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Comparative Long-Term Demography of Three Species of Pinguicula
Brita M. Svensson, Bengt A. Carlsson, P. Staffan Karlsson and K. Olle Nordell
Journal of Ecology
Vol. 81, No. 4 (Dec., 1993), pp. 635-645
Published by: British Ecological Society
Stable URL: http://www.jstor.org/stable/2261662
Page Count: 11
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1 The population dynamics of the perennial geophytes Pinguicula alpina, P. villosa and P. vulgaris are presented for the first 8 years of an on-going study in the Swedish Subarctic. 2 Between-year variation in density was highest for P. villosa, and this species also had the steepest depletion curve, suggesting that it has a shorter life-span than the other two, perhaps as a result of its more competitive habitat. The short life-span could also be an effect of its allocation pattern, since investment in flowering structures by P. villosa is relatively high and flowering increases the risk of mortality. 3 There was less synchronization regarding flowering and seedling frequencies among quadrats for P. villosa, than for the other two species. This suggests that micro-environmental factors are more important than overall weather factors for the performance of this species. 4 Flowering frequencies were positively correlated with the average summer temperature the previous year for P. vulgaris and P. villosa. This may indicate that flower primordia in these two species are formed the year before flowering. Early season precipitation in the current years was positively correlated with both flowering and seedling frequencies only in P. vulgaris. 5 Relative flowering frequencies varied from 8% to 50% over the years, but were not synchronized among the species. Greatest probability of flowering in the following season was observed in large vegetative individuals of P. villosa and P. vulgaris, but in large flowering individuals for P. alpina. This may be a reflection of the lower cost of reproduction in P. alpina compared with the other two species, and of this species' perennial root system. 6 Seedling establishment was highest for P. vulgaris and lowest for P. alpina. Seedling survival was most varied between cohorts of P. alpina, probably due to larger and more erratic frost movements in the P. alpina quadrats. 7 Elasticity analyses of the size-class-based transition probability matrices showed that the important transitions were vegetative individuals that either remain vegetative or flower the following year. Overall population growth rate $(\lambda)$ was close to 1.0 for all three species, but quite significant between-year deviations were found, especially for P. villosa. The most important factors for the future fate of P. alpina and P. vulgaris individuals were size, time and stage, and for P. villosa time and size, in that order.
Journal of Ecology © 1993 British Ecological Society