Evidence for mega‐landslides as drivers of island colonization

Abstract

Aim How non‐dispersive taxa colonize islands is generalized as being by wind, or rafting, with the implicit assumption that such events involve one (wind) or a few (rafting) individuals. However, because of the evolutionary time‐scale for colonization events, the fit of individual species to a conceptual model of wind or rafting is difficult to assess. Here, we describe an alternative testable geological model for inter‐island colonization that can result in larger effective founding population sizes than traditionally accepted colonization mechanisms. We then test for the fit of genetic data to this model using weevils from the Laparocerus tessellatus species complex. Location Canary Islands. Methods Using a combination of geological data for the Canary Islands, and mtDNA data from a weevil radiation within the Canary Islands, we test three species‐level predictions for mega‐landslides as drivers of oceanic rafting between islands and subsequent speciation: (1) colonization should involve multiple female lineages, (2) founding lineages should have a common geographical origin, consistent with a mega‐landslide event, and (3) colonization direction should be consistent with ocean currents. Results Both individual‐level and population‐level analyses support a mega‐landslide event as the driver of colonization from the island of Tenerife to La Palma. At least four female lineages colonized La Palma from Tenerife, with the geographical range of ancestral sequences to these four lineages describing the limits of the La Orotava mega‐landslide in Tenerife. Main conclusions In the context of island biogeographical theory, mega‐landslides may be an important driver of colonization, and subsequent lineage diversification. They provide a framework for hypothesis testing using genetic data from species, or closely related species, with ranges that encompass landslides and potential areas of colonization.

Climate drives community‐wide divergence within species over a limited spatial scale: evidence from an oceanic island

“…), led to partial seaward collapse, estimated between 4.1 and 4.7 Ma (Walter et al ) of c . 15 km 2 of surface area (García‐Olivares et al ). A more than 4 million‐year‐old topographic footprint of the Anaga mega‐landslide is visible today as steep northern slopes and an approximately 115 m drop in elevation between sites 4 and 5 (Fig.…”

“…The absence of younger volcanoclastics on Anaga indicate minimal impact from intense volcanic activity over the last several million years in the centre and south of the island (Carracedo ). Additionally, while most of the northern flank of Tenerife has suffered catastrophic flank collapses, some as recently as 150 Ka (thousand years ago) (García‐Olivares et al ), only one such flank collapse is known for the Anaga Peninsula, estimated to have occurred 4.1–4.7 Ma (Walter et al ). Thus, the Anaga peninsula represents a relatively geologically stable region, where millennial‐scale erosional activity and climate variation have been more consequential than catastrophic geological events, at least over the last 3 Ma.…”

Island biogeography: Taking the long view of nature’s laboratories

“…Viable seeds of dozens of plant species eaten by Canarian island lizards (Gallotia atlantica) have been found in pellets of predatory birds, capable of interisland movements (79), while 63% of the Azorean native flora (most of which are not endemic) have unspecialized diaspores (80). Similarly, the survival of snails and beetles swallowed by birds allows for their movement between islands (81), and even exceptional geophysical events, including volcano flank collapses, have been invoked as potentially explaining particular colonization events (82). Comparative analysis of the Galápagos flora rather remarkably suggests that the availability of suitable habitat on the islands provides a more general explanation of species assembly than dispersal limitation (83).…”

Extending phylogeography to account for lineage fusion

“…Oceanic islands are considered natural laboratories for studying evolution, and they provide a setting where near‐instantaneous merging of two or more genetically divergent lineages could occur. For example, mega‐landslide events brought about by volcanic flank collapse can create large volumes of floating organic material that enable synchronous rafting of many individuals from one island to another (García‐Olivares et al., ), and subsequent volcanic events could drive extinction of the remaining source population on its island of origin. Even within an island, new connections between long isolated populations can establish rapidly via geologically‐driven changes (Garrick et al., ; Waters, Craw, Youngson, & Wallis, ).…”