Abstract
We studied all Campanula species occurring on Mt Olympos, a total of nine species. Their distribution on the mountain, along the altitudinal gradient permitted the testing of hypotheses concerning the change of plant characteristics with elevation. These characteristics included plant and flower morphology, biomass allocation, flower phenology, pollination and reproduction. Studying these characters we can sketch the life history strategies of the species and comprehend the way with which the formation of these strategies is affected by their habitat. Additionally, we estimated the size, density and spatial patterns of Campanula populations in order to assess not only changes of the population parameters in space or time, but also their effect on the plant characters under study. For each species, altitudinally different populations were chosen. Field data were collected from 1992 to 1995. We searched for altitudinal patterns mainly at the genus level. This is the first such an approac ...
We studied all Campanula species occurring on Mt Olympos, a total of nine species. Their distribution on the mountain, along the altitudinal gradient permitted the testing of hypotheses concerning the change of plant characteristics with elevation. These characteristics included plant and flower morphology, biomass allocation, flower phenology, pollination and reproduction. Studying these characters we can sketch the life history strategies of the species and comprehend the way with which the formation of these strategies is affected by their habitat. Additionally, we estimated the size, density and spatial patterns of Campanula populations in order to assess not only changes of the population parameters in space or time, but also their effect on the plant characters under study. For each species, altitudinally different populations were chosen. Field data were collected from 1992 to 1995. We searched for altitudinal patterns mainly at the genus level. This is the first such an approach is attempted. Patterns described until now have been observed at the community or species level. The genus level approach is advantageous compared to species level approaches in having a wider range of elevation. Compared to community level approach it has the advantage of analyzing phylogenetically related species instead of random congregations. Additionally, in the case of Campanula species of Mt Olympos, the growth form is the same (herbaceous) while seven species have the same life form (hemicryptophytes). The analysis was conducted also at the species level in order to test whether altitudinal patterns revealed at the genus level are expressed within the restricted altitudinal distribution of each particular species. The main conclusions of this research are the following: • For every 100 m of altitude increase on Mt Olympos the temperature decreases by almost 0.7 °C (summer estimation) while the rainfall increases. Consequently, Campanula populations even of the same species experience different climatic regimes at different altitudes. Climatic differences between years were also observed. Year 1993 was the driest of a 15-year period (1980-1994). Climatic differences can explain the significant between-year differences revealed in certain characters. • Among the soil characteristics of the sites on which the studied Campanula populations occur, only field capacity was found to differ with elevation. Differences in soil characteristics between Campanula species do not seem sufficient to explain the differences between the altitudinal distributions of these species on Mt Olympos. • The populations of most Campanula species on Mt Olympos occupy small areas and in most cases the distribution of individuals is clumped. Clump densities increase linearly with the increase of density of individuals. • C. versicolor, a lowland chasmophyte, differs markedly from all other Campanula species of Mt Olympos in its corolla shape - rotate instead of campanulate. This difference is reflected by phenological and pollination characters resulting in divergence from overall patterns. • The total biomass and the per-plant flower and fruit production are density-dependent characters. They decrease as density increases. The same is not true for the number of seeds per fruit or per plant. • Plant height decreases linearly with altitude. Individuals from high altitude populations invest proportionally less in stem biomass and produce less flowers and fruits. High altitude plants contain fewer but heavier seeds. • As altitude increases, flowering is delayed while individual flower life span increases. Population flowering duration does not change. • The pollinators of Campanula species are insects. Insect visitation rates to flowers decreases linearly with altitude. • In pollinator exclusion conditions, the individual flower life span increases drastically and no seeds are produced. • The pollinating fauna composition of three species differs markedly from the rest. This concerns C. versicolor and the alpine C. oreadum and C. rotundifolia. In C. versicolor a divergent flower morphology is responsible for this difference while for the latter two it is the altitudinal range in which they occur. • Solitary bees comprise the majority of insect species pollinating Campanula species on Mt Olympos. Among them dominate the families of Andrenidae and Megachilidae. • The insect pollinators carry pollen of variable purity. Purest is that from insects pollinating populations of intermediate altitudes. These insects are the most constant pollinators of Campanula species. There is no difference between pollinators of low and high altitudes as far as their fidelity is concerned. • At high altitudes, Campanula species respond to the reduced availability and relatively low fidelity of insect pollinators with an increase of flower life span. • Despite the trade-off mechanism of reduced pollinator potential at high altitudes, the reproductive output of Campanula species, in terms of number of dispersal units, is reduced. • The temperature optimum for seed germination shifts with altitude. Large differences are found between altitudinally different populations, even for the same species, regarding the germination of their seeds at the same temperature. • At low and intermediate altitudes, the studied species follow different life history strategies: competition, dispersal at disturbed habitats, and stress-tolerance. At high altitudes, stress-tolerance dominates. • Most reproductive losses due to human activities are from livestock grazing (sheep and goats). The impact is more severe on annual and biennial species, the demographic characteristics of which change to a large extent. Nevertheless, no Campanula species on Mt Olympos can be regarded as rare or endangered.
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