What we measure matters: Trait choice shapes inferences about grassland functional diversity under altered precipitation
Journal Article
Overview
abstract
Abstract; ; ; ; Trait‐based approaches are powerful tools for understanding ecosystem resistance and resilience under global change. Yet, relationships between global change drivers, functional trait diversity and ecosystem stability remain unclear. Some inconsistencies arise from differences in trait selection and diversity indices, which reflect distinct hypotheses and can lead to divergent interpretations. This complicates determining whether observed patterns stem from methodological choices or true ecological variation.; ; ; We evaluated how methodological decisions influence ecological inference by comparing functional diversity metrics and community‐weighted means calculated from different trait subsets. Using a four‐year rainfall manipulation experiment in a semi‐arid grassland near Boulder, Colorado, USA, we quantified community responses to extreme drought, irrigation and ambient conditions. We measured nine leaf, root and whole‐plant traits and grouped them into six sets based on trait‐based literature: (1) all traits, (2) commonly used traits (e.g. specific leaf area, root dry matter content), (3) mechanistic drought traits, (4) economic spectrum traits, (5) above‐ground traits and (6) below‐ground traits. For each set, we assessed drought and irrigation effects on community composition using community‐weighted means and four functional diversity indices: richness, evenness, divergence and dispersion. We also examined how trait and metric selection influenced temporal biomass stability across treatments.; ; ; Treatment effects varied across metrics: functional divergence was generally robust to trait selection, while evenness, richness and dispersion were more trait‐dependent. Relationships between functional diversity and biomass stability were both metric‐ and trait‐dependent: functional dispersion tended to decrease stability under drought and irrigation for above‐ground and commonly used traits. Functional evenness increased stability under irrigation for select sets, and functional divergence and richness showed weak or inconsistent relationships with stability across treatments and trait sets.; ; ; ; Synthesis; . Our results show that methodological choices in trait selection and metrics influence conclusions about functional diversity. Trait suites aligned with environmental drivers (e.g. mechanistic drought traits) captured community responses differently than commonly used traits, highlighting the value of hypothesis‐driven selection. We recommend prioritizing traits linked to the focal ecological mechanism and testing robustness across alternative trait subsets and diversity metrics. This approach improves mechanistic interpretation, clarifies when and where diversity stabilizes ecosystem function and increases comparability across systems and studies.; ; ; ;
