Origin, diversification, and biogeography of forest birds across temperate forest regions in the Northern Hemisphere

Jacques Blondel

doi:10.21425/f5fbg51998

Abstract

Technological and methodological advances in biogeography, phylogenetics, and bioinformatics during the past couple of decades provide greatly enhanced insights into the evolutionary history of birds in space and time. Molecular data, especially next-generation DNA sequencing, have produced a revolution in reconstructing the phylogenetic history of lineages. These advances shed a new light on the mode, tempo, and spatial context of differentiation processes that shaped the composition and structure of extant forest bird communities of temperate forests of the Northern Hemisphere. This paper offers a framework for understanding this history based on analytical tools that allow us to decipher the imprint of changes in the geographic configuration of land masses and in climates since the Mesozoic, with a focus on the temperate-tropical flyways that connect the massive forest blocks of the Northern to those of the Southern Hemispheres. Differentiation of most extant bird lineages and species has been shown to have begun in a deeper past than formerly thought, although recent analyses from molecular phylogenies also support the much-debated Late Pleistocene model of speciation. Geographical connections between tropical and temperate realms make north-south flyways important drivers of differentiation for many lineages. The histories of differentiation and colonisation of clades, including both resident and long-distance migrants, are discussed in relation to two alternative theories, the ‘southern home theory’ and the ‘northern home theory’. The region-specific characters of the bird faunas and differences between the main temperate forest blocks of the Northern Hemisphere are discussed in light of the hypotheses concerning dispersal processes related with geographical configuration of land masses. Differential dispersal-colonisation rates from tropical regions and subsequent diversification in temperate regions (and vice versa) are also considered. The causes of the observed decline in diversification rates during the Pleistocene are examined from phylogenetic reconstructions of various clades.

Highlights

Because more than two thirds of the Northern Hemisphere were forested before large-scale deforestation by humans took place, forest-dependent birds represent a very diverse element of this hemisphere’s terrestrial bird fauna
They are the western North American block, the eastern North American block, and two blocks in Eurasia, which are separated by large areas of steppe, deserts, and massive mountain ranges, except in the far North where the belt of boreal forests is uninterrupted
As more specieslevel phylogenies are published with comprehensive taxonomic and geographic sampling, applying the new generation of phylogenetic comparative methods has the potential to increase our understanding of how variation in diversification rates in the various parts of the Northern Hemisphere can explain differences in bird communities, as well as general patterns of change in migratory behaviour across the avian tree of life (Morlon 2014)

Summary

Introduction

Because more than two thirds of the Northern Hemisphere were forested before large-scale deforestation by humans took place, forest-dependent birds represent a very diverse element of this hemisphere’s terrestrial bird fauna. Temperate and boreal forested regions of the Northern Hemisphere consist of four main blocks, which are either deciduous or mixed deciduous and coniferous They are the western North American block (which is distinct from the other areas in its size, structure, and distribution of forested areas), the eastern North American block (part of the North American continent north of the US-Mexican border and east of the 95°W), and two blocks in Eurasia, which are separated by large areas of steppe, deserts, and massive mountain ranges, except in the far North where the belt of boreal forests is uninterrupted.

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