Grasping at the routes of biological invasions: a framework for integrating pathways into policy

Abstract

Summary 1.Pathways describe the processes that result in the introduction of alien species from one location to another. A framework is proposed to facilitate the comparative analysis of invasion pathways by a wide range of taxa in both terrestrial and aquatic ecosystems. Comparisons with a range of data helped identify existing gaps in current knowledge of pathways and highlight the limitations of existing legislation to manage introductions of alien species. The scheme aims for universality but uses the European Union as a case study for the regulatory perspectives. 2. Alien species may arrive and enter a new region through three broad mechanisms: importation of a commodity, arrival of a transport vector, and/or natural spread from a neighbouring region where the species is itself alien. These three mechanisms result in six principal pathways: release, escape, contaminant, stowaway, corridor and unaided. 3. Alien species transported as commodities may be introduced as a deliberate release or as an escape from captivity. Many species are not intentionally transported but arrive as a contaminant of a commodity, for example pathogens and pests. Stowaways are directly associated with human transport but arrive independently of a specific commodity, for example organisms transported in ballast water, cargo and airfreight. The corridor pathway highlights the role transport infrastructures play in the introduction of alien species. The unaided pathway describes situations where natural spread results in alien species arriving into a new region from a donor region where it is also alien. 4. Vertebrate pathways tend to be characterized as deliberate releases, invertebrates as contaminants and plants as escapes. Pathogenic micro-organisms and fungi are generally introduced as contaminants of their hosts. The corridor and unaided pathways are often ignored in pathway assessments but warrant further detailed consideration. 5. Synthesis and applications. Intentional releases and escapes should be straightforward to monitor and regulate but, in practice, developing legislation has proved difficult. New introductions continue to occur through contaminant, stowaway, corridor and unaided pathways. These pathways represent special challenges for management and legislation. The present framework should enable these trends to be monitored more clearly and hopefully lead to the development of appropriate regulations or codes of practice to stem the number of future introductions.

Alien species in a warmer world: risks and opportunities

“…In times of human domination of ecosystems of the Earth, their transfer to the new habitat might have occurred directly with human assistance [18,63,64] or indirectly profiting from human infrastructures linking previously unconnected areas [25]. Hence, it becomes increasingly difficult to assess the role of humans in the observed range expansion [65,66], especially if species originate from the same continent or adjacent regions, but human assistance in their transfer cannot be excluded.…”

Taxonomy, time and geographic patterns. Chapter 2

“…Expanding world-wide trade, globalisation of economies and climate change are all factors that contribute to an accelerated international movement and establishment of alien organisms, allowing them to overcome geographic barriers (Hulme et al 2008, Hulme 2009, Walther et al 2009, Roques 2010. Th ese alien species have already been shown to impose enormous costs on agriculture, forestry as well as to threaten human health and biodiversity (Williamson 1996, Wittenberg and Cock 2001, Pimentel et al 2002, Vilá et al 2009).…”

Focusing Ecological Research for Conservation

“…One concern is that by increasing connectivity, corridors might channel spread of invasive plant and animal species (Hulme et al 2008), and also could serve as pathways for disease transmission (Hess 1996). Pushing knowledge boundaries for the ecology of movement in the context of connectivity is important given that fragmentation is a major driver of extinction, aggravating the impacts of habitat loss especially at low proportion of available habitats (Swift and Hannon 2010).…”