Abstract

In the Andes, pairs of ecologically similar species are often separated by narrow elevational sympatry zones but the mechanisms mediating sympatry are not fully understood. Here, we describe niche partitioning within a sympatry zone in a fragmented Andean landscape between two closely related flush-pursue species: a high-elevation montane forest dweller, (Myioborus melanocephalus), and a mid-elevation montane forest dweller, (M. miniatus). As all flush-pursuers use very similar hunting techniques involving visual displays to flush and pursue insects in air, and benefit from being the “rare predators”, ecological sorting between species in sympatry zones should allow their co-existence. We found that both species occupied vegetation resembling their typical allopatric habitats: a mosaic of pastures, clearings, and shrubs with small proportion of high trees for M. melanocephalus, and dense high forests with high proportion of trees, lower irradiance and higher humidity for M. miniatus. M. melanocephalus often foraged in bushes and at lower heights, whereas M. miniatus often foraged in tree crowns. The two species differed relatively little in their foraging technique. These results demonstrate how ecological sorting permits species of divergent elevational distributions and habitats to successfully coexist in sympatric zones where habitat diversity allows both species to find their preferred habitat.

Highlights

  • In the Andes, pairs of ecologically similar species are often separated by narrow elevational sympatry zones but the mechanisms mediating sympatry are not fully understood

  • There are three non-exclusive and likely interacting mechanisms that may contribute to the origin and maintenance of elevational d­ ivergence[6]: (1) stochastic processes occurring on evolutionary time scale and resulting in higher degree of elevational divergence among the evolutionary older species, (2) elevational divergence actively driven by direct competitive interactions in zones of sympatry and (3) ecological sorting mechanisms that permits species of sufficiently divergent elevational distributions and ecological niches in allopatry to successfully attain sympatry following secondary contact in a zone of ­sympatry[7]

  • Interspecific aggression in sympatry zone within pairs of closely related species of specialized and relatively similar foraging ecology may suggest that competition mechanisms are involved

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Summary

Introduction

In the Andes, pairs of ecologically similar species are often separated by narrow elevational sympatry zones but the mechanisms mediating sympatry are not fully understood. As all flush-pursuers use very similar hunting techniques involving visual displays to flush and pursue insects in air, and benefit from being the “rare predators”, ecological sorting between species in sympatry zones should allow their co-existence We found that both species occupied vegetation resembling their typical allopatric habitats: a mosaic of pastures, clearings, and shrubs with small proportion of high trees for M. melanocephalus, and dense high forests with high proportion of trees, lower irradiance and higher humidity for M. miniatus. The isolation among the lower elevation populations was less pronounced and led to intraspecific differentiation within the low-elevation species, the Slate-throated ­Whitestart[19] ranging from North/Central America (South of USA/Mexico) to Bolivia (Fig. 1a;9) This situation, with one geographically diverse species at lower elevations and a series of separate species at higher elevations, with occasional sympatry zones between them at middle elevations, is typical for the Andean ­birds[35] as exemplified by studies on finches, E­ mberizidae[7,36] and Metallura ­hummingbirds[5]. The Spectacled Whitestart occurs at higher altitudes, mainly 2300–4000 m above sea a b c d

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