Global trade networks determine the distribution of invasive non‐native species

Abstract

Aim Although global trade is implicated in biological invasions, the assumption that trade networks explain the large‐scale distributions of non‐native species remains largely untested. We addressed this by analysing relationships between global trade networks and plant pest invasion. Location Forty‐eight countries in Europe and the Mediterranean. Time period Current. Major taxa studied Four hundred and twenty‐two non‐native plant pests (173 invertebrates, 166 pathogens, 83 plants). Methods Ten types of connectivity index were developed, representing potential roles of trade networks, air transport links, geographical proximity, climatic similarity and source country wealth in facilitating invasion. Generalized linear mixed models (GLMMs) identified the connectivity index that best explained both historical and recent invasion. Then, more complex GLMMs were developed including connectivity through trade networks for multiple commodities relevant for pests (live plants, forest products, fruit and vegetables and seeds) and species’ transport associations with those commodities. Results Total import volumes, species’ global prevalence and connectivity measures based on air transport, geographical distance or climate did not explain invasion as well as connectivity through global trade networks. Invasion was strongly promoted by agricultural imports from countries in which the focal species was present and that were climatically similar to the importing country. However, live plant imports from nearby countries provided a better explanation of the most recent invasions. Connectivity through multiple trade networks predicted invasion better than total agricultural trade, and there was support for our hypothesis that species known to be transported with a particular network had greater sensitivity to its connectivity. Main conclusions Our findings show that patterns of invasion are governed to a large extent by global trade networks connecting source areas for non‐native species and the dispersal of those species through multiple trade networks. This enhances potential for developing a predictive framework to improve risk assessment, biosecurity and surveillance for invasions.

Effect of distance, area, and climate on the frequency of introduction and extinction events on islands and archipelagos

“…For example, the number of extinction or introduction events might be underestimated, because there is usually a time lag before an endemic species becomes extinct or a non-native species becomes established (Kuussaari et al 2009, Rouget et al 2016). Moreover, human activities such as the commodity trade and human movements are a key factor that affects both species introductions and extinctions (Sax and Gaines 2008, Blackburn et al 2016, Chapman et al 2017, thus influencing community similarity and different events. Moreover, human activities such as the commodity trade and human movements are a key factor that affects both species introductions and extinctions (Sax and Gaines 2008, Blackburn et al 2016, Chapman et al 2017, thus influencing community similarity and different events.…”

Invasion of freshwater ecosystems is promoted by network connectivity to hotspots of human activity

“…Doing so could involve applying similar analyses to the occurrence or abundance of individual non‐native species. Also, given the importance of multiple introduction pathways in freshwater invasions (Copp et al, ; Zieritz et al, ), extending our current models to include connectivity to multiple human activities could be of interest (Chapman et al, ). We suggest that this could provide a better evidence base for risk mapping to support invasive non‐native species surveillance and management, where high resolution predictions of invasion risk are valuable for prioritizing resources (McGeoch et al, ).…”

“…Among these, human activities clearly play a major role. Firstly, humans are responsible for the propagule pressure by which species are introduced into new non-native regions and dispersed regionally from established non-native populations (Bullock et al, 2018;Chapman, Purse, Roy, & Bullock, 2017;Lockwood, Cassey, & Blackburn, 2005). Secondly, humans cause the ecosystem disturbance and resource inputs that are thought to lessen biotic resistance of recipient communities to establishment of non-native species (Davis, Grime, & Thompson, 2001).…”

The DIARS toolbox: a spatially explicit approach to monitor alien plant invasions through remote sensing

“…Unfortunately, the number of alien species colonizing and impacting ecosystems is likely to increase (Levine et al 2003, Seebens et al 2017 due to the increase in global trade with dominant pathways for IAS being horticulture and nursery trade (Chapman et al 2017). In particular, invasive alien plants (hereafter IAPs) may have significant impacts on ecosystem functioning.…”