https://science.sciencemag.org/content/sci/165/3889/131.full.pdf

Speciation in amazonian forest birds.

The fossil record for angiosperm pollen types which are comparable to recent taxa is evaluated, following a similar survey published in 1970. Special attention is paid to the dating of the sediments. Evidence for 139 families is considered to be reliable, for others the records are cited as provisional, pending the accumulation of more evidence. Some published records are shown to be erroneous.

Fossil pollen records of extant angiosperms.

The Pleistocene Changes of Vegetation and Climate in Tropical South America

In recent years, the view that Pleistocene climatic events played a major role in the evolution of the biotas of southern, primarily tropical continents has begun to displace the previously held conviction that these areas remained relatively stable during the Quaternary. Studies of speciation patterns of high Andean plant and avian taxa (7-14) have led to the conclusion that Pleistocene climatic events were the factors that ultimately shaped the patterns now observed in the paramo-puna and the related Patagonian flora and fauna. The final uplift of the Andes at the end of the Tertiary automatically limits the age of the high Andean habitats and their biotas to the Quaternary. Within this period, the number of ecological fluctuations caused by the glaciations could easily have provided the mechanism behind the patterns now present in these habitats (Appendix, 1; Figs. 1 and 2; Table 1). In glacial periods, when vegetation belts, were lowered, organisms in the paramo-puna habitat were allowed to expand their ranges. In interglacial periods, these taxa were isolated on disjunct peaks, where differentiation could occur. At times of ice expansion, glacial tongues and lakes provided local barriers to gene exchange, whereas in warm, interglacial times, dry river valleys were a major deterrent to the interbreeding of populations on different mountains (Fig. 2; Table 2). A preliminary analysis of about 10 to 12 percent of the total South American avifauna (14), subsequent to the study of the high Andean biota, suggested that the birds of all the major habitats of the continent possess, with about equal frequency, similar stages of speciation. This correspondence in levels of evolution indicated that the avifauna of vegetation zones which were thought to have been more stable (for example, tropical rainforests) are as actively speciating as are those of the more recent paramo-puna habitats. More intensive work on lowland tropical taxa (16, 19-21) and recent work on montane forest elements (40) now justify the conclusion that the floras and faunas of these areas were also greatly affected by Pleistocene climatic shifts. In the broad region of South America that lies within the tropics, a series of humid-arid cycles (Appendix, 6, 8-10) drastically and repeatedly altered vegetation patterns during the Quaternary. Both montane and lowland rainforests were fragmented during dry periods and were able to reexpand during humid phases. Speciation of forest elements was initiated-and sometimes completed-in isolated patches of the fragmented forest. Secondary contact, with hybridization or reunition of populations that did not become reproductively isolated, occurred in periods of reexpansion. These biological data, combined with supportive geological evidence (Appendix, 1-11), show that climatic events during the last million or so years have affected the biota of South America as much as the Pleistocene glacial changes affected the biotas of Eurasia and North America. Since most of South America lies within tropical latitudes, it is suggested here that part of the diversity of species in the tropical areas of this continent is due to two historical factors: the lack of wholesale elimination of species (compared with northern and high latitudes), and ample opportunity for speciation in successive periods of ecological isolation. The apparent paradox of the wealth of species in the "stable tropics" is partially explained by the fact that the tropics have probably been quite unstable, from the point of view of their biotas, during the Pleistocene and perhaps part of the Tertiary.

https://science.sciencemag.org/content/sci/173/3999/771.full.pdf

Pleistocene Changes in the Fauna and Flora of South America

An Ecological History of the Lake Victoria Basin

The uppermost 32 metres of a 2436 metre core principally of lake sediments, Pleistocene and Holocene in age from the Sabana de Bogota were analysed for its pollen content, at intervals of 10—15 cm. About seventy species, genera of families could be recognized, many of them for the first time. The rest of the core is being analysed and the results will be published later. The Sabana de Bogota lies at an altitude of approximately 2500 metres above sea level, 4½°—5° North of the equator, and 74°—74½° West of Greenwich. From the diagram it may be deduced that glacial and interglacial periods affected the tropics equally as Europe and North America. It also shows that the glacial periods were at the same time pluvials, and the interglacials interpluvials. Curves for the real fluctuations of the tree-line, changes of annual precipitation and changes of temperature have been calculated (fig. 5). Temperatures during the high-glacial phases of the Wurm glacial were ± 8° C lower than today, the altitude of the tree-line was some 1300 metres less than now and the snow-line showed an even greater difference (fig. 5). Radiocarbon dates prove that the parts of the section considered to be respectively Holocene and later Wurm-glacial really correspond to those ages. Moreover the temperature curve for the upper Pleistocene of the Sabana de Bogota corresponds surprisingly well with that published by Emiliani for surface ocean water and by Gross for Europe (fig. 6). With this knowledge it seemed fully justified to correlate also the older phases with the glacials and interglacials of Europe and North America, using principally the alpine nomenclature. The lowest part of the diagram seems to correspond to the end of Hiss I (= Drenthe stadial), followed by the Riss I—II interstadial, and the Riss II (= Warthe stadial). Then follows the Riss-Wurm interglacial, the Wurm-glacial (subdivided by two long interstadials, together called Interpleniglacial), and the Holocene. The more important conclusions of the present study are summarized in paragraph 12.

/pdf/upper-pleistocene-and-holocene-climate-and-vegetation-of-the-4rwu4ik2sp.pdf

Upper pleistocene and holocene climate and vegetation of the “Sabana de Bogota” (Colombia, South America)

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Upper pleistocene and holocene climate and vegetation of the “Sabana de Bogota” (Colombia, South America)