Avian Diversity in Humid Tropical and Subtropical South American Forests, with a Discussion About Their Related Climatic and Geological Underpinnings

Abstract

The tropical and subtropical regions of South America occupy ca. 14,250,000 km², of which 8,000,000 km² are covered by humid forests. Among these, Amazonia, the Atlantic Forest, the forests of the Eastern Andean Slopes, and the Pacific Forest stand out. About 1014 species of birds (324 non-passerines and 690 passerines) are endemic to these forests. Their lineages are believed to have been impacted by five major geological and climatic events in the Neogene and the Pleistocene: the uplift of the Andes, the formation of the Isthmus of Panama, glaciations, sea-level rise, and alternating period of differing humidity. In this contribution, inspired by an analysis of bird distribution patterns inferred from superimposed species ranges, I discuss possible processes that may have influenced biological diversification in tropical and subtropical South America. Data demonstrate that the Andean uplift divided the original pan-Amazonia into a trans-Andean region (the Pacific forest) and a cis-Andean region (present-day Amazonia), and, about 10–7 Ma, induced the formation of large Amazonian rivers. There is evidence that Amazonia and other tropical forests remained predominantly forested over time, even during the cooler and drier glacial periods. Marine transgressions during the upper Tertiary and lower Quaternary, and the formation of the Amazonian rivers following the rise of the Andes, likely fragmented the forest and operated as mechanisms to generate new species. Moreover, the closing of the Panama Isthmus and connections between Amazonia and the Atlantic forest, and the southern Andean and the Paranaense/Atlantic forests, led to the migration of taxa from other biogeographic regions—substantially increasing diversity in these biomes. Biogeographical patterns can promote insight and lead to the generation of hypotheses about the processes that have shaped present-day patterns of avian biodiversity in the region, but testing the latter will require multidisciplinary studies that integrate geology, paleoecology, molecular phylogenetics, and phylogeography. Moreover, despite the historical processes responsible for the extraordinary richness of the tropical and subtropical avifauna, available data point out to a serious problem affecting bird populations in humid forests of South America—especially in Amazonia, the lower Eastern Andean Slopes, and the Pacific Forest: a severe reduction in the diversity of birds. This drop in diversity is appreciable not only in disturbed habitats, but also in national parks and reserves, suggesting that climate change may be involved.

Appendices

Appendices

1.1 Appendix 1: Endemic Birds of the “Pacific Slopes Center”

Odontophorus melanonotus, Heliangelus strophianus, Heliodoxa imperatrix, Coeligena wilsoni, Urosticte benjamini, Aglaiocercus coelestis, Eriocnemis mirabilis, Calliphlox mitchellii, Haplophaedia lugens, Megascops columbianus, Glaucidium nubicola, Semnornis ramphastinus, Andigena laminirostris, Micrastur plumbeus, Sipia nigricauda, Grallaria flavotincta, Scytalopus vicinior, Pseudocolaptes johnsoni, Thripadectes ignobilis, Margarornis stellatus, Pipreola jucunda, Cephalopterus penduliger, Machaeropterus deliciosus, Cyanolyca pulchra, Entomodestes coracinus, Diglossa indigotica, Anisognathus notabilis, Chlorochrysa phoenicotis, Bangsia edwardsi, B. aureocincta, Ixothraupis rufigula, Chlorothraupis stolzmanni, Oreothraupis arremonops, Chlorospingus semifuscus, C. flavovirens, Chlorophonia flavirostris.

1.2 Appendix 2: Endemic Birds of the “Atlantic Forest Mountains Center”

Piculus aurulentus, Dysithamnus xanthopterus, Drymophila rubricollis, D. genei, D. ochropyga, Myrmoderus loricatus, Merulaxis ater, Anabazenops fuscus, Cranioleuca pallida, Phylloscartes difficilis, Carpornis cucullata, Tijuca atra, T. condita, Ilicura militaris, Sporophila frontalis, Castanozoster thoracicus, Tangara cyanocephala, T. desmaresti, T. cyanoventris.

1.3 Appendix 3: Species that Would Have Been Involved in the Corridor Joining the Atlantic Forest with the Yungas

Crypturellus obsoletus, Penelope obscura, Lurocalis semitorquatus, Antrostomus sericocaudatus, Lophornis chalybeus, Tigrisoma fasciatum, Parabuteo leucorrhous, Aegolius harrisii, Batara cinerea, Thamnophilus ruficapillus, Herpsilochmus rufimarginatus, Chamaeza campanisona, Xenops minutus, Lochmias nematura, Philydor rufum, Phylloscartes ventralis, Phyllomyias burmeisteri, Elaenia obscura, Poecilotriccus plumbeiceps, Ramphotrigon megacephalum, Pachyramphus castaneus, Oxyruncus cristatus, Piprites chloris, Turdus albicollis, Trichothraupis melanops, Cissopis leverianus, Pipraeidea melanonota, Arremon flavirostris, Habia rubica, Myiothlypis rivularis, Cacicus chrysopterus, Euphonia cyanocephala, Chlorophonia cyanea.