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The Temporal Component of Diversity Among Species of Birds

Robert E. Ricklefs
Evolution
Vol. 20, No. 2 (Jun., 1966), pp. 235-242
DOI: 10.2307/2406576
Stable URL: http://www.jstor.org/stable/2406576
Page Count: 8
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The Temporal Component of Diversity Among Species of Birds
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Abstract

Data from 11 localities of wide geographic distribution indicate that the average length of the breeding season of individual species of birds occupies very nearly the same proportion of the total breeding season in all localities. This essentially eliminates a temporal component to increased tropical species diversity. Further analysis gives no evidence that closely related sympatric species stagger their nesting seasons to avoid competition, but in fact, the seasons of such pairs consistently overlap more than 90 per cent. This and other evidence indicates that the temporal diversity found within the total breeding season is the result of specific feeding differences together with temporal diversity in the availabilities of the different food resources. It also appears that the longer tropical breeding seasons differ from temperate ones only in having an expanded time scale; the relative position within the season and the portion used corresponding closely for pairs of similar tropical and temperate species. While differences in the timing of breeding cannot account for increased diversity, lower intensity of breeding caused by longer breeding cycles, smaller clutches, and lower nesting success may well reduce interspecific competition.

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