Exclusion by interference competition?

The relationship between red and arctic foxes.

By Åshild Elverland

 

    

Arctic fox                                                   Red fox

 

 

 

The arctic fox, Alopex lagopus or white fox is a small fox with a shoulder height at 30cm, a weight at only 3-5 kilos, and a length at 60 cm without the tail. It has two colour morphs; white and bluish. The white and bluish colours are present during the winter months, while it changes to grey/brown/black during the summer. The arctic fox has territories in Scandinavia, northern parts of the Kola Peninsula, arctic parts of Russia, northern America and arctic islands such as Greenland, Jan-mayen and Spitsbergen among others.

The fox feeds on pretty much everything that can be eaten. It is omnivorous and Norwegian lemmings (Lemmus lemmus), birds, hare and reindeer cadavers are high priority food.  

It is monogamous and a couple can stay together all life. Their dens are large (average: 363m² and 27 openings!) and can be used for many years, all year around. Sometimes they even share dens with other couples. It has a litter of about 6-16 cubs, and their survival depend on the access to food.

 

The red fox, Vulpes vulpes, is larger than the arctic fox. The shoulder height is 35-40 cm, it weights 4-8 kg and the length is 85 cm without the tail. It has three colour morphs; red, black and “cross”, and it keep the same colour all the year. It is the most common predator in fennoscandia and is very adapting concerning the living areas and is therefore found in cities and mountains as well as in deserts. The litters of the red fox contain 1-14 cubs.

The arctic fox was preserved in the northern parts of Norway and Sweden in the 1930s, at that time the population was quite low from hunting. Strangely the population has never recovered since then, and there are many theories what the problem might be, such as reduced access to carcass because of reduction of the wolf population, increased competition with red fox, increased predation from red foxes, human activity in the mountains, diseases such as scabies from red foxes or indirect effects from climate changes. But there are scientific studies concluding that the arctic fox is decreasing in numbers all over the northern hemisphere. This may indicate a larger, more global problem than hunting, or maybe a combination of two or more of the previous mentioned factors.

The limit between the arctic foxes territory and the territory of the red fox will be regulated by the climate (temperature) and the access to food. Since there has been a gradually global warming, the temperature in the northern parts of Norway and Sweden has increased with 0.4 - 1.2 °C since 1876. Because of this the red fox can move its territory to higher altitudes and as a result excluding the arctic fox. This is because the arctic fox only can survive in the areas which have so low productivity of red foxes that they can’t survive there.

 

In a study performed in Sweden over a nine year period they tried to find out if the lack of recovery among arctic fox populations actually had something to do with the interspecies competition with the red foxes.

They predicted that the arctic fox should avoid breeding in dens close to breeding sites used by red foxes, that they would breed in dens in less productive habitats than red foxes, and that the dens would be located in high altitude areas of their former range, and thirdly that removing red foxes could be used to prevent further extinction of the arctic fox.

Through these studies they saw that the arctic foxes more often bred in high quality dens if there were no red foxes nearby. If there were red foxes present within 8 km the cubs often got killed or injured so badly by the red foxes that they died. They also found that the arctic foxes bred in higher altitudes than the red fox. However did they not come any closer to a solution by removing red foxes from the area, partly because it is impossible to remove all the individuals.

This study proved that red foxes in fact do kill adult and juvenile arctic foxes in the competition of the best dens and hunting areas. However there is also indirect competition through the exploitation of food. Both the arctic and red fox populations follow the peaks of the Norwegian lemmings. The arctic fox are forced towards the higher altitudes as a result of the red fox moving higher. These areas have lower productivity, and during rodent population lows the arctic fox is forced to search for alternative food which may be hard in these areas.  

Even though this study was not conclusive in its theory of removal of red foxes, this would be a way of helping the population of the arctic fox. The population is already way to low with its 100 adults in Norway and Sweden, so something has to be done to save this small fox from total extinguishing. In Norway there have been several attempts to increase the population by making the arctic fox breed in preservation parks. This has not been successful, so now there is a study going on in the Varanger Peninsula where the scientists try to remove some of the red foxes to strengthen the potential of viable population of arctic foxes.

 

Angerbjörn A, Tannerfeldt M, Elmhagen B (2002)

Exclusion by interference competition?

The relationship between red and arctic foxes

Oecologia (2002) 132:213-220

 

http://www.ecosystem-finnmark.com/

http://nidaros.nina.no/fjellrev/n%C3%A6ring.htm

http://www.zoologi.no/fakta/fjellrev.htm

http://no.wikipedia.org/wiki/Fjellrev

http://en.wikipedia.org/wiki/Arctic_fox