Phytogeographical relations of the Andean dry valleys of Bolivia

Abstract

Aim The objective of this study is to examine the phytogeographical affinities of the Andean dry valleys of Bolivia in order to contribute to a better understanding of the Andean dry flora's distribution, origin and diversity. Particular emphasis is given to the analysis of the floristic connections of this flora with more austral parts of South America. Location The dry valleys of Bolivia are located in the Andes of the southern half of the country, at elevations between 1300 and 3200 m. Methods An extensive floristic list compiled by the author to evaluate plant diversity in these Andean regions was used as the base for this study. To accomplish this, all recorded genera and species were assigned, respectively, to 11 and 12 phytogeographical elements established previously by the author. Two phytogeographical spectra were thus obtained and analysed. Results At the genus level, the Andean dry valleys of Bolivia are clearly dominated by genera that have widespread distributions (cosmoplitan and subtropical genera). Many of these reached the Andes from the lowland region of the Chaco. At species level, Andean elements constitute more than 60% of the species total, most of which are restricted to the central‐southern Andes. This suggests that Chaco‐related and Andean genera had considerable levels of speciation in these valleys. Many genera and more than half the species have their northernmost distribution in the dry valleys of Bolivia, thereby underlining strong relationships with central‐southern South America (mainly Argentina, Paraguay and southern Brazil). The data supports the belief of the existence, in central‐southern Peru, of a floristic disjunction in dry to arid environments that separates a tropical dry flora north of this limit from a dry subtropical/warm temperate flora south of it. Main conclusions The Andean dry valleys of Bolivia are diverse plant communities with high levels of endemism (c. 18% of the species). The species of this region are more related to those present in central‐southern South America than to the flora of northern South America that ranges southwards to Peru. Many of the species have restricted distributions in the dry Andes of Bolivia and Argentina, and many genera of these dry valleys have their northernmost distribution in Bolivia/southern Peru, too. The data point to high levels of speciation also in the central Andes.

Representation of Andean Dry Ecoregions in the Protected Areas of Bolivia: The Situation in Relation to the New Phytogeographical Findings

“…Nonetheless, the latter also demonstrate high diversity and, in addition, they possess high levels of endemism, unlike lowland humid plant formations, which are composed predominantly of wide-ranging species. On the other hand, xeric ecosystems of Bolivia are floristically more related to the southern part of the Neotropic (Chile, Paraguay, and, especially, Argentina) (Lo´pez 2003b), forming a distinct biogeographical unit very different from northern Bolivia, where most of the PAs are concentrated. This criterion has not been considered either in the establishment of protected areas.…”

A New Collared Lizard (Tropidurus: Tropiduridae) Endemic to the Western Bolivian Andes and Its Implications for Seasonally Dry Tropical Forests

“…Tropidurus azurduyae is endemic to the Bolivian Montane Dry Forests (Olson et al, 2001), restricted to inter-Andean dry valleys from central and southern Bolivia (López, 2003a(López, , 2003bfig. 2).…”

“…The origin of high-altitude formations such as the dry valleys is contingent on the last phase of the Andean orogenesis, and consequently, the evolution of these areas is unlikely to be historically linked to ancient regions from central South America. López (2003b) pointed out that the Andes apparently reached half their present altitude only 10 Ma bp, and suggested that the intense speciation leading to the present flora found in the dry valleys of Bolivia likely took place in the Pliocene and extended even to the Pleistocene. In his phytogeographic analysis, Lopez (2003b) interprets the occurrence of very few genera and absence of endemic plant families in the inter-Andean dry valleys as evidence of a relatively recent origin of its FIGURE 11.…”

“…There, we found a new form of Tropidurus endemic to high-altitude formations of seasonally dry tropical forests known as "inter-Andean dry valleys" (López, 2003a(López, , 2003b. This new species had been previously overlooked as T. etheridgei Cei, 1982, whose distribution range has been long assumed to comprise besides the inter-Andean dry valleys of central and southern Bolivia also the Chaco of northwestern Argentina, southeastern Bolivia, and western Paraguay, rock outcrops in eastern Bolivia and central Brazil, and disjunct patches of sandy habitats in central and northeastern Brazil (Cei, 1982;Rodrigues, 1987;Dirksen and De La Riva, 1999;Carvalho, 2013).…”

An estimation of the floristic richness of Bolivia’s Andean dry valleys

“…From the 21 more diverse genera in the dry valleys of Bolivia, only four are Compositae (Lo´pez 2003a). Speciation events have been particularly intense mainly in Bromeliaceae and Cactaceae, but this seems to be related to life history traits such as succulence and CAM physiology (Cactaceae) or life form (epiphytes or rupicoles in the case of Bromeliaceae) (Lo´pez 2003b). In Compositae, on the contrary, its anemochorous dispersal mechanism would seem to preclude the necessary isolation which would foster speciation.…”