Repost: Honey, I Shrunk the Coyote
- 10:23 am |
[I'm out in Grand Staircase-Escalante National Monument for some late season fieldwork this week. Here's an essay from the archive, originally posted on February 27th, 2012.]
When I think of the La Brea asphalt seeps, coyotes don’t immediately jump to mind. Sabercats and dire wolves are the sorts of carnivore I have come to associate with the oozing predator trap. Yet coyotes were there in abundance. According to a monograph on the site I picked up from the Page Musuem gift shop — written by paleontologist Chester Stock and later revised by John Harris — coyotes are regularly found in the asphalt and are about one-eighth as numerous as their fearsome cousins, the dire wolves.
The prehistoric coyotes were not quite the same as those we know today. They belonged to the very same species — Canis latrans — but the Ice Age versions were significantly larger than their modern counterparts. More than that, the coyotes had deeper jaws and wider teeth — signs that they were coping with more intense stresses while capturing and consuming prey. Rather than being small-prey specialists, La Brea’s coyotes competed with wolves and big cats for prey. As explained in a new study by paleontologists Julie Meachen and Joshua Samuels, the machinations of “nature red in tooth and claw” might explain why super-sized coyotes roamed the Pleistocene plains.
That Ice Age coyotes were extra large is not a new observation. Paleontologist John Campbell Merriam noticed the difference between the past and present canids a century ago, Meachen explained, but “No one really looked at these coyotes again until I came along.” Exactly why the Pleistocene coyotes were larger than their modern counterparts was treated as a simple quirk of nature and not a mystery that required explanation.
On the surface of things, changes in the global climate might seem to be a reasonable trigger for the trend. The world warmed significantly between the time of the La Brea coyotes and today, and as temperatures rose then it might be expected that coyotes downsized. This stems from an idea called Bergmann’s rule — a notion that cooler temperatures favor larger bodies better at retaining heat and warmer climates favor smaller bodies better suited to shedding heat.
Wolves are key to testing this idea. While dire wolves are certainly among the La Brea celebrities, prehistoric grey wolves were also present in Pleistocene California. They managed to survive whatever killed off so many Ice Age megamammals. If Bergmann’s rule was behind the size shift, then, we would expect that both grey wolves and coyotes would have shrunk as climates warmed since both were similar animals which shared the same habitats over the past 40,000 years.
Meachen and Samuels looked to the postcranial skeletons of coyotes and grey wolves from the late Pleistocene to the modern era to track how the canids changed. The dogs did not change in the same ways. In fact, grey wolves have hardly changed at all. Citing similar results obtained by Bob Dundas and Jennifer Leonard, Meachen pointed out that the grey wolves at La Brea “basically looked like modern wolves, and they were very gracile compared to Alaskan and Beringian wolves” found much further north. Grey wolves showed no sign of growing smaller with a warming climate.
But coyotes didn’t stay in stasis. Meachen and Samuels confirmed that the coyotes were larger and more robust than modern representatives of the species. “They would have still looked like coyotes,” Meachen said, “just bigger and stronger.”
This difference — similar wolves, different coyotes — indicates that climate change probably can’t account for coyote changes. Vanished interactions between Ice Age predators and prey may instead be the key. The disparity in coyote anatomy, Meachen said, “was most likely caused by interactions — or cessation of interactions — with an extinct fauna. The big prey species went extinct, so big was less abundant. Their major giant competitors (dire wolves) went extinct, so they didn’t have to be so big to fight off bullies.”
With so many predators around at the same time, being a heavyweight came with an advantage. Packs of larger coyotes may have been better able to take down larger prey and defend kills from other carnivores. “When there are big competitors around,” Meachen said, “coyotes band together to protect themselves,” and she added “When they exist in groups, it is easier for them to kill bigger prey together.” This seems to be an extension of modern coyote behavior. While wolves are large prey specialists, coyotes are behaviorally malleable — they can hunt small prey on their own, or work in groups to tackle larger game. The same would have been true during the Pleistocene, when coyotes might have preferentially targeted the young of extinct bison, camels, horses, and sloths.
The competition between wolf species might have made such changes possible. The rarity of grey wolves at the La Brea site and elsewhere has been taken as an indication that they were being out-competed and displaced by the bigger, badder dire wolves. If this was the case, Meachen and Samuels hypothesized, coyotes might have moved up into the grey wolf size class.
Why coyotes have shrunk during the past 12,000 years isn’t as clear. The extinction of other carnivores might have something to do with it. When the dire wolves, sabercats, and other predators died off, coyotes no longer faced the same frenetic levels of competition. Beefier bodies were no longer needed. Then again, perhaps the depleted variety of prey had something to do with the changes. North America’s various megamammals died out between about 12,000 and 10,000 years ago, and when they disappeared the stock of relatively large prey coyotes had been adapted to hunt disappeared. Maybe both phenomena played some role. Whatever the reason, though, coyotes were flexible enough to survive. They will likely be with us for some time to come.
For more on life at La Brea, see:
Meachen, J., Samuels, J. (2012). Evolution in coyotes (Canis latrans) in response to the megafaunal extinctions PNAS : 10.1073/pnas.1113788109
Stock, C., & Harris, J. (2001) Rancho La Brea: A Record of Pleistocene Life in California, 7th ed. Science Series – Natural History Museum of Los Angeles County. No. 37, p. 29