ausblenden:
Schlagwörter:
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Zusammenfassung:
1. As a rule, communities consist of few abundant and many rare species, which is reflected
in the characteristic shape of species abundance distributions (SADs). The processes that
shape these SADs have been a longstanding problem for ecological research. Although many
studies found strong negative effects of increasing land-use intensity on diversity, few reports
consider land-use effects on SADs.
2. Arthropods (insects and spiders) were sampled on 142 grassland plots in three regions in
Germany, which were managed with different modes (mowing, fertilization and/or grazing)
and intensities of land use. We analysed the effect of land use on three parameters characterizing
the shape of SADs: abundance decay rate (the steepness of the rank abundance curve,
represented by the niche-preemption model parameter), dominance (Berger-Parker dominance)
and rarity (Fisher’s alpha). Furthermore, we tested the core-satellite hypothesis by
comparing the species’ rank within the SAD to their distribution over the land-use gradient.
3. When data on Araneae, Cicadina, Coleoptera, Heteroptera and Orthoptera were combined,
abundance decay rate increased with combined land-use intensity (including all modes). Among
the single land-use modes, increasing fertilization and grazing intensity increased the decay rate
of all taxa, while increasing mowing frequency significantly affected the decay rate only in interaction
with fertilization. Results of single taxa differed in their details, but all significant interaction
effects included fertilization intensity. Dominance generally increased with increasing
fertilization and rarity decreased with increasing grazing or mowing intensity, despite small differences
among taxa and regions. The majority of species found on <10% of the plots per
region were generally rare (<10 individuals), which is in accordance with the core-satellite
hypothesis.We found significant differences in the rarity and dominance of species between plots
of low and high intensity for all three land-use modes and for the combined land-use intensity.
4. We conclude that effects of land-use intensity on SADs lead to a stronger dominance of
the most abundant species. Furthermore, species which have restricted distributions are more likely to also be rare species in the local SAD and therefore are at high risk of being lost under intensive land use.
