fossils

Predator “superpacks” may have kept mammoths in check

34f1d64c52c45a6bdce31bc5e48b86cc

Julio
Lacerda

Staff Artist and Writer
While adult megaherbivores were too large for predators to take down, juvenile mammoths, mastodons, and ground sloths might have fallen prey to packs of sabretooth cats, cave lions and giant hyenas. This balance made sure there was enough plant matter for smaller animals to thrive on during Ice Age North America.

Some thousands of years ago, during the Pleistocene Ice Age, most of North America was much like a colder version of the modern African savannahs, except with some bigger animals. The familiar fauna of today’s US and Canada coexisted with enormous mammoths, mastodons, ground sloths and giant bison while saber-tooth cats, dire wolves and giant lions stalked the plains.


In Africa today, the largest living herbivore is the bush elephant. Weighing on average 6 tons and living in family groups of up to 20 individuals, even juvenile animals are almost impervious to predation. They are a powerful force that can reshape the environment around them, and herds are known to cause localized plant devastation and habitat destruction if their numbers get too high.


But the Ice Age saw not one, but many herbivores around the weight range of modern elephants; some were grazers and some browsers. The largest ground sloths like Megatherium were about the same size, while mammoths and mastodons could reach 8 to 12 tons and presumably lived in family groups as well.


So how did the prehistoric landscapes cope with those huge, ravenous plant-eaters? It seems that unlike modern elephants that usually don’t need to worry about being preyed upon unless they’re babies, the Ice Age megaherbivores needed to stay alert. UCLA Paleontologist Blaire Van Valkenburgh and his colleagues propose that the large predators that coexisted with those herbivores had a crucial role in keeping their populations in check.


They examined the fossils of extinct predators such as dire wolves, saber-tooth cats, cave lions and giant hyenas and compared their skeletons with their modern equivalents to estimate their mass. They came to the conclusion that the extinct predators were, on average, 50 to 100 percent larger than today’s apex predators. They did the same with elephants and the remains of mammoths and mastodons and found similar results.


The scientists then analyzed the usual size range of victims for modern hunters and the rare cases in which African elephants do fall prey to lions, estimating the average size of the attacked elephants and how many lions work together to bring them down. By comparing these results with the estimated sizes for the extinct animals, the team concluded that by forming large groups, the carnivores could indeed take down even large juvenile herbivores weighing 2 tons - about the same size as a rhino.


They also looked at fossil teeth to see how big these predator packs, prides and clans could be. When competition over food is high among modern meat-eaters, carnivores tend to eat as much as they can from a carcass since there’s less food to go around. This means they have to eat more bones along with the flesh, resulting in broken teeth.


Fossils from the Ice Age’s large predators show three to five times more incidences of tooth fractures compared to their living equivalents, meaning a higher density of predators than what we see today – which could be evidence of larger groups that were able to take down larger animals.


The team’s results point to a complex ecology that involved animals big and small in Pleistocene environments. By culling juvenile mammoths, mastodons and ground sloths – which had low birth rates and long gestations - the giant carnivore packs would control their impact on the vegetation and prevent overfeeding. This ensured that there were enough plants to sustain multiple species of animals including smaller mammals and birds, and may even have affected river ecosystems by preserving the vegetation on riverbanks and diminishing the rate of erosion.


They also highlight how so many carnivore species shared the same habitat, and the domino effect that may have taken place at the end of the period. With climate change leading to the extinction of the megaherbivores, in turn the giant predators, specialized in big game, followed suit. Only carnivores that could survive on smaller prey, such as the common wolves and mountain lions, had what it took to go through the mass extinction.


Reference:
"The Impact of Large Terrestrial Carnivores on Pleistocene Ecosystems," Blaire Van Valkenburgh, Matthew Hayward, William Ripple, Carlo Meloro and V. Louise Roth. Proceedings of the National Academy of Sciences, Early Online, Oct. 26, 2015. DOI: 10.1073/pnas.1502554112

Image Credit: Mauricio Anton

34f1d64c52c45a6bdce31bc5e48b86cc

Julio
Lacerda

Staff Artist and Writer


http://sulc.us/3egaz
http://www.eartharchives.org/articles/predator-superpacks-may-have-kept-mammoths-in-check/