Defining eradication units to control invasive pests

Abstract

Summary 1.Pest eradication is an important facet of conservation and ecological restoration and has been applied successfully to invasive rat species on offshore and oceanic islands. Successful eradication requires the definition of a target population that is of manageable size, with low recolonization risk. We applied a molecular genetic approach to the identification of populations suitable for eradication (eradication units) to provide a new tool to assist the management of brown rats Rattus norvegicus on South Georgia (Southern Ocean). 2. A single eradication attempt on South Georgia (4000 km 2 ) would be an order of magnitude larger than any previously successful rat eradication programme (110 km 2 ). However, rats are demarcated into glacially isolated populations, which could allow sequential eradication. We examined genetic variation at 18 nuclear microsatellite loci to identify gene flow between two glacially isolated rat populations. One population, Greene Peninsula (30 km 2 ), was earmarked for an eradication trial. 3. Genetic diversity in 40 rats sampled from each population showed a pronounced level of genetic population differentiation, allowing individuals to be assigned to the correct population of origin. 4. Our study suggests limited or negligible gene flow between the populations and that glaciers, permanent ice and icy waters restrict rat dispersal on South Georgia. Such barriers define eradication units that, with due care, could be eradicated with low risk of recolonization, hence facilitating the removal of brown rats from South Georgia. 5. Synthesis and applications . We propose that the molecular definition of eradication units is a valuable approach to management as it (i) provides a temporal perspective to gene flow, which is important if dispersal events are rare; (ii) allows an eradication failure (i.e. surviving individuals) to be distinguished from a recolonization event, opening the way for adaptive management in the face of failure; and (iii) can aid the management of pest species in habitat continua by resolving meta-population dynamics, so guiding pest eradication/control strategies. This study further illustrates the developing array of applied ecological issues in which molecular techniques can help guide management.

Red foxes colonizing the tundra: genetic analysis as a tool for population management

“…Otherwise, it is a prevalent risk that the tundra will be rapidly recolonized from the boreal forest (e.g. Robertson and Gemmel 2004). Furthermore, the finding of high connectivity between the boreal zone and the tundra emphasizes the importance of conducting red fox management as a permanent action.…”

“…For successful eradication, for example, it is necessary for removal rates to exceed population growth and that the population is isolated from immigration (Bomford and O'Brien 1995;Harding et al 2001). Clearly identifying the invasive pathways and source population is crucial to avoid devoting effort towards populations that are likely to become recolonized in a short time perspective (Robertson and Gemmel 2004;Estoup and Guillemaud 2010). Including genetic analysis as a tool can thus supplement management decisions with information about the recent and historical origin, composition and connectivity of expanding populations (Estoup and Guillemaud 2010).…”

Using population genetic tools to develop a control strategy for feral cats (Felis catus) in Hawai'i

“…Only recently have these tools been applied in invasive species management (Robertson and Gemmell 2004;Abdelkrim et al 2005;Rollins et al 2006). Invasive species are the main cause of species extinctions in island ecosystems (Courchamp et al 1999) and the second main cause of biodiversity loss after habitat destruction (Vitousek et al 1997).…”

“…Invasive species are the main cause of species extinctions in island ecosystems (Courchamp et al 1999) and the second main cause of biodiversity loss after habitat destruction (Vitousek et al 1997). Successful management of invasive species requires identifying a target population of manageable size that has a low recolonisation risk (Robertson and Gemmell 2004). Attempts to control only a fraction of the population or a sink population could result in rapid recolonisation (Robertson and Gemmell 2004;Abdelkrim et al 2005).…”

“…Successful management of invasive species requires identifying a target population of manageable size that has a low recolonisation risk (Robertson and Gemmell 2004). Attempts to control only a fraction of the population or a sink population could result in rapid recolonisation (Robertson and Gemmell 2004;Abdelkrim et al 2005). Identifying routes of potential migration is difficult using direct observations, but vital for controlling invasive species (Robertson and Gemmell 2004;Abdelkrim et al 2005;Rollins et al 2006).…”