Pleistocene extinctions as drivers of biogeographical patterns on the easternmost Canary Islands

Abstract

Subtropical islands are often viewed as refuges where Quaternary climatic shifts driving global episodes of extinction were buffered. Island biodiversity, however, may have been impacted by climatic fluctuations at local scales, particularly in spatially heterogeneous island systems. In this study, we generated a conceptual framework for predicting the potential impact of Pleistocene extinctions on the biogeographical pattern of the Canarian spermatophyte flora, with a focus on the easternmost Canarian islands (ECI). Then, we performed an exhaustive bibliographic revision (270 studies) to examine whether taxonomic, phylogenetic and phylogeographical data support our predictions. Although molecular information is limited for many lineages, the available data suggest that the majority of extant ECI plant taxa may be the result of relatively recent (<1 Ma) dispersal from surrounding insular and mainland areas. Different lines of evidence are compatible with the idea of a Pleistocene period of frequent lineage extirpation on ECI. Extinction may thus have provided new ecological opportunities for recent (re)colonization, with some cases of recent establishment mediated by facilitation. Considering background extinction on ECI, we describe five general patterns of colonization for Canarian plant lineages. In addition to factors related to island ontogeny and long‐distance dispersal, we suggest that Pleistocene extinctions may have significantly contributed to extant biogeographical patterns in the Canarian archipelago, such as the biased distribution ranges of island plants and the low endemic richness on ECI. This new scenario provides testable hypotheses for future studies dealing with the phylogeography, taxonomy and conservation of terrestrial biodiversity on the Canarian islands, and possibly, on other near‐shore islands.

Colonization history of the Canary Islands endemic Lavatera acerifolia, (Malvaceae) unveiled with genotyping‐by‐sequencing data and niche modelling

“…The highest nucleotide diversity in Lanzarote‐Fuerteventura (D, Appendix S2: Table S2) is also consistent with non‐extirpation. According to García‐Verdugo, Caujapé‐Castells, Illera, et al (), persistence of eastern populations is more frequent in recently diverged groups (<0.8 Ma) like Phoenix (Saro et al, ) and Rumex (Talavera et al, ). Since Villa‐Machío et al () inferred an early Pleistocene split of L. acerifolia from its sister species, L. maritima , the persistence of old populations in the eastern islands could be noteworthy.…”

“…As an alternative to the island progression rule model for L. acerifolia , García‐Verdugo, Caujapé‐Castells, Illera, et al () proposed extinctions in the eastern islands during the Pleistocene followed by recolonization events. Such extinctions and recolonizations, in principle, may have been facilitated by the low topographical complexity of Lanzarote and Fuerteventura, which offer few micro‐refuges except for the Famara and Morro del Halconcillo massifs (Reyes‐Betancort, Guerra, Guma, Humphries, & Carine, ).…”

“…The highest nucleotide diversity in Lanzarote-Fuerteventura (D, Appendix S2: Table S2) is also consistent with non-extirpation. According to García-Verdugo, Caujapé-Castells, Illera, et al (2019), persistence of eastern populations is more frequent in recently diverged groups (<0.8 Ma) like…”

Iconic, threatened, but largely unknown: Biogeography of the Macaronesian dragon trees (Dracaena spp.) as inferred from plastid DNA markers

“…Such an estimate agrees well with the discovery of fossil dragon tree imprints dating back to the late Pliocene (Marrero, 2013). Under the temporal framework depicted by fossil and molecular data, it is quite probable that, following successful dispersal, the islands provided Dracaena with habitat suitability throughout episodes of widespread extinction, such as those derived from Quaternary climatic oscillations (reviewed in García-Verdugo & al., 2019c; see also Schüßler & al., 2019).…”

“…Sunding (1979), for instance, cited Dracaena as an example of colonization of the Cape Verde archipelago by African source populations already extinct in the mainland; he regarded as unlikely the alternative of dispersal from an area located 1400 km away to the north (i.e., direct dispersal from the Canarian archipelago). The impact of extinction on mainland and easternmost island populations of Dracaena during the Pleistocene probably limits the accuracy of our biogeographic reconstructions at regional scales (García-Verdugo & al., 2019c), but what the information available to date clearly rules out is the possibility that the extant mainland population could have acted as a direct source of Cape Verde colonizers (Figs. 3B, 4).…”