Martinez-Andrade, F. | bioRxiv Science

bioRxiv2026

Evenness and Taylor's law scaling shape biodiversity-stability relationships in subtropical estuarine communities

Understanding the mechanisms that link biodiversity to ecological stability is crucial for predicting ecosystem responses to global change. Using three decades of standardized monitoring data from eight subtropical estuaries, we analyze diversity components (richness, evenness, dissimilarity, and variance-mean scaling) and interpret stability patterns through synchrony or portfolio mechanisms. Regional {gamma}-diversity increased steadily over time, reflecting sustained gains in fish and invertebrate assemblages. Community stability, defined here as community invariability, was strongly and consistently predicted by Shannon diversity index but not by species richness, underscoring the stabilizing role of evenness. Portfolio effects were robust, with community stability averaging approximately threefold higher than mean population stability, and the strength of this effect more than doubled with each unit increase in Shannon diversity. Structural equation models paired with a null model revealed that shared environmental forcing synchronizes estuarine populations. Shannon diversity generated a large portfolio effect that stabilized the community despite this environmental forcing, whereas richness effects were weak or absent. Taylors law scaling confirmed that abundant, persistent taxa such as blue crab (Callinectes sapidus), brown shrimp (Farfantepenaeus aztecus), and pinfish (Lagodon rhomboides) exhibited higher baseline invariability, contributing to community buffering, while rarer, more variable taxa introduced volatility. In contrast, compositional turnover strongly eroded stability, with high Bray-Curtis dissimilarity predicting reductions in community stability. Together, these results show that long-term estuarine community stability emerges from the interplay of portfolio averaging, demographic variance scaling of dominant species, and the persistence of community composition, highlighting the central role of evenness in biodiversity-stability relationships.

ecology↗

bioRxiv2026

Community reorganization without collapse in a warming world: Habitat-contingent, trait-mediated biodiversity change within a conserved multi-scale structure

Biodiversity change under sustained environmental pressure is increasingly understood as a process of long-term reorganization across spatial scales rather than uniform loss or gain. Estuarine ecosystems, which experience strong environmental gradients and frequent short-term extreme disturbances, provide an ideal context for evaluating how local (), spatial ({beta}), and regional ({gamma}) diversity reorganize across habitat domains and functional guilds through time. Here, we examined four decades of fish and invertebrate community data from a coastwide, ecological monitoring program, spanning multiple estuarine systems along the Texas coast. We asked three main questions: whether habitat context modifies the direction of trait-mediated biodiversity responses across the full -{beta}-{gamma} structure; whether spatial homogenization is detectable through dominance-weighted {beta}-diversity metrics and how they relate to richness-based metrics; and whether the pace of reorganization has intensified over time. Functional traits related to dispersal capacity and thermal affinity structured the magnitude of biodiversity change within habitat domains, but habitat context determined its direction, the same guilds exhibited opposite diversity trajectories across gear-defined habitat domains despite broadly similar functional composition, demonstrating that trait-based forecasting frameworks will mispredict reorganization direction when habitat context is ignored. Spatial homogenization proceeded undetected by richness-based {beta}-diversity metrics but was revealed through dominance-weighted measures, indicating that dominance-weighted homogenization operates through two distinct habitat-dependent mechanisms: convergence on shared warm-adapted dominant taxa in shallow assemblages, and convergence toward impoverished assemblages as dominant taxa declined in deeper habitats, both processes invisible to richness-based metrics. Despite a measurable intensification in the pace of local and regional diversity change after approximately 2000, spatial turnover among bays remained stable and -{beta}-{gamma} scaling relationships were preserved across all diversity orders, demonstrating that rapid reorganization can proceed without destabilizing fundamental metacommunity structure. Across all findings, biodiversity change was persistent, directional, and strongly habitat dependent, following a chronic rather than episodic trajectory consistent with sustained environmental processes as the primary driver.

ecology↗