Charles Darwin Was Wrong and Now He's Right...At Least Regarding Biogeography
New advanced simulations now predict that Darwin was right about how many animals got to disparate parts of the earth. Instead of land bridges, many may have hitched rides across the ocean.
Darwin made many predictions in his day, large ones and small ones, sometimes based on an incredible paucity of evidence compared to what we have at our disposal today.
One of these tried to explain how certain animals and plants that were obviously closely related, happened to exist vast distances from each other with no clear way to walk from one to the other. Also many isolated island species were puzzling…how did they get there? This is part of a field called biogeography which studies the distributions of species around the world throughout time.
Darwin’s thoughts on this hinged around the idea called Jump Dispersal in which animals hitched rides any way they could across the water to populate distant lands. This could include floating mats of vegetation, logs, or perhaps even icebergs. Seeds as well could have become embedded in the feathers of birds before over sea migrations.
This idea was deemed too fanciful by biogeographers over the years. They instead preferred the theory of Vicarience which states that animals generally got to distant parts of the earth by using land bridges that appear and disappear throughout history between continents and even islands.
That does seem eminently reasonable but there is one big problem with it. Often continents had completely broken up and separated long before many of these animals evolved.
Recently, the theories of Jump Dispersal and Vicarience were pitted against each other in a computer program developed by postdoctoral fellow N.J. Matzke at the National Institute for Mathematical and Biological Synthesis.Using data from species in Hawaii and nearby archipelagos, he concluded that Jump Dispersal had much better retro-predictive power than Vicarience did.
This is interesting to me because it means that how animals and plants are dispersed around the planet is even more contingent than I had thought. As Matzke said:
“Jump dispersal helps us remember that events that are rare on human timescales can be common over geological timescales, and that biodiversity might be structured largely by these rare chance events.”
My only problem with this right now involves breeding communities. I can picture one or two animals hopping on something and floating to a new life across the sea but so few animals would hardly make a genetically viable future community for their species. Perhaps multiple trips by different groups got to the same place or maybe those matts of floating vegetation were fracking huge enough for many dozens to ride on at once.
Image Credit: Mike Fisher