Biodiversity Effects: Competitors

Comparing the adult male body size of the American mink, polecat and European mink

Graphic generated by Noelle Le Tourneau

Data from (Sidorovich et al., 1999)

         In addition to its effect on prey, American mink outcompete many native species. The mink’s competitors, most commonly the European mink, the European polecat and the Eurasian otter, live in a similar riparian habitat and the native competitors with the most similar niches were the ones most affected by the presence of the American mink. Understandably, American mink were established most rapidly in areas, like Spain, where the mink have no native competitors or predators. The American mink's predators of otters and polecats were mostly missing due to pollution and overhunting respectively when the American mink spread throughout Europe, allowing the mink to expand rapidly (Wildlife Conservation Research Unit). We've already explored the traits that make American mink good competitors, such as its ability to survive at colder climates compared to its European rivals. In addition,  the American mink’s large body size compared to the European mink and the polecat causes the smaller competitors to be often driven out of the shared habitat (Sidorovich et al., 1999). 

Let's explore the common native competitors of the invasive American mink!

European Polecat (Mustela putorius L.)

European Polecat

(a) Annual relative abundance (RA) trends of European 

polecat based on a captures from 2000 to 2008 in Spain

As the abundance of American mink increased, 

the abundance of European polecat greatly decreased.

Courtesy of Melero et al. 2012

          The European polecat is a slightly smaller, less aggressive competitor of the American mink. In the UK, the polecat was intensely hunted in the 1800s (Harrington, 2008). Now that polecat populations are beginning to reestablish themselves, they are affected by the competition of the American mink in their former native ranges of wetland habitats. The presence of American mink has been correlated with a decrease in the presence of the European polecat in Spain (Melero, 2012). In areas where polecats and American mink were both present, such as in Belarus, it was recorded that resident "female polecat increased as measured in absolute mass, length and relative mass" but populations of polecats did not significantly decrease in the presence of mink (Sidorovich et al., 1999). 

European Mink (Mustela lutreola)

European mink

          Undoubtedly, the biggest impact the American mink has had on biodiversity is the effect on its smaller European counterpart. Pollution and habitat loss likely contributed to most of the European mink's decline, but in a few remaining areas the decline has been directly linked to the presence of the American mink. There has been recorded dramatic decline in European mink populations in Estonia, France and Belarus due to the American mink (Bonesi, 2007). 

Historic and Current Range of European Mink
The European mink are critically endangered and 
of its few remaining habitats, most are threatened 
by the American mink.
Courtesy of http://www.furcommission.com/farming/mink-biology/

Though more research needs to be done, the current hypotheses for the effect the American mink has on European mink is based on the competition for food, transmission of disease, and interspecific aggression. As American mink are very territorial, they tend to show aggression towards competitors, most specifically the European mink. In Belarus, the American mink are driving European mink out of their usual riparian habitat. The European mink "are responding to direct aggression from American mink"(Sidorovich et al, 1999). Both female and male European mink increased in body mass and length after the arrival of the American mink (Sidorovich, 1999). This increase  in body size is likely due to a selective advantage, as a larger body size would make the European mink a better competitor against the American mink.

Because of the dwindling populations, the European mink is listed as critically endangered under the IUCN's Red List.

Another hypothesis for the decline in the European mink is based on hybridization between the two mink species. The European mink is much more closely related to the polecat than to the American mink (Sidorovich, 1999). Similarities between the American and European mink are due to convergent evolution as an amphibious mammal. Hybrids between American mink and European mink are not viable, and it is suggested that the American mink is ruining the reproduction of European mink (Kauhala, 1996). Male American minks outcompete male European  mink for mates. However the since the hybrids are not viable, the potential offspring are never born. This is swamping the reproductive system of the female European mink and may be contributing to the decline in the remaining European mink populations. More research needs to be done to determine whether or not the decline of remaining European mink can be attributed to this. 

Eurasian Otter (Lutra lutra)

Eurasian Otter

As the Eurasian otter is seven times the American mink's size (MacDonald et al, 2003), the Eurasian otter is a dominant competitor of the mink. Though previously negatively affected by pollutants, with human help, the Eurasian otter is beginning to reestablish itself in the wild (Kauhala, 2006). The otter's populations are not significantly affected by American mink presence (Melero et al, 2012). Otters maintained the same aquatic prey whether or not American minks were present, displaying that the American mink does not outcompete the otter. However, when the otter is absent in a habitat, the American mink is between able to spread out into the land, occupying the otter's niche. In the presence of otters, American mink tend to stick to terrestrial prey as the much larger otter dominates the aquatic prey (Melero, 2012). The otter is a specialist predator, focusing mainly on fish consumption. 

Because the otter is the only competitor with a negative impact on American mink populations, it may be used to control growing mink populations as it is reintroduced.

Created by Noelle Le Tourneau
Data Courtesy of Melero, Kauhala, MacDonald, Sidorovich, Bonesi & Nordstrom

Caution: It is important to note that the size of the competitors and prey change slightly depending on each country, so the extent of the effect of American mink on native species varies by country. More studies need to be done, to understand the exact impacts American mink have in each country.