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The Role of Competition in the Evolution of Migration

George W. Cox
Evolution
Vol. 22, No. 1 (Mar., 1968), pp. 180-192
DOI: 10.2307/2406662
Stable URL: http://www.jstor.org/stable/2406662
Page Count: 13
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The Role of Competition in the Evolution of Migration
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Abstract

Intraspecific and interspecific competition are suggested as primary selective agents in the evolution of migration. Selection should favor genetic mechanisms leading to incipient migratory movements by individuals of normally resident species into seasonally favorable adjacent areas if gains in survival or reproduction due to reduced competition exceed the migration cost. Evolution of partial migration patterns may thus result from high overall competition or high intraspecific competition alone. Disjunct migration may evolve through elimination of resident, and selection for migrant, populations by intense interspecific competition, thus representing a complex behavioral-spatial mechanism of ecological isolation. An analysis of ecological isolating mechanisms utilized by migrant and resident American land birds supports this hypothesis. Migration occurs most frequently in groups apparently less able to solve problems of ecological isolation by morphological differentiation of the feeding apparatus, and which are characterized by small beak size, low actual beak variability, and low beak variability relative to that of tropical resident species of the same group. The high frequency of migration in passerine birds is interpreted as a consequence of their having evolved in competition with an already existing, diverse fauna of non-passerines occupying many of the potential morphologically characterizable feeding niches.

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