Weather driven demography and population dynamics of an endemic perennial plant during a 34-year period

1. Increased anthropogenic influence on the environment has accentuated
the need to assess how climate and other environmental factors drive vital
rates and population dynamics of different types of organisms. However, to
allow distinction between effects of multiple correlated variables, and to
capture the effects of rare and extreme climatic conditions, studies
extending over decades are often necessary. 2. In this study we used an
individual-based dataset collected in three populations of Pulsatilla
vulgaris subsp. gotlandica during 34 years, to explore the effects of
variation in precipitation and temperature on vital rates and population
dynamics. 3. Most of the observed conspicuous variation in flowering among
years was associated with differences in precipitation and temperature in
the previous summer and autumn with a higher incidence of flowering
following summers with high precipitation and low temperatures. In
contrast, climatic variables had no significant effects on individual
growth or survival. 4. Although the weather-driven variation in flowering
had only moderate absolute effects on the population growth rate,
simulated persistent changes in average precipitation and temperature
resulted in considerable reductions in population sizes compared with
current conditions. Analyses carried out with with subsets of data
consisting of 5 and 10 years yielded results that strongly deviated from
those based on the full data set. 5. Synthesis: The results of this study
illustrate the importance of long-term demographic monitoring to identify
key climatic variables affecting vital rates and driving population
dynamics in long-lived organisms.