Mainland Counterparts Research Articles

Living on an Island: Start-Ups, Spatial Heterogeneity and Remote Entrepreneurial Ecosystems

In this paper we focus specifically on start-ups in remote island entrepreneurial ecosystems (EEs) and consider the differences between these entrepreneurs compared to their mainland Scottish and UK counterparts. We find that Island new start-up entrepreneurs tend to be older, less well educated, more likely to be female, and less likely to be from an ethnic minority. They borrow similar amounts of start-up capital than their mainland counterparts and are equally likely to survive. Despite their geographical remoteness, this suggests that entrepreneurial activity makes a meaningful contribution to their respective EEs.

The tale of the rattle: Using rattle size to understand growth and sexual dimorphism in an insular population of rattlesnakes (Crotalus oreganus caliginis).

Islands have played a key role in our understanding of rapid evolution. A large body of literature has examined morphological changes in response to insularity and isolation, which has yielded useful generalizations about how animals can adapt to live in very small geographic areas. However, understanding the evolution of morphological variation in insular populations often requires detailed data sets on longitudinal patterns of growth and development, and such studies typically necessitate long-term mark-recapture on a large sample of individuals. Rattlesnakes provide a unique opportunity to address some of these difficulties because the addition of rattle segments to the rattle string occurs with regular periodicity and their size directly correlates with the body size of the snake at the time of the ecdysis cycle generating the segment. Here, we used a large database of rattle segment sizes recorded from island (Isla Coronado Sur, Baja California, Mexico) and mainland (Camp Pendleton, California, United States) populations of Western Rattlesnakes (Crotalus oreganus and C. o. caliginis) that separated approximately 10,000 years ago to compare body sizes at different ecdysis cycles, which allowed us to assess differences in growth rates and patterns of sexual size dimorphism. Our results show that rattlesnakes on Isla Coronado Sur appear to be born smaller and grow more slowly than their mainland counterparts, resulting in a "dwarfed" island population. However, despite significant differences in body size, both populations exhibited the same degree of sexual dimorphism. Our study demonstrates the potential to use rattle characteristics to recover detailed estimates of fundamental demographic parameters.

Rectifying a century of misidentifications: a taxonomic re-evaluation of sipo snakes (Colubridae: Chironius) on Trinidad

The island of Trinidad has several endemic reptile species that in some cases are morphologically indistinguishable, or almost so, from their mainland counterparts. In particular, many snakes from the island have not been examined thoroughly with modern scientific methods and may therefore be misidentified. At least two species of sipo snakes (Chironius carinatus, C. septentrionalis) are reported to inhabit Trinidad, both being considered species already inhabiting the mainland, though their identities are based solely on morphology. Here, we evaluate the molecular distinctiveness of these Trinidadian snakes and assess their relationships to other members of the genus. We constructed a multi-locus data set (12S rRNA, 16S rRNA, cyt b, ND4, cmos, NT3, Rag-1, Rag-2) including novel sequences and those available on GenBank to perform Bayesian and maximum likelihood phylogenetic analyses. Our phylogenetic reconstruction elucidates the identity of both Trinidad species, which have been misidentified since their discovery, and we provide a literature review of their taxonomic history. More specifically, our results suggest that the Trinidad population of Chironius carinatus is an undescribed species, that we describe herein as Chironius nigelnoriegai sp. nov., and is the sister to C. flavopictus. Our results also demonstrate that the Trinidad population previously identified as C. septentrionalis is instead the mainland species C. cochranae, a member of a clade with C. foveatus, C. laurenti, and C. multiventris. Finally, we generated a time tree and inferred that our new species separated from C. flavopictus approximately 4 million years ago in the Pliocene, a time when the island of Trinidad detached from Northern Venezuela. This work contributes to a better understanding of species diversity of Trinidad and we hope that it assists in conservation efforts towards this important endemic region. These findings support the prospect of rapid speciation on Trinidad and implies that more extensive surveys of island squamates will reveal additional cryptic diversity. http://zoobank.org/urn:lsid:zoobank.org:pub:500DB91B-62CD-4051-9831-0BEEAC64C8E2

Paradoxical Exception to Island Tameness: Increased Defensiveness in an Insular Population of Rattlesnakes.

Island tameness results largely from a lack of natural predators. Because some insular rattlesnake populations lack functional rattles, presumably the consequence of relaxed selection from reduced predation, we hypothesized that the Santa Catalina Island, California, USA, population of the southern Pacific rattlesnake (Crotalus helleri, which possesses a functional rattle), would exhibit a decrement in defensive behavior relative to their mainland counterparts. Contrary to our prediction, rattlesnakes from the island not only lacked tameness compared to mainland snakes, but instead exhibited measurably greater levels of defensiveness. Island snakes attempted to bite 4.7 times more frequently as we endeavored to secure them by hand, and required 2.1-fold more time to be pinned and captured. When induced to bite a beaker after being grasped, the island snakes also delivered 2.1-fold greater quantities of venom when controlling for body size. The additional venom resulted from 2.1-fold larger pulses of venom ejected from the fangs. We found no effects of duration in captivity (2-36 months), which suggests an absence of long-term habituation of antipredator behaviors. Breeding bird surveys and Christmas bird counts indicated reduced population densities of avian predators on Catalina compared to the mainland. However, historical estimates confirmed that populations of foxes and introduced mammalian predators (cats and pigs) and antagonists (herbivorous ungulates) substantially exceeded those on the mainland in recent centuries, and therefore best explain the paradoxically exaggerated defensive behaviors exhibited by Catalina's rattlesnakes. These findings augment our understanding of anthropogenic effects on the behaviors of island animals and underscore how these effects can negatively affect human safety.

Genetic Basis and Evolution of Structural Color Polymorphism in an Australian Songbird.

Island organisms often evolve phenotypes divergent from their mainland counterparts, providing a useful system for studying adaptation under differential selection. In the white-winged fairywren (Malurus leucopterus), subspecies on two islands have a black nuptial plumage whereas the subspecies on the Australian mainland has a blue nuptial plumage. The black subspecies have a feather nanostructure that could in principle produce a blue structural color, suggesting a blue ancestor. An earlier study proposed independent evolution of melanism on the islands based on the history of subspecies divergence. However, the genetic basis of melanism and the origin of color differentiation in this group are still unknown. Here, we used whole-genome resequencing to investigate the genetic basis of melanism by comparing the blue and black M. leucopterus subspecies to identify highly divergent genomic regions. We identified a well-known pigmentation gene ASIP and four candidate genes that may contribute to feather nanostructure development. Contrary to the prediction of convergent evolution of island melanism, we detected signatures of a selective sweep in genomic regions containing ASIP and SCUBE2 not in the black subspecies but in the blue subspecies, which possesses many derived SNPs in these regions, suggesting that the mainland subspecies has re-evolved a blue plumage from a black ancestor. This proposed re-evolution was likely driven by a preexisting female preference. Our findings provide new insight into the evolution of plumage coloration in island versus continental populations, and, importantly, we identify candidate genes that likely play roles in the development and evolution of feather structural coloration.

Global patterns of plumage color evolution in island-living passeriform birds

Island environments have the potential to change evolutionary trajectories of morphological traits in species relative to their mainland counterparts due to habitat and resource differences, or by reductions in the intensity of social or sexual selection. Latitude, island size, and isolation may further influence trait evolution through biases in colonization rates. We used a global dataset of passerine plumage color as a model group to identify selective pressures driving morphological evolution of island animals using phylogenetically-controlled analyses. We calculated chromaticity values from red and blue scores extracted from images of the majority of Passeriformes and tested these against the factors hypothesized to influence color evolution. In contrast to predictions based on sexual and social selection theory, we found consistent changes in island female color (lower red and higher blue chromaticity), but no change in males. Instead, island size and distance from mainland and other islands influenced color in both sexes, reinforcing the importance of island physiognomy in shaping evolutionary processes. Interactions between ecological factors and latitude also consistently influenced color for both sexes, supporting a latitudinal gradient hypothesis. Finally, patterns of color evolution varied among families, indicating taxon-specific microevolutionary processes in driving color evolution. Our results show island residency influences color evolution differently between sexes, but the patterns in both sexes are tempered by ecological, island characteristics, and phylogenetic effects that further vary in their importance among families. The key role of environmental factors in shaping bird plumage on islands further suggests a reduced importance of sexual and social factors in driving color evolution.

Differences in phenotypic variance between old and young congeneric species on a small island

AbstractAimInsular environments theoretically promote within‐species phenotypic variance, in part but not only because insular species enjoy a lower number of trophic interactions than their mainland counterparts. However, environmental factors apparently confound empirical comparisons between insular and mainland systems. To address this issue, we studied sympatric, congeneric species from the same small island, but that stemmed from separate colonization events. We predicted that the time since the species had colonized the island would correlate positively with the within‐species variance in morphometrics.LocationLifu island, New Caledonia, South Pacific.TaxaZosterops inornatus, Z. minutus, Z. lateralis (Passeriformes).MethodsWe measured seven morphological traits and used principal component analysis to compute axes of variation.ResultsThe within‐species variance in bill size and in feet/tail ratio corrected for body size increased with the estimated time since the species had been on the island. A similar but non‐significant trend existed for body size and bill width.Main ConclusionsThe morphometrics of the three species of Zosterops birds from Lifu supported the hypothesis that insular environments promote within‐species phenotypic variance, and cast a new light on the role of competition in the erosion of phenotypic variance.

Adaptation to the High-Arctic island environment despite long-term reduced genetic variation in Svalbard reindeer

Typically much smaller in number than their mainland counterparts, island populations are ideal systems to investigate genetic threats to small populations. The Svalbard reindeer (Rangifer tarandus platyrhynchus) is an endemic subspecies that colonized the Svalbard archipelago ca. 6,000-8,000 years ago and now shows numerous physiological and morphological adaptations to its arctic habitat. Here, we report a de-novo chromosome-level assembly for Svalbard reindeer and analyze 133 reindeer genomes spanning Svalbard and most of the species' Holarctic range, to examine the genomic consequences of long-term isolation and small population size in this insular subspecies. Empirical data, demographic reconstructions, and forward simulations show that long-term isolation and high inbreeding levels may have facilitated the reduction of highly deleterious-and to a lesser extent, moderately deleterious-variation. Our study indicates that long-term reduced genetic diversity did not preclude local adaptation to the High Arctic, suggesting that even severely bottlenecked populations can retain evolutionary potential.

Insularity determines nestling sex ratio variation in Egyptian vulture populations.

Variation in offspring sex ratio, particularly in birds, has been frequently studied over the last century, although seldom using long-term monitoring data. In raptors, the cost of raising males and females is not equal, and several variables have been found to have significant effects on sex ratio, including food availability, parental age, and hatching order. Sex ratio differences between island populations and their mainland counterparts have been poorly documented, despite broad scientific literature on the island syndrome reporting substantial differences in population demography and ecology. Here, we assessed individual and environmental factors potentially affecting the secondary sex ratio of the long-lived Egyptian vulture Neophron percnopterus. We used data collected from Spanish mainland and island populations over a ca. 30-year period (1995-2021) to assess the effects of insularity, parental age, breeding phenology, brood size, hatching order, type of breeding unit (pairs vs. trios), and spatial and temporal variability on offspring sex ratio. No sex bias was found at the population level, but two opposite trends were observed between mainland and island populations consistent with the island syndrome. Offspring sex ratio was nonsignificantly female-biased in mainland Spain (0.47, n = 1112) but significantly male-biased in the Canary Islands (0.55, n = 499), where a male-biased mortality among immatures could be compensating for offspring biases and maintaining a paired adult sex ratio. Temporal and spatial variation in food availability might also have some influence on sex ratio, although the difficulties in quantifying them preclude us from determining the magnitude of such influence. This study shows that insularity influences the offspring sex ratio of the Egyptian vulture through several processes that can affect island and mainland populations differentially. Our research contributes to improving our understanding of sex allocation theory by investigating whether sex ratio deviations from parity are possible as a response to changing environments comprised by multiple and complexly interrelated factors.

Evolutionary history of an island endemic, the Azorean common quail.

Oceanic islands are characterized by conditions that favour diversification into endemic lineages that can be very different from their mainland counterparts. This can be the result of fast phenotypic divergence due to drift or the result of slower adaptation to local conditions. This uniqueness can obscure their evolutionary history. Here we used morphological, stable isotope, genetic and genomic data to characterize common quails (Coturnix coturnix) in the Azores archipelago and assess the divergence from neighbouring common quail populations. Historical documents suggested that these quails could have a recent origin associated with the arrival of humans in the last centuries. Our results show that Azorean quails constitute a well-differentiated lineage with small size and dark throat pigmentation that has lost the migratory ability and that diverged from mainland quail lineages more than 0.8 mya, contrary to the notion of a recent human-mediated arrival. Even though some Azorean quails carry an inversion that affects 115 Mbp of chromosome 1 and that has been associated with the loss of the migratory behaviour in other common quail populations, half of the analysed individuals do not have that inversion and still do not migrate. The long coexistence and evolution in isolation in the Azores of two chromosomal variants (with and without the inversion) is best explained by balancing selection. Thus, a unique and long evolutionary history led to the island endemic that we know today, C. c. conturbans.

Genetics of behavioural evolution in giant mice from Gough Island.

The evolution of behaviour on islands is a pervasive phenomenon that contributed to Darwin's theory of natural selection. Island populations frequently show increased boldness and exploration compared with their mainland counterparts. Despite the generality of this pattern, the genetic basis of island-associated behaviours remains a mystery. To address this gap in knowledge, we genetically dissected behaviour in 613 F2s generated by crossing inbred mouse strains from Gough Island (where they live without predators or human commensals) and a mainland conspecific. We used open field and light/dark box tests to measure seven behaviours related to boldness and exploration in juveniles and adults. Across all assays, we identified a total of 41 quantitative trait loci (QTL) influencing boldness and exploration. QTL have moderate effects and are often unique to specific behaviours or ages. Function-valued trait mapping revealed changes in estimated effects of QTL during assays, providing a rare dynamic window into the genetics of behaviour often missed by standard approaches. The genomic locations of QTL are distinct from those found in laboratory strains of mice, indicating different genetic paths to the evolution of similar behaviours. We combine our mapping results with extensive phenotypic and genetic information available for laboratory mice to nominate candidate genes for the evolution of behaviour on islands.

GEOGRAPHIC VARIATIONS IN THE SHAPE OF THE UPPER TOOTHROW OF THE ARTCIC FOX (<i>VULPES LAGOPUS</i> L. 1758): EFFECTS OF ASYMMETRY AND ALLOMETRY

Geographic variations in the shape of the upper cheek toothrow were studied using geometric morphometrics. For this, 288 specimens from 19 localities (North America, Eurasia, and Pacific and Arctic islands) were employed. Monomorphism of the toothrow for mainland foxes, both from North America and Eurasia, as well as the foxes from Greenland and St. Lawrence Island was found. The Arctic foxes of four Pacific island populations, i.e. two from the Commander Islands and two from the Pribilof Islands, differ significantly from the mainland counterparts in toothrow shape. The Arctic foxes from the Mednyi Island, the Bering Island and the Pribilof Islands differ from each other by toothrow shape as well. The Mednyi Island Arctic foxes show the shortest toothrow, a wide hard palate, and the most massive teeth. On the contrary, the Pribilof Islands Arctic foxes are the most small-toothed. Allometry does not affect geographic variations in the shape of the Arctic fox toothrow. High-level fluctuating asymmetry is found in the Mednyi Island and St. George Island Arctic foxes. Most probably the high level of fluctuating asymmetry is conditioned by both the extremely low genetic diversity as the result of a dramatic numbers decline in the recent past and the strong impact of heavy metals as the result of a coastal diet. We suppose that the same reasons. i.e. low genetic diversity and coastal diet, could have determined the high level of fluctuating asymmetry of the Arctic fox toothrow on the St. George Island.

Differences in seed morphometrics of representative orchids native to North America and Hawaii using scanning electron microscopy

Ultrastructure and dimensions of whole seed, embryo, and testa cells of 10 orchid species native to North America and Hawaii are reported. Seeds of seven terrestrials (Cleistes bifaria, Isotria medeoloides, Liparis elata, L. hawaiensis, Platanthera holochila, P. integrilabia, and P. leucophaea), two epiphytes (Encyclia tampensis, Epidendrum nocturnum), and one semi-aquatic (Habenaria repens) orchid were studied by light and scanning electron microscopy. In contrast to the epiphytes and the semi-aquatic orchid, seeds of terrestrial species were larger in size evidenced by a small length/width ratio, had greater seed volume, a larger number of testa cells, and embryos with the highest mean area, supporting the existing literature. Interestingly, seeds of both Hawaiian species differed noticeably from their mainland counterparts (L. hawaiensis vs. L. elata; P. holochila vs. P. integrilabia and P. leucophaea). Our study lends support for differences between genera, but also within at least two genera (Liparis, Platanthera), for orchids occupying different habitats separated by thousands of km (Hawaii, Florida). For orchids threatened with immediate extinction in North America and worldwide, a better understanding of seed morphometrics, and especially the structure and function of the testa, may be useful in developing more effective protocols aimed at in vitro seed germination.

Obama in the Americas: The Politics of Hope and Disappointment

The aim of this article is to analyze what accounted for the hope Caribbean leaders and the general Caribbean population had regarding U.S. engagement in the region with the election of Barack Obama. The paper provides a brief analysis of Obama’s foreign policy in the Americas, with particular focus on the small island developing states in the Caribbean region. Utilising public discourse (online discussions and local news coverage), the paper explores the affection and the benefit of the doubt that was given to Obama as president, despite the historical asymmetrical relationship and experience of American foreign policy in the Caribbean and Latin America. The paper draws on the long history and experience of U.S. engagement in Latin America and the Caribbean broadly, but focuses on the smaller island nations of the Caribbean as they generally find themselves in more precarious economic, political, and social situations than their larger mainland counterparts. The paper also provides a review of some highlighted events in the region over the eight years of Obama’s presidency, including a discussion on the role of “blackness” in the Caribbean and the Caribbean Diaspora in the United States. The analysis shows that while the Caribbean harbors deep affection for Obama, his policies were no different from his predecessors. His policies toward the region were no more progressive or consultative or less hegemonic and dictatorial than previous American presidents. The affection and benefit of the doubt given to Obama had little to do with policies and more to do with “skinship” on the one hand and the dependent mindset of many Caribbean leaders on the other hand.

The ‘island syndrome’ is an alternative state

AbstractAimIn the half‐century since publication of the Theory of Island Biology, ecologists have come to recognize the importance of predation as a decisive determinant of alternate states in many ecosystems. Island species are notorious for their vulnerability to introduced predators, yet the strength of island predator regimes has not been fully incorporated into our understanding of the forces that structure island consumer communities.LocationThe Greater and Lesser Antilles.TaxonBirds andAnolislizards.MethodsField surveys of sclerophyll and rainforest sites on islands ranging in size from 3.5 km2Terre‐de‐Haut to 76,000 km2Hispaniola.ResultsEvidence gathered in the 1970s and 1980s shows that Antillean anoles live at higher densities on fewer resources, grow more slowly, reproduce later and live longer than mainland counterparts in conformity with the ‘island syndrome’. Data from this period show that Antillean bird communities display density overcompensation, community saturation, size‐structured foraging guilds, low species diversity and low species packing, all traits consistent with the island syndrome and a regime of low predation and intense competition. Mainland species and communities display none of these features.Main conclusionsI propose that the island syndrome is an alternative state that distinguishes low‐predation island communities from high‐predation mainland counterparts. It follows that strong mainland predation regimes tend to prevent island species from colonizing. Conversely, invasion‐resistant, size‐structured island communities, despite low species diversity, prevent mainland species from colonizing islands. These predictions are experimentally testable withAnolislizards and, if confirmed, could set island biogeography on a new course.

Home range and activity patterns of the Critically Endangered endemic pygmy raccoon of Cozumel Island, México

AbstractIndividuals from island and continental mammal populations have shown a number of differences in their behavioral ecology. We predicted that, like other island carnivores exhibiting dwarfism, the pygmy raccoon (Procyon pygmaeus), a Critically Endangered carnivore endemic to Cozumel Island, México, would show differences in its home ranges and activity patterns when compared to its mainland counterpart, the racoon, P. lotor. We radio-tracked 11 individuals (six males, five females) from February to July 2017 and used location data derived from triangulation to estimate the home range size, diel activity patterns, and distances traveled of pygmy raccoons. Individuals showed an average home range size between 96.9 ± 18.8 ha (95% minimum convex polygon) and 123.3 ± 31.2 ha (95% fixed kernel). Home ranges of males (109.4–142.8 ha) were larger than those of females (81.8–99.9 ha). Average home ranges were in the lower extreme of those reported for continental raccoons. Activity patterns of pygmy raccoons generally begin at sunset and continue up to 04:00 with rare activity peaks during the day; there were no significant differences in activity patterns between sexes. Data on spatial needs of individuals, and differences between sexes or insular versus continental populations have implications for conservation planning and management.

Recent and rapid ecogeographical rule reversals in Northern Treeshrews

Two of the most-studied ecogeographical rules describe patterns of body size variation within species. Bergmann’s rule predicts that individuals have larger body sizes in colder climates (typically at higher latitudes), and the island rule predicts that island populations of small-bodied species average larger in size than their mainland counterparts (insular gigantism). These rules are rarely tested in conjunction or assessed across space and time simultaneously. We investigated these patterns in the Northern Treeshrew (Tupaia belangeri) using museum specimens collected across a wide spatial and temporal range. Contrary to Bergmann’s rule, size increases with temperature in T. belangeri, a signal that is highly consistent across space and time. We also show that these rules are intertwined: Bergmann’s rule is reversed on the mainland but holds on islands, and therefore the island rule is upheld at higher, but not lower, latitudes. Moreover, we demonstrate a rapid reversal of both rules over time. The mechanism behind these inversions remains unclear, though temperature and precipitation are significant predictors of body size. Ecogeographical rules rely on the assumption of a constant relationship between size and the factors driving its variation. Our results highlight the need to question this assumption and reevaluate these rules in the context of accelerating and uneven climate change.

Epigenetics and island-mainland divergence in an insectivorous small mammal.

Geographically isolated populations, specifically island-mainland counterparts, tend to exhibit phenotypic variation in many species. The so-called island syndrome occurs when different environmental pressures lead to insular divergence from mainland populations. This phenomenon can be seen in an island population of Nova Scotia masked shrews (Sorex cinereus), which have developed a specialized feeding habit and digestive enzyme compared to their mainland counterparts. Epigenetic modifications, such as DNA methylation (DNAm), can impact phenotypes by altering gene expression without changing the DNA sequence. Here, we used a de novo masked shrew genome assembly and a mammalian methylation array profiling 37 thousand conserved CpGs to investigate morphological and DNA methylation patterns between island and mainland populations. Island shrews were morphologically and epigenetically different than their mainland counterparts, exhibiting a smaller body size. A gene ontology enrichment analyses of differentially methylated CpGs implicated developmental and digestive system related pathways. Based on our shrew epigenetic clock, island shrews might also be aging faster than their mainland counterparts. This study provides novel insight on phenotypic and epigenetic divergence in island-mainland mammal populations and suggests an underlying role of methylation in island-mainland divergence.

Evolution of vocal performance and song complexity in island birds

Oceanic islands share distinctive characteristics thought to underlie a set of parallel evolutionary trends across islands and taxonomic groups – including life‐history traits, morphology and visual signals. To which extent acoustic signals also change in parallel on islands is less clear. Some important processes associated with insularity, such as founder effects and reduced sexual selection, could lead to a decrease in vocal performance and song complexity on islands. In a field‐based study, we recorded 11 insular species and their closest mainland relatives. Out of the 11 species pairs, 6 live in the tropics (São Tomé/Mount Cameroon) and 5 in the temperate region (Madeira/southern France). For each species, we measured two proxies of vocal performance (song duration and syllable rate) and one proxy of song complexity (syllable diversity). This study did not recover a clear relationship between the island environment and song traits. If as expected, syllable rate was lower in island species than in their mainland counterparts, the two other proxies showed no clear island–mainland pattern of divergence. Several factors may explain the absence of reduction for song duration and syllable diversity. Among those, relaxation of interspecific competition on islands may have led to an increase in syllable diversity, or correlations between song variables may have constrained song evolution. More studies on island species are needed to draw a better picture of divergence patterns and go beyond the confounding ecological factors that could explain peculiar song characteristics in islands.

Rapid morphological change in a small mammal species after habitat fragmentation over the past half‐century

AbstractAimTo compare the rapid shifts in body size of mainland and island populations of a native rodent and examine the mechanisms underlying these changes.LocationThousand Island Lake, China, which was created in 1959 when the Xin'anjiang Dam was constructed for generating hydroelectricity.TaxonThe Chinese white‐bellied rat,Niviventer confucianus.MethodsField surveys were conducted from 2015 to 2018 to collect data on body size of the rodents from a set of islands and nearby mainland sites. We constructed multiple linear models to examine the relationships between body size (length and mass) of rodents and biological variables (predators, competitors and food availability). We also conducted structural equation modelling (SEM) by constructing models via confirmatory path analysis.ResultsAll island populations ofN.confucianushad significantly larger body size (both body mass and body length) than their mainland counterparts. Moreover, populations on small and more isolated islands had larger body size than their relatives on big islands. The relative absence of predators (large‐bodied mammals, snakes and raptors) on islands was most strongly associated with shifts in the body size of rodents. The documented changes occurred after only a half‐century of fragmentation.Main conclusionsThe observed rapid body enlargement of rodents after habitat fragmentation is consistent with a release from predation pressure. SEM indicated that island area, rather than island isolation, had positive effects on the abundance of predators, interspecific competitors and food resources, which then had an indirect impact on body size of the rodents. In this study, we report a remarkably rapid case of mammal morphological shifts in a small mammal in response to habitat fragmentation. Given the omnipresence of dams and other anthropogenic disturbances, our findings suggest that a wave of rapid phenotypic shifts in terrestrial vertebrates is taking place in the Anthropocene.