Inherently at risk: Low floral morphological variability predicts conservation risk

Abstract

Extinction risk should, in theory, be shaped not only by extrinsic pressures but also by intrinsic biological traits, including intraspecific floral morphological variability, which may influence ecological flexibility and pollination success. We evaluated whether reduced floral morphological dispersion, measured as species-level coefficients of variation (CVs) for seven floral dimensions, is associated with elevated conservation risk in Caribbean orchids. Class-weighted logistic regressions were fitted across multiple imputations, with exhaustive Bayesian Information Criterion selection across 127 candidate models. Single-trait models were favoured, petal-length CV best supported, followed by sepal-width and labellum-length. Sign-direction analyses confirmed that five perianth traits were predominantly negatively associated with risk (lower CV → higher risk), whereas column-length CV was robustly positive. Discrimination of Threatened from Not-Threatened species was modest but consistently above chance; under a precautionary threshold penalising missed detections, nearly all Threatened species were flagged. Because threat status was phylogenetically clustered (Fritz and Purvis D = 0.62), the full model set was refitted using phylogenetic logistic regression and taxonomic and phylogenetic mixed models; effect signs, magnitudes and rankings were preserved. Species at higher risk therefore tend to exhibit reduced intraspecific floral variation, and the model offers a biologically interpretable triage tool for prioritizing unassessed Caribbean orchids.