A recent study suggests that the consumption of human food has a pronounced effect on the microbiome of black bears. Specifically, researchers at North Carolina State University and Northern Michigan University found that wild bears that ate a lot of processed foods had much less diversity in the microbial ecosystems in their gut.
“We know that a ‘western’ diet can reduce microbial diversity in the intestines of humans, mice and other species, which can have an adverse effect on their health,” says Erin McKenney, co-author of the study and assistant professor of applied sciences. ecology in the NC state. “We want to know if the same is true for wildlife, especially given the growing overlap between where people live and where wildlife lives. One possibility that our work raises here is that if wildlife begins to consume of human foods, it may affect their ability to derive as much nutrition from their traditional, wild diet if they stop eating human foods. “
“One step to see if the same is true for wildlife is to assess the impact of human food on the gut microbiome of wild mammals,” says Sierra Gillman, lead author of the study and PhD. student at the University of Washington. “In this particular study, we wanted to know how human food influences the gut microbiome of black bears.” Gillman did the job as a graduate student at NMU.
The researchers focused the study on Michigan, which allows hunters to “bait” bears by leaving out large amounts of human food, such as sugary cereals and candy. Hunters will bait specific sites for weeks or months to regularly attract bears to a specific area. As a result, some bears eat a diet rich in human junk food for an extended period of time.
To collect samples of the wild bear population, the researchers worked with guides who lead scheduled trips with hunters to Michigan’s upper peninsula. The guides collected bear samples which were collected during their regular trips with the hunters. Specifically, the guides followed a detailed protocol to retrieve hair samples and two bowel samples. The intestine samples came from the jejunum, which is the middle part of the small intestine, and the colon, also called the large intestine. In the end, the researchers were able to recover samples from 35 legally harvested bears.
The researchers processed the gut samples to identify both the types of microbes present in each bear’s microbiome as well as the number of each type of microbe present.
The researchers also performed a carbon isotopic analysis of bear hair, which allowed them to assess each bear’s long-term diet. Specifically, the analysis told researchers how well each bear consumed sugar and corn, which are more likely to be found in processed foods.
When analyzing the data, the researchers looked at two measures of gut biodiversity. They first look at the total number of different species present. Second, they looked at a metric called Faith’s phylogenetic diversity, which examines the number of different types of species present.
“Basically, Faith’s phylogenetic diversity assesses the number of branches of the bacterial family tree represented,” says Gillman.
Both measures of gut biodiversity were significantly lower in bears that ate more processed foods.
“Essentially, we found that the more human food black bears eat, and the longer they eat, the less diverse their gut microbiomes are,” says Gillman.
“Sugar is very easy to digest,” says McKenney. “A lot of bacteria can eat it. In practical terms, this means that processed human food actually has less food available for bacteria that specialize in breaking down fiber or other micro-accessible carbohydrates. These bacteria specialists find it difficult to compete with other bacteria for sugar, and their niche in the food web is not sustainable if bears do not eat enough of their traditional diet. We believe this is one of the mechanisms for reducing gut microdiversity.
“And if gut biodiversity suffers when bears start consuming more human food, this raises the possibility that it is more difficult for bears to derive so much nutritional value from non-human foods if they return to a ‘wild diet’. “” McKenney said. “Basically, it’s not clear how quickly the microbial species that break down fibers etc. would come back.”
“Now that we have identified this association between human food consumption and microbial biodiversity, we need to do further work to determine what this means for the health of these animals – and potentially other animals,” said Gillman. .
“Many hunters use camera traps to monitor their bait sites, and the people we worked with told us they saw a wide variety of species – raccoons, fishermen, martens, deer, hares – eating bear bait, ”says Diana Lafferty, co-author of the article and assistant professor of wildlife ecology at NMU.
“It’s unclear exactly how the baits might affect the microbiomes or the health of other wildlife that benefit from the free food. When we think of conservation, assessing the impact of our activities on diversity may need to extend to the protection of microbial diversity. There is growing evidence to suggest that many of these microbial organisms are essential to the health of wildlife. How does the bait fit in there? These are questions that I think we will need to explore. “
The article, “Human-supplied foods reduce gut microbiome diversity in American black bears (american bear) “is published in the Mammalogy Journal.
The work was carried out with support from the National Science Foundation, under grant 1000263298; and Sigma Xi, the Scientific Research Honor Society, under grant G2018100198233997.