Wild orangutans inhabit extremely variable dietary environments with fluctuations in fruit availability that cause significant changes in their dietary compositions and total caloric intake. Many studies on mammals and primates show clear signals of seasonal variation in gut microbiota. A few primate studies demonstrate that gut microbiota may be helping hosts maintain energy balance during seasonal fluctuations in diet by energetically compensating for nutritional stress or reductions
in intake. We measured temporal changes in wild orangutan diets and gut microbiota across a shifting nutritional landscape that is highly variable and unpredictable, without clear seasons or cycles. Our results suggest that orangutan gut microbiomes are enhancing their ability to exploit periods of caloric abundance, rather than compensating for reductions in dietary intake during lean periods.