Biomes as evolutionary arenas structuring the global floristic assembly
By reconstructing the evolutionary histories of 160 plant lineages, this study reveals that global plant diversity is primarily assembled through within-biome speciation driven by phylogenetic conservatism, while biome shifts are asymmetric processes governed by biome area, evolutionary history, and geographic distance, establishing biomes as fundamental evolutionary arenas that both constrain diversification and mediate biotic exchange.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer
The story of life on Earth is written in the landscape. For decades, scientists have understood that different environments—from scorching deserts to lush rainforests—host distinct groups of plants. We know that a cactus thrives in the dry heat while a fern prefers the damp shade, and that these environmental differences act as filters, deciding which species can survive where. But a deeper question has long remained unanswered: how did the global map of plant diversity actually come to be? Did plants mostly evolve in place, slowly adapting to the specific conditions of their home, or did they constantly jump between different environments, reshaping the world's green cover through movement and migration? To answer this, researchers had to look beyond simple maps and into the deep history of plant families, tracing their family trees to see where they lived millions of years ago and how they moved through time.
A team of researchers, led by Gengchen Yang and Wenna Ding, set out to solve this puzzle by treating the world's major vegetation types, known as biomes, as distinct evolutionary stages. They gathered a massive dataset, compiling the family trees of 160 different groups of plants, which together represent about 20,000 species. This sample covers a vast portion of the world's plant life, spanning from the tropical rainforests of the Amazon to the frozen tundra of the Arctic. By using advanced computer models to reconstruct the history of these plants, the team could watch, in a sense, how each lineage moved or stayed put over millions of years. They were looking for a pattern: did plants tend to stay in the same type of environment as they evolved new species, or did they frequently switch habitats?
The results revealed a striking and dominant pattern: plants overwhelmingly stay home. The study found that the vast majority of plant diversity in any given biome is the result of species evolving right there, within that specific environment. Roughly 86 percent of the variation in how many plant species exist in a biome can be explained by this local evolution. Only about 12 percent of the diversity comes from plants moving from one biome to another and adapting to a new life. This confirms a concept known as phylogenetic biome conservatism, which means that plant families tend to stick to the environmental conditions their ancestors knew. It is as if the world's biomes are not just collections of plants, but rather enclosed arenas where evolution plays out in relative isolation. While some plants do move, the study shows that the global map of green life is primarily built by species diversifying in place, rather than by a constant, chaotic shuffling of species between different worlds.
However, the story is not entirely static. When plants do move, they do not jump randomly. The researchers discovered that these movements follow a strict set of rules governed by geography and history. Some biomes act as sources, constantly sending out new lineages, while others act as sinks, receiving them. Tropical forests and Mediterranean shrublands, which have deep evolutionary histories and high species richness, function as major sources. They are the evolutionary engines that produce lineages which then spread to other places. In contrast, younger or more unstable environments, like the Arctic tundra or boreal forests, tend to act as sinks, receiving more plants than they send out. This flow is not random; it is heavily influenced by how big a biome is, how well it is connected to others, and how long it has existed. Larger, well-connected biomes receive more immigrants, much like a large island in the ocean receives more visitors than a tiny, isolated one.
The path a plant takes is also dictated by the distance it must travel and how similar the destination is to its home. Plants are most likely to move between biomes that are geographically close and environmentally similar. A plant moving from a tropical forest to a nearby savanna faces fewer barriers than one trying to cross from a tropical forest to a frozen desert. The study showed that geographic proximity is the strongest driver of these movements; if two biomes share a border, plants are far more likely to cross it. Environmental similarity also plays a role, helping plants adapt if they do manage to cross a geographic gap, but it is the physical closeness that opens the door. This means that the current arrangement of the world's biomes—how they are spaced out and what they are like—directly shapes the flow of life across the planet.
By combining these findings, the researchers propose a new way to understand the assembly of global plant diversity. They view biomes not just as passive backdrops, but as active evolutionary arenas that both constrain and guide the history of life. Most diversity is born within the walls of these arenas, but the exchange of life between them follows predictable patterns based on size, connection, and history. This framework helps explain why the world's plant life is distributed the way it is today. It suggests that to understand the future of biodiversity, we must look at how these environmental boundaries are shifting and how they might either block or facilitate the movement of species in a changing world. The study does not just map where plants are; it reveals the deep, historical rules that determined how they got there, showing that the green tapestry of our planet is woven from threads of local evolution and guided by the geography of the Earth itself.
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