Phylogenetic biome conservatism on a global scale

Abstract

The degree to which plants and animals retain their ancestral ecological traits and environmental distributions ('niche conservatism') is hotly debated, in part because of its relevance to the fate of modern species facing climate change. A tendency towards conservatism has been demonstrated previously on the local and regional scales, and now a study of more than 11,000 plant species from across the Southern Hemisphere confirms a similar phenomenon on a global scale. Only 3.6% of the evolutionary divergences observed involved a shift of biome, suggesting that many species have only a limited capacity to adapt to new biomes, making them particularly susceptible to ecological change. How constrained is the ecology of a species by its phylogenetic history? The authors assess the extent of biome conservatism — the tendency of a species to occupy the same niche as its ancestors — in over 11,000 Southern Hemisphere plants, 15% of the total flora of the Southern Hemisphere continents. They show that only 3.6% of the evolutionary divergences in their study involved a shift of biome, demonstrating the strong influence of biome conservatism. How and why organisms are distributed as they are has long intrigued evolutionary biologists1,2,3,4. The tendency for species to retain their ancestral ecology has been demonstrated in distributions on local and regional scales5,6,7, but the extent of ecological conservatism over tens of millions of years and across continents has not been assessed8,9,10,11,12,13. Here we show that biome stasis at speciation has outweighed biome shifts by a ratio of more than 25:1, by inferring ancestral biomes for an ecologically diverse sample of more than 11,000 plant species from around the Southern Hemisphere. Stasis was also prevalent in transocean colonizations. Availability of a suitable biome could have substantially influenced which lineages establish on more than one landmass, in addition to the influence of the rarity of the dispersal events themselves. Conversely, the taxonomic composition of biomes has probably been strongly influenced by the rarity of species’ transitions between biomes. This study has implications for the future because if clades have inherently limited capacity to shift biomes13, then their evolutionary potential could be strongly compromised by biome contraction as climate changes.