Ábrahám Levente (szerk.): Válogatott tanulmányok VI. - Natura Somogyiensis 19. (Kaposvár, 2010)
HORVÁTH GY., HERCZEG R., TAMÁSI K. & SALI N.: Nestedness of small mammal assemblages and role of indicator species in isolated marshland habitats
298 NATURA SOMOGYIENSIS made by ATMAR & PATTERSON (1993) is extinction, therefore we can draw important inferences about the extinction sequence by the nestedness community patterns ( BÁLDI et al. 2003a, b; GALEANO et al. 2009). In terms of the mammals of Kis-Balaton marshlands one of the main tasks of the project is connected with the critically endangered root vole, which proved to be the most vulnerable species in the analysis of small mammal responses to disturbing effects. Therefore, in the case of the macro-habitats of KisBalaton the most important question in the conservation management of root vole is how large habitat fragments does the species occurs in? The main aim of the 11-year long small mammal monitoring programme applied in the wetlands of Kis-Balaton area was the population-level examination of the root vole. However, the joint effects of human disturbance, interventions (burning, mowing, enclosure) and the dry weather altered the habitat structure, because of which the structure of small mammal assemblages has changed significantly. After the dry period the extensive sampling of the sedge-dominated macro-habitats provided the ecological evaluation of the typical small mammal assemblages based on the nestedness pattern and definition of indicator and character species. For the evaluation of nestedness we used a recently developed program, the wieghted-interaction nestedness (WINE), which contains many innovations: it is independent from matrix size and fill, in addition to taking into account the relative position of the links in the matrix, it accounts for the number of events of links (GALEANO et al. 2009). Our basic question was how much the species turnover processes and the water-level increase following bountiful precipitation as a natural disturbance predominate in directing the composition of small mammal assemblages and in the nestedness pattern in human disturbed habitat patches. The results of the WINE randomization statistic showed that the small mammal assemblages of Kis-Balaton marshland habitat patches show, instead of a random pattern, an ordered one. The value of the weighted-interaction nestedness estimator was positive all in the three years, which expressed the relative position between the maximum nestedness pattern and the random state. The summarised statistical results of the nestedness analysis showed - especially in 2005 and 2006 - that the small mammal assemblages of the isolated Kis-Balaton marshland habitat patches are nested without doubt. Comparing the results of the nestedness and the IndVal analysis we can highlight 5 species as idiosyncratic species based on the 2005 data matrix. These species determined the nestedness patterns and they got significant maximum indicator values for a given habitat patch. We suggest that the root vole (M oeconomus), as a habitat specialist species has a great importance because it indicates on the one hand its own optimal environment, on the other hand its local extinction influenced considerably the nestedness patterns because it is one of the most vulnerable species of the community. However, the lesser white-toothed shrew (C. suaveolens ) appeared as an asymmetrical indicator species in that habitat patch, where human interventions and disturbances changed the structure of tha habitat. This unexpected presence was confirmed by the high weightedinteraction distance received through the nestedness analysis and thus it appeared as a idiosyncratic species. The rare occurrence in 2005 of some species that are not typical in original homogeneous sedgy habitats showed that despite of the bountiful precipitation following the dry season the previously disturbed habitat patch of Keleti-berek (KE_1) can not recover properly through one year compared to the undisturbed state. Synthesizing the results of the two community typifying approaches in 2006 we could highlight only three species that received significant indicator value in the IndVal analysis as an idiosyncratic species. The yellow-necked mouse (A. flavicollis) as a symmetrical-, while the mound-building mouse (M spicilegus) as an asymmetrical indicator have
