May 9, 2013
Picky Eating Drove Saber-Tooth Tiger To Extinction In Last Ice Age
April Flowers for redOrbit.com - Your Universe Online
During the Pleistocene epoch, an astounding diversity of large-bodied mammals inhabited the so-called “mammoth steppe” — a cold and dry, yet productive, environment that extended from western Europe through northern Asia and across the Bering land bridge to the Yukon territory. Three types of large predators roamed the steppe during the Pleistocene, wolves, bears and large cats. After the end of the last ice age, only wolves and bears were able to maintain their ranges.
"We found that dietary flexibility was strongly species-specific, and that large cats were relatively inflexible predators compared to wolves and bears. This is a key observation, as large cats have suffered severe range contractions since the last glacial maximum, whereas wolves and bears have ranges that remain similar to their Pleistocene ranges," said Justin Yeakel, now a postdoctoral researcher at Simon Fraser University in British Columbia who worked on the study as a graduate student at UC Santa Cruz.
The findings were published recently in the journal Proceedings of the Royal Society B are are based on an analysis of stable isotope ratios, chemical traces in fossil bones that can be used to reconstruct an animal´s diet. The data was obtained from previously published stable isotope datasets. These datasets were used to reconstruct predator-prey interactions at six sites located from Alaska to western Europe. The sites cover a range of time from before, during and after the last glacial maximum. The maximum occurred between 20 and 25 thousand years ago when the ice sheets reached their greatest extent.
The researchers found that the large cats´ diet was similar across the different locations, especially in the post-glacial period. In contrast, wolves and bears ate different things in different locations. Bison, horses, yaks, musk oxen, caribou and mammoths were all prey species on the mammoth steppes. Changes in predator diets coincided with an increase in caribou abundance, the researchers noticed, starting around 20,000 years ago.
"During and after the last glacial maximum, many predators focused their attention on caribou, which had been a marginally important prey resource before then," Yeakel said. "Large cats began concentrating almost solely on caribou in both Alaska and Europe. Wolves and bears also began consuming more caribou in Alaska, but not in Europe."
Though morphologically similar to modern lions, the cave lions and saber-toothed cats of the mammoth steppes went extinct within the past 10,000 years. The bears of that time were also morphologically similar to modern bears, such as the short-faced bear that was larger than a polar bear and has since gone extinct. The researchers found that the short-faced bear was the only bear species that did not focus on caribou as prey in the post-glacial period.
The demise of the mammoths and other large fauna of the mammoth steppes coincided with a growing human population after the last ice age. Many species, including wolves and bears, are still around, however. Previous studies of past ecosystems can inform scientists´ understanding of modern carnivores and their capabilities, said Yeakel.
"If you look at wolves today, they are specialist carnivores preying on large herbivores like deer and elk, but when we look in the fossil record we see that wolves are remarkably flexible. Their environment today is fairly artificial compared to when they evolved," he said.
The researchers found that large-scale patterns of interactions differed between locations but remained stable over time. Predator-prey interactions had relatively little overlap in the preferred prey of different predator species in Alaska. In Europe, however, predator-prey interactions were less “compartmentalized.”
"The large-scale patterns don't seem to change, which suggests this community was resilient to the climate changes associated with the last glacial maximum. That makes sense, because it survived multiple ice ages further back in time," Yeakel said.