Abstract
Introduced alien species can negatively affect native competitors by reducing their populations or eliminating them from ecosystems. However, studies do not always find evidence for anticipated impacts, and changes in native populations can be difficult to estimate. Interactions between the invasive American mink Neovison vison and native European polecat Mustela putorius have been studied in several countries, but the mink’s impact on polecat populations at a large spatiotemporal scale remains unclear. In the years 1995–2018, we live-trapped mink and polecats at 60 study sites in Poland, and we analysed hunting bags of mink and polecats from the years 2009–2018. During 13,766 trap-nights, we captured 905 individuals. Mink comprised 91.2% and polecats 8.8% of trapped animals. The mean mink and polecat trappability was 6 and 0.6 individuals per 100 trap-nights, respectively. At rivers, polecat and mink trappability were negatively correlated, whereas at lakes, they were not correlated. The sex ratio of trapped polecats was more skewed toward males than that of mink. Mink comprised 63.6% and polecats 36.4% of 59,831 animals killed by hunters. Over 10 years, the numbers of mink shot annually increased slightly, whereas the numbers of polecat decreased slightly. There was a positive correlation between numbers of mink and polecats shot annually. We found weak evidence that at a large spatiotemporal scale, the invasion of mink has led to a decline in polecat numbers. Although the datasets we analysed were based on large samples, they were insufficient to show evidence of competitive interactions between these two mustelids.
Highlights
One of the fundamentals in ecology predicates that species can co-exist in a community if they at least partly segregate their ecological niches (Pianka 1974)
The only available large-scale and long-term (10–20 years) data that we could use to analyse European polecat and American mink abundance and their interspecific interactions in Poland came from live-trapping and hunting bag records. Both datasets were based on large samples, we found them inadequate for showing evidence of the competitive interactions between the polecat and mink
We found weak evidence that polecats in Poland have declined since the country was colonized by American mink, and 40 years after the beginning of mink invasion, the polecat still occurs at a landscape scale
Summary
One of the fundamentals in ecology predicates that species can co-exist in a community if they at least partly segregate their ecological niches (Pianka 1974). Competition between invasive and native species with overlapping ecological niches is based on resource exploitation or interference between individuals (Polo-Cavia et al 2011; Peck et al 2014; Le Louarn et al 2016). Regardless of the mechanisms behind it, competition may be lower in complex environments with high resource availability, and in such contexts, the negative impact of an invasive competitor can be negligible. Competition from invasive species can cause extinction of native species at local scales but unlike predation seldom causes global extinction (Sax et al 2007). The scientific literature probably underestimates how often invasive and native species coexist over long periods, as it is easier to show (publish) that an invasive species has a negative impact on a native species than to find evidence of no effect
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