Disparate relatives: Life histories vary more in genera occupying intermediate environments

Species within clades are commonly assumed to share similar life history traits, but within a given region some clades show much greater variability in traits than others. Are variable clades older, allowing more time for trait diversification? Or do they occupy particular environments, providing a wider range of abiotic or biotic opportunities for the establishment and maintenance of diverse trait attributes? Does environmental opportunity increase trait variability across all species, or is it specific to species belonging to the same clade, increasing only within-clade trait variability? We studied the variability of six life-history traits (initiation of flowering, duration of flowering, plant life span, seed mass, stress tolerance, type of reproduction) within 383 angiosperm genera from Central Europe distributed along six abiotic gradients. We compared patterns of within-genus variability to those present in the entire dataset, independent of genus membership. We found that trait variability differed strongly between genera, but did not depend on their age. Trait variability was higher within genera occupying intermediate positions along regional abiotic environmental gradients, compared with patterns across the entire dataset (and unbiased by geographical sampling, family membership or species richness). Increasing trait variability within genera reflected increasing independence of traits from the abiotic environment. We conclude that intermediate abiotic environments play an important role in maintaining and possibly generating the striking diversity of life history traits present within certain clades. They may do so by relaxing the abiotic constraints on the evolution and maintenance of species traits within clades.