Region versus site variation in the population dynamics of three short-lived perennials


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1. When range shifts or invasions of plant species are studied, it is important to know whether large-scale spatial variation in a species’ demography can be ignored or approximated by variation observed over smaller spatial scales.

2. Here, we studied the population dynamics of three similar (as shown by elasticity analysis) short-lived perennial plant species in multiple sites in different European countries over 2 years. We constructed a total of 40 transition matrices and analysed the spatio-temporal variation in the projected population growth rate (λ) with spatially nested life table response experiments (LTRE).

3. All species (Carlina vulgaris, Tragopogon pratensis and Hypochaeris radicata) showed considerable life-history variation among regions on top of variation among sites within regions.

4. Net variance contributions (NVC), a novel LTRE statistic, revealed that in each species, variation in one group of vital rates contributed most to variation in λ among regions as well as among sites. However, that most important type of vital rates differed between species: plant growth in C. vulgaris, flower head production in T. pratensis and establishment probability of seedlings in H. radicata. The rankings of the NVCs of other vital rates varied between site and region effects, suggesting that buffering through negative vital rate correlations varies over different spatial scales, while the identity of the main contributor to λ variation is more constant.

5. Temporal effects were smaller than spatial effects, but the LTREs showed strong interactions between time and space (region or site), suggesting that the effect of, e.g. climate fluctuations are not synchronized throughout the distribution of a species.

6.Synthesis. This study shows that the life histories of plant species are distinguishable even when mean elasticity values show only small differences, and that life histories vary over the distribution range of a species. Demographic differences over large spatial scales can therefore only be partly substituted by small scale spatial variation in modelling studies on the population dynamics of a species across its entire distribution.