Islands as biological substrates: Continental

Abstract

Aim Describe the main geo‐physical features of the various sorts of marine islands that are associated with the continents and consider how the ontogenetic pathways of each landmass type might have shaped the hosted biotas. Location Global. Methods Review of the literature that underpins understanding of the “continental” marine islands, particularly those publications with biological, geological, geophysical, oceanographical and palaeoceanographical foci. Results Based on their geo‐physical settings, islands with continental basements/close connections to the continents can be assigned to one of nine categories: shelf, shelf volcano, orogenic margin, continental arc, continental fore‐arc, rifted arc‐raft, isolated raft atoll, isolated block and micro‐continental terrane. As each functions in a distinctive manner, this must have strongly imprinted the native biotas. Main conclusions “Continental” marine islands can be allocated to one of nine groups based on their respective geo‐physical locations. When geological time is considered, then the unique histories of each insular landmass type will have played a critical role in moulding the land‐locked faunal assemblages that have amassed and evolved atop them. Researchers investigating insular biotas, particularly those exploring biodiversity growth, may wish to accommodate these insights.

Biodiversity growth on the volcanic ocean islands and the roles of in situ cladogenesis and immigration: case with the reptiles

“…However our investigation indicates that the process is of minimal importance for the reptiles. While substantial marine-island reptile radiations have been documented (Losos and Schluter 2000, Siler et al 2011, Tallowin et al 2018, these are on the larger, usually older, landmasses comprising composite terranes and/or geologically complex pieces of crust built atop ophiolitic basement (Ali 2017(Ali , 2018, also see Meiri 2017). Reptile assemblages on individual volcanic ocean islands thus develop primarily through immigration.…”

“…Volcanic islands such as Milos and Santorini (eastern Mediterranean) are not oceanic; they are constructed upon crust that is 24-27 km thick (thinned continental) and easily connect (< 20 km) to other islands and large patches of sea-bed that during the Last Glacial Maximum would have been subaerial (verified using Ryan et al 2009). In the scheme of Ali (2018), they would be categorized as 'continental arc islands'. In any case, none of these excepted islands harbour reptiles that result from in situ diversification (Meiri unpubl.…”

“…For the lizards, a value of 108 km 2 was proposed based on the Phelsuma geckos on Rodrigues. This claim was bolstered following the identification of sister Hemidactylus gecko species on the 133 km 2 Abd Al Kuri Island (Garcia-Porta et al 2016) on the western end of the Socotra micro-continental terrane (Ali 2018). For snakes, Pyron and Burbrink (2014) reported a figure of 3707 km 2 (Leptotyphlops on Socotra).…”

Are island‐like systems biologically similar to islands? A review of the evidence

“…De-novo system biotic communities are initially dominated by successional colonists, either from adjacent systems or from the matrix, and eventually experience speciation events that produce 'neo-endemics' (i.e. Ali (2017Ali ( , 2018 reviewed the geo-physical origin of true islands and suggested that the traditional classification of islands into three groups (recent continental, ancient continental, and oceanic), introduced by Darwin and Wallace in the 19th century, is over-simplistic. In contrast, biota of fragmented systems, once contiguous with mainland communities, experience diversity relaxation and a high rate of extinction, and are therefore a relict subset of the original biota, supplemented by a few successful colonizers .…”

“…Here I focus both on the biogeographic theories that have received the most attention in the literature regarding ILS: species-area relationship (SAR), species-isolation relationship (SIR), and community composition structure (i.e. Gillespie and Roderick (2002) sought to categorize insular systems according to their origin -either 'de-novo' or 'fragment' islands, thus segregating the fundamental processes of community assembly (Warren et al 2015, but see also Ali 2017Ali , 2018. It is important to note that comparisons are made among ILS, between insular systems and their mainland, and between ILS and true islands, depending on available evidence.…”