Transvolcanic Jay (Aphelocoma ultramarina)

Niche expansion can lead to adaptive differentiation and speciation, but there are few examples from contemporary niche expansions about how this process is initiated. We assess the consequences of a niche expansion by Mexican jays ( Aphelocoma ultramarina ) along an elevation gradient. We predicted that jays at high elevation would have straighter bills adapted to feeding on pine cones, whereas jays at low elevation would have hooked bills adapted to feeding on acorns. We measured morphological and genetic variation of 95 adult jays and found significant differences in hook length between elevations in accordance with predictions, a pattern corroborated by analysis at the regional scale. Genetic results from microsatellite and mtDNA variation support phenotypic differentiation in the presence of gene flow coupled with weak, but detectable genetic differentiation between high- and low-elevation populations. These results demonstrate that niche expansion can lead to adaptive divergence despite gene flow between parapatric populations along an elevation gradient, providing information on a key precursor to ecological speciation.

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Relationships Between Mexican Jays (Aphelocoma Ultramarina) and Northern Flickers (Colaptes Auratus) in an Arizona Oak Savanna

The Auk ◽

10.1093/auk/120.2.429 ◽

2003 ◽

Vol 120 (2) ◽

pp. 429-432

Author(s):

Zach F. Jones ◽

Carl E. Bock

Keyword(s):

Alarm Calls ◽

Oak Savanna ◽

Shared Resources ◽

Interspecific Associations ◽

Avian Predators ◽

Colaptes Auratus ◽

Aphelocoma Ultramarina ◽

Agonistic Encounters

Abstract We observed Mexican Jays (Aphelocoma ultramarina) and Northern Flickers (Colaptes auratus) from June 2000 to March 2001, recording interspecific associations and inter-actions. Flickers were seen with jays only once in summer, but they were observed together 62 times in winter, in mixed flocks of up to 20 jays and 12 flickers, while jays were alone only 4 times, and flickers were alone 31 times. Jays always initiated flock movement, and flickers followed. Flickers were more likely to forage when they accompanied jays than when they were alone. While jays searched under and around oaks for acorns and grasshoppers, flick-ers probed for subterranean ants. We found no evidence that flickers attempted to rob the jays' acorn caches, and we observed no agonistic encounters between the two species. Avian predators approached mixed flocks on six occasions, and in each case flickers responded to jay alarm calls by flying with the jays into oak foliage. All predation attempts were unsuccessful. We conclude that Northern Flickers most likely were associated with Mexican Jays in winter because of increased security from predation, and not because of shared resources.

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