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ZEISS DTI thermal imaging cameras. For more discoveries at night, and during the day.

Amazonian river barriers (1 Viewer)

Rivers as barriers has been studied in Monkeys and Birds for a long time. Antbirds wont even cross tracks when they follow ant swarms. 1999 Gascon Lougheed proposed mountain ridges in the Amazon basin helped species proliferation especially in Epipedobate Frogs and suggested that rivers didnt match up with the patterns of variation but matched up very closely with the ridges. Bird and primate diversity that seemed to match rivers could be artefact but that the ridges matched more closely.

Will be interesting to read this article focusing on birds
 
discors said:
Bird and primate diversity that seemed to match rivers could be artefact but that the ridges matched more closely.
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May well depend on where you are. In the headwaters, the rivers are small and the ridges high barriers, but lower down in the floodplain, the rivers are wide barriers and the ridges inconsequential :t:
 
Weir et al

Weir, Faccio, Pulido-Santacruz, Barrera-Guzmán & Aleixo (in press). Hybridization in headwater regions, and the role of rivers as drivers of speciation in Amazonian birds. Evolution. [abstract]
 
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Richard Klim said:
Weir et al 2015. Evolution 69(7): 1823–1834. [pdf]
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"In conclusion, our results confirm the presence of gene flow across headwater regions of Amazonia, despite the very old ages of some of the taxon pairs involved. Our current level of sampling is insufficient to measure hybrid zone width or test for levels of selection against hybrids, and further sampling is necessary to address hybrid zone dynamics in each of these taxon pairs in further detail. Nevertheless, our data do demonstrate low levels of interspecific heterozygosity and suggest the presence of hy-brid individuals that have backcrossed with parental populations. These results demonstrate incomplete reproductive isolation and challenge the generality of the River-barrier hypothesis as a driver of in situ speciation in the Amazon."

Does this mean I don't have to see 7 "Lineated Woodcreepers", 5+ "Curve-billed Scythebills, XX "Yellow-margined Flycatchers" and so on?! I seem to recall the HBW special volume "new species" skated over the headwaters issue, perhaps with the exception of the paper on the Tolmomyias. What does Zander II say? ;)

cheers, alan
 
lewis20126 said:
Does this mean I don't have to see 7 "Lineated Woodcreepers", 5+ "Curve-billed Scythebills, XX "Yellow-margined Flycatchers" and so on?! I seem to recall the HBW special volume "new species" skated over the headwaters issue, perhaps with the exception of the paper on the Tolmomyias. What does Zander II say? ;)
Click to expand...

Stable hybrid zones are no barrier to recognition as BSc species AFAIK. If you're having all those crappy black-and-white Ficedulas and dirty gulls in the WP then we can have a load of suboscines that diverged several million years ago - rather than a week last Wednesday like this Palearctic dross. ;)
 
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Reiterating, the most important lesson from the Weir paper is that despite the lack of physical barriers in headwater regions these taxa taxa maintain their genotypes and phenotypes and are in contact across very narrow zones where there is apparently little hybridisation. I'd say that was a plus rather than a minus for considering species status for these birds and ought to go some way to placate the folk at SACC who place such weight on the need for vocal differences. We have no idea how important vocal yardsticks might be for woodcreepers but many long recognised species show no vocal differentiation from their inferred species species.
 
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