Images of lions, giraffes, wildebeests and other creatures depicted on ancient Egyptian artifacts have helped scientists create a 6,000-year record of local mammal extinctions, according to a new study. Several of the extinction episodes correlate with known periods of drought and rapid human population growth.
While the correlations aren't proof thatdrought and population pressures caused the animals to disappear, "it is an interesting pattern," Justin Yeakel, a biologist at the Santa Fe Institute in New Mexico, told NBC News. What's more, he added, "as the communities lost species, the system became more unstable and this was largely due to the loss of redundancy in the system."
In other words, when an herbivore went locally extinct several thousand years ago, it wasn't a big deal because there were plenty of other herbivores around for the carnivores to eat. Now, there are so few of any mammals left, that the loss of any one species has a larger impact on those that remain.
The research is published Monday in the Proceedings of the National Academy of Sciences and is based on records compiled by zoologist Dale Osborn, whose 1998 book, "The Mammals of Ancient Egypt," provides a detailed picture of the region's historical animal communities.
"When you look at the paleontological records or the archaeological records you get these large time slices that generally aren't high resolution just because preservation doesn't occur that way," Yeakel explained. "This is a unique opportunity to take advantage of human observations in addition to paleontological and archaeological records."
The ability to see interactions between mammals and their changing environmental conditions play out at high resolution over several thousand years, Yeakel noted, provides conservationists with a deeper understanding of how ecosystems might change in the future as species are lost or saved.
The new paper is "a creative combination of art history, environmental history, and ecological modeling to recreate the wildlife community of ancient Egypt and illuminate the process by which humans simplified that ecosystem," wildlife ecologist Justin Brashares at the University of California at Berkeley told NBC News in an email. He was not part of the new research, but served as its editor for the journal.
Egypt was much wetter 6,000 years ago than it is today and was home to 37 species of large mammals, including lions, hyenas, wild dogs, giraffes, elephants, wildebeest and hartebeests — "animals that we associate with east Africa. This is the Serengeti that I'm describing in terms of the animals that were there," Yeakel said. Only eight large mammal species exist in the region today.
He and colleagues identified five periods when the mammalian community of Egypt radically changed. Three of them coincide with known periods of extreme drought and the collapse of human societies, including the Old Kingdom around 4,000 years ago and the fall of the New Kingdom about 3,000 years ago. The fifth period, about 100 years ago, coincides with population growth and industrialization.
The Nile River valley, Yeakel noted, is likely more sensitive to drought and population pressures than other regions because it is the main source of water in the region and the lifeblood for not only plants and animals, but humans and irrigated agriculture. "It is a very spatially limited area and that is bound to just heighten the intensity of whatever is going on," he said.
For example, humans could have competed with the animals for plants, as well as hunted them. As agriculture advanced, there was also greater competition for habitat, as there is today.
"We can't put weight on any of those different drivers, we don't really test that," Yeakel said. "But you can imagine it was probably a combination of the three in some capacity that led to the changes in the community that we saw."
Implications for humans
As the loss of mammals in Egypt has made those that remain more sensitive to further disturbances, so too are human societies sensitive to changes in their natural surroundings, Yeakel added. "One of the chief purposes of this paper was to try to understand how modern communities function with respect to how they used to function and … then be able to extrapolate to tomorrow."
A key finding from the paper, noted Brashares, is that humans "set in motion the destabilization of their ecosystem that cascaded into the loss of many species. Of course, science observes very similar cascading effects in human activities today and that should give us all reason for pause: where will 5,000 or more years of pulling pieces from nature's 'machinery' leave us?"