title: Pollen limitation is not the rule in nival plants: A study from the European Central Alps.
abstract: OBJECTIVE
  Seed output of high-mountain plants in the uppermost life zones is highly variable. One possible reason might be pollen limitation due to inadequate pollinator services.
  
  
  METHODS
  We tested this hypothesis for the insect-pollinated species Cerastium uniflorum, Ranunculus glacialis, and Saxifraga bryoides, which have their distribution center in the subnival and nival zone of the European Central Alps. We recorded insect visitors and determined their impact as pollinators. By analyzing pollination success and seed set following natural and saturating hand pollination, the magnitude of quantitative and qualitative pollen limitation was assessed.
  
  
  RESULTS
  Anthomyiid and muscid flies had the highest pollination impact for R. glacialis and S. bryoides and syrphids for C. uniflorum. Natural stigma pollen load was highly variable in individual flowers of all species, but in most cases the number of conspecific pollen grains clearly exceeded the number of ovules to be fertilized. There was also a surplus in germinated pollen grains, whereas the pollen tube to ovule ratio was only sufficient in R. glacialis (2.6 on average) and S. bryoides (1.3), but not in C. uniflorum (0.6). Accordingly, seed to ovule ratio was around 0.8 in R. glacialis, 0.7 in S. bryoides but 0.4 in C. uniflorum. In C. uniflorum, saturating pollination slightly increased seed set. Regression analyses revealed that natural pollination success was more frequently limited by quality than by quantity.
  
  
  CONCLUSIONS
  Our results do not support the idea of chronic, widespread pollen limitation in the subnival but rather fit into the concept of parental optimism by overinvesting in the number of ovules as an adaptation to variable resource availability.
authors.affiliation: Institute of Botany, Faculty of Biology, University of Innsbruck, Sternwartestraße 15, 6020 Innsbruck, Austria johanna.wagner@uibk.ac.at.
authors.forename: Johanna
authors.initials: J
authors.lastname: Wagner
authors.affiliation: Institute of Botany, Faculty of Biology, University of Innsbruck, Sternwartestraße 15, 6020 Innsbruck, Austria.
authors.forename: Martin
authors.initials: M
authors.lastname: Lechleitner
authors.affiliation: Institute of Botany, Faculty of Biology, University of Innsbruck, Sternwartestraße 15, 6020 Innsbruck, Austria.
authors.forename: Daniela
authors.initials: D
authors.lastname: Hosp
mesh_terms: D000818:Animals; D017753:Ecosystem; D035264:Flowers / Q000502:physiology; D018525:Germination; D007313:Insecta / Q000502:physiology; D010944:Plants / Q000378:metabolism*; D011058:Pollen / Q000502:physiology*; D053205:Pollen Tube / Q000254:growth & development; D054817:Pollination; D012044:Regression Analysis; D012639:Seeds / Q000502:physiology; D014741:Video Recording
keywords: Caryophyllaceae; Ranunculaceae; Saxifragaceae; alpine plants; insect pollination; pollen limitation; pollen load; pollen quality; pollen tubes; pollinator frequency; reproductive success