The scale of the new meta-analysis is notable in a field where individual studies often examine only a handful of species or a single habitat type. By pooling 1,443 high-quality samples from 173 wild mammalian species, the researchers were able to test ecological hypotheses across a breadth of evolutionary history that no single field campaign could achieve. The analysis pipeline relied on QIIME 2, a widely used open-source platform for microbiome data processing, combined with phylogenetic diversity metrics such as Faith’s phylogenetic diversity, which measures the total evolutionary branch length represented by the microbial taxa in a sample rather than simply counting species. This distinction matters because two gut communities can contain the same number of bacterial types while differing dramatically in how evolutionarily distinct those types are, and phylogenetic metrics can therefore reveal patterns of deep evolutionary divergence that simple richness measures obscure.

The finding that herbivores carry roughly 2.1 times the phylogenetic diversity of carnivores, with a 95 percent confidence interval spanning 1.86 to 2.31, aligns with a long-standing body of comparative work on mammalian gut symbiosis. Plant cell walls are structurally difficult to digest, and herbivorous mammals depend on dense, functionally specialized microbial communities to break down cellulose, hemicellulose, and other complex polysaccharides through fermentation. This functional demand appears to favor a richer and more phylogenetically varied microbial repertoire. Carnivores, by contrast, process diets that are comparatively uniform in composition and easier to digest with host enzymes alone, which may relax the selective pressure for maintaining a large and diverse microbial workforce. The confidence interval reported in the study suggests that this herbivore advantage is robust to sampling uncertainty, making it one of the more firmly supported ecological patterns in gut microbiome research.

The role of habitat range as a predictor of microbial diversity adds an interesting biogeographic dimension to the findings. Species with smaller geographic distributions supported distinctly higher microbial diversity in this analysis, a pattern that may seem counterintuitive at first glance. One possible interpretation is that small-ranging species often occupy narrow, specialized niches where stable local conditions allow complex microbial communities to persist over evolutionary time. Alternatively, restricted-range species may experience reduced microbial exchange with conspecific populations elsewhere, leading to greater differentiation and accumulation of locally distinctive symbionts. The study’s data cannot fully disentangle these mechanisms, but the association itself provides a useful variable for future predictive models of microbiome structure across the mammalian tree of life.

Host taxonomic order also emerged as a robust predictor, which underscores that microbial community structure is not determined by diet and environment alone but also by aspects of host biology that are conserved within evolutionary lineages. Factors such as gut morphology, digestive physiology, transit time, gut pH, and immune system architecture all vary systematically across mammalian orders, and each of these traits can filter which microbes establish and persist. The strong order-level signal suggests that some component of microbiome assembly is phylogenetically conserved, echoing the concept of phylosymbiosis observed in other animal groups, where more closely related hosts tend to harbor more similar microbial communities.

The metric-dependent relationship with body mass is a methodologically important result. Body mass was significantly associated with phylogenetic diversity but not with evenness, the latter describing how evenly individuals are distributed among the microbial taxa present. This dissociation illustrates why microbiome researchers increasingly caution against relying on any single diversity metric. Richness, evenness, and phylogenetic diversity each capture different facets of community structure, and a factor can influence one without influencing the others. For body mass, the pattern is consistent with the idea that larger animals may simply accommodate more microbial lineages in absolute terms, given their larger gut volumes and longer digestive tracts, without necessarily altering the relative abundances of the taxa already present.

Perhaps the most unexpected environmental result concerns precipitation. Rather than showing a simple linear increase or decrease in microbial evenness, precipitation displayed a non-monotonic relationship, with both very-low and very-high precipitation zones supporting greater evenness than intermediate zones. Non-monotonic patterns of this kind often point to multiple underlying mechanisms operating at different ends of an environmental gradient. In arid environments, water scarcity may impose strong physiological constraints that favor a streamlined but evenly balanced microbial community, while in very wet environments, abundant moisture and lush vegetation may support diverse, well-distributed communities through different pathways. Intermediate precipitation zones, by contrast, may experience greater seasonal variability or disturbance regimes that disrupt evenness. The study’s cross-sectional design cannot confirm these mechanisms, but the shape of the relationship itself is a valuable empirical pattern for researchers modeling microbiome responses to shifting rainfall regimes under climate change.

Equally informative are the factors that did not predict microbial diversity. Temperature showed no significant association, and neither did IUCN conservation status. The absence of a temperature effect is striking given how frequently temperature is invoked in discussions of climate-driven ecological change, and it may reflect the buffering capacity of the mammalian gut itself. As warm-blooded endotherms, mammals maintain relatively stable internal body temperatures regardless of external conditions, which could decouple gut microbial communities from ambient thermal gradients in ways that do not apply to ectothermic animals. The lack of an IUCN status effect suggests that threat category, which integrates many pressures including habitat loss, hunting, and population decline, does not map cleanly onto microbiome diversity in this dataset. This does not mean that endangered species have healthy microbiomes; rather, it indicates that conservation status is too coarse and multifactorial a variable to serve as a direct proxy for microbial community structure, and that more specific measures of anthropogenic disturbance may be needed.

For conservation practitioners, the study’s implications cut in two directions. On one hand, microbiome-based conservation strategies could benefit from the identified ecological determinants, using diet type, habitat range, and taxonomic order as practical predictors when designing interventions such as translocations, captive breeding programs, or habitat restoration. On the other hand, the finding that ecological and environmental factors govern microbiome assembly through complex multidimensional interactions serves as a caution against simplistic applications. A translocated animal moved into a new precipitation zone, for example, might experience shifts in microbial evenness that affect digestion and immunity, with consequences for survival that managers should anticipate. The non-monotonic precipitation pattern in particular suggests that even modest changes in rainfall could push communities across thresholds where evenness declines sharply.

The research also contributes to a growing appreciation that microbial biodiversity deserves consideration alongside host biodiversity in conservation planning. Because many gut symbionts are host-specific, the extinction of a mammalian species could entail the co-extinction of its distinctive microbial lineages, eroding symbiotic diversity that may include yet-undiscovered functions. Meta-analyses of this kind, by identifying which host traits and environments support the richest microbial communities, help pinpoint where this hidden microbial diversity is concentrated and therefore where it is most at risk. As global environmental change continues to alter habitats, diets, and species ranges, the framework established here offers a starting point for predicting how the mammalian gut microbiome, and the ecological functions it performs, will respond across the coming decades.

Subject of Research: Microbial Ecology

Article Title: Ecological and Environmental Factors Influence the Gut Microbiome Structure in Wild Mammals

Article References: Basumatary, P., Saikia, D., Talukdar, M. P., & Bora, U. (2026). Ecological and Environmental Factors Influence the Gut Microbiome Structure in Wild Mammals. Microbial Ecology. https://doi.org/10.1007/s00248-026-02857-5

Image Credits: AI Generated

DOI: 10.1007/s00248-026-02857-5

Keywords: gut microbiome, wild mammals, meta-analysis, diet, herbivores, carnivores, Faith's phylogenetic diversity, precipitation, conservation, QIIME 2, Ecological, Environmental