Thursday, April 1, 2010

Interspecific predatory relationships

Asian Black Bears and Ussuri Brown Bears constitute 5-8% of the Siberian tiger's diet. The brown bear's input is estimated to be 1-1.5%. Certain tigers have been reported to imitate the calls of Asiatic black bears to attract them. Brown bears are typically attacked by tigers more often than black bears, due to their habit of living in more open areas and their inability to climb trees. When hunting bears, tigers will position themselves from the leeward side of a rock or fallen tree, waiting for the bear to pass by. When the bear passes, the tiger will spring from an overhead position and grab the bear from under the chin with one forepaw and the throat with the other. The immobilized bear is then killed with a bite to the spinal column. After killing a bear, the tiger will concentrate its feeding on the bear's fat deposits, such as the back, hams and groin. Tiger attacks on bears tend to occur when ungulate populations decrease. While tigers can successfully hunt bears, there are also records of brown bears killing tigers, either in disputes over prey or in self defense, and in at least one instance, of a bear consuming a tiger. There have been observations of bears that changed their path after coming across tiger trails, as well as of bears following tiger tracks with no signs of fear and sleeping in the same den. However, despite the threat of predation, some brown bears actually benefit from the tiger's presence by appropriating tiger kills that the bears may not be able to successfully hunt themselves, as they usually dominate these disputes over kills.

In areas where wolves and tigers share ranges, the two species typically display a great deal of dietary overlap, resulting in intense competition. Wolf and tiger interactions are well documented in Sikhote-Alin, which until the beginning of the 20th century, held very few wolves. It is thought by certain experts that wolf numbers increased in the region after tigers were largely eliminated during the Russian colonization in the late 1800s and early 1900s. This is corroborated by native inhabitants of the region claiming that they had no memory of wolves inhabiting Sikhote-Alin until the 1930s, when tiger numbers decreased. Tigers depress wolf numbers, either to the point of localized extinction or to such low numbers as to make them a functionally insignificant component of the ecosystem. Wolves appear capable of escaping competitive exclusion from tigers only when human pressure decreases tiger numbers. Today wolves are considered scarce in tiger inhabited areas, being found in scattered pockets, and usually seen travelling as loners or in small groups. First hand accounts on interactions between the two species indicate that tigers occasionally chase wolves from their kills, while wolves will scavenge from tiger kills. Tigers are not known to prey on wolves, though there are four records of tigers killing wolves without consuming them. This competitive exclusion of wolves by tigers has been used by Russian conservationists to convince hunters in the Far East to tolerate the big cats, as they limit ungulate populations less than wolves, and are effective in controlling wolf numbers.

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