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Square Tower House at Mesa Verde National Park

A Square Tower House at Mesa Verde National Park. Researchers created a food web from the Ancestral Puebloan Southwestern United States that shows the complexity and interconnectedness of humans, other animals, and crops, and the environment.

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Stefani Crabtree, a postdoctoral fellow in human behavioral ecology in the Department of Anthropology at PennState University, and a team of researchers reconstructed food webs from the Ancestral Puebloan Southwestern U.S. that show the complexity and interconnectedness of humans, other animals, and crops, and the environment in an area of uncertain climate and resources. The researchers believe that climate change and human decisions then may shed light on future human choices.

"As southwestern archaeologists, we know that Ancestral Puebloan people were intrinsically connected to the environment, but, most food webs have omitted humans," says Crabtree.

Unlike traditional food webs, which map the interaction of all the animals and plants in an area but don't typically emphasize the human component, Crabtree and colleagues created a digital food web that captures all categories of consumers and what's consumed. The digital food web can be defined for specific time periods and can also represent food webs after major food sources or predators disappear from an area. If an area suddenly becomes devoid of deer or humans or corn, for example, a food web of that situation can show where predators went to find prey, or which prey thrived for lack of a predator.

The team did not produce just one overall food web, but also food webs corresponding to three archaeological locations and three time periods of Ancestral Pueblo occupation in the area: Grass Mesa Pueblo for Pueblo I, Albert Porter Pueblo for Pueblo II and Sand Canyon Pueblo for Pueblo III. They began with using archaeological assemblages from these sites, incorporating all human prey and all human predators into the food web. Then they included the prey of the primary prey of humans and then predators of these human-prey species. Prey, in this case, includes animals, insects and plants.

Knockout food webs -- webs missing a specific predator or prey -- show the changes and pressures on the food sources substituted for the missing ones, ohe changes that occur when pressure is removed by removing a major consumer. "Knockout food webs are one of the best ways to understand how people interact with the environment," said Crabtree. "Because we can remove something, predator or prey, and see what would happen."

When food becomes scarce, most mobile creatures, animals and insects move to another location. During the time of the Ancestral Puebloans, this was possible and eventually, these people moved to the area of the Rio Grande in New Mexico and other places in New Mexico and Arizona.

In the past, people migrated, said Crabtree. Unless we figure out better strategies, where are we going to migrate out to? We do not have a place to go, she said.

This research was funded in part by the National Science Foundation (NSF) (grant DEB 08-16400) and was conducted while supported by NSF Graduate Research Fellowship DGE 08-06677 and an NSF GROW fellowship.

To learn more about this research, see the Penn State news story Food webs entangle humans, animals, crops and the environment.(Date image taken: 2014-2017; date originally posted to NSF Multimedia Gallery: July 12, 2017)

Credit: Nate Crabtree Photography

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