods survive in unwooded marshes from north-western Discussion Romania is given by the colder and more humid climate of the region (Stoenescu et al. The highest consumption of isopods was re- 1966). Thus, in these swamps there are glacial corded at Andrid, the unwooded habitat and relicts attached to a colder and more humid where forests are lacking even in the vicinity. climate, that belong to other animal groups too However, half of the species identified in the (Covaciu-Marcov et al. 2005a,b, Sas et al. 2008). diet of these frogs are sylvan: P. politus, P. The explanation for the occurrence of forest conspersum, T. arcuatus. P. politus is dominant species in swamps seems plausible, these spe- and constant in the oak forests from Hungary cies being in fact, tributaries of certain climatic (Farkas & Krčmar 2004), being a typical litter conditions. A comparable situation with simi- species (Radu & Tomescu 1981). The fact is re- lar explanation was recently described for the markable especially since the number of iso- presence of the meadow lizard (Darevskia prati- pods species and individuals generally de- cola) in a treeless habitat (Covaciu-Marcov et al. creases with the increase of the degree of land 2009a). In the same time, T. nodulosus appears usage (Emmerling 1995) and at Andrid the predominantly in warm and dry habitats habitat is surrounded by agricultural fields. (Purger et al. 2007), which is not the case for Probably the sylvan isopods inhabited for- the marsh from Andrid, being thus probably ests existing previously in the area (Ardelean & present at the edge of the agricultural fields. Karácsonyi 2002) and survived after deforesta- A notable fact is the presence of P. con-

North-West J Zool, 6, 2010 Terrestrial isopods eaten by frogs from Romania 271 spersum, also at Andrid, a species considered in tain types of isopods, but possibly the activity Hungary, hence in the neighbourhood, as be- of these invertebrates. A species that stays hiding rare and present at higher altitudes, above den will be more difficult to meet by amphibi- 500m (Vilisics et al. 2008). This species has not ans and so it will appear less frequently in the been previously identified in western Romania, stomach contents. and now it is reported at Andrid, at plain, at an Intake of isopods is facilitated primarily by altitude of only 115m. The reason for the spe- the microhabitat in which frogs are foraging cies presence at plain has to be integrated into and in which isopods are having different den- the general situation of low areas from north- sities. It may also be involved that certain pe- western Romania, where other faunistical ele- riod of the day when activity of preys and ments too, generally attached to mountain ar- predators overlaps. In both groups, this is in- eas descend at much lower altitudes (Covaciu- fluenced by temperature, at isopods the length Marcov et al. 2005a,b, 2008, 2009b). In the of movements depending on temperature swamp from Andrid it is present even the liz- (Paris 1963). At Andrid, the foraging territory ard Zootoca vivipara (Covaciu-Marcov et al. of the frogs is extremely clearly defined as be- 2008), a species traditionally considered in ing located between water and the adjacent ag- Romania as a mountainous lizard (Fuhn & ricultural fields. Thus, in this territory, frogs Vancea 1961). Thus, this is just a piece in a encounter more frequently isopods. The high much larger mosaic. number of A. vulgare from Andrid may be re- The isopods caught by amphibians were lated to a locality neighbourhood or to that of generally large-sized, up to 10-15 mm, more agricultural fields, this species being very rarely being consumed individuals of only 5-8 common in disturbed habitats (Vilisics et al. mm. This could be seen as an indicator of 2007). Perhaps, the more limited habitat for the frogs’ trophical selectivity, which is the orien- ecological requirements of both predators and tation towards larger sized preys. Still, frogs, preys facilitates the contact between them, in- including those with the largest size, fed on ex- creasing the consumption of isopods by frogs. tremely small sized preys too, such as aphids The habitat from Livada is more natural, but or collembolans (Santos et al. 2004, Sas et al. the consumption of isopods is lower. This can 2009). Thus, the consumption of large-sized be explained by a richer trophical offer at isopods does not indicate a preference over Livada likely to reduce the consumption of them, but either their greater abundance in the isopods, but this is not obvious when compar- habitat or the fact that they are more easily met ing diet of the two populations (Aszalós et al. by frogs. 2005, Sas et al. 2007). Rather, the forest, a far The capture of isopods by amphibians more extensive habitat, allows exploitation of seems to be influenced rather by the speed and more diverse microhabitats in which the diver- way of life of these preys. Thus, H. transsylvani- sity of isopods is variable, while at Andrid the cus a very mobile, paludicolous species was smaller territory brings preys into contact with very rarely consumed. Paludicolous species are predators. fast, but they also stay hidden in various shel- All isopods consumed by R. dalmatina were ters for long time. The less mobile sylvan spe- sylvan species, a fact consistent with the eco- cies have instead high percentage abundances logical requirements of this frog, which is also in the stomach contents. But frogs can seize a species attached to forests (Fuhn 1960). The preys even more mobile than the most mobile consumption exclusively of sylvan isopods in- isopods. Thus, either the speed cannot be con- dicates that R. dalmatina does not leave the for- sidered a reason for preferential intake of cer- est not even for hunting.

North-West J Zool, 6, 2010 272 Tomescu, N. et al.

P. lessonae and P. esculentus have consumed by amphibians. They are opportunistic preda- aquatic isopods (Asellus aquaticus) too. This tors, capturing the most accessible preys from may seem expectably as both species were their habitat (Santos et al. 2004, Balint et al. caught from water. However, at these species 2010, de Paula-Lima et al. 2010) and this ulti- too, the largest part of eaten isopods and of mately depends on the conditions of the envi- food in general consisted of terrestrial species ronment. The exact knowledge, when it is pos- (Sas et al. 2007). P. lessonae had eaten only two sible, of the species of isopods consumed by terrestrial isopods, both sylvan species. It be- frogs, allows us to accomplish a complex eco- comes obvious that this species is foraging in logical vision about the quality of the used the forest adjacent to the inhabited pond. habitat, possibly related to the trophical strate- P. esculentus had consumed praticolous gies and ecological requirements of the frogs. isopods as well as paludicolous and sylvan Also, such studies allow establishing some ones. Thus, P. esculentus has probably the larg- unique biogeographical connections offering est foraging territory from all the four analyzed an overview about the biodiversity of certain frogs, foraging both in the pond (proved by the regions, in the conditions when soil macroin- aquatic preys from the stomach contents) and vertebrates are poorly represented in the data in the forest, but also in pastures or meadows. concerning biodiversity (Pressey 2004). It is moving at least a few tens of meters, even up to 100 m from the pond in which it was captured, because for example A. vulgare does not live in the immediate vicinity of the aquatic ba- Acknowledgements. We express our special thanks to L. Aszalós for providing us their data and the collected stomach sins. At 30 meters from the pond there are contents in order to identify the isopod species. open, dry and sunny areas at the level of a railway bed from where probably the frogs have captured this species. It is evident that the two green frogs are mostly foraging in terres- References trial habitats, even if they are staying in the Anderson, A.M., Haukos, D.A., Anderson, J.T. (1999): Diet water where they breed or go into hiding. For composition of three anurans from the playa wetlands of example, in the same pond Bombina bombina northwest Texas. Copeia 1999: 515-520. Anderson, J.M. (1988): Spatiotemporal effects of invertebrates had only consumed aquatic isopods (24 indi- on soil processes. Biology and Fertility of Soils 6(3): 216- viduals of Asellus aquaticus). 227. The percentage abundance and the fre- Ardelean, G., Karácsonyi, C. (2002): Flora şi fauna Văii quency of occurrence of isopods in the diet of Ierului, înainte şi după asanare. Editura Bion, Satu Mare, Romania. [in Romanian] amphibians differs widely depending on the Arroyo, S.B., Serrano-Cardozo, V.H., Ramírez-Pinilla, M.P. period of the year (Sas et al. 2003, David et al. (2008): Diet, microhabitat and time of activity in a 2008, Yu et al. 2009), which is valid for the Pristimantis (Anura, Strabomantidae) assemblage. Phyllomedusa 7(2): 109-119. studied species too. This is also determined by Aszalós, L., Bogdan, H., Kovács, É.H., Peter, V.I. (2005): Food the activity of the frogs whose feeding is gen- composition of two Rana species on a forest habitat erally higher in autumn (Kovács et al. 2007), (Livada Plain, Romania). North-Western Journal of Zoology 1: 25-30. but also by the fluctuations of isopods popula- Balint, N., Indrei, C., Ianc, R., Ursuţ, A. (2010): On the diet of tions, whose abundance in the environment the Pelophylax ridibundus (Anura, Ranidae) in Ţicleni, undergoes seasonal changes (Radu & Tomescu Romania. South-Western Journal of Horticulture, Biology and Environment 1(1): 57-66. 1972, Zimmer & Brauckmann 1997). Cicort-Lucaciu, A.Ş. (2009): Food Composition of a Low In fact, the consumption of isopods by am- Altitude Salamandra salamandra L. 1758 (Amphibia) phibians is not so much decided by isopods as Population from Western Romania. Acta Zoologica Bulgarica 61(3): 329-333.

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