Seria: 9 Biologie UNIVERSITATEA DIN CRAIOVA 9 Horticultură UNIVERSITY OF CRAIOVA 9 Tehnologia prelucrării produselor agricole 9 Ingineria mediului Vol. XV ( XLXI ) - 2010 THE TROPHIC SPECTRUM OF A BOMBINA VARIEGATA POPULATION FROM ARGEŞ COUNTY (NUCŞOARA LOCALITY) Hodişan Oana1*, Covaciu-Marcov S.D.¹ KEY WORDS: Bombina variegata, feeding, prey category ABSTRACT This study was realised at the end of 2009 and aimed to analyze the trophic spectrum of a Bombina variegata population. The individuals populate a habitat situated in the hydrographic basin of Râu Doamnei, at approximately 630 m altitude, near Nucşoara locality, Argeş County. The most important preys were the Diptera Nematocera, respectively the Hymenoptera Formicidae, followed by Arachnida Araneae and Coleoptera, which registered lower values. In comparison to the males, the females consumed large preys that were rich in nutritive substances (Coleoptera, Gastropoda, Lumbricidae, Lepidoptera larvae). Capturing these preys involves a minimum effort, thus the females trying to save their energetic resources. There were not registered any stomachs without content. Most of the consumed preys were terrestrial. Beside the invertebrate preys, we also encountered the consumption of vegetal parts, shed skin and mineral elements. INTRODUCTION On overall look upon the entire amphibian group has highlighted that almost a third of the species are threatened with extinction (Alford and Richards, 1999; Blaustein and Kiesecker, 2002). Amphibians have populated Earth for over 300 millions years, but in the last two decades the number of extinctions has raised in an alarming manner, approximately 40% of the populations having decreased. This fact indicates that the number of extinct and threatened species will probably continue to grow (Stuart et al., 2004). Most certainly the most important factors in their decline are the destruction, alteration and fragmentation of their habitats (Marsh and Trenham, 2001). However, it has been recorded that amphibians are also decreasing in the protected and unexplored areas (Lips, 2000). Amphibians are important components of the ecosystems, due to the fact that they direct the energy from the invertebrates, especially from the detritovore and phytophagous ones, to the upper trophic levels, thus playing a special role in the trophic dynamic (Blaustein et al., 1994). Bombina variegata (Linnaeus 1758) is a common, unpretentious species, its area including central and southern Europe, the species ranging from 100 (Madej, 1964) to 1900 m altitude (Cabela et al., 2001). Knowing the food composition of the amphibians offers specific clues regarding the conditions provided by the occupied habitat (Perry and Pianka, 1 University of Oradea, Faculty of Sciences, Department of Biology, Oradea, Romania *Corresponding author: E-mail address: [email protected] 291 1997), thus the frogs can be considered as important indicators of the environmental conditions (Bellocq et al., 2000). There are recent data regarding the trophic spectrum of this species in Romania (Sas et al., 2005; Ghiurcă and Zaharia, 2005; Szeplaki et al., 2006; Dimancea et al., 2008; Ferenţi and Covaciu-Marcov, 2009). There are no data regarding the composition of the trophic spectrum of this species from the studied region. Therefore, we wish to add new information or to complete the present studies that refer to the trophic spectrum of Bombina variegata species. MATERIALS AND METHODS The studied B. variegata population belongs to a region that has a piedmont character, from Argeş County (Nucşoara locality – hydrographic basin of Râu Doamnei). The habitat is situated at an altitude of 630 metres, being represented by a bogging area formed from the artificial damming of the main course of Râu Doamnei. Our study took place in august 2009, when we captured 35 individuals, from which 14 were males and 21 females. The water level allowed their capture directly by hand, afterwards having collected the stomach contents of the frogs. In this respect we used the stomach flushing method (Sole et al., 2005), technique which allows the study of the amphibians’ feeding without having any negative effect upon the individuals. It was tried to reduce as much as possible the time between the capturing of the animals and the performing of the stomach flushing due to fact that amphibians digest their food in a short period (Cadwell, 1996), fact that can modify our results. The content was preserved in a 4% solution of formaldehyde and stored in air tight test tubes. The analysis of the contents was realised at the magnifying glass, while the scientific literature was used for determining the taxonomic affiliation of the prey categories. The prey taxa were mostly determined until the order, family and where it was possible, genus level. We analysed different parameters, such as: the feeding activity rate, the taxonomic affiliation of the consumed prey, the feeding intensity, the origin of the preys identified in the stomach contents of the individuals, as well as the amount and frequency with which these were consumed. The obtained results were discussed regarding the differences that appear between the sexes. RESULTS AND DISCUSSIONS Following the analysis of the stomach contents of the 35 individuals, there were identified 161 preys, which were grouped in 31 taxonomic categories. The identified preys mostly belong to the insect class. In this case, there was not registered any empty stomachs, thus the rate of the feeding activity being of 100%. During the period when the study took place, the temperatures were relatively high, although the habitat is situated in the Middle Carpathians. However, it provides goof feeding conditions to the analysed population. We also identified vegetal fragments, shed skin and mineral elements in the stomach contents, beside the animal preys. It can be noticed that there is a difference regarding the consumption of vegetal debris between the two sexes: thus, 42.85 % of the males consumed vegetal parts, while the females consumed more frequently these elements, registering 57.14% (Table 1). These values can be associated with the feeding intensity, which is different between the two sexes, the females feeding more intensely than the males. The toads’ consumption of vegetal parts cannot be regarded as an active one, due to the fact that they are carnivores (Cogălniceanu et al., 2000), only their larvae consume plants, especially algae (Jenssen, 1967). The consumption of vegetal parts is considered to 292 be accidental, being swallowed together with the followed mobile prey (Stebbins and Cohen, 1995). Shed skin can also be considered as being swallowed together with the mobile preys, or accidentally. Some authors consider that, due to their rich-protein content, their consumption can be interpreted as an aspect related to the recycling of the epidermal proteins (Weldon et al., 1993). Differences between the two sexes can be noticed regarding the shed-skin consumption, thus the females having consumed twice as much than the males (Table no. 1). In comparison with other studies (Peter et al., 2006; Toth et al., 2007; Ferenţi and Covaciu-Marcov, 2009), their percentage is relatively low. It can be said that the habitat displays a varied trophic offer, rich in nutritive substances, thus the frogs do not have to supplement their food through the consumption of shed-skin. Its consumption in a more active manner in the case of the females, can represent an additional source of obtaining energy. Table 1 The frequency of the vegetal parts, shed skin and mineral elements in the stomach contents; The feeding intensity (the average and maximum number of preys/individual); The origin of the preys (terrestrial or aquatic medium) Males Females Total Vegetal parts (%) 42.85 57.14 51.42 Shed skin (%) 14.28 28.57 22.85 Mineral elements (%) 14.28 19.04 17.14 Average no. of preys/ individual 4.35 4.76 4.6 Maximum no. of preys/individual 9 11 11 (%) Terrestrial preys 88.53 89 88.82 (%) Aquatic preys 11.47 11 11.18 Regarding the mineral parts, their consumption is considered to be accidental in the scientific literature, these elements having no nutritive value. The difference between the two sexes was not very high, the females registering a value of 17. 14%, while the males, 14.28%. The presence of the minerals could be explained by the type of the habitat, which is a bogging area of a mountainous river, with its specific characteristics, thus a rocky, sandy substratum. The probability of swallowing small pebbles in cases like these is quite high, these being ingested together with the mobile prey. As the individuals move more actively, they bring about the pebbles from the substratum. We can observe from the analysis of the three elements, that the females registered on every occasion higher values than the males. Thus, it can be deduced that the females hunt more actively than the males, attacking every prey that appeared in their sight. We analysed the average and maximum number of preys/individual in order to establish the intensity with which the frogs have fed. These parameters are influenced by the size of the consumed preys. Concerning the average number of preys/individual, this is very close at both sexes: 4.35 preys/individual registered the males and 4.76 preys/individual the females. These values are low, in comparison to other studies, but the consumed preys are also of large size (Coleoptera, Gastropoda, Araneae, Lumbricidae, Gammaridae), thus the individuals did not have to abundantly consume these preys in order to satisfy their energetic needs. Close values at both sexes were also registered in the case of the maximum number of preys/individual (Table 1). Even if the values are low, it cannot 293 be stated that the habitat does not provide rich trophic resources, but, the larger preys practically replace the smaller ones. The high thermal values registered at the time of study, probably participated in the decrease of the feeding intensity.