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Successes and Failures of Tropical Mammals and Birds

M. Moynihan
The American Naturalist
Vol. 105, No. 944 (Jul. - Aug., 1971), pp. 371-383
Stable URL: http://www.jstor.org/stable/2459629
Page Count: 13
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Successes and Failures of Tropical Mammals and Birds
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Abstract

Tropical species may be more often successful in invading the temperate zones than are temperate species in invading the tropics. The reasons why are not immediately obvious. Some possibilities can be discarded. Many tropical birds and mammals have particularly complex interspecific relations (mixed flocks or bands, various kinds of commensalism, parasitism, mimicry, etc.). Others have evolved unique feeding habits. These are not the animals which have spread most easily or frequently from one climate zone to another. A survey of the mammals for which there is good evidence of movements from the tropics into north temperate regions reveals that they have one distinctive feature in common: unusually good or varied defenses against predators (they can fight or repel attackers in addition to hiding or escaping). There are other indications that predators may be relatively more important or dangerous to terrestrial vertebrates in the North Temperate Zone than in the tropics and, conversely, that other causes of mortality (diseases?) may be relatively more important in the tropics than in the North Temperate Zone. If this is so, this might be sufficient in itself to explain the distinctiveness of the mammals which are known to have been successful in invading the north.

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