THE INCIDENCE OF HERBIVORY IN HIGH-ELEVATION POPULATIONS OF RANUNCULUS-GLACIALIS - A REEVALUATION OF STRESS-TOLERANCE IN ALPINE ENVIRONMENTS

Growing conditions in the upper alpine zone are characterized by low t emperature, low partial pressures of CO2 and, in the temperate zone, a short growing period. The plants which have evolved under these condi tions presumably share a number of characteristics that were ascribed to stress-tolerance, namely slow growth, extended longevity, resource limitation and low palatability to herbivores. Hence chronic biomass r emovals by herbivores should be a threat to plant persistence in alpin e environments. as predicted by Grime's C-S-R theory. I tested this hy pothesis on populations of an alpine buttercup, Ranunculus glacialis. A survey along an altitudinal transect in the Central Alps of Austria indicated that between 15 and 26% of the R. glacialis plants in each p opulation examined exhibited signs of herbivory damage. Merely a small population, isolated by glaciers, at the highest site (3310 m a.s.l.) showed no traces of herbivory. Ar two sites (2600 m and 3180 m a.s.l. ) twenty plants each were tagged and examined for a two-year period. H erbivory damage was considerable: on an average nearly 25% of a plant' s total leaf area was removed in 1987. primarily by snow mice (Microtu s nivalis). Inflorescences of 65-85% of all flowering plants were remo ved as well. Ar the lower sire (2600 m, roughly 600 m above the treeli ne) up to 5 g dry matter and 140 mg nitrogen m(-2) were consumed in on e season. Despite the magnitude of these losses both reproductive inve stment and the number of leaves initiated per plant did not change app reciably in the subsequent year. Since populations of R. glacialis are able to support populations of herbivores at the altitudinal limits o f plant growth without obvious reductions in vigor,these plants and ot her food species (e.g. Oxyria digyna) cannot fit the stress-tolerator scheme proposed by Grime. The widespread occurrence of herbivory at hi gh elevations and plant traits challenge the concept of stress-toleran ce as it is commonly applied to alpine environments.