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The role that global trade plays in facilitating biological invasions in agricultural systems is well recognized. Urban areas increasingly need energy and materials to support their metabolism (Decker et al. 2000), and thus, they depend on the infrastructure to receive, store, and distribute domestic and international goods (Hesse and Rodrigue 2004). Manufactured and agricultural goods, including associated packaging material and cargo containers, can harbor exotic pests (Haack 2006, McCullough et al. 2006, Haack and Petrice 2009, Haack et al. 2010). Many exotic pests threaten our major crop and tree species. For instance the light brown apple moth (Fig. 1), first detected in California in 2007, has over 1000 crop and tree host species and can cause up to US $93 million/year in damages (Fowler et al. 2007). Inspections at ports of entry (Fig. 2) are the first line of defense, but less than 2% of imports are actually inspected because of their sheer volume (NRC 2002). If exotic pests gain access to agricultural systems, then the second line of defense is their early detection (Magarey et al. 2009). As international trade intensifies (Hulme 2009), there is an urgent need to improve our understanding of factors that determine vulnerability to pest invasions in urban and agricultural hot spots (Fig. 3).


Fig. 1. Light brown apple moth adult

Light brown apple moth adult

Source: Department of Primary Industries and Water, Tasmania Archive, www.insectimages.org

Fig. 2. Inspection in imported cargo

Inspection in imported cargo

Source: USDA APHIS PPQ Archive, USDA APHIS PPQ, Bugwood.org


Several authors have documented and discussed the complexity of biotic and abiotic factors that influence the establishment of invasive species in terrestrial and aquatic ecosystems (Fig. 4). This complexity is compounded by the fact that in many situations, initial populations of invaders (or propagules) are small. Small populations may go extinct due to allee effects and other stochastic factors (Taylor and Hastings 2005, Drake and Lodge 2006, Liebhold and Tobin 2008).


Fig. 3 Dead trees in a landscape setting due to the emerald ash borer. Ann Arbor, MI, June 2005

EAB affected trees

Source: Steven Katovich, USDA Forest Service, www.bugwood.org


Fig. 4. Factors involved in the establishment of invasive species

Establishment factors Baker 2002 Brooks 2007 Carey 1996 Cassey et al. 2004 Crawley et al. 1986 Hulme 2009 Kolar and Lodge 2001 Kühn and Klotz 2007 Lattin and Oman 1983 Liebhold and Tobin 2008 Lockwood et al. 2005 Lodge et al. 2006 Marvier et al. 2004 Moyle and Marchetti 2006 NRC 2002 Ricciardi and Rasmussen 1998 Roll et al. 2007 Worner 2002


In the midst of all the discussion of establishment factors, there is one recurrent theme that states that arriving populations are able to overcome the many constraints to establishment when their numbers are high, i.e., abundant propagule pressure (Carlton 1996, Kolar and Lodge 2001, Sakai et al. 2001, Cassey et al. 2004, Lockwood et al. 2005, Colautti et al. 2006, Lodge et al. 2006, Moyle and Marchetti 2006, Reaser et al. 2008). In fact, under high propagule pressure there are only three factors that are significantly relevant: diet breadth, resource availability, and disturbance (Cassey et al. 2004, Lockwood et al. 2005, Colautti et al. 2006).



[ Last updated: May 3, 2010 ]


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Global trade, Metro areas, and Invasive species



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