Ábrahám Levente (szerk.): Válogatott tanulmányok V. - Natura Somogyiensis 17. (Kaposvár, 2010)

LANSZKI, J., MÓROCZ, A. & CONROY, J. W. H.: A vidra (Lutra lutra) kora tavaszi táplálék-összetétele a Gemenci Tájegység (Duna-Dráva Nemzeti Park, Magyarország) természetes élőhelyein

318 NATURA SOMOGYIENSIS characteristic skeletal remains, and integuments (PAUNOVIC 1990, KNOLLSEISEN 1996, and reference collections). All dried preyremains for each prey group recovered from the spraints were weighed and their weight multiplied by an appropriate coefficient of digestibility (amphibians 18, fish - 25, molluscs and crayfish - 7, insects - 5; summarised in JEDRZEJEWSKA & JEDRZEJEWSKI 1998) to obtain an estimate of the percentage fresh weight of food consumed (%B). Statistical analysis The following four main prey taxa were used in the calculations: 1 fish; 2 amphibians; 3 crayfish and 4 other invertebrates. Trophic niche breadth (B) was calculated according to Levins (1986 in KREBS 1989): B = 1/ 2 p;

2, where p, = is the proportion of the biomass of a given taxon (expressed as a percentage) present in the diet; and standardized across the four main food taxa: B

A = (B-l)/(n-l), rating from 0 to 1. The Chi-square test was used for distribution analysis of genaral and fish diet composition of the otters. Hierarchical cluster analysis (cluster method: between-groups linkage; interval of measure: Euclidean distance) was used to compare data of diet compositions (%B) recorded for different study locations. The SPSS (1999) statistical package was used for the processing of the data obtained. Results and discussion Distribution of the four main food types eaten by otters differed significantly between areas (Chi-square test: X

215 = 70.19, P<0.001). During the cold period, the principal prey of otter in all six areas studied was fish (>80%), with, in some areas, this was closer to 100% (Table 1, Fig. 2a). In four areas the main prey was gibel carp, but pike dominated in the fish diet in DD and consumption of this species was also high on ND. Roach (HS), bleak (HK), nase (BD), and common carp (TD, HS, BD) were also of considserable importance. The secondary food of otters was amphibians, including frogs (Rana spp.) and toads (Bufo spp.), but consumption of these food items was not considerable (Table 2). Other foods such as crayfish (Astacus spp. in TD), water beetles e.g. Dytiscus marginalis, a) 100% 73% § 30% H 23% • CQ 0% J a m Food types

: • Other • Crayfish 9 Amphiian • Fish TD HS HK DD ND BD Area HS ND BD HK DD TD Relative distance 5 10 15 20 25 —I Fig. 2: Distribution of prey types in the diet of otters (a) and dendogram of diet similarity (b) in the Gemenc area, Hungary. For locations see Fig. 1. Calculation was performed with hierarchical cluster analysis on the basis of estimated percentage biomass (%B) data. Short horizontal lines (—) are separate clusters.