Colonization Of Islands Research Articles

Climatic niche pre-adaptation facilitated island colonization followed by budding speciation in the Madeiran ivy (Hedera maderensis, Araliaceae).

The path followed by species in the colonization of remote oceanic islands ultimately depends on their phylogenetic constraints and ecological responses. In this study, we aim to evaluate the relative role of geographical and ecological forces in the origin and evolution of the Madeiran ivy (Hedera maderensis), a single-species endemic belonging to the western polyploid clade of Hedera. To determine the phylogenetic placement of H. maderensis within the western polyploid clade, we analyzed 40 populations (92 individuals) using genotyping-by-sequencing and including Hedera helix as outgroup. Climatic niche differences among the study species were evaluated using a database with 867 records representing the entire species ranges. To test species responses to climate, 13 vegetative and reproductive functional traits were examined for 70 populations (335 individuals). Phylogenomic results revealed a nested pattern with H. maderensis embedded within the south-western Iberian H. iberica. Gradual niche differentiation from the coldest and most continental populations of H. iberica to the warm and stable coastal population sister to H. maderensis parallels the geographical pattern observed in the phylogeny. Similarity in functional traits is observed for H. maderensis and H. iberica. The two species show leaves with higher specific leaf area (SLA), lower leaf dry matter content (LDMC) and thickness and fruits with lower pulp fraction than the other western polyploid species H. hibernica. Acquisition of a Macaronesian climatic niche and the associated functional syndrome in mainland European ivies (leaves with high SLA, and low LDMC and thickness, and fruits with less pulp content) was a key step in the colonization of Madeira by the H. iberica/H. maderensis lineage, which points to climatic pre-adaptation as key in the success of island colonization (dispersal and establishment). Once in Madeira, budding speciation was driven by geographical isolation, while ecological processes are regarded as secondary forces with a putative impact in the lack of further in situ diversification.

The ScMo‐350 site, Haumi, Moʻorea (Society Islands): Preliminary analysis of coastal occupation spanning the colonization phase to classic phase

ABSTRACTIn the Society Islands, multi‐phase coastal sites with successive occupations spanning several centuries have been difficult to find and have been poorly studied, resulting in a vague understanding of this archipelago's founding cultural complex and its adaptations to specific island environments through time. Discovery and excavation of ScMo‐350, a well‐stratified coastal site in Haumi, Moʻorea, Society Islands, provides robust sample sizes for understanding the timing and function of early Māʻohi coastal settlements and their constellation of use through time. My discussion of the site focuses on four topics: methodological issues for identifying early colonization sites in Central Eastern Polynesia; site stratigraphy and dating; the timing of island colonization on Moʻorea and its comparison to the Faʻahia site on Huahine; and preliminary analysis of ScMo‐350 sub‐surface features and artifacts to understand site function and its change through time. Bayesian analysis of short‐lived samples from ScMo‐350's earliest deposits and those from the Faʻahia site are described in an effort to refine our understanding of the Society Islands’ Colonization Phase.

Global Patterns in Island Colonization during the Holocene

Analysis of the spatial and temporal structure of global island colonization allows us to frame the extent of insular human cultural diversity, model the impact of common environmental factors cross-culturally, and understand the contribution of island maritime societies to big historical processes. No such analysis has, however, been undertaken since the 1980s. In this paper we review and update global patterns in island colonization, synthesizing data from all the major island groups and theaters and undertaking quantitative and qualitative analysis of these data. We demonstrate the continued relevance of certain biogeographic and environmental factors in structuring how humans colonized islands during the Holocene. Our analysis also suggests the importance of other factors, some previously anticipated—such as culturally ingrained seafaring traditions and technological enhancement of dispersal capacity—but some not, such as the relationship between demographic growth and connectivity, differing trophic limitations impinging on colonizing farmers versus hunter-gatherer-foragers, and the constraining effects of latitude. We also connect colonization with continental dynamics: both the horizontal transmission of farming lifestyles earlier in the Holocene, and subsequent centrifugal processes associated with early state formation later in the Holocene.

Ancient Maltese genomes and the genetic geography of Neolithic Europe

SummaryArchaeological consideration of maritime connectivity has ranged from a biogeographical perspective that considers the sea as a barrier to a view of seaways as ancient highways that facilitate exchange. Our results illustrate the former. We report three Late Neolithic human genomes from the Mediterranean island of Malta that are markedly enriched for runs of homozygosity, indicating inbreeding in their ancestry and an effective population size of only hundreds, a striking illustration of maritime isolation in this agricultural society. In the Late Neolithic, communities across mainland Europe experienced a resurgence of hunter-gatherer ancestry, pointing toward the persistence of different ancestral strands that subsequently admixed. This is absent in the Maltese genomes, giving a further indication of their genomic insularity. Imputation of genome-wide genotypes in our new and 258 published ancient individuals allowed shared identity-by-descent segment analysis, giving a fine-grained genetic geography of Neolithic Europe. This highlights the differentiating effects of seafaring Mediterranean expansion and also island colonization, including that of Ireland, Britain, and Orkney. These maritime effects contrast profoundly with a lack of migratory barriers in the establishment of Central European farming populations from Anatolia and the Balkans.

The Syngameon Enigma.

Despite their evolutionary relevance, multispecies networks or syngameons are rarely reported in the literature. Discovering how syngameons form and how they are maintained can give insight into processes such as adaptive radiations, island colonizations, and the creation of new hybrid lineages. Understanding these complex hybridization networks is even more pressing with anthropogenic climate change, as syngameons may have unique synergistic properties that will allow participating species to persist. The formation of a syngameon is not insurmountable, as several ways for a syngameon to form have been proposed, depending mostly on the magnitude and frequency of gene flow events, as well as the relatedness of its participants. Episodic hybridization with small amounts of introgression may keep syngameons stable and protect their participants from any detrimental effects of gene flow. As genomic sequencing becomes cheaper and more species are included in studies, the number of known syngameons is expected to increase. Syngameons must be considered in conservation efforts as the extinction of one participating species may have detrimental effects on the survival of all other species in the network.

Peopling island rainforests: global trends from the Early Pleistocene to the Late Holocene

ABSTRACTThis paper is a cross-comparative examination of how tropical forested islands were populated by humans. It first describes the unique ecological conditions of these environments, how they fluctuated during glacial cycles, and the challenges and affordances they provided people. The paper then explores the global archaeological record, classifying modes of colonisation that led insular tropical forests to be populated. These modes include terrestrial colonisation followed by insularisation (Mode A), maritime colonisation followed by major landmass reconfiguration (Mode B), maritime colonisation of uninhabited islands that always remained insular (Mode C), and maritime colonisation of already inhabited islands (Mode D). Finally, the paper discusses how, amongst Homo sapiens, ongoing dynamism between human adaptive behaviours and environmental flux stimulated processes of diversification, specialisation, and connectivity in these crucial ecologies; by contrast, archaic hominins like Homo erectus, Homo floresiensis, and Homo luzonensis may have found changes associated with forest expansion and insularity extremely challenging.

Interspecific Hybridization and Island Colonization History, not Rarity, Most Strongly Affect the Genetic Diversity in Diospyros a Clade of Mascarene-Endemic Trees.

Many factors shape the genetic diversity of island-endemic trees, with important implications for conservation. Oceanic island-endemic lineages undergo an initial founding bottleneck during the colonization process and subsequently accumulate diversity following colonization. Moreover, many island endemics occur in small populations and are further threatened by anthropogenic factors that cause population declines, making them susceptible to losses in genetic diversity through genetic drift, inbreeding, and bottlenecks. However, life-history traits commonly found in trees, such as outcrossing mechanisms, long lifespans, and a propensity for interspecific hybridization, may help buffer against losses of genetic variation. To assess the relative importance of colonization history, rarity, and distribution in shaping genetic diversity of island-endemic trees, we conducted a comparative population genomic analysis of 13 species of Diospyros (Ebenaceae) endemic to the Mascarene Islands that differ in island colonization history, distribution, population size, and IUCN threat status. We genotyped 328 individuals across the islands using 2b-RADseq, compared genetic diversity both among and within species, and assessed patterns of genetic structure. Genetic diversity did not vary significantly by IUCN status, but we found that species that co-occur with others on the same intermediate-aged island (Mauritius) had much greater genetic diversity than those that occur solitarily on an island (Réunion and Rodrigues), likely because of greater interspecific hybridization among species with overlapping distributions and processes related to time since island colonization. Results presented here were used to determine priority localities for in situ and ex situ conservation efforts to maximize the genetic diversity of each Mascarene Diospyros species.

Single-Island Endemism despite Repeated Dispersal in Caribbean Micrathena (Araneae: Araneidae): An Updated Phylogeographic Analysis

Island biogeographers have long sought to elucidate the mechanisms behind biodiversity genesis. The Caribbean presents a unique stage on which to analyze the diversification process, due to the geologic diversity among the islands and the rich biotic diversity with high levels of island endemism. The colonization of such islands may reflect geologic heterogeneity through vicariant processes and/ or involve long-distance overwater dispersal. Here, we explore the phylogeography of the Caribbean and proximal mainland spiny orbweavers (Micrathena, Araneae), an American spider lineage that is the most diverse in the tropics and is found throughout the Caribbean. We specifically test whether the vicariant colonization via the contested GAARlandia landbridge (putatively emergent 33–35 mya), long-distance dispersal (LDD), or both processes best explain the modern Micrathena distribution. We reconstruct the phylogeny and test biogeographic hypotheses using a ‘target gene approach’ with three molecular markers (CO1, ITS-2, and 16S rRNA). Phylogenetic analyses support the monophyly of the genus but reject the monophyly of Caribbean Micrathena. Biogeographical analyses support five independent colonizations of the region via multiple overwater dispersal events, primarily from North/Central America, although the genus is South American in origin. There is no evidence for dispersal to the Greater Antilles during the timespan of GAARlandia. Our phylogeny implies greater species richness in the Caribbean than previously known, with two putative species of M. forcipata that are each single-island endemics, as well as deep divergences between the Mexican and Floridian M. sagittata. Micrathena is an unusual lineage among arachnids, having colonized the Caribbean multiple times via overwater dispersal after the submergence of GAARlandia. On the other hand, single-island endemism and undiscovered diversity are nearly universal among all but the most dispersal-prone arachnid groups in the Caribbean.

A complex genetic architecture underlies mandibular evolution in big mice from Gough Island.

Some of the most compelling examples of morphological evolution come from island populations. Alterations in the size and shape of the mandible have been repeatedly observed in murid rodents following island colonization. Despite this pattern and the significance of the mandible for dietary adaptation, the genetic basis of island-mainland divergence in mandibular form remains uninvestigated. To fill this gap, we examined mandibular morphology in 609 F2s from a cross between Gough Island mice, the largest wild house mice on record, and mice from a mainland reference strain (WSB). Univariate genetic mapping identifies 3 quantitative trait loci (QTL) for relative length of the temporalis lever arm and 2 distinct QTL for relative condyle length, 2 traits expected to affect mandibular function that differ between Gough Island mice and WSB mice. Multivariate genetic mapping of coordinates from geometric morphometric analyses identifies 27 QTL contributing to overall mandibular shape. Quantitative trait loci show a complex mixture of modest, additive effects dispersed throughout the mandible, with landmarks including the coronoid process and the base of the ascending ramus frequently modulated by QTL. Additive effects of most shape quantitative trait loci do not align with island-mainland divergence, suggesting that directional selection played a limited role in the evolution of mandibular shape. In contrast, Gough Island mouse alleles at QTL for centroid size and QTL for jaw length increase these measures, suggesting selection led to larger mandibles, perhaps as a correlated response to the evolution of larger bodies.

Ecology, conservation status, and phylogenetic placement of endemic Pristimantis frogs (Anura: Craugastoridae) in Trinidad and Tobago and genetic affinities to northern Venezuela

AbstractTrinidad and Tobago are home to three endemic species in the anuran genus Pristimantis, of which two (Pristimantis charlottevillensis and Pristimantis turpinorum) occur in Tobago alone and the third (Pristimantis urichi) is present on both islands. Earlier, the IUCN assessed the conservation status of these species as: P. urichi, Endangered (EN); P. charlottevillensis, Least Concern (LC); P. turpinorum, Vulnerable (VU). However, these assessments were based on very little field‐based evidence. Here, we present survey results which contributed to reassessments as LC, VU and Data Deficient for these three species, respectively. Despite the close proximity of Trinidad to northern Venezuela, the islands do not share any Pristimantis species with the mainland, which holds a rich endemicity of Pristimantis regionally. In this study, we used genetic sequencing from several island populations and compared them to northern Venezuelan endemics to assess genetic divergence for the first time. The time tree analyses found that only the northern Tobago species P. turpinorum is closely related to mainland Pristimantis, with a genetic split dating to the Late Miocene, suggesting a vicariant event of mainland and island species. Pristimantis urichi, although identical between the two islands, remains highly divergent from the mainland species. Similar results were found for P. charlottevillensis. In addition, there was a high level of divergence between P. urichi and P. charlottevillensis. These findings indicate different island colonization events by different lineages. Sequencing other Venezuelan species remains pivotal to unravel the complexity of the colonization episodes in the region, likely influenced by the changing topography and multiple connection and isolation episodes of the islands by eustatic sea‐level changes.

Ecological specialization, rather than the island effect, explains morphological diversification in an ancient radiation of geckos.

Island colonists are often assumed to experience higher levels of phenotypic diversification than continental taxa. However, empirical evidence has uncovered exceptions to this 'island effect'. Here, we tested this pattern using the geckos of the genus Pristurus from continental Arabia and Africa and the Socotra Archipelago. Using a recently published phylogeny and an extensive morphological dataset, we explore the differences in phenotypic evolution between Socotran and continental taxa. Moreover, we reconstructed ancestral habitat occupancy to examine if ecological specialization is correlated with morphological change, comparing phenotypic disparity and trait evolution between habitats. We found a heterogeneous outcome of island colonization. Namely, only one of the three colonization events resulted in a body size increase. However, in general, Socotran species do not present higher levels or rates of morphological diversification than continental groups. Instead, habitat specialization explains better the body size and shape evolution in Pristurus. Particularly, the colonization of ground habitats appears as the main driver of morphological change, producing the highest disparity and evolutionary rates. Additionally, arboreal species show very similar body size and head proportions. These results reveal a determinant role of ecological mechanisms in morphological evolution and corroborate the complexity of ecomorphological dynamics in continent-island systems.

Genetic data from the extinct giant rat from Tenerife (Canary Islands) points to a recent divergence from mainland relatives.

Evolution of vertebrate endemics in oceanic islands follows a predictable pattern, known as the island rule, according to which gigantism arises in originally small-sized species and dwarfism in large ones. Species of extinct insular giant rodents are known from all over the world. In the Canary Islands, two examples of giant rats, †Canariomys bravoi and †Canariomys tamarani, endemic to Tenerife and Gran Canaria, respectively, disappeared soon after human settlement. The highly derived morphological features of these insular endemic rodents hamper the reconstruction of their evolutionary histories. We have retrieved partial nuclear and mitochondrial data from †C. bravoi and used this information to explore its evolutionary affinities. The resulting dated phylogeny confidently places †C. bravoi within the African grass rat clade (Arvicanthis niloticus). The estimated divergence time, 650 000 years ago (95% higher posterior densities: 373 000–944 000), points toward an island colonization during the Günz–Mindel interglacial stage. †Canariomys bravoi ancestors would have reached the island via passive rafting and then underwent a yearly increase of mean body mass calculated between 0.0015 g and 0.0023 g; this corresponds to fast evolutionary rates (in darwins (d), ranging from 7.09 d to 2.78 d) that are well above those observed for non-insular mammals.

Modelling the Pleistocene colonisation of Eastern Mediterranean islandscapes.

Predictive models have become an integral part of archaeological research, particularly in the discovery of new archaeological sites. In this paper, we apply predictive modeling to map high potential Pleistocene archaeological locales on the island of Cyprus in the Eastern Mediterranean. The model delineates landscape characteristics that denote areas with high potential to unearth Pleistocene archaeology while at the same time highlighting localities that should be excluded. The predictive model was employed in surface surveys to systematically access high probability locales on Cyprus. A number of newly identified localities suggests that the true density of mobile hunter-gatherer sites on Cyprus is seriously underestimated in current narratives. By adding new data to this modest corpus of early insular sites, we are able to contribute to debates regarding island colonisation and the role of coastal environments in human dispersals to new territories.

Phylogeography of cicadas on continental and oceanic islands in the northwestern Pacific region

AbstractAimGenetic differentiation of terrestrial organisms among islands is assumed to be affected by the geological history of the islands, such as the time elapsed since the formation of islands or straits. Cicadas are generally poor dispersers, but some cicada groups have colonised continental and oceanic islands and evolved into endemic species. Here, we focused on a cicada group in the northwestern Pacific region to reveal the association between intra‐ and interspecific genetic differentiation and the geological history of islands for cicadas on continental islands. We also clarified whether colonisation of oceanic islands was achieved by long‐distance dispersal or artificial introduction.LocationJapanese Archipelago, Ogasawara Islands, Ryukyu Archipelago.TaxonCicadas of the genus Meimuna (Hemiptera: Cicadidae).MethodsWe performed phylogenetic analysis, divergence time estimation, and ancestral area reconstruction using two mitochondrial and four nuclear gene sequences and population genetics analyses, including Bayesian skyline plotting using a mitochondrial gene sequence.ResultsMeimuna opalifera in the Japanese Archipelago, which was connected to the continent during the glacial periods, diverged from the continental populations 0.4 million years ago (Ma). In the Ryukyu Archipelago, which became disconnected from the continent earlier, two endemic species Meimuna kuroiwae and M. oshimensis diverged 2.4 Ma; these species showed differences in intraspecific genetic differentiation and range expansion. Furthermore, Meimuna iwasakii colonised the South Ryukyus from Taiwan Island later than 1.4 Ma, whereas M. boninensis, which is endemic to the oceanic Ogasawara Islands, diverged from M. kuroiwae in the Middle Ryukyus 1.04 Ma.Main conclusionsGenetic divergence among Meimuna species was larger on the continental islands that disconnected earlier, as was expected from the geological history of the islands. However, the pattern of intraspecific genetic differentiation differed between species within the same island region, possibly due to their ecological characteristics. In addition, colonisation of oceanic islands was achieved by long‐distance (possibly wind‐borne) dispersal from the continental islands. Thus, the formation of island cicada fauna was affected by islands’ geological history and species’ ecological characteristics, as well as accidental long‐distance dispersal events.

Evaluating the correlation between area, environmental heterogeneity, and species richness using terrestrial isopods (Oniscidea) from the Pontine Islands (West Mediterranean)

Area and environmental heterogeneity influence species richness in islands. Whether area or environmental heterogeneity is more relevant in determining species richness is a central issue in island biogeography. Several models have been proposed, addressing the issue, and they can be reconducted to three main hypotheses developed to explain the species-area relationship: (1) the area-per se hypothesis (known also as the extinction-colonisation equilibrium), (2) the random placement (passive sampling), and the (3) environmental heterogeneity (habitat diversity). In this paper, considering also the possible influence of geographic distance on island species richness, we explore the correlation between area, environmental heterogeneity, and species richness by using faunistic data of Oniscidea inhabiting the Pontine Islands, a group of five small volcanic islands and several islets in the Tyrrhenian Sea, located about 60 km from the Italian mainland. We found that the colonisation of large Pontine Islands may occur via processes independent of geographic distance which could instead be an important factor at a much smaller scale. Such processes may be driven by a combination of anthropogenic influences and natural events. Even in very small-size island systems, environmental heterogeneity mostly contributes to species richness. Environmental heterogeneity could influence the taxocenosis structure and, ultimately, the number of species of Oniscidea via direct and indirect effects, these last mediated by area which may or may not have a direct effect on species richness.

Rapid range expansion predicted for the Common Grackle (Quiscalus quiscula) in the near future under climate change scenarios

BackgroundClimate change due to anthropogenic global warming is the most important factor that will affect future range distribution of species and will shape future biogeographic patterns. While much effort has been expended in understanding how climate change will affect rare and declining species we have less of an understanding of the likely consequences for some abundant species. The Common Grackle (Quiscalus quiscula; Linnaeus 1758), though declining in portions of its range, is a widespread blackbird (Icteridae) species in North America east of the Rocky Mountains. This study examined how climate change might affect the future range distribution of Common Grackles.MethodsWe used the R package Wallace and six general climate models (ACCESS1-0, BCC-CSM1-1, CESM1-CAM5-1-FV2, CNRM-CM5, MIROC-ESM, and MPI-ESM-LR) available for the future (2070) to identify climatically suitable areas, with an ecological niche modelling approach that includes the use of environmental conditions.ResultsFuture projections suggested a significant expansion from the current range into northern parts of North America and Alaska, even under more optimistic climate change scenarios. Additionally, there is evidence of possible future colonization of islands in the Caribbean as well as coastal regions in eastern Central America. The most important bioclimatic variables for model predictions were Annual Mean Temperature, Temperature Seasonality, Mean Temperature of Wettest Quarter and Annual Precipitation.ConclusionsThe results suggest that the Common Grackle could continue to expand its range in North America over the next 50 years. This research is important in helping us understand how climate change will affect future range patterns of widespread, common bird species.

Human influence on brown trout juvenile body size during metapopulation expansion.

Change in body size can be driven by social (density) and non-social (environmental and spatial variation) factors. In expanding metapopulations, spatial sorting by means of dispersal on the expansion front can further drive the evolution of body size. However, human intervention can dramatically affect these founder effects. Using long-term monitoring of the colonization of the remote Kerguelen islands by brown trout, a facultative anadromous salmonid, we analyse body size variation in 32 naturally founded and 10 human-introduced populations over 57 years. In naturally founded populations, we find that spatial sorting promotes slow positive changes in body size on the expansion front, then that body size decreases as populations get older and local density increases. This pattern is, however, completely different in human-introduced populations, where body size remains constant or even increases as populations get older. The present findings confirm that changes in body size can be affected by metapopulation expansion, but that human influence, even in very remote environments, can fully alter this process.

How did the toad get over the sea to Skye? Tracing the colonisation of Scottish inshore islands by common toads (Bufo bufo)

Processes of island colonisation have long been of interest to biologists. Colonisation events themselves are rarely observed, but the processes involved may be inferred using genetic approaches. We investigated possible means of island colonisation by common toads (Bufo bufo) in western Scotland (the Isle of Skye and five neighbouring small islands), using evidence derived from nuclear microsatellites and mitochondrial (mt) DNA. Levels of microsatellite allelic richness for populations on Skye were high and comparable to adjacent mainland populations, but lower for populations on small islands. Pairwise measures of genetic distances between populations and a clustering algorithm were both suggestive of frequent gene flow between Skye and the mainland. For small islands the levels of genetic differentiation were higher, implying stronger isolation and no evidence for inbreeding. The distribution of mtDNA haplotypes broadly mirrored the genetic structure revealed by microsatellites. Reconciled with existing palaeoclimatological evidence, since the last glaciation, our findings rule out the possibility that the B. bufo populations stem from glacial refugia, or that recent anthropogenic transfer of toads is responsible for their current distribution. The most parsimonious explanation of our data is that the studied inshore islands have been repeatedly colonised via rafting from the mainland or neighbouring islands. This may give us insights into the processes likely to take place when ice sheets retreat poleward as a result of climate change. It also has implications for the colonisation of both native and invasive non-native species, and hence the biosecurity of island refugia.

Anthropogenic transitions from forested to human-dominated landscapes in southern Macaronesia

The extinction of iconic species such as the dodo and the deforestation of Easter Island are emblematic of the transformative impact of human colonization of many oceanic islands, especially those in the tropics and subtropics. Yet, the interaction of prehistoric and colonial-era colonists with the forests and forest resources they encountered can be complex, varies between islands, and remains poorly understood. Long-term ecological records (e.g., fossil pollen) provide the means to understand these human impacts in relation to natural change and variability pre- and postcolonization. Here we analyze paleoecological archives in forested landscapes of the Canary Islands and Cabo Verde, first colonized approximately 2,400 to 2,000 and 490 y ago, respectively. We demonstrate sensitivity to regional climate change prior to human colonization, followed by divergent but gradual impacts of early human settlement. These contrast with more rapid transformation in the colonial era, associated with significant increases in anthropogenic pressures. In the Canary Islands, at least two native tree taxa became extinct and lowland thermophilous woodlands were largely converted to agricultural land, yet relictual subtropical laurel forests persisted with limited incursion of nonnative species. In Cabo Verde, in contrast, thermophilous woodlands were depleted and substituted by open landscapes and introduced woodlands. Differences between these two archipelagos reflect the changing cultural practices and societal interactions with forests and illustrate the importance of long-term data series in understanding the human footprint on island ecosystems, information that will be critically important for current and future forest restoration and conservation management practices in these two biodiversity hotspots.

Mycorrhizal types influence island biogeography of plants

Plant colonization of islands may be limited by the availability of symbionts, particularly arbuscular mycorrhizal (AM) fungi, which have limited dispersal ability compared to ectomycorrhizal and ericoid (EEM) as well as orchid mycorrhizal (ORC) fungi. We tested for such differential island colonization within contemporary angiosperm floras worldwide. We found evidence that AM plants experience a stronger mycorrhizal filter than other mycorrhizal or non-mycorrhizal (NM) plant species, with decreased proportions of native AM plant species on islands relative to mainlands. This effect intensified with island isolation, particularly for non-endemic plant species. The proportion of endemic AM plant species increased with island isolation, consistent with diversification filling niches left open by the mycorrhizal filter. We further found evidence of humans overcoming the initial mycorrhizal filter. Naturalized floras showed higher proportions of AM plant species than native floras, a pattern that increased with increasing isolation and land-use intensity. This work provides evidence that mycorrhizal fungal symbionts shape plant colonization of islands and subsequent diversification.