Correlates of range size variation in the Australian seed-plant flora

AimTo map and analyse range size variation in the terrestrial seed-plant flora of Australia in relation to latitude, habitat availability, climate and soils, and to compare mean range size between biomes and growth forms. LocationAustralia. MethodsRange sizes were estimated from herbarium records using alpha-hulls for 19,227 species and mapped into a set of 0.5 degrees x0.5 degrees grid cells across Australia. Ordinary-least squares regressions were used to test for relationships between mean range size, latitude and habitat availability. Simultaneous autoregressive models (SAR) with spatial error terms were used in a multi-model framework to assess the role of aridity, mean annual temperature (MAT), soil pH, depth and total P concentration in shaping range size variation. Species-level differences between growth forms (graminoids, herbs, trees, shrubs, climbers) and biomes were assessed using one-way analysis of variance (ANOVA). Results68% of Australian seed-plant species have ranges which cover <1% of the continent. Generally, large ranges are characteristic of graminoids and herbs and are associated with arid and grassland biomes. The smallest ranges were found in Mediterranean ecosystems in the SW corner of the continent, and were typically shrub species. Range size peaked at mid-latitudes and was not consistently smaller at lower latitudes (contrary to Rapoport's Rule). Increasing aridity, MAT and soil pH were strong predictors of large range size; however, soil depth and P content had little influence in SAR models. Main conclusionsAridity and temperature are the primary drivers of range size variation in the Australian flora. Trait syndromes which promote colonization and survival in arid and grassland habitats (e.g. C4 photosynthesis, wind pollination) have allowed grasses and herbs to occupy large areas of the continent. Ranges were not smaller, on average, in the tropics due to the concentration of large-ranged species in the widespread arid biome in the centre of the continent.