Browsing by Autor "Niels Krabbe"

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A rapid assessment of Bolivian and Ecuadorian montane avifaunas using 20-species lists: efficiency, biases and data gathered
(Cambridge University Press, 1997) Bent Otto Poulsen; Niels Krabbe; Amy Frølander; Marcelo B. Hinojosa; Carmen Quiroga
summary Tropical forests are disappearing very rapidly, so there is often not time for thorough quantitative studies. It therefore becomes increasingly important to use rapid, reliable and informative methods which are also adjusted to tropical logistic constraints. In this paper we use data from seven dry and semi-humid temperate forest patches in Bolivia and three humid, temperate forests in Ecuador to estimate the efficiency, potential biases and the amount of information obtained by the 20-species list method, which we applied in a rapid assessment of avian species richness. Even when used without any standardizations, 20-species lists produce more data than simple species lists, particularly on the amount of survey effort, the order of species richness, the relative abundances of species and the α-diversity index. This approach precludes comparisons with lists from other sites. However, when applied with standardization of area, altitude and effort, the method is neither easier to use nor superior to point counts (based upon vocalizations) in combination with dawn chorus tape-recordings. In species-poor habitats, it is more appropriate to use lists of fewer species. The method is recommended due to its simplicity and the increased quantity of information produced, but it requires a reasonable amount of observer competence and is therefore unfit for use by people ignorant of local avifaunas.
Systematics, biogeography and diversification of <i>Scytalopus</i> tapaculos (Rhinocryptidae), an enigmatic radiation of Neotropical montane birds
(2019) Carlos Daniel Cadena; Andrés M. Cuervo; Laura N. Céspedes; Gustavo A. Bravo; Niels Krabbe; Thomas S. Schulenberg; Graham E. Derryberry; Luís Fábio Silveira; Elizabeth P. Derryberry; Robb T. Brumfield
Abstract We studied the phylogeny, biogeography and diversification of suboscine birds in the genus Scytalopus (Rhinocryptidae), a widespread, speciose, and taxonomically challenging group of Neotropical birds. We analyzed nuclear (exons, regions flanking ultraconserved elements) and mitochondrial (ND2) DNA sequence data for a taxonomically and geographically comprehensive sample of specimens collected from Costa Rica to Patagonia and eastern Brazil. We found that Scytalopus is a monophyletic group sister to Eugralla , and consists of three main clades roughly distributed in (1) the Southern Andes, (2) eastern Brazil, and (3) the Tropical Andes and Central America. The clades from the Southern Andes and Eastern Brazil are sister to each other. Despite their confusing overall uniformity in plumage coloration, body shape and overall appearance, rates of species accumulation through time in Scytalopus since the origin of the clade in the Late Miocene are unusually high compared to those of other birds, suggesting rapid non-adaptive diversification in the group which we attribute to their limited dispersal abilities making them speciation-prone and their occurrence in a complex landscape with numerous barriers promoting allopatric differentiation. Divergence times among species and downturns in species accumulation rates in recent times suggest that most speciation events in Scytalopus predate climatic oscillations of the Pleistocene. Our analyses identified various cases of strong genetic structure within species and lack of monophyly of taxa, flagging populations which likely merit additional study to establish their taxonomic status. In particular, detailed analyses of species limits are due in S. parvirostris, S. latrans, S. speluncae , the S. atratus complex, and the Southern Andes clade.