Tenet 4

Any organism that ignores Nature’s limits
threatens its own existence

We know from ecological studies that when organisms disregard limits they threaten their very existence. One such classic study is that of David R. Klein’s research on the St. Matthew Island Reindeer1.

ReindeerIn 1944, 29 Reindeer (Rangifer tarandus) were released by the U.S. Coast Guard onto St. Matthew Island in the Bering Sea off the west coast of Alaska. The island was free from large predators. Biologists began to monitor the Reindeer numbers in 1957 when 1,350 animals were counted, all in excellent condition. The habitat, as well, was considered very favourable.

Another survey in 1963 revealed 6,000 animals on the island. The Reindeer were in significantly poorer shape due to increased population pressures on their habitat, which was under intense grazing pressure. Although the summer range had seemed to recover from excessive grazing, the winter range was impacted significantly.

Reindeer graph

The rise and collapse of the Reindeer population on St. Matthew Island, Alaska. Note the relatively long, slow climb but the precipitous fall.

When biologists returned to the island in 1966 only 42 Reindeer were found alive and evidence suggested that a major die-off had occurred during the winter of 1963-64. Klein found that “…range carrying capacity involves two quite different criteria: the winter component which governs the upper limit of the population, and the summer component which determines the physical stature of the individual.”

Klein concluded that the large scale die-off during the winter of 1963-64 was the result of: 1) overgrazing of lichens on the island, which are normally the most important winter forage [the limiting factor]; 2) excessive numbers of reindeer [overpopulation] competing for the limited available forage; 3 ) the relatively poor condition of the reindeer going into the winter as a result of competition for high quality summer forage [overpopulation]; and 4) extreme weather conditions, particularly deep snow accumulation [additional stressor], during the winter of 1963-64, further restricting the availability of the already depleted winter forage.

Because the Reindeer couldn’t control their own numbers, they exceeded the carrying capacity of the island; because they couldn’t solve the problem of their limiting resource—winter food—their population collapsed.

Nor are humans exempt from physical and ecological limits…

…Humans and Limits

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1Klein, D.R. 1968. The introduction, increase, and crash of reindeer on St. Matthew Island. J. Wildlife Management 32:350-367. Note: this link opens a new window.

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