Seed characteristics in Cacataceae: Useful diagnostic features for screening species for invasiveness?

Abstract

Invasive alien species impose a wide range of negative impacts in invaded ecosystems. Management strategies aiming to minimize these impacts include measures to prevent the introduction of potentially invasive species, early detection and eradication, and control/containment of widespread invaders. Prevention is the most cost-efficient component of these strategies. Therefore, accurate screening of potentially invasive species and practical measures for identifying and intercepting such species along introduction pathways are crucial. Many studies have identified correlates of invasive success in plant species, but few have identified traits that are easy to measure and can be applied practically in screening protocols. Because hundreds of species in the Cactaceae family are being moved around the world, and many of them are already invaders, we assessed the potential for using seed characteristics to identify potentially invasive cacti. We reviewed websites advertising cactus seeds for sale and found that at least seeds of 266 cactus species are being traded worldwide, including 24 species already known to be invasive. We bought seeds of each species and recorded their mass, size and appearance (form, color, brilliance and surface). Already-invasive species had significantly larger and heavier seeds than non-invasive species. All cactus species identified as potentially invasive taxa in a previous study also had significantly larger and heavier seeds than non-invaders. We found no clear link between seed appearance and invasiveness. Overall, our study shows that the traits seed mass and size should be used for improving screening protocols for cactus species as they are easy to measure and provide an indication of invasiveness in this group.