Human landscape disturbance and wildlife gut microbiota: global knowledge gaps

Wildlife gut microbiota (GM) comprises a dynamic microbial community that plays a key role in host adaptation, ecological interactions and health. Human landscape disturbances (e.g., habitat loss and fragmentation) may alter the diversity and composition of wildlife GM. Therefore, it is important to understand whether these changes are driven by habitat loss, fragmentation per se, or a combination of fragmentation and additional disturbances (e.g., human activities, interaction with domestic animals). We reviewed recent literature (2013-2023) concerning the effects of human landscape disturbance on wildlife GM alpha diversity, focusing on studies employing quantitative or qualitative landscape metrics. Of 119 reviewed studies, 62.2% (n = 74) used some type of landscape metrics, 58% (n = 69) incorporated landscape disturbance as a variable in their analyses, and 49.5% (n = 59) reported significant differences in at least one alpha diversity index. Among studies on free-ranging wildlife that found significant differences in any alpha diversity index (n = 52), 69.2% (n = 36) employed landscape metrics, and 55.8% (n = 29) explicitly described the type of disturbance associated with changes in GM alpha diversity index, with higher values in less disturbed landscapes compared to more disturbed landscapes (binomial sign test; p = 0.04). With respect to host species exhibiting significant variations in their GM alpha diversity index due to human landscape disturbance, there is an overrepresentation of species classified as "Least Concern" and an underrepresentation of species from certain regions, particularly South America. Despite growing research interest in this field, the available studies remain insufficiently extensive to establish clear overall patterns and trends, both globally and across different taxonomic groups. This review identifies methodological and geographical biases and emphasizes the need for more comprehensive studies in this field, considering host species ecology and quantitative landscape metrics as a substantial contribution for predicting ecosystem-level responses and informing effective conservation efforts.