The extinction of large northern herbivores is a puzzle for many biologists. Is it caused by climate change or human activity? The survival of the weak trophic competitors promotes the "anthropogenic" hypothesis. The extant species of Pleistocene communities allow us to easily test this assumption. The rein deer and musk ox have been until now coexisting in the Arctic territory. Their island populations form a unique natural experiment for assessing the role of competition. On Wrangel Island, changes in their abun dance occur with the opposite trends. The same situation recurs on other Arctic islands. The reindeer popu lation decreases, while the musk oxen population becomes larger. We have found that the above trends are determined by the food web structure. The niche overlap between species is considerable and cannot be facil itated by habitat partitioning. The number of plant species in the musk oxen diet is higher than in the reindeer. The exclusive part of the musk ox diet was higher as well. The reindeer occupies a worse position in all of the habitat types. However, the changes in herbivores distribution during the Pleistocene demonstrate opposite results. Therefore, the competitive advantage could not save the Palaearctic musk ox, and its extinction seems to be the result of selective overkill. Conclusively, human activity may be considered as the main factor of the Late Pleistocene herbivore extinctions, and reintroduction of the musk ox should be coupled with extensive conservation.

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