The assembly of montane biotas: linking Andean tectonics and climatic oscillations to independent regimes of diversification in Pionus parrots

Abstract

The mechanisms underlying the taxonomic assembly of montane biotas are still poorly understood. Most hypotheses have assumed that the diversification of montane biotas is loosely coupled to Earth history and have emphasized instead the importance of multiple long-distance dispersal events and biotic interactions, particularly competition, for structuring the taxonomic composition and distribution of montane biotic elements. Here we use phylogenetic and biogeographic analyses of species in the parrot genus Pionus to demonstrate that standing diversity within montane lineages is directly attributable to events of Earth history. Phylogenetic relationships confirm three independent biogeographic disjunctions between montane lineages, on one hand, and lowland dry-forest/wet-forest lineages on the other. Temporal estimates of lineage diversification are consistent with the interpretation that the three lineages were transported passively to high elevations by mountain building, and that subsequent diversification within the Andes was driven primarily by Pleistocene climatic oscillations and their large-scale effects on habitat change. These results support a mechanistic link between diversification and Earth history and have general implications for explaining high altitudinal disjuncts and the origin of montane biotas.

Figure 1

Topologies generated by the combined analysis of cyt b and ND2 (2181 bp). Numbers in parenthesis indicate the number of specimens sampled. Boxes highlight the tree montane clades. (a) ML topology using the GTR+Γ model. Numbers along branches indicate ML bootstrap values greater than 50%/Bayesian posterior probabilities greater than 0.9. Solid circles indicate a bootstrap value greater than 95% and a posterior probability of 1.0. (b) MP topology. Numbers along branches are MP bootstrap values greater than 50% without/with the morphological characters included in the analysis. Solid circles indicate a bootstrap value greater than 95%.

Figure 2

Distribution and altitudinal ranges of the menstruus, chalcopterus and tumultuosus species groups. Phylogenetic relationships are based on ML analysis (figure 1a). See electronic supplementary material for detailed discussion about distributions and altitudinal ranges. Plates courtesy of William T. Cooper (Parrots of the world, 1st edn, 1973).

Figure 3

Distribution and altitudinal ranges of the sordidus and maximiliani species groups and P. fuscus. Phylogenetic relationships are based on ML analysis (figure 1a). See electronic supplementary material for detailed discussion about distributions and altitudinal ranges. Plates courtesy of William T. Cooper (Parrots of the world, 1st edn. 1973).

Figure 4

Bayesian Multidivtime chronogram based on the combined ND2 and cyt b datasets. Nodes 1 and 2 are fixed calibration points derived from a Bayesian Multidivtime analysis of RAG-2 data. Time scale is in millions of years. Numbered nodes correspond to those of table 1. Montane clades are shown in boxes. Shaded area shows estimated window of time during which montane/lowland vicariance occurred.