Abstract
In this paper I use the different measures of species mobility to describe the fine small-scale dynamics of calcareous grassland built mainly by perennial species and developed in the highly heterogeneous habitat of calcareous rocks. The community showed the low dynamics on a plot-scale (100 m<sup>2</sup>) and a high one on the scale of 1 m<sup>2</sup>. However, the studied species differed greatly in calculated indices: turnover rate, (T; 6-64), residence time (RT; 0.5-21.8 y) and carousel time (CT; 4-420 y) as well as the observed tendency to persistence on the spots (PERSIST) and their re-colonisation (AGAIN). This allowed to distinguish the three groups of species: (1) "core species" characterized by high frequency and low T and high CT and RT values, which determine the low dynamics of a community on the plot scale, (2) species with intermediate mobility rate and (3) the group with high mobility rate. The observed cumulative frequencies of all the studied species (CFobs) were much lower than expected under the random re-assignation model (CFRR). Moreover, they were also lower than those predicted by random immigration model (CFRI). The results showed that the "complex carousel" model rather than "single carousel" one explained better the small-scale dynamics of calcareous grasslands.
Highlights
The knowledge about non-directional spatial and temporal changes in the community is essential for understanding a plant community function, and for determining the baselines for studies on long-term responses of comunity to environmental changes (Palmer and Rusch 2001)
Species-rich plant communities which seem stable and homogenous on a large scale appear to be very mobile on a smaller one, in dry species-rich grasslands, built mainly by annuals and biennials
The analysed calcareous grassland was very stable on plot scale (100 m2)
Summary
The knowledge about non-directional spatial and temporal changes in the community is essential for understanding a plant community function, and for determining the baselines for studies on long-term responses of comunity to environmental changes (Palmer and Rusch 2001). In the carousel model, as proposed by van der Maarel and Sykes (1993, 1997), all species present in the community move around the community and eventually reach all microhabitats in a relatively short time These authors introduced the term cumulative species richness, i.e. the number of species occurring in the area over a series of consecutive years, and cumulative frequency, i.e. the sum of plots in which species occurred during the study period. The field research by Herbén et al (1994) and lately Otsus and Zobel (2002) showed that the studied grasslands were composed of coexisting species with high and low mobility, it was impossible to determine whether this variation underlied the species richness of these grasslands
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