No abstract

No abstract

Short growing seasons, low temperatures, and frequent strong wind classify high mountains as adverse environments, in which pollinator abundance and activity are reduced. In such environments, plants growing in dense stands comprising several species and thus exhibiting larger and more diverse flower displays may profit by attracting more visits from scarce alpine pollinators than do plants that grow alone or in patches only composed of conspecifics. To study whether aggregation of plants increases (facilitation) or decreases (competition) the attraction of pollinators, we measured the rate and numbers with which insects entered experimental plots in the Swiss Alps, and their behaviour at flowers in plots that they entered. The plots contained individuals of the blue-flowering cushion plant Eritrichium nanum, either alone or mixed with white-to yellowish-flowering Saxifraga species. Pollinators were generally rare: in 55% of 236 observation periods, no pollinators were observed. Over 95% of the pollinators were Diptera. The average probability of observing any insect at all was higher in plots that contained some Saxifraga flowers, including mixed plots, than in those containing only E. nanum flowers. However, although insects tended to choose Saxifraga as the first flower visited in mixed plots, in all other regards their visitation of Saxifraga and E. nanum flowers in such plots was statistically indistinguishable.We also detected no effect of floral neighbourhood on the frequencies of potentially geitonogamous visits or of transitions among individual plants of the same or different species. Thus, our study suggests that the presence of Saxifraga may facilitate visitation to E. nanum at larger spatial scales, but gives no evidence for either competition or facilitation at small scales within floral neighbourhoods. exhibiting larger and more diverse flower displays may profit by attracting more visits from 24 scarce alpine pollinators than do plants that grow alone or in patches only composed of 25 conspecifics. To study whether aggregation of plants increases (facilitation) or decreases 26 (competition) the attraction of pollinators, we measured the rate and numbers with which 27 insects entered experimental plots in the Swiss Alps, and their behaviour at flowers in plots 28 that they entered. The plots contained individuals of the blue-flowering cushion plant 29Eritrichium nanum, either alone or mixed with white-to yellow-flowering Saxifraga species. 30 Pollinators were generally rare: in 55% of 236 observation periods, no pollinators were 31 observed. Over 95% of the pollinators were Diptera. The average probability of observing 32 any insect at all was higher in plots that contained some Saxifraga flowers, including mixed 33 plots, than in those containing only E. nanum flowers. However, although insects tended to 34 choose Saxifraga as the first flower visited in mixed plots, in all other regards their visitation 35 of Saxifraga and E. nanum flowers in such plots was statistically indistinguishabl...

Changes in abscisic acid (ABA) content and several water relations parameters were studied in the epiphytic orchid Dimerandra emarginata in the tropical lowlands of Barro Colorado Island, Panama. Similar to previous observations of size dependency of physiological parameters in vascular epiphytes, we found significant differences in ABA accumulation (both in terms of temporal patterns and amount) in small and large plants under drought stress. The highest values of ABA content in leaves, stems, and roots were found in the smaller specimens, reaching the levels of poikilohydric resurrection plants. Substantial accumulation of ABA occurred after stomatal closure, indicating other functions of ABA than stomatal regulation in this bark epiphyte.

No abstract