Sarracenia evolution, climate and elephants
Apr 6, 2019 4:42:30 GMT -5
stevebooth, calen, and 1 more like this
Post by chimaera on Apr 6, 2019 4:42:30 GMT -5
I am intrigued with the evolution of Sarracenia (I am a palaeontologist who works on shark evolution normally) and in particular how they speciated and got through the ice ages. There have been a couple of papers which have discussed this, but seem to largely make the mistake of assuming that conditions have remained pretty stable, which is far from the truth. So I am 'thinking aloud' on this and wondered what other opinions people had.
Climate and ice
The last 3 million years has seem some pretty dramatic changes in climate and vegetation, with an ice age every 100 thousand years or so, each more severe than the last. During the last advance, only 20k years ago, whilst ice only covered the northernmost part of the current range of Sarracenia, the climate belts south of that would have all been very different and many would have been pretty inhospitable for them- tundra on the hills where the current mountain species live, and cool, dry forest or coniferous forest covering most of the rest of their current range, with only the Gulf Coast being comparable to now. BUT sea levels were 100 metres lower and the coast was way out into what is now the Gulf, and peninsular Florida was several times as large as now. Unfortunately much of this new land would have been arid and also has limestone soils and thus unsuitable, so plants could not retreat south to avoid the cold. So species must have been only present in small pockets of coastal and riverine swamps. I would expect that many species may have become extinct, whilst fragmentation may have aided speciation. Any species in more northern or upland areas today cannot have been there throughout and must have recolonised as the ice retreated, presumably becoming extinct in their original sites. Could it also be that only the most cold tolerant species survived these glacials? It always surprised me how easily species from subtropical sites survive way below freezing in cultivation- could these be traits that helped them survive in the past?
Elephants
All ecosystems are an interaction of all the animals and plants. We think of N America as always being like it is today, but until 11000 years ago it was a very different place. Before humans arrived, eastern N America had 3 species of elephants (columbian mammoth in the south, woolly mammoth largely in the northern prairies and mastodon in the forests, but all overlapping in range) as well as several multi-tonne ground sloths, glyptodonts (imagine a VW Beetle crossed with an armadillo), camels, horses, peccaries, and many others. Where elephants live today they have a profound influence on the ecology, especially in boggy areas. They drink and wallow a lot and feed on scrub and grass near water. This elephant action must have been great for Sarracenia- removing shade and competition whilst maintaining swampy habitat. Indeed trampling may have acted to break up rhizomes and help spreading. In addition there was a giant beaver, Casteroides, and if that had behaved like the modern species this must have dramatically influenced watercourses and caused flooding. Glyptodonts are often found in swamp sediments and so could their wallowing and grazing also have had a similar effect?
So, prior to humans helping to kill off these tasty animals and using fire extensively, would elephants and other giant animals have been the main maintainer of Sarracenia habitat and not fire? Did Sarracenia once have a far wider diversity, but with species becoming extinct during the glacial advances and maybe when elephants became extinct and stopped maintaining some habitats? Could some more variable species contain genes of extinct relatives?
Climate and ice
The last 3 million years has seem some pretty dramatic changes in climate and vegetation, with an ice age every 100 thousand years or so, each more severe than the last. During the last advance, only 20k years ago, whilst ice only covered the northernmost part of the current range of Sarracenia, the climate belts south of that would have all been very different and many would have been pretty inhospitable for them- tundra on the hills where the current mountain species live, and cool, dry forest or coniferous forest covering most of the rest of their current range, with only the Gulf Coast being comparable to now. BUT sea levels were 100 metres lower and the coast was way out into what is now the Gulf, and peninsular Florida was several times as large as now. Unfortunately much of this new land would have been arid and also has limestone soils and thus unsuitable, so plants could not retreat south to avoid the cold. So species must have been only present in small pockets of coastal and riverine swamps. I would expect that many species may have become extinct, whilst fragmentation may have aided speciation. Any species in more northern or upland areas today cannot have been there throughout and must have recolonised as the ice retreated, presumably becoming extinct in their original sites. Could it also be that only the most cold tolerant species survived these glacials? It always surprised me how easily species from subtropical sites survive way below freezing in cultivation- could these be traits that helped them survive in the past?
Elephants
All ecosystems are an interaction of all the animals and plants. We think of N America as always being like it is today, but until 11000 years ago it was a very different place. Before humans arrived, eastern N America had 3 species of elephants (columbian mammoth in the south, woolly mammoth largely in the northern prairies and mastodon in the forests, but all overlapping in range) as well as several multi-tonne ground sloths, glyptodonts (imagine a VW Beetle crossed with an armadillo), camels, horses, peccaries, and many others. Where elephants live today they have a profound influence on the ecology, especially in boggy areas. They drink and wallow a lot and feed on scrub and grass near water. This elephant action must have been great for Sarracenia- removing shade and competition whilst maintaining swampy habitat. Indeed trampling may have acted to break up rhizomes and help spreading. In addition there was a giant beaver, Casteroides, and if that had behaved like the modern species this must have dramatically influenced watercourses and caused flooding. Glyptodonts are often found in swamp sediments and so could their wallowing and grazing also have had a similar effect?
So, prior to humans helping to kill off these tasty animals and using fire extensively, would elephants and other giant animals have been the main maintainer of Sarracenia habitat and not fire? Did Sarracenia once have a far wider diversity, but with species becoming extinct during the glacial advances and maybe when elephants became extinct and stopped maintaining some habitats? Could some more variable species contain genes of extinct relatives?