Invasive American Mink Neovison Vison Research Articles

Polecat body size and sex ratio change over time: Impact of invasive competitor or climate warming?

Change in body size is considered to be one of the animal responses to climate warming, although in many cases it is difficult to show whether it is evolutionary or a result of phenotypic plasticity. In this study, we analysed long-term changes in the body size and sex ratio of the European polecat Mustela putorius in relation to two factors: climate warming and competition with the invasive American mink Neovison vison . In the years 1959–2021, the average body mass of polecats inhabiting north-eastern Poland increased from 869 to 1109 g in males and from 449 to 690 g in females, whereas structural body size (the condylobasal length of the skull) increased from 64.4 to 68.0 mm in males and from 55.9 to 59.6 mm in females. The rates of these increases were different for both measures; in consequence, the index of body condition changed non-linearly over time with a high increase in last 30–40 years. The observed increase in polecat body mass and skull size correlated with the rise of mean winter and summer temperatures. We explain the recorded trends by easier access to amphibians (the staple food of polecats in the study area) in mild winters, which increases the survival rate of larger polecats and/or leads to a faster growth rate of subadults in warmer summers. Competition for food between the native polecat and invasive mink could play a role in the increase of polecat body size simultaneously with climate warming, but the timing of recorded changes suggests the second factor to be more important. Our study also confirmed a previous observation of increasing skewed sex-ratio towards polecat males, which, similarly to changes in polecat body size, could have resulted both from climate warming and competition with mink.

Does the American mink displace the European polecat? A need for more research on interspecific competition between invasive and native species

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.

Low individual diet variation and high trophic niche overlap between the native polecat and invasive American mink

AbstractIntroductions of invasive species increase competitive interactions in a community proportionally to the similarity between the ecological niches of invasive and native species. Food represents one of the most important resources influencing competition, and differences in the trophic niche of native and invasive species can affect their ability to coexist. Moreover, in sympatric native and invasive species of similar body size and high sexual dimorphism, competition for food between individuals of the same sex may be higher than intraspecific competition between males and females, thus making the overall competitive interactions more complex. The aim of this study was to investigate the intraspecific and intrasexual competition for food resources between two sexually dimorphic mustelids, the native polecat Mustela putorius and invasive American mink Neovison vison, in riparian habitats of Białowieża Forest (Poland). Based on an analysis of 1215 scats, we studied the food habits of eight polecat and 24 mink individuals. The trophic niches of the polecat and mink were narrow and overlapped considerably. The diet of both predators was dominated by amphibians (mainly the common frog Rana temporaria), which comprised up to 94.1% and 89.7% of polecat and mink prey biomass, respectively. Individual diet variation was low within each sex group of both species. Interspecific similarities in body mass of the sexes and intraspecific differences in body mass between the sexes did not affect pairwise niche overlaps. However, we observed some mechanisms of food segregation between the sexes and species that reduced intra‐ and interspecies competition. Polecat males hunted more common toads Bufo bufo than polecat females, mink males and mink females. They also hunted larger frogs than polecat females, and the opposite pattern was recorded in mink. We conclude that two predator species exploiting abundant prey can coexist despite a very high overlap in their food niches.

Detection probabilities of the native Eurasian otter and the invasive American mink are independent of their co-occurrence

Detection probability is an important input when studying and managing species. It reduces the miscalculations of the estimates of occupancy, population abundances and their trends inherent to the imperfect detection during sampling. However, detection probability may vary in relation to environmental and biological factors, such as the presence of other species of similar ecological niche. We used a two-species single-season occupancy model to analyse the detection probability of the native Eurasian otter Lutra lutra and the invasive American mink Neovison vison in the northeast of the Iberian Peninsula and to test for potential differences in their detection when co-occurring and when not. Despite the known behavioural change of American mink towards a more terrestrial diet and a more diurnal activity pattern in the presence of Eurasian otter, their detectability did not vary when both species co-occurred versus when they did not. However, we observed seasonal differences in the probability of detection. Specifically, the probability of detection was higher in winter for both species. Furthermore, Eurasian otter was more often detected in sites with clay substrate, whereas American mink in sites with clay and rocks. These results indicate that the effectiveness of monitoring of Eurasian otter and American mink remains independent of the species co-occurrence. Yet, seasonal variations in the detection should be taken into account when monitoring.

Recovery of Eurasian Coot Fulica atra and Great Crested Grebe Podiceps cristatus Breeding Populations in an Area Invaded by the American Mink Neovison vison

In birds, adaptations that mitigate predators' impact are usually ineffective in confrontation with introduced and rapidly expanding invasive non-native predators. As a consequence, bird populations often decline in the period following the time when predator population is established. Changes in bird numbers and nest spatial distributions in breeding populations of the Eurasian Coot Fulica atra and Great Crested Grebe Podiceps cristatus were studied in Mazurian Lakeland, northeastern Poland in 2002–2003 and 2016, and were analyzed with reference to the abundance of invasive American Mink Neovison vison, whose density declined since mid 1990s. The study was based on a census of breeding pairs and a search of nests at 31 lakes. The numbers of breeding Coots and Grebes increased 2.6-fold and 1.2-fold, respectively. In both study periods Grebes displayed a strong tendency to nest in the vicinity of human settlements and in colonies; however, the percentage of Grebe pairs nesting near settlements and in colonies decreased from 51% to 34% and from 73% to 57%, respectively. Coots also preferred to nest in the vicinity of human settlements. Distributions of their nests have not changed significantly over time: in both periods 55–60% of Coot nests were found in close proximity to human settlements and 13–19% in Grebe colonies. The obtained results suggest that breeding populations of the Coot and Great Crested Grebe can cope with the invasive American Mink, whose predation was considered to be the main reason for waterbird declines in Mazurian Lakeland at the end of 20th century.

Space use, habitat selection and daily activity of water voles Arvicola amphibius co-occurring with the invasive American mink Neovison vison

A water vole Arvicola amphibius population inhabiting midfield ponds was studied by live-trapping, radio-telemetry and with camera traps. Within the midfield ponds, water voles did not prefer any particular type of littoral vegetation and avoided open water areas within the ponds. The mean distance of daily movements was 118 m for males and 53 m for females. The maximum distance between two locations of a radio-tracked individual within its home range during the whole study period was 450 m. Water vole movements between the studied ponds were very limited. Most of the hiding places were located in the areas around ponds. Water voles were active mostly during the night.

An invasive predator affects habitat use by native prey: American mink and water vole co‐existence in riparian habitats

AbstractThis study examines the occurrence of invasive American mink Neovison vison and native water voles Arvicola amphibius along the shorelines of eutrophic lakes and at small midfield ponds in the Mazurian Lakeland, north‐east (NE) Poland. The main hypothesis tested in this study is that built‐up areas and small midfield ponds are avoided by mink; therefore, they can serve as refuges that protect water voles from mink predation. Floating rafts were used to monitor mink and water vole distribution. Mink presence was negatively associated with urbanization at lake shorelines and midfield ponds, and these two characteristics positively correlated with occurrence of water voles in the study area. The probability of occurrence of water voles was significantly lower at sites where mink occurred. The occupancy rates for mink at lakes and at midfield ponds were higher in autumn than in spring and conversely the occupancy rates for water voles were higher in spring and lower in autumn. Our study shows that within a postglacial landscape, urban areas and midfield ponds distant from lakes are avoided by the American mink and thus these areas may function as refuge habitats for water voles and may maintain populations of this rodent at the landscape scale despite the presence of mink.

Invasive predator control program in Austral Patagonia for endangered bird conservation

In 2011, the invasive American mink Neovison vison became the most acute threat to the globally critically endangered Hooded Grebe Podiceps gallardoi (global population <800 individuals) when mink killed over 4 % of their global population. The Hooded Grebe is endemic to the Argentinean Austral Patagonia. In 2014, we established a control program in the Buenos Aires Lake Plateau area; the first attempt to systematically control mink in Patagonia. Our aim was to preserve the Hooded Grebes throughout the reproductive season by eradicating mink from the highland lakes and the rivers that mink use as corridors. We used a combination of methods (live trapping, lethal trapping and hunting) to maximize mink removal during the short climate window that permits work in the area. Control effort in the summer seasons of 2014 and 2015 involved 47–91 traps working for 128–137 days and we also hunted for mink along 186 km of river. No mink predation on grebes has been observed since the beginning of the control program and 71 mink were removed from the area. Percentage of sites occupied by mink decreased after the first control season (occupancy estimation decreased ca. 50 %). However, there was also a decline in the number of mink trapped, indicating that mink removal was more difficult in the second control season. We show that mink culling can be established successfully in an area with challenging logistics, avoiding negative impacts on non-target native species and providing positive outcomes for a species of global conservation importance.

Evolutionary status of the invasive American mink Neovison vison revealed by complete mitochondrial genome

The American mink, Neovison vison, is native to North America and listed as one of the most widely distributed invasive species into the Eurasian mainland. Even though facing serious over-hunting and habitat degradation problems, this species has successfully dispersed into most areas of northeast China in the past decades, which may have a huge impact on local species composition and structure. We determined and annotated the whole mitochondrial DNA genome of the American mink N. vison to better understand the evolutionary relationship of this invasive species with other Mustelidae distributing in China. The complete mitogenome is 16 627 bp in length, includes 13 protein-coding genes, 22 tRNA genes, 2 rRNA genes and one control region. We built the phylogenetic tree of American mink and other 10 most closely Mustelidae species.

Habitat- and sex-related differences in a small carnivore’s diet in a competitor-free environment

The alien invasive American mink Neovison vison is fully established in the low species richness and competitor-free environment of Iceland. This study documents the diversity as well as seasonal and sexual variation in the diet of mink in Iceland based on stomach contents. Seasonal changes mainly reflected variation in abundance of migratory birds and wood mice Apodemus sylvaticus. In comparison with mink elsewhere in similar habitats, the mink in Iceland consumed more fish and birds and fewer mammals, which is in accordance with local availability. This reinforces evidence of opportunistic foraging. Females generally ate more fish and fewer birds than males and this might be explained by their smaller body size and possible limitation in catching larger birds. Mink in coastal habitats showed greater sexual differences in diet than mink in riparian habitats, probably reflecting less prey diversity in riparian habitats than coastal ones. This study is an input towards explaining the ecological consequences of sexual size dimorphism and supports the hypothesis that generalist species might be successful invaders due to their capability in utilising new and diverse resources. The mink in Iceland can be regarded as a model for a small-bodied semi-aquatic carnivore away from the confounding effects of inter-specific competition.