So now, let us look at what happened to the other passerine lineage that for 40 million years evolved in splendid isolation in South America. This is a phylogeny based on a multigene study made in collaboration with Jan Ohlson and Martin Irestedt, at Per Ericson's lab at our partner institution in Sweden, the Swedish Natural History Museum. This is an endemic radiation of 1,200 species and 83% of these have been included in molecular phylogenetic studies; in this diagram we only include representatives of each of the lineages. What you should note is here in the difference between the colours The main radiation with lots of species is coloured with green here and they comprise 210 antbird species, 138 spinetails (the group Synallaxinae), 102 flatbills and todi-tyrants, 95 elaenine flycatchers and 104 fluvicoline flycatchers. This means that 60% of all the species are in just five lineages that had diverged in the mid-Miocene, from around 15 million years ago, so most of the species are just in so few groups. This expansion has been around the time when the global temperature began to drop and open habitats and grasslands began to develop around the world. Yellow branches in the graph show lineages with small numbers of species and the red represent the really small clades, some of them just a single species, others 2-4 forms that have diverged quite recently as separate populations, but the lineage is actually old and goes far back in time. Thus, we can see that there are many such lineages that are survivors since the very early period of evolution of this great group. Thus, the mixture of radiations with lots of species and small clades represent a striking asymmetry in the phylogeny. This is in fact typical of very many phylogenies. Rapid radiations mixed between groups where nothing seems to happen. What does this reflect Well, one may say that the deep branches may simply be some species that were not able to speciate in some ways, but they may also be relict forms and look we have one strange long branch here on the phylogeny the basal branch here to the big flycatcher group. These birds are actually frugivorous (fruit-eaters as we can see here on these illustrations) and one could well imagine that this long branch reflects extinction of fruit-eater birds 34 million years ago when the climate suddenly changed in connection with the first Antarctic freeze. Before that there was rainforest all over Paragonia that suddenly disappeared. There may have been great extinctions; then after warming started again, they could start to diversify. Now, how are such asymmetries reflected in the geographical diversity pattern in the way species are distributed in space The ancient forms are distributed as we see here some of them are very widespread, and have even expanded (after the closure of the Panama channel) to Central America. However, the majority of them are very concentrated in the upper Amazon basin, i.e. in the most extensive area of tropical lowland forest. Some of them live in the tropical Andes, which since the mid-Miocene has been more or less isolated as a peninsula at the western edge of the continent. So the grid-cells that are right on the edge between the Andes and the Amazon area have an inflated high beta diversity of species. But overall relict species survived only in the most extensive and warm, humid habitats. Moderate-sized clades in the phylogeny are somewhat different in their distribution, adding strongly to the tropical biodiversity. Here is a diversity map for one of the five expanding groups (the Fluvicolinae flycatchers); here the species with short rootpaths in the phylogeny are shown in purple colour that represent the early diversification and these species are mainly found in tropical and subtropical areas (the highest species richness thus being in the bright violet in the savanna regions of southern Brazil and Bolivia). The group comprises three big radiations shown in green colour. One (the chat-tyrants and their allies) diversified in the scrubby environments that developed in the tropical Andes region; another radiation started in the tropical Andes and expanded rapidly to North America (this is the various small North American flycatchers) and the third diversification happened in the open and windy environments that developed in Patagonia and in the rain shadow zone east of the Andes, and then expanded up to the north in the steppe habitats of the highest parts of the Andes. All three expansions are in new environments that were formed as a consequence of the climate change, and as the Panama Isthmus closed during the Plio-Pleistocene period and facilitated dispersal to North America. Here is another diversifying group, the wood creepers and ovenbirds of South America, a big group with about 300 species. They comprise a mixture of lineages with different rates of speciation, including the rapidly radiating spinetail group that was on the phylogeny before. According to a big analysis or the phylogeny based on a study by Derryberry et al. in Evolution 2011 suggests that this group showed a constant rate of speciation over 30 million years. It is simply more and more and more species at a constant rate. So we can see on the maps now how that rate could be maintained in spite of competition between the species. In these distribution maps, the species are divided into age groups based on the time-calibrated phylogeny. First map shows species lineages that are 20-7.5 million years old they are Amazonian in their distribution; 7.5-5 million years old are still Amazonian. You can see that there is some small variation because the dynamics of the Amazon Basin is actually very complicated. The Amazon first ran to the Pacific Ocean. Then it was blocked by the Andes, then it ran to the north to Venezuela and there were enormous wetlands in this basin, levees and floodplain forest that had been shifting in time and species had just been moving around in this area. Finally 5 million years ago and at the end of the Miocene period, the Amazon broke through to the west and we can see here actually a high diversity emerging right on the Amazon where it flows towards the Atlantic Ocean. This is actually an artefact when I say caused by isolation or population north and south of the river, so right on the river we get a lot of extra species in these graphs. Now there are a lot of changes happening during the very late period. In the Pleistocene there is an increased diversification in the savannas of southern Brazil to Argentina, and along the Andes region (2.5-1.5 Mya) and later (during the last 1.5 Mya) it happened in Patagonia and in the highest parts of the Andes. And note now in this final period, nothing more happens in the tropical lowland rainforest. In the past people believed for a long time that species richness in the featureless lowland rainforest was caused by vegetational changes during a glacial period and that the rainforest broke up into refuges during glacial periods and populations became isolated. This idea is now dead and it happened long before. The diversification in the Amazon area was actually driven by landscape dynamics up through the upper Tertiary, which involved these enormous inundations and development of swamp formation and finally the infilling with sedimentation fans, and in the end erosion and establishment of the new river channel to the Atlantic, and few tropical forest birds would want to cross such rivers, so they form barriers.
