Can plant traits and habitat be used as indicators of vulnerability for insular endemic species?

Abstract The IUCN threat categories are widely used to assess the conservation status of plants and other organisms, primarily based on population size and trends vis-à-vis geographical ranges. However, other factors could also predict plant vulnerability. Here, we analysed plant traits that could be potential predictors of vulnerability for the endemic flora of the Balearic Islands (western Mediterranean Basin). We first compiled the list of entomophilous plant species endemic to the Balearic Islands and categorized their vulnerability as “threatened” (EW, CR, EN, VU) or “not threatened” (NT, LC) according to the regional Red Data Book. We then gathered bibliographic information on several variables related to flower complexity (floral traits related to pollinator specificity), flowering season, flowering duration, life form, capability of asexual reproduction, and main habitat. The endemic entomophilous flora of the Balearic Islands comprises 155 taxa, of which 57 (37%) are currently listed as threatened. Our results showed that floral colour, flowering duration and habitat type were the main predictors of vulnerability for the endemic flora of the Balearic Islands. Species with green and blue/violet/purple/pink/red flowers were more endangered than plants with white flowers, while species with yellow flowers showed intermediate levels of vulnerability. Besides, plant vulnerability was higher in plants with short flowering duration, and those inhabiting mountain and coastal habitats. These findings highlight the importance of considering additional traits when assessing extinction risk and planning conservation strategies. In particular, conservation efforts in the Balearic Islands should prioritize taxa inhabiting coastal habitats and mountain areas.