Lanszki József - Ábrahám Levente (szerk.): Magyarországon élő ragadozó emlősök táplálkozás-ökológiája - Natura Somogyiensis 4. (Kaposvár, 2002)

172 NATURA SOMOGYIENSIS sionally low frequency of occurrence (less than 50-60 %) offish in the diet indicated that the amount of available fish stock was less than adequate or varied greatly from season to season. In these habitats the secondary source of prey (birds, amphibians and reptiles) played an important role. In wetland habitats that partly dry out during the summer, such as the Lankóci Forest or certain canals and streams, the importance of small mammals and water insects also increased, while the significance of fish in the diet was reduced. The diet of the otters living in the area of the Tetves Stream (which can be considered a special case) contained an extremely large proportion (62 %) of crayfish during the summer. Due to the greater amount of fish consumption the trophic niche of otters living in ponds was narrower than that of the ones near the Drava's aquatic habitats. The correlation between the frequency of occurrence and the biomass data of the otters' diet was analysed using samples collected at the Ponds of Petesmalom, the Lankóci Forest, and the Tetves Stream. Data according to the various taxa showed significant (P<0.001) Pearson correlation coefficients of 0.92 (mammals), 0.80 (birds), 0.93 (reptiles and amphibians), 0.90 (fish), 0.88 (invertebrates) and -0.78, P=0.066 (plants). The data indicates that frequency of occurrence of prey taxa quantify the consumed biomass with high reliability. The most important elements of the stoat's diet consisted of small mammals, mainly voles. The proportion of small mammals in the stoat's diet was the highest during the winter and decreased continuously towards the summer and the autumn. At the same time the importance of birds and insects increased but reptile and plant consumption could also be detected. In habitats, which differed significantly compared to some of the others, like the Fonó Fishpond region (agricultural landscape) and the Lankóci Forest, in spite of the monotony of the stoats' diet their trophic niche was wide according to the main taxa. The number of prey and plant taxa at these habitats studied was 18 or 11, and 4 or 1, respectively. Body weight of the stoats' major prey varied between 15-50 gramms. The majority of prey species was terrestrial but the proportion of arboreal prey was also substantial and aquatic species occurred in the diet as well. The diet composition of the stone marten was analysed in agricultural landscape (around the Fonó Fishpond) and in a village (at the inner area of Fonó). Individuals of the different habitats often utilised the same source of diet and the size of their niche overlap was 78%. The primarily important food taxa were plants, mainly fruits in the diet at both habitats (based on the annual mean of 34% and 31 % frequency of occurrence, respectively). Besides plants the most important prey taxa consisted of small mammals (20%) in the agricultural area, and of birds (20%) in the village. There was a substantial difference in the consumption of domesticated (mainly poultry) species (4% vs. 15%). The fact that stone martens in the agricultural area more frequently consumed terrestrial and wild prey contrary to their "urban" counterparts contributed to their trophic niche segregation. The number of prey and plant taxa of these two areas was 55, 35 and 17, 19, respectively. Prey was typically in the 15-50 g weight category (55, and 47% in the agricultural landscape and the village, respectively) and lived on ground level (81 and 71%, resp.), but martens living in the village hunted more frequently preys above 50 g (14 and 24%, resp.) and arboreal prey (17 and 29%, resp.). The diet of the stone martens living in the agricultural area showed high similarity to those of other carnivores of small and medium body size. The most important items of the pine martens' diet consisted of small mammals both in the Boronka Nature Conservation Area and in the Lankóci Forest. Their proportion was especially high during the winter and spring season. The most important prey spe-