From nature to provisioned food: linking feeding strategies to mercury exposure in an endangered primate across human-disturbed limestone landscapes.

Under the Anthropocene, pollution increasingly threatens wildlife, especially in human-modified landscapes with elevated contaminant levels. Wildlife often adjust their strategies in response to habitat alteration and human interactions, resulting in changes in diet composition and, consequently, altered exposure risks, as foods from different sources vary in pollutant content. Despite this, human-mediated changes in feeding behavior are rarely incorporated into risk assessments. Here, we examined how human-influenced foraging alters mercury (Hg) exposure and associated risks in three groups of François' langurs (Trachypithecus francoisi), an endangered primate inhabiting fragmented karst forests in southwestern China. Combining year-round behavioral observations with analyses of food and fecal Hg, we found significant differences in Hg concentrations among food types (wild plant > crop > provisioned food) and plant parts (mature leaf> young leaf > fruit > flower > seed), with wild plant containing 2.6-4 times higher Hg than crop and provisioned food. Fecal Hg concentrations did not differ among groups but were more variable in human-impacted groups, indicating increased heterogeneity of exposure linked to altered foraging. Seasonal patterns were evident, with winter showing the highest fecal Hg levels, and 88% of samples exceeding safety thresholds. Adult females were identified as the highest-risk subpopulation. Overall, human disturbance-mediated feeding influences Hg exposure and that reliance on wild vegetation in Hg-rich landscapes elevates exposure risk. Integrating behavioral ecology into risk assessments is therefore crucial to inform targeted conservation strategies aimed at reducing Hg exposure in vulnerable primates inhabiting human-modified karst ecosystems.