DOI: 10.5061/dryad.0sq68
title: Data from: Why are tropical mountain passes ‘low’ for some species? genetic and stable-isotope tests for differentiation, migration, and expansion in elevational generalist songbirds

description: 1.Most tropical bird species have narrow elevational ranges, likely
 reflecting climatic specialization. This is consistent with Janzen's
 Rule, the tendency for mountain passes to be effectively ‘higher’ in the
 tropics. Hence, those few tropical species that occur across broad
 elevational gradients (elevational generalists) represent a contradiction
 to Janzen's Rule. 2.Here we aim to address the following questions.
 Are elevational generalists being sundered by diversifying selection along
 the gradient? Does elevational movement cause these species to resist
 diversification or specialization? Have they recently expanded, suggesting
 that elevational generalism is short-lived in geological time? 3.To answer
 these questions, we tested for differentiation, movement, and expansion in
 four elevational generalist songbird species on the Andean west slope. We
 used morphology and mtDNA to test for genetic differentiation between
 high- and low-elevation populations. To test for elevational movements, we
 measured hydrogen isotope (δ2H) values of metabolically inert feathers and
 metabolically active liver. 4.Morphology differed for House Wren
 (Troglodytes aedon) and Hooded Siskin (Spinus magellanicus), but not for
 Cinereous Conebill (Conirostrum cinereum) and Rufous-collared Sparrow
 (Zonotrichia capensis), respectively. mtDNA was structured by elevation
 only in Z. capensis. δ2H data indicated elevational movements by two tree-
 and shrub-foraging species with moderate-to-high vagility (C. cinereum and
 S. magellanicus), and sedentary behavior by two terrestrial-foraging
 species with low-to-moderate vagility (T. aedon and Z. capensis). In S.
 magellanicus, elevational movements and lack of mtDNA structure contrast
 with striking morphological divergence, suggesting strong diversifying
 selection on body proportions across the ~50 km gradient. All species
 except C. cinereum exhibited mtDNA-haplotype variation consistent with
 recent population expansion across the elevational gradient, potentially
 concurrent with Holocene anthropogenic habitat conversion for agriculture.
 5.In different ways, each species defies the tendency for tropical birds
 to have long-term stable distributions and sedentary habits. We conclude
 that tropical elevational generalism is rare due to evolutionary
 instability.
description: Hydrogen Isotope
 DataThis table contains
 hydrogen isotope ratios for flight feather, contour feather, and liver
 tissue of four focal taxa. All isotope data are reported with species
 name, elevation of capture, and Arctos URLs for extended data
 accessibility.Gadek-et-al-Isotope-Data
 .xlsxMorphometric
 DataThis table contains
 morphometric measurements in millimeters of the four focal taxa.
 Measurements are: length of innermost retrices, wing chord, culmen length,
 and tarsus length. Elevation of capture is reported along with Arctos
 links, when available, for extended data accessibility.Gadek-et-al-morphometric-data.xlsxHand-Wing Index DataThis table contains hand-wing index measurements obtained from dry round museum skins, secondary length (SL) in millimeters and total wing length (WL) in millimeters derived from Kipp 1959 and Claramunt et al. 2012 indices. Arctos URLs are included for extended specimen data accessibility.Gadek-et-al-HWI-data.xlsxFlight Muscle DataThis table contains wet muscle mass and body mass reported in grams. Live Arctos URL links are provided for extended specimen data accessibility.Gadek-et-al-flight-muscle-data.xlsx