Geographical variation in the evolutionary diversity of tree communities across southern South America

Abstract

Aim To determine the principal drivers of variation in the evolutionary diversity of forest tree communities, with a focus on the temperate forests of South America.Location Forests across southern South America, extending from tropical forests in southern Brazil, to the temperate forests of southern Chile and Argentina. MethodsWe compiled a database of 742 forest tree community inventories spread over six countries and 12 biomes, or major vegetation types. In total, these inventories covered 3075 species of shrubs and trees. We combined this dataset with a temporally calibrated phylogeny that included all species. For each community, we evaluated multiple measures of evolutionary diversity, including phylogenetic diversity sensu stricto (PD), which is the sum of the branch lengths of a phylogeny that includes all species in a community, and its equivalent standardized for variation in species richness (ses.PD), which we refer to as lineage diversity. ResultsWe found that biome affiliation is the most important determinant of the evolutionary diversity of woody plant communities, with climate also showing a significant influence. Communities in wet evergreen tropical forest have the highest species richness and the highest PD, but the lowest lineage diversity, while temperate forests in southern South America show the lowest species richness and PD, but the highest lineage diversity.Main conclusions Our results contradict the idea that temperate floras represent recently derived, evolutionarily poor subsets of tropical floras. Rather, the high lineage diversity we find in the temperate forest communities supports the 'austral conservatism hypothesis', which states that the flora of southern South america has evolved independently from the Neotropical Domain over tens of millions of years. Our identification of the evolutionary distinctness and richness of this flora suggests that it deserves as much conservation attention as the more species-rich tropical forests of South America and that southern South American forests should not be lumped into the Neotropical Floristic Province.

Neotropical Forests from their Emergence to the Future Scenario of Climatic Changes

“…Therefore, RFs are still found on the vast Amazon domain and on the Atlantic, Pacific, and Caribbean windward coastlands-the latter three much more fragmented than original [14]. Additionally, RFs are also found as riverine seasonal forests across drylands, as well as temperate rain forests in the Southern Cone [10,29]. The scattered distribution SDF concentrates across the so-called Pleistocene Arc that surrounds the Amazon basin before stretching into Mesoamerica and the Caribbean [11,15,30].…”

“…In this way, many lineages, such as Aextoxicon, Citronella, Cryptocarya, Drimys, Gomortega, Laurelia, Persea, Laureliopsis, Legrandia, Nothofagus, Pitavia, and Podocarpus, have diversified outside the tropics, keeping their ancestral preference for temperate conditions. Although the southern floras are considerably poorer than their tropical counterparts, they have a higher lineage diversity, that is, they hold more diversity on broader groups, such as families, which means older diversification with higher conservatism of clades in the temperate floras [10,18]. There is also a high conservation of ancestral genetic polymorphism in SDF, which is due to factors such as their arrested dynamics (see session V), low immigration rates, and notorious discontinued distribution, whose combination results in a long persistence of SDF populations and also increasing the endemism levels [11,38].…”

“…Therefore, forests under different precipitation conditions may have similar growth periods, species compositions, and ecological traits [9]. It must be also stressed that the RF and SDF concepts are expanded here to include the southern temperate NF in spite of their strikingly distinct flora and environment [10].…”

Exploring the Concept of Lineage Diversity across North American Forests

“…In its most basic form, quantifying the number of lineages in assemblages could consist of counting the number of species. However, the term lineage diversity is generally applied when the units are not species, but a shallower or deeper evolutionary level, i.e., within or above the species taxonomic rank (see [5][6][7][8][9] for examples below species rank; see [10][11][12][13][14] for examples above species rank). In this paper, we focus on lineage diversity above the species rank.…”

“…Assemblage B has 4x as many lineages at 70 Ma, while Assemblage D has 4x as many lineages at 5 Ma. For this reason, researchers have suggested that the amount of PD an assemblage contains above or below that expected given its SR is a better measure of ALD [12,13]. However, if we were to follow that approach, then Assemblage C might be considered to have more ALD than Assemblage D (its ratio of PD:SR is twice that of Assemblage D), even though at all phylogenetic depths Assemblage D has the same or more lineages than Assemblage C. Clearly, more work is needed to determine which metrics derived from phylogenies may provide the best measures of ALD that integrate over evolutionary timescales.…”