Do plant reproductive traits influence species susceptibility to decline?

Background and aims – Habitat destruction, eutrophication and fragmentation are the main drivers of plant extinctions. In addition to these environmental factors, it has been suggested that features related to intrinsic characteristics of the species play a role in their decline, however leading to widely divergent results. This paper aims at exploring whether intrinsic factors (species traits) can play a role in the decline of plant species, by specifically asking whether: (1) plant reproductive traits are significantly different between declining species and species that are doing well; and (2) these traits are related differently to species trend in different countries, suggesting context-dependent relationships. Methods – Species traits and trend indices were compared for large datasets from UK (1136 species) and Northern Belgium (1055 species) using multiple trait analysis (GLM) and single trait analysis (Kruskal-Wallis analysis of variance). Key results – Of the ten traits considered, type of reproduction and pollen vector showed by far the strongest association with species trend, although differently in each of the datasets considered. Species trends were also associated to flower class, floral reward, diaspore type, dicliny and breeding system, but patterns were not consistent among countries confirming a context-dependence of these findings. Conclusions – The relationships between decline and plant traits likely depend primarily upon extrinsic (environmental) factors, which might explain the difficulty in recognising consistent patterns. Consequently, environmental degradation (e.g.habitat destruction) is likely the main driver of plant decline and may cause extinctions irrespective of species traits. This context-dependence of the findings indicates that reliably identifying those species most prone to extinction based on their reproductive traits is problematic. We therefore recommend great caution when interpreting patterns emerging from the study of species traits