Intra- versus inter-regional variation in the population dynamics of short-lived perennials

Background/Question/Methods: When range-shifts or invasions of plant species are studied, it is important to know whether large-scale spatial variation in a plant’s demography can be ignored or approximated by variation observed over smaller spatial scales. Here we studied the population dynamics of three short-lived perennial plant species between and within different European countries, to examine at what spatial scale most of the variation between demographies occurs. We constructed a total of 40 transition matrices and analysed the spatiotemporal variation in the projected population growth rate (λ) with Life Table Response Experiments (LTRE) to investigate (dis)similarities between the inter- and intra-regional demographic vital rate variations that contributes to λ fluctuations. Results/Conclusions

The λ-differences between years within regions and within sites did not differ much in magnitude from the overall year effect. Two species (Carlina vulgaris and Tragopogon pratensis) showed more variation in λ between regions, whereas Hypochaeris radicata had more λ-variation between sites within regions. The LTRE analyses furthermore showed that the region and site effects not only differed in magnitude, but more importantly also in the contributions of the deviations of the vital rates summing up to the region and site effects. Still, the same single group of vital rates covaried most closely with λ between regions and between sites: growth of survivors in C. vulgaris, seed production of flowering plants in T. pratensis and establishment probability of seedlings in H. radicata. We conclude that the life history of plant species can vary qualitatively differently between and within regions, resulting in more λ-variation between regions in some species, but in less λ-variation in another. Differences in spatial scales can therefore not be ignored when demographic variation is included in modelling studies on the population dynamics of a species across its entire distribution, for instance when investigating invasions or range-shifts due to climate change.