A microbial mirage: when microbiome metrics may obscure ecological meaning.

Abstract

Metrics such as alpha diversity, inferred functional potential and network complexity have become standard metrics in microbiome research. While they offer convenient ways to summarize complex data, these metrics may sometimes obscure more than they reveal. Alpha diversity, for example, measures richness and evenness. However, two samples may exhibit identical diversity scores, yet one could be dominated by beneficial taxa and the other by pathogens. Similarly, the presence of genes associated with particular functions does not guarantee that those functions are expressed or ecologically relevant under given conditions. Functional inference is also limited by database bias and often lacks empirical validation. Likewise, correlation-based network analyses can produce spurious associations driven by shared environmental covariates, sequencing depth or batch effects. These issues are routinely encountered in genomic workflows - from 16S/ITS amplicon surveys to shotgun metagenomics, genome-resolved metagenomics and gene-centric network analyses - where apparently 'clean' summary metrics can mask very different ecological realities. Here, we use simple, domain-relevant examples to illustrate how over-reliance on these metrics can lead to misinterpretation. Rather than rejecting these approaches, we outline when they are most informative, when they require caution and what complementary analyses can strengthen ecological inference. We propose a practical framework based on four questions: what exactly is being summarized, at what biological level, under which ecological conditions and with what form of validation? While acknowledging their value, we argue for greater critical scrutiny in their application and interpretation, and advocate for approaches that prioritize functional validation, temporal resolution and systems thinking to support more meaningful ecological insight.