**3.1. Historical associations between biogeography and diversification**

Many studies identified that past biogeographic movements (i.e., dispersals) between regions acted as a trigger for species diversification. This recent tendency to identify dispersals as drivers of biological diversification have increased with time (**Figure 1**). This tendency is related with the growing recognition of dispersal not only as a process able to generate congruent distributional patterns [11, 49, 61, 72], but also as a driver of species diversification [41]. It seems that the traditional and senseless dispute about whether vicariance or dispersal explains biotic distribution is a thing of the past [34, 49]. Both biogeographical events contribute to explain current and past geographic distributions and explain how biodiversity evolved in some regions. Accordingly, it is necessary to evaluate simultaneously which of these events were more prevalent through the biogeographic history of a taxa.

Theoretically, dispersal can promote exceptional shifts in species diversification by ecological opportunity (e.g., absence of related competitors) in a new colonized region or climate regime [1, 32, 33, 71, 73]. When lineages disperse to these new selective regimes they are likely to experience ecological release that can promote increases in speciation rates [33, 73]. Ecological opportunity can facilitate changes in diversification dynamics after a dispersal event [33, 73]. This is partially supported by evidence showing that dispersal events did not occur randomly across geography, and for some groups colonizing islands it was a notable increase in speciation rates after that events [4, 16, 21, 56, 57, 61]. For instance, dispersal of the palm tribe Trachycarpeae to different island systems promoted parallel diversifications connected with climatic and geological changes [4]. For bird clades distributed in the Indo-Pacific archipelago, species diversification rates increased on islands where few dispersal events were inferred, whereas clades occupying islands with high immigration rates exhibited constancy in diversification rates [16]. In the case

**Figure 1.** A hypothetical example showing inference of dispersal and vicariance and shifts in diversification dynamics across the phylogenetic diversification of a taxa. Nodes labeled with circles denote the position in the tree where it was inferred a dispersal (square) or a vicariance event (circles). Nodes labeled with stars denote where shifts in macroevolutionary regimes occurred. These shifts might involve increase in speciation rates or decrease in extinction rates or shifts in diversification dynamics from a time-dependent process to diversity-dependent cladogenesis (star). Under a dispersal scenario, where a lineage colonizes a new region with ecological opportunity, it is expected that ecologically relevant traits evolved through a pattern of niche divergence (dash). Whether all dispersal events promote speciation through ecological opportunity, it is expected that all events generated the same pattern of niche-trait divergence. By contrast, in a vicariance event, where the emergence of geographical barriers (e.g., a mountain uplift) promotes allopatric speciation, it is expected that ecologically relevant traits evolved little (i.e., phylogenetic niche conservatism) or under a neutral (drift) process in response to the changing environment (cross). Similarly, it is expected that all vicariant events generated the same pattern of niche conservatism or neutral evolution. Many other dispersal or vicariance events can be nested in the phylogeny; therefore, the inference of an event does not preclude that subsequent speciation events occur in sympatry or allopatry.

of Malagasy vangids, early dispersal from Africa to Madagascar promoted an increase in species diversification rates by ecological opportunity followed by a decline through time suggesting an ecological limit for this adaptive radiation [57].

Although these studies suggest a historical association between one or several dispersal events and shifts in net species diversification rates, it is still not clear which mechanisms were involved in this link between biogeography and macroevolution. Even more, it is not clear exactly how these past biogeographic events facilitate speciation in some regions and not in others or the mode of speciation involved in each event.

In contrast to the role of dispersal, vicariance has been associated as the only valid explanation for current distributional patterns and speciation for traditional biogeographers (e.g., Refs. [23, 45, 46]). However, few studies reviewed identified a vicariance event as a trigger of species diversification. Although these associations are congruent with the hypothesis of speciation by vicariance [38], it is still unknown whether the emergence of geographical barriers promoted habitat and reproductive isolation in taxa examined. For instance, rapid Andean uplift during the Miocene, with the concomitant climate changes, likely promoted allopatric speciation in *Heliotropium* plant lineages, which adapted to new arid conditions in southern South America [31]. Similarly, the Miocene uplift of the Qinghai-Tibetan plateau promoted allopatric speciation in Asteraceae clades plants [27] and *Rheum* plants [66]. These two clades of plants evolved as a response of temperature changes and the apparition of dry habitat conditions. It is likely that climate changes facilitated bursts of diversification [19, 27, 66]. Again, although these studies show an association between vicariance and species diversification, likely mediated through climate change or emergence of new barriers, it is not clear which mechanisms were involved here. All these studies suggest that we lack the ecological and evolutionary processes in these narrative biogeographic studies and we should look forward to identify at least which main processes underlying these historical associations.

It is evident that dispersal and vicariance events can be associated, either in a narrative or quantitative way, with shifts in species diversification. The link can be inferred directly in some cases [4, 41]; however, again the mechanisms operating behind these events are unknown. Although it is necessary to identify these evolutionary or ecological mechanisms, it is still not clear how these mechanisms can be disentangled. I consider that a full integration of current phylogenetic comparative methods with modern parametrical biogeographical methods and incorporation of ecologically relevant traits might offer new avenues to understand how biodiversity was generated after dispersal or vicariance events.
