EXPERIMENTAL STUDIES ON THE DISPERSAL OF PLANTS AND ANIMALS ON SHEEP IN CALCAREOUS GRASSLANDS

1. In June to September 1993 a transhumant flock of sheep on the Schwa bische Bib was examined with respect to which plants and animals are t ransported on and in the wool of sheep within calcareous grasslands. S everal factors possibly influencing the attachment and detachment of d iaspores on fleeces were studied, as well as the distribution of diasp ores on the various body-parts of a sheep. The effects of different mo des of sheep locomotion on dispersal were examined with the help of a sheer dummy. In order to assess the retention time of diaspores and an imals on sheep, some experiments with marked diaspores and animals wer e carried out on two tamed sheep. 2. In 16 intensive examinations of t he fleece of a single sheep, over 8500 diaspores of 85 vascular plants species were found. The highest numbers of diaspores were attached at the breast and neck of the sheep. 3. Height of diaspore presentation, surface structure of diaspores and sheep locomotion were found to be the decisive factors for the reception and transport of diaspores in t he wool. In additional plant frequency and the length of the dissemina ting period are of importance. 4. Marked diaspores with both adhesive and smooth surfaces remained on the sheepskin for up to seven months, and can consequently be dispersed over the entire roaming area of the sheep. 5. Amongst the animals transported by sheep, only grasshoppers (13 species) Mere observed frequently on the flock of sheep. The perio d of time marked grasshoppers staved on sheep ranged from 1 to 69 min, with an average of 14 min. During this period sheep can cover distanc es of over 100 m when prating and well over 500 m when roaming. 6. Our study indicates that the importance of the dispersal of diaspores, an d especially animals, by animals has so far been largely underestimate d. This is mostly due to the methods previously used to examine disper sal mechanisms. 7. Conservation management of rare and endangered spec ies should consider the importance of sheep for maintaining the specie s richness of calcareous grasslands, It is likely that transhumant she ep farming is irreplaceable in the restoration of grasslands threatene d by fallow and woody successional stages. Moreover, traditional sheph erding facilitates the exchange of individuals of both plants and anim als between isolated patches. That is, sheep are able to maintain dyna mic processes even in our greatly fragmented landscape; this is probab ly essential to long-term population viability of many species.