Abstract
Attempts to mitigate the impact of invasive species on native ecosystems increasingly target large land masses where control, rather than eradication, is the management objective. Depressing numbers of invasive species to a level where their impact on native biodiversity is tolerable requires overcoming the impact of compensatory immigration from non-controlled portions of the landscape. Because of the expected scale-dependency of dispersal, the overall size of invasive species management areas relative to the dispersal ability of the controlled species will determine the size of any effectively conserved core area unaffected by immigration from surrounding areas. However, when dispersal is male-biased, as in many mammalian invasive carnivores, males may be overrepresented amongst immigrants, reducing the potential growth rate of invasive species populations in re-invaded areas. Using data collected from a project that gradually imposed spatially comprehensive control on invasive American mink (Neovison vison) over a 10,000 km2 area of NE Scotland, we show that mink captures were reduced to almost zero in 3 years, whilst there was a threefold increase in the proportion of male immigrants. Dispersal was often long distance and linking adjacent river catchments, asymptoting at 38 and 31 km for males and females respectively. Breeding and dispersal were spatially heterogeneous, with 40 % of river sections accounting for most captures of juvenile (85 %), adult female (65 %) and immigrant (57 %) mink. Concentrating control effort on such areas, so as to turn them into “attractive dispersal sinks” could make a disproportionate contribution to the management of recurrent re-invasion of mainland invasive species management areas.
Highlights
The feasibility of control or eradication is a central question for invasive species management efforts aiming to limit the impacts of invasive non native species on native biodiversity (Saunders and Norton 2001)
Using data collected from a project that gradually imposed spatially comprehensive control on invasive American mink (Neovison vison) over a 10,000 km2 area of NE Scotland, we show that mink captures were reduced to almost zero in 3 years, whilst there was a threefold increase in the proportion of male immigrants
Across river sections the number of mink captured per km of waterway showed a clear decrease with increasing years of mink control, from an average of 0.16 to 0.06 to 0.01 for river sections in the first, second and third years of control respectively, there was variability in the trend, with increases in some river sections between the first and second years of control
Summary
The feasibility of control or eradication is a central question for invasive species management efforts aiming to limit the impacts of invasive non native species on native biodiversity (Saunders and Norton 2001). Glen et al (2013) convincingly argued that management should embrace a landscape planning approach so as to maximise conservation benefits, and the perspective of management has broadened with an appreciation of the necessity to address the effect of species invasions at larger spatial scales, where target areas may be nested within large land masses. Some such large-scale projects take a ‘‘Mainland Island’’ approach and seek to create a contiguous area in which immigration by invasive species can be limited. Because non-ecological factors such as availability of financial resources and the protection designation of land masses often define management areas (e.g. Nordstrom et al 2003), protected areas may be surrounded by, or interspersed with, areas where invasive species are left unmanaged
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