New clues as to when and why hooved mammals began to migrate
Nature documentaries capture breathtaking images of the migrations of hooved animals.
The trait helps enlarge populations and maintain ecosystems, but when and how did it evolve? New research in the journal Nature Ecology & Evolution offers some clues.
"We're looking at migration kind of broadly — like, any species that has populations that will seasonally migrate for any time of the year — and then trying to map that onto what we know about the evolutionary relationships between species," said co-author Nathan Upham, assistant research professor and associate curator of mammals at ASU. "And understand how that migratory behavior originated in an evolutionary context."
Nearly half of all hooved animals, or ungulates, migrate.
The behavior arose independently 17 times, likely as grasslands emerged and seasonal changes in the high latitudes required wider foraging.
It also produced larger animals that could cover distances efficiently and exploit more food sources.
“If there's a big change from winter to spring to summer in the growth of the vegetation that the animals are dependent on, that is what drives migratory behavior, and then that's what drives the evolution of larger body size,” said Upham.
The authors tried several causal relationships before determining that this explanation fit the data best. For example, they also considered that ungulates might have developed larger body sizes in response to latitude, which drove them to become dependent on grasses and, ultimately, to migrate.
"It's interesting that what we ended up finding is that it's the behavior that's driving the morphological change and not the other way around," said Upham.
He added that migration disruptions likely killed off some ungulates in the past. Upham sees that as a grim warning of what could await today's species due to habitat loss and climate change.
"If we continue to lose migrations, it's more than just losing a species; you're losing a key part of current ecosystems," he said.