AmericanBison_C4Grass_Kilby_David_SanMarcosTX_30March2023_Reel4147.mp3

David Kilby [00:00:00] The end of the Pleistocene is not just a gradual transition. You get this warming and drying for over two or three thousand years and then fairly abruptly, about 12,800 years ago, you get this kind of whiplash return to Ice Age conditions that lasts a few hundred to about a thousand years.

David Kilby [00:00:23] We call it the Younger Dryas.

David Kilby [00:00:25] And it's right in that whiplash for whatever reason that most of the megafauna check out. That's when mammoths go extinct or at least they go missing from the, from the paleontological record. Mastodon, sabre-toothed tiger, all these other animals seem to meet their demise right there at the beginning of the Younger Dryas.

David Kilby [00:00:43] But, the megafauna that survives that is the bison. And the bison become sort of the keystone species of the grasslands from that point forward.

David Kilby [00:00:54] And genetically, it looks like bison go through what we call a bottleneck at that time, too, meaning that they were impacted by that abrupt climate change.

David Kilby [00:01:04] But, what we see coming out the other side of that is relatively smaller animals in much bigger herds. There's a transitional form that is sort of imperfectly defined called, "Bison occidentalis", which may be between Bison antiquus and modern bison.

David Kilby [00:01:22] And then we see the emergence of what we would consider fully modern bison by about 6000 years ago, six to eight thousand years ago.

David Kilby [00:01:31] And one of the things that probably carried them through that big ecological change is that they have these specialized multi-chambered stomachs that allow them to subsist on lower quality grass.

David Kilby [00:01:47] Elephants, and presumably mammoth and horse, and these other grazers were dependent on these high-quality, high-calorie, what we call, "C3", grasses on the plains.

David Kilby [00:01:58] And those contract after the end of the Ice Age and there's an expansion of these C4, more drought-tolerant grasses, which are probably part of the, part of the reason that some of the bigger animals check out.

David Kilby [00:02:12] But, bison are able to exist on that, and are able to eventually thrive on the lower-nutrient grasslands.

David Kilby [00:02:19] And so, they become the dominant species on the plains and they start to play that same role that mammoths had previously as being a keystone of the ecology of the plains. Their manure, their trails, their existence on the plain drives a lot of the health and quality of other habitats.