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: tomescun@yahoo.com, S. Ferenţi, e-mail: ferenti_sara@yahoo.com 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 alti- tudes. 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.

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