“Happy families are all alike; each unhappy family is unhappy in its own way.” So goes the first line of Leo Tolstoy’s “Anna Karenina.” Little did the Russian novelist know his famous opening line would one day be used to describe microbial communities, their health and their relationships to their hosts.

"It's this idea that an unhealthy or stressed host to a microbiome has a more diverse microbiome than its healthy counterpart," said UC Santa Barbara ecologist An Bui, a graduate student researcher in the lab of theoretical ecologist Holly Moeller. The diversity, she said, is a response to variable conditions that may in turn indicate an unstable or stressed environment. "Healthy hosts are probably going to have very similar microbiomes," she said, "while unhealthy hosts are different in their own ways."

Bui and colleagues recently put the Anna Karenina hypothesis to the test in California’s Tehachapi mountains as they sought to understand how climate change might affect fungal communities in woodland soil in a future California.

“Fungi are really important for woodland systems,” said Bui, the lead author of a study that appears in the journal FEMS Microbiology Ecology. “But we don’t necessarily know how they will change with climate change.”