Humans are the cause of biotic homogenization (a process in which different ecosystems become more similar over time) among mammals in North America, according to a new study published earlier in July.
The study, which was published in the peer-reviewed Nature journal, analyzed 8,831 fossils from 365 mammal species in North America.
This is the first study of this kind that analyzed homogenization as a human-generated process. Previous studies have either focused on climate millions of years ago or on human effect in the last century. This study, however, covered the last 30,000 years, encompassing the time before humans were in North America, their migration there and the shift from hunter-gatherers to farmers.
Humans: The biggest cause of homogenization
The researcher concluded that humans are the biggest cause of homogenization in North America with modern-day mammal communities twice as homogenous as they were 10,000 years ago.
Another sign of human involvement is that homogenization began to accelerate about 12,000 years ago when humans were hunting mammoths, saber-toothed felines, dire wolves and other large mammals to extinction.
Another acceleration was marked in the past 5,000 years when there was a surge in the human population in North America as well as the emergence of farming, particularly in the east and center of the continent.
“It happened much later in North America than on other continents,” said Kate Lyons who led the study. “But that’s really when humans in North America went from being hunter-gatherers to being more settled and dependent on agriculture.”
The homogenization process was caused by a number of human-related causes. Human settlements attracted animals like coyotes, raccoons and rodents who took advantage of the byproducts of human activity, converted habitats for agriculture chased away the animals in those habitats and human-made boundaries like roads and fields also acted as boundaries for animals.
The extinction of keystone species in the last 500 years has only made the homogenization process more rapid.
“A lot of what we’re finding is that when we lose species — particularly when we lose large species that tend to be what we call ecosystem engineers — there’s a dramatic change in the ecosystem that’s left,” explained Lyons.
“Large mammals do all kinds of stuff in ecosystems."
Kate Lyons
“Elephants eat a lot, they move around a lot, and they poop a lot, so they actually move nutrients around ecosystems a lot. What we’re finding, then, is that nutrients essentially get lost from ecosystems (in their absence).”
As far as the effects of climate on the homogenization process, the researchers found little evidence to support that theory.
“What we find when we look at the climate patterns is that all of that happened very early on before we see this dramatic homogenization,” said Lyons.