Experiment meets biogeography: plants of river corridor distribution are not more stress tolerant but benefit less from more benign conditions elsewhere

Abstract

Aims: Factors limiting distributions of species are fundamental to ecologyand evolution but have rarely been addressed experimentally formultiple species. The conspicuous linear distribution patterns ofplant species confined to river corridors in the Central Europeanlowlands constitute an especially long-standing distribution puzzle.We experimentally tested our novel hypothesis that the tolerance ofspecies to river corridor conditions is independent of the degree ofconfinement to river corridor habitats, but that species not confinedto river corridors are better able to take advantage of the more benignnon-river corridor conditions.Methods: We grew 42 herbaceous species differing in their confinement toriver corridors in a common garden experiment on loamy soil typicalfor river corridor areas and sandy soil typical for non-river corridorareas, and with and without a flooding period. For a subset of species,we grew plants of both river corridor and non-river corridor origin totest for adaptation to river corridor conditions.Important findings: Species more confined to river corridor areas benefited less from the more benign non-flooded and non-river corridor soil conditionsthan species of wider distributional range did. For subsets of 7 and12 widespread species, the response to flooding and soil origin, respectively,did not differ between plants from river corridor sites and plants from other sites, suggesting that the habitat tolerance of widespread species is due to phenotypic plasticity rather thanto local adaptation. Overall, we found clear support for our novelhypothesis that species not confined to river corridors are more ableto take advantage of the more benign non-river corridor conditions.Our study provides a general hypothesis on differences between speciesconfined to stressful habitats and widespread species out for testin further multispecies comparative experiments.