Megafauna

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The mammoth, an extinct genus of megafauna.
The mammoth, an extinct genus of megafauna.

Megafauna are generally defined as animals that weigh over 500 kg to 1 tonne, i.e., any animal larger than the largest widespread domestic animal, the domestic bull. Some authors use much lower thresholds, even as low as 50 kg (making humans a megafauna species), but they are not widely accepted. The term is also used to refer to particular groups of large animals, both to extant species and, more often, those that have become extinct in geologically recent times.

Megafauna animals are generally K-strategists, with great longevity, slow population growth rates, low death rates, and few or no natural predators capable of killing adults. These characteristics make megafauna highly vulnerable to human exploitation. Many species of megafauna have become extinct within the last million years, and, although some biologists dispute it, human hunting is often cited as the cause.

Contents

The tense in which the term is used is usually apparent from the context:

  1. A particular group of large, extinct animals. For example, American megafauna, meaning "the various species of large American mammal that became extinct about 13,000 years ago".
  2. Any group of large animals. For example, South American megafauna, meaning "all large animals in South America today".

Two major hypotheses have been proposed to explain the extinction of megafauna. The first cites human intervention, noting that the time of human appearances on the various continents was the time that they became extinct. However, this is not widely accepted because megafauna actually began to decline before humans arrived in some places (North America) and did not decline due to human predation (France) in others. There is also a distinct lack of massive kill sites in the archaeological record.[citation needed]

The second is that climate changes, most notably increases in average temperature, caused them to die. While the woolly mammoth survived on at least two islands in the region of the Bering Strait for thousands of years after the end of the last glaciation 12,000 years ago, this indicates that it was not just a change in climate and accompanying vegetation that killed off megafauna in other regions, but that the replacement of other species more optimally adapted for the conditions that came with the end of the Pleistocene caused significant population duress.

New evidence suggests that humans were the ultimate cause of the extinction of megafauna in Australia. The evidence indicates the arid regional climate at the time of extinction was similar to arid regional climate of today, and that the megafauna were strongly adapted to an arid climate. These pieces of evidence rule out climate change as a cause of extinction. The evidence indicates that all forms of megafauna became extinct in the same rapid timeframe — approximately 47,000 years ago — this being the time at which humans entered the landscape. The evidence indicates the main mechanism for extinction was human burning of a then much less fire-adapted landscape. Isotopes from the teeth indicate such burning caused sudden drastic changes in vegetation and sudden drastic changes in the diet of surviving species, as well as the loss of megafaunal species [1] [2] [3].


"†" denotes extinct megafauna

See also: Australian megafauna

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