Flower and Fruit Characteristics in Small and Isolated Populations of a Fleshy‐Fruited Shrub

Abstract

During a warm period after the last glaciation the fleshy‐fruited shrub, Prunus mahaleb, extended its area of distribution from the Mediterranean basin towards central Europe. Under a subsequent cooler climate, and probably increased competition from trees, the species became restricted to steep, south‐facing cliffs and scree slopes with a particularly sunny and warm microclimate. Thus, the small relict populations in central Europe have been isolated for about 5000 ‐ 6000 years. To investigate whether or not reproductive traits of P. mahaleb are affected by isolation and population size, several flower and fruit characteristics were sampled in ten populations in Switzerland. A Canonical Correlation Analysis (CCA) based on these reproductive characteristics differentiated the populations. The first CCA axis was determined by flower size, pollination frequency, pulp and seed mass. This ran parallel to increasing precipitation and decreasing altitude. The second axis correlated with the number of fruits per raceme and seed viability, and ran parallel to increasing sunshine. None of the six flower and fruit variables correlated with population size or with the degree of isolation. However, flower size, pollination frequency, pulp and seed mass showed a negative correlation with altitude. The results suggest that, in populations of P. mahaleb in central Europe, climatic conditions explain more of the observed variation in flower and fruit characteristics than population size or degree of isolation.

Population structure of a fleshy-fruited species at its range edge – the case of Prunus mahaleb L. in northern Switzerland

“…In southern Switzerland, some large continuous populations (>1000 individuals) can be found in the Valais, whereas in northern Switzerland most populations are isolated and rather small (10-100 individuals; Kollmann and Pflugshaupt 2001). This pattern of distribution is interpreted as a relict of a warm period after the last glaciation (7500-4500 years BP), when the species was probably more widespread (Burga and Perret 1998).…”

“…The selection of study populations was based on published sources, herbarium records and personal observations in northern Switzerland and neighbouring areas in eastern France (Moor 1962(Moor , 1979Welten and Sutter 1982;Köppler 1995;Kollmann and Pflugshaupt 2001). Fifteen populations were chosen with no recent human disturbance but sufficient accessibility.…”

“…Plant performance in small and isolated populations is a central topic of current ecological research (Oostermeijer et al 1994;Colas et al 1997;Fischer and Matthies 1998a,b;Kahmen and Poschlod 2000;Kollmann and Pflugshaupt 2001;Pluess and Stöcklin 2004). Small population size and isolation have both natural and anthropogenic causes, with natural isolation more often occurring at the edge of a species range (Gaston 2003).…”

“…Flowering, fruiting and seed dispersal of P. mahaleb have been intensively studied in Spain and Switzerland (Guitián 1993(Guitián , 1994Guitián et al 1993;Jordano 1993;Kollmann and Pflugshaupt 2001;Pflugshaupt et al 2002). Swiss plants proved to be smaller than Spanish ones; they often have a more prostrate growth form and produce fewer flowers and fruits (Kollmann and Pflugshaupt 2001).…”

“…Swiss plants proved to be smaller than Spanish ones; they often have a more prostrate growth form and produce fewer flowers and fruits (Kollmann and Pflugshaupt 2001). The small size and low reproductive success of Swiss populations might have implications for their demographic structure, i.e.…”