Macroevolutionary insights into the range limits of species and lineages

Understanding the intrinsic and extrinsic factors that determine the range limits of species is an important goal in biology. Much work has focused on understanding the range limits of populations and individual species, whereas the factors that determine the distributions of evolutionary lineages have received less attention in the range limits literature. In this review I highlight recent macroscale insights into the range limits of flowering plant lineages, and briefly compare these to findings from other taxa. Although life on Earth has managed to adapt to practically all environments, recent methodological and analytical advances in macroevolution and biogeography show that adaptation to novel environments is relatively rare: multiple large-scale studies estimate that well over 80% of speciation events are confined within their ancestral macroclimatic environment, or biome. This high degree of phylogenetic biome conservatism reflects that Earth is crossed by various major environmental adaptive barriers, or hard range limits, that strongly constrain the ranges of both species and lineages. These adaptive barriers differ significantly in how often they are surmounted: some barriers, like fire, are crossed relatively frequently, whereas others, such as frost or salinity, delimit species' ranges over many millions of years. Some barriers thus structure the global distribution of terrestrial lineages more stringently than oceans between landmasses. Furthermore, broad congruencies in large-scale distributions of plants, animals, and fungi tentatively suggest that these are shaped by similar processes, and/or biotic interactions. Environmental adaptive barriers therefore provide an important framework for understanding the range limits of populations, species, and lineages.