The building of a biodiversity hotspot across a land-bridge in the Mediterranean

Abstract

Many of the macroevolutionary processes that have shaped present-day phylogenetic patterns were caused by geological events such as plate tectonics and temporary land-bridges. The study of spatial patterns of phylogenetic diversity can provide insights into these past events. Here we focus on a western Mediterranean biodiversity hotspot located in the southern Iberian Peninsula and northwest Africa, two regions that are separated by the Strait of Gibraltar. We explore the spatial structure of the phylogenetic relationships within and across large-scale plant assemblages. Significant turnover in terminal lineages tends to occur between landmasses, whereas turnover in deep lineages tends to occur within landmasses. Plant assemblages in the western ecoregions of this hotspot tend to be phylogenetically overdispersed but are phylogenetically clustered on its eastern margins. We discuss our results in the light of potential scenarios of niche evolution (or conservatism) and lineage diversification. The significant turnover between landmasses suggests a common scenario of allopatric speciation that could have been facilitated by the intermittent joining of the two continents. This may have constituted an important stimulus for diversification and the emergence of this western Mediterranean biodiversity hotspot.

Climatic and topographical correlates of plant palaeo- and neoendemism in a Mediterranean biodiversity hotspot

“…These new combinations and diversity of climatic and geological conditions have probably generated unoccupied environmental conditions providing an ecological opportunity for the diversification of certain lineages. Furthermore, centres of neoendemism on both sides of the Baetic-Rifan complex are constituted to a great extent by phylogenetically related species assemblages (Molina-Venegas et al, 2015a), which supports the hypothesis that the last opening of the Strait of Gibraltar favoured the parallel diversification of closely related lineages on both sides of the hotspot MolinaVenegas et al, 2015a). The 'Sierra Nevada-Filabres' ecoregion (Fig.…”

“…Recent progress in phylogenetic methods has allowed us to explicitly tackle the phylogenetic position of endemic species and explore the evolutionary history of species assemblages (see Mishler et al, 2014;Schmidt-Lebuhn et al, 2015). The incorporation of phylogenetic information may shed new light on the processes that generate and maintain spatial patterns of species endemism, as these processes leave tractable imprints on present-day phylogenies (Cantalapiedra et al, 2014;Molina-Venegas et al, 2015a).…”

Climate and plant community diversity in space and time

“…Global patterns of phylogenetic diversity in higher plants parallel the latitudinal gradient in species richness, supporting the interpretation that most modern lineages arose in tropicallike climates and have tended to conserve their climatic niches (8,73). This so-called tropical conservatism (or climatic niche conservatism) hypothesis, implying limited rates of transition into cold or arid climates, also appears consistent with the climatic gradients in phylogenetic diversity within many regions [e.g., the Mediterranean Basin (74) and China (75)]. The same hypothesis is also capable of predicting alternative patterns under certain circumstances; for example, where cold or arid conditions have persisted for a long time, where particular lineages have proliferated unusually rapidly in harsh environments, or where geographic barriers have limited the opportunities for preadapted lineages to colonize novel climates, taxonomic, and phylogenetic diversity may be expected to be elevated in cold or arid climates, in contrast to the general global patterns (8,76,77).…”

The widespread misconception about the Japanese major biogeographic boundary, the Watase line (Tokara gap), revealed by bibliographic and beta diversity analyses

“…Island area is also a significant determinant of island biota (the species-area relationship) [2,3]. In the case of land-bridge islands, a geohistory involving sea barrier and land-bridge formation is also an essential factor characterizing the terrestrial and freshwater biota on the island [4-7].…”