Breaching the dispersal barrier to invasion: quantification and management

Abstract

Abstract. Globalization has resulted in unprecedented movements of people, goods, and alien species across the planet. Although the impacts of biological invasions are widely appreciated, a bias exists in research effort to post-dispersal processes because of the difficulties of measuring propagule pressure. The Antarctic provides an ideal model system in which to investigate propagule movements because of the region's isolation and small number of entry routes. Here we investigated the logistics operations of the South African National Antarctic Programme (SANAP) and quantified the initial dispersal of alien species into the region. We found that over 1400 seeds from 99 taxa are transported into the Antarctic each field season in association with SANAP passenger luggage and cargo. The first ever assessment of propagule drop-off indicated that 30-50% of these propagules will enter the recipient environment. Many of the taxa include cosmopolitan weeds and known aliens in the Antarctic, indicating that logistics operations form part of a globally self-perpetuating cycle moving alien species between areas of human disturbance. In addition, propagules of some taxa native to the Antarctic region were also found, suggesting that human movements may be facilitating intra-regional homogenization. Several relatively simple changes in biosecurity policy that could significantly reduce the threat of introduction of nonnative species are suggested.

Continent-wide risk assessment for the establishment of nonindigenous species in Antarctica

“…We estimated the number of propagules per visitor for ∼2% of all visitors (853 individual scientists, science-support personnel, tourists, tourist support personnel, and ships' crew) to all major areas of the Antarctic during the first summer season of the IPY (2007-2008) by collecting seeds from their outer clothing, footwear, walking poles, day packs, and camera bags (21,41) (Table S6) using Philips FC9154/01 vacuum cleaners. For most sampled visitors, the material collected from clothing and equipment was retained in a single bag, but for 349 visitors, the material from each item was kept separately (Table S6).…”

“…Similarly, mean number of seeds per visitor was estimated, again with 95% CI, for each visitor category. Sampling was considered to capture the large majority of seeds, although this somewhat underestimated propagule pressure (21). The number of seeds that would drop off a visitor was considered proportional to the number of seeds found during sampling, and propagule viability was considered high (41,46).…”

“…We do so based on an assessment of the following factors: (i) Vascular plant propagules (seeds) carried inadvertently by the main categories of visitors to the region-i.e., scientists, tourists, and their support personnel (4,5,21) (14). Previous work elsewhere in the broader Antarctic region, on a more limited scale, indicated that an assessment of vascular plant propagules carried by visitors provides a reasonable approximation of inadvertent introductions by other vectors, such as cargo, and of other terrestrial taxa, such as invertebrates (4,5,22).…”

Troubling travellers: are ecologically harmful alien species associated with particular introduction pathways?

“…Unfortunately, robust data for propagule pressure that can be compared across individual pathways for the respective taxonomic groups are rarely available. If such data exist, they are limited to specific pathways such as direct release for biocontrol (Rossinelli and Bacher 2015) or landscaping (but see Lee and Chown 2009). Our knowledge thus mostly depends on proxies such as trade volume, numbers of botanic gardens, human population density or road density (Carlton and Ruiz 2005, Wilson et al 2009, Kaluza et al 2010Hulme 2015b).…”

“…Some pathways are increasingly well studied, such as horticulture and forestry as a source for plant invasions (Mack and Erneberg 2002, Dehnen-Schmutz et al 2007a, b, Hanspach et al 2008, Dawson et al 2009, Pyšek et al 2009, Smith et al 2015, Pergl et al 2016a, ballast water transport and aquaculture disseminating aquatic invaders (Galil et al 2009, Mizrahi et al 2015, live plants and plant products introducing pest insects and plant diseases (Roques 2010, Bacon et al 2012, Liebhold et al 2012, Eschen et al 2015a, as well as snails (Bergey et al 2014) and spiders (Nentwig 2015), the aquarium trade (MacedaVeiga et al 2013, Chucholl 2013, tourism (Anderson et al 2015), the pet trade for terrestrial vertebrate invaders (Duncan et al 2003, van Wilgen et al 2010, GarciaDiaz and Cassey 2014, and -more generally -the online trade (Kikillus et al 2012, Humair et al 2015. However, the role of pathways related to unintentional introductions has been difficult to quantify (Lee and Chown 2009, Pyšek et al 2011, Bacon et al 2012. Additionally, whether particular introduction pathways are associated disproportionally with the subsequent impacts of alien species has received little attention (Pyšek et al 2011).…”