Island Biogeography Research Articles

Macrophyte islands as an experimental model: new perspectives and a step-by-step protocol to access assumptions of Island Biogeography theory and habitat fragmentation

To evaluate whether artificially built macrophyte islands could be used as a short-term and cost-effective experimental model for the study of island biogeography and habitat fragmentation, 20 islands of two different sizes were built and fishes were sampled. Habitat complexity and source-island distance were standardized. A macrophyte bank 200 times larger than the islands was used as a source of individuals. The results show that, in four days, several fish species colonized both small and large islands. After four days, larger islands bore significantly more species than smaller ones. We raise the caveats and new perspectives for studies using this methodology, which can be largely applicable due to its cost-effectiveness in terms of materials, short time required, and flexibility.

Island area and remoteness shape plant and soil bacterial diversity through land use and biological invasion

Abstract Biodiversity is declining dramatically due to human‐driven land use change and biological invasion, but our knowledge of how such drivers influence plant and heterotroph diversity on island ecosystems remains limited. Historically island biogeography theory has focused solely on direct effects of island size and remoteness on biodiversity, but these factors can also indirectly affect species gain and/or loss through impacting land use change and biological invasion. We built the structural equation model to explore direct effects of island size and remoteness, and indirect effects of these factors via land use intensity and pinewood nematode invasion, on the diversity of plants and soil bacteria across 37 continental shelf islands in the largest land‐bridge archipelago in eastern China. As expected we found that increasing island area directly promoted plant diversity. However, land use intensity increased with island area which also promoted plant diversity, and loss of pine forest by the pinewood nematode invasion increased with island remoteness which reduced plant diversity. Island remoteness only indirectly reduced plant diversity through increasing pine forest loss. Soil bacterial diversity was directly negatively impacted by island remoteness, and indirectly negatively impacted by island remoteness through increased soil electrical conductivity likely caused by greater salinity from sea spray. Furthermore, soil bacterial diversity was indirectly promoted by island area through increased plant diversity and decreased soil electrical conductivity, and indirectly reduced by pine forest loss through decreased plant diversity. Our findings highlight that island biogeography theory has relevance to understanding human impacts in the Anthropocene, and that there is a need to more explicitly recognizing how island size and remoteness affect biodiversity not only directly, but also indirectly via their effects on human‐induced drivers of biodiversity, such as land use change and biological invasion. Read the free Plain Language Summary for this article on the Journal blog.

Phylogenetic relationships of the North American catfishes (Ictaluridae, Siluriformes): Investigating the origins and parallel evolution of the troglobitic species

Insular habitats have played an important role in developing evolutionary theory, including natural selection and island biogeography. Caves are insular habitats that place extreme selective pressures on organisms due to the absence of light and food scarcity. Therefore, cave organisms present an excellent opportunity for studying colonization and speciation in response to the unique abiotic conditions that require extreme adaptations. One vertebrate family, the North American catfishes (Ictaluridae), includes four troglobitic species that inhabit the karst region bordering the western Gulf of Mexico. The phylogenetic relationships of these species have been contentious, and conflicting hypotheses have been proposed to explain their origins. The purpose of our study was to construct a time-calibrated phylogeny of Ictaluridae using first-occurrence fossil data and the largest molecular dataset on the group to date. We test the hypothesis that troglobitic ictalurids have evolved in parallel, thus resulting from repeated cave colonization events. We found that Prietella lundbergi is sister to surface-dwelling Ictalurus and that Prietella phreatophila + Trogloglanis pattersoni are sister to surface-dwelling Ameiurus, suggesting that ictalurids colonized subterranean habitats at least twice in evolutionary history. The sister relationship between Prietella phreatophila and Trogloglanis pattersoni may indicate that these two species diverged from a common ancestor following a subterranean dispersal event between Texas and Coahuila aquifers. We recovered Prietella as a polyphyletic genus and recommend P. lundbergi be removed from this genus. With respect to Ameiurus, we found evidence for a potentially undescribed species sister to A. platycephalus, which warrants further investigation of Atlantic and Gulf slope Ameiurus species. In Ictalurus, we identified shallow divergence between I. dugesii and I. ochoterenai, I. australis and I. mexicanus, and I. furcatus and I. meridionalis, indicating a need to reexamine the validity of each species. Lastly, we propose minor revisions to the intrageneric classification of Noturus including the restriction of subgenus Schilbeodes to N. gyrinus (type species), N. lachneri, N. leptacanthus, and N. nocturnus.

Patterns and drivers of beta diversity across geographic scales and lineages in the Macaronesian flora

AbstractAimHow spatial, historical and ecological processes drive diversity patterns remains one of the main foci of island biogeography. We determined how beta diversity varies across spatial scales and among organisms, disentangled the drivers of this variation, and examined how, consequently, biogeographic affinities within and among archipelagos vary among land plants.LocationMacaronesia.TaxonBryophytes, pteridophytes, spermatophytes.MethodsSpecies turnover and nestedness were compared within and among archipelagos across taxonomic groups. The relationship between species turnover and nestedness, climatic, geological and geographic factors was analysed using generalized dissimilarity models.ResultsSpecies turnover, but not nestedness, increased with the geographic scale. This increment decreased from spermatophytes, pteridophytes and bryophytes, wherein the median turnover was less than half that in spermatophytes. Bryophytes exhibited a significantly higher nestedness and lower turnover than spermatophytes. Extant climatic conditions and island age contributed the most to all models but the importance of island age for bryophyte and pteridophyte turnover was marginal. Spermatophyte floras clustered by archipelago, whereas the clustering patterns in pteridophyte and bryophyte floras reflected macroclimatic conditions.Main ConclusionsThe lower increment of species turnover with spatial scale and the higher nestedness in bryophytes and pteridophytes than in spermatophytes reflect the variation in dispersal capacities and distribution ranges among land plants. Accordingly, extant climatic conditions contributed more to explain turnover in bryophytes and pteridophytes than in spermatophytes, whereas factors associated with dispersal limitations, including island age, geographic distance and archipelago structure, exhibited the reverse trend. The differences in beta diversity patterns, caused by different responses of Macaronesian land plant lineages to the main factors shaping their community composition, explain their different biogeographic affinities. These differences reflect a distinct origin and different mechanisms of speciation among Macaronesian land plant lineages and archipelagos.

The anthropogenic threat for insular microcrustacean fauna (Copepoda and Cladocera) – the case of Madeira Island

Substantial loss of biodiversity and the proliferation of invasive alien species can occur due to land cover anthropogenic transformations on islands. However, the effect of anthropogenic habitat modifications on the distribution of insular freshwater microcrustaceans is unknown. In the present paper, we examine the consequences of human activity on the insular diversity of microcrustaceans in the context of the theories of island biogeography and intermediate disturbances. The samples were collected in Madeira Island at 38 freshwater sampling sites with different anthropopressure. Morphology-based species identification of the copepods and cladocerans was supplemented with genetic analysis (COI) in some species. To estimate the species richness of the island, rarefaction, and extrapolation methods were used. Canonical Correspondence Analysis (CCA) was applied to assess the influence of geospatial and environmental variables on the species distribution. A total of 20 species belonging to six families were identified, of which 16 species are new to Madeira. There was low similarity between the fauna recorded and known previously on the island. The observed species richness was higher than the predictions by the island biogeography models for Madeira. CCA revealed a strong influence of anthropogenic land use on crustaceans. Anthropogenic transformations locally led to the depletion of fauna, but on the island scale they contributed to the increase of species richness including seven putative alien species. An increase in the artificial land cover and a decrease in the forest areas could lead to a further shift in the domination of non-indigenous microcrustaceans.

Science maps for biogeography—The field's place within the sciences and its change over the past quarter century

AbstractAimThe field of biogeography is often described as a hub between research disciplines. Here we apply science mapping to study how biogeography has changed and evolved between 1995 and April 2022, and to analyse the mix of disciplines used in this field. We explore how research foci have changed over time and if biogeographical topics have entered the public discourse.LocationLocal to global.TaxonAll taxa.MethodsWe created a semantic map of the field based on co‐occurrences of keywords or composite keywords from 40,000+ scientific papers published between the 1970s and April 2022, structuring these data into three hierarchical sets. A fourth set of Top 100 researchers was constructed in September 2022. To address our public‐discourse question, we used the Factiva archive of global media.ResultsFive core journals contained 14,386 papers (or 35.7% of the full set), while the remaining papers appeared in 2247 journals of which 59% included only one or two biogeographical papers. Since 1995, frequencies of keywords related to core concerns of biogeography have remained stable or even decreased, while ‘computing’ and ‘climate change’ have increased. There is an increasing association with Mathematics & Statistics, Computer Sciences, and Planning & Management, and a decreased association with Physical Geography. Biogeography‐related terms increasingly appearing in the public discourse are ‘biodiversity’, ‘urban nature’, ‘conservation’, ‘extinction’ and ‘rewilding’, while more technical concepts, such as ‘ecoregions’, ‘macroecology’ and ‘island biogeography’ remain at very low rates.Main ConclusionsBiogeographical research is moving towards the social sciences, probably linked to a growing concern over global environmental issues and the Anthropocene. It is difficult to disentangle to what extent the public discourse is influenced by biogeographical research or vice versa, but ‘rewilding’ and ‘extinction’ are examples of topics that began in basic ecological‐biogeographical research and are now debated publicly.

What Influences the Prevalence and Intensity of Haemoparasites and Ectoparasites in an Insular Lizard?

Island biogeography theories predict that characteristics such as island size, age, and isolation interplay in host-parasite dynamics. In this study, we analyzed haemogregarines of the Aegean wall lizard, Podarcis erhardii, to investigate how island characteristics relate to parasite prevalence and intensity. A previous assessment of 19 Greek island populations suggested that isolation time and host population density were key predictors of haemogregarines. Here, by combining microscopy and genetic techniques, we extend this previous study to four additional islands: Syros, Folegandros, Santorini and Nea Kameni. We also recorded the prevalence of ticks and mites, definitive hosts for these parasites. The genetically identified haemogregarines are part of a clade with parasites from other lizard species, including some considered as Karyolysus, but others assigned to Hepatozoon. The prevalence of these parasites differed significantly between islands, while their intensity did not. The presence of ticks was associated with endoparasite prevalence, and males were more frequently infected by haemogregarines than females. Combining our data with that of the previous study, we found no significant impact of the island age and area on parasite prevalence. We also confirmed the presence of the unrelated parasite genus Schellackia through microscopy and DNA sequencing, which is the first record of this genus in this host species. Our results further highlight the complexity of host-parasite systems.

Genomic data reveal contrasting patterns of divergence among island and mainland birds of the Eastern Mediterranean

Islands have been characterized as natural laboratories because of their distinct and often identifiable role in promoting genetic variation and population differentiation, but they have also been considered evolutionary sinks of biodiversity. Here, we extend classical studies of island biogeography based in the Eastern Mediterranean to compare genetic divergences and population structure among birds in insular and continental populations. We focused on populations of six passerine species (Short‐toed Treecreeper, Great Tit, Eurasian Wren, Eurasian Blackbird, Common Chaffinch and Sardinian Warbler) with breeding populations on the islands of Cyprus and Crete and compared those with a continental population from mainland Greece. We sampled 172 individuals from six species and used double‐digest RAD sequencing to examine population‐level genetic divergence and structure. Population structure analyses using single nucleotide polymorphisms revealed structure between the islands and mainland for all six species, and this was most pronounced in Short‐toed Treecreeper, Great Tit and Eurasian Wren. For all species with the exception of the Sardinian Warbler, the populations from the two islands were more differentiated from each other than either was from mainland Greece, reflecting variation in island colonization dynamics. Patterns ranged from pronounced population differentiation among populations, e.g. in Short‐toed Treecreeper, where taxonomic revisions are potentially warranted, to others with weak structure among insular and continental populations, such as in Common Chaffinch and Sardinian Warbler. Although some patterns are consistent with increased rates of genetic drift in smaller populations explaining greater differences among the island populations than either insular population has from continental source populations, in others, including in Eurasian Blackbird and Common Chaffinch, higher nucleotide diversity in Cyprus may reflect a demographic pattern of post‐glacial north‐westward expansion.

Geographic variation and biogeography of the greater Japanese shrew mole Urotrichus talpoides (Eulipotyphla: Talpidae)

The island rule has been generally studied as a morphological evolution between continents and islands. Recently, an evolution between islands of the larger main islands and smaller peripheral islands in Japan has been implied. This study revealed island–island biogeography and examined the island rule between islands. We studied the skull morphology of the greater Japanese shrew mole Urotrichus talpoides Temminck, 1841 (Eulipotyphla: Talpidae). Univariate and multivariate analyses were conducted on the basis of 20 measurements obtained from 296 specimens. Our results revealed morphological differences among islands, in the overall skull size, distance of the fourth premolar to the third molar in the upper and lower jaws (P4M3 and P4M3), and the slender–robust proportion of the rostrum and braincase. P4M3 and P4M3 were commonly larger in the peripheral island populations than in the main island populations. By contrast, the overall skull size and proportion of the rostrum and braincase diverged among the peripheral islands. Therefore, gigantism of P4M3 and P4M3 was suggested in the peripheral island populations, and the island rule was partially supported; however, the island–island morphological evolution should be considered to have a different direction from the island rule due to divergent morphology in small–large skull size and slender–robust proportion among peripheral island populations.

Variations in Soil Blue Carbon Sequestration between Natural Mangrove Metapopulations and a Mixed Mangrove Plantation: A Case Study from the World’s Largest Contiguous Mangrove Forest

Sundarban is the world's largest mangrove wetland. This study, conducted in 2016, to compare blue carbon sequestration with different natural metapopulations and a four-year-old Avicennia marina (30% area)-Rhizophora mucronata (70% area)-mixed mangrove plantation under anthropoganic stress. The aims of the study is to find out the variations in soil ecological function indicators (pH, electrical conductivity, bulk density, soil texture, available nitrogn, phosphorus and soil organic carbon) and key ecological service indicator (soil blue carbon pool) between sites. Simpson's Index of dominance, diversity and Shannon-Weiner Index revealed that all the sites are under ecological stress, with the Suaeda maritima-dominated mudflat having the least biodiversity. It is also revealed that pH and electrical conductivity were highest in Suaeda maritima and Phoenix padulosa-dominated metapopulations, whereas organic carbon was the highest under the mangrove plantation and Avicennia marina-dominated site. Available nitrogen was recorded highest in the community with the Sonneretia sp.-Avicennia marina association. The mixed mangrove plantation had the highest blue carbon pool. The species diversity was not found to be related with the distance from the nearby conserved mangrove forest, contrary to the island biogeography theory. This study concludes with a recommendation of mixed mangrove plantations to restore the degraded saline mudflats along the human settlements across the globe.

The island biogeography of human population size.

For decades, biogeographers have sought a better understanding of how organisms are distributed among islands. However, the island biogeography of humans remains largely unknown. Here, we investigate how human population size varies among 486 islands at two spatial scales. At a global scale, we tested whether population size increases with island area and declines with island elevation and nearest mainland, as is common in non-human species, or whether humans escape such biogeographic constraints. At a regional scale, we tested whether population sizes vary among islands within archipelagos according to the positioning of different cultural source pools. Results illustrate that on a global scale, human populations increased in size with island area, similar to non-human species, yet they did not decline in size with elevation and distance to nearest mainland. At a regional scale, human population size often varied among islands within archipelagos relative to the location of different cultural source pools. Despite broad-scale similarities in the geographical distribution of human and non-human species among islands, results from this study indicate that the island biogeography of humans may also be influenced by archipelago-specific social, political and historical circumstances.

The Importance of Including Spatial Autocorrelation When Modelling Species Richness in Archipelagos: A Bayesian Approach

One of the aims of island biogeography theory is to explain the number of species in an archipelago. Traditionally, the variables used to explain the species richness on an island are its area and distance to the mainland. However, increasing evidence suggests that accounting for other variables is essential for better estimates. In particular, the distance between islands should play a role in determining species richness. This work uses a Bayesian framework using Gaussian processes to assess whether distance to neighbouring islands (spatial autocorrelation) can better explain arthropod species richness patterns in the Azores Archipelago and in the Canary Islands. This method is flexible and allows the inclusion of other variables, such as maximum altitude above sea level (elevation). The results show that accounting for spatial autocorrelation provides the best results for both archipelagos, but overall, spatial autocorrelation seems to be more important in the Canary archipelago. Similarly, elevation plays a more important role in determining species richness in the Canary Islands. We recommend that spatial autocorrelation should always be considered when modelling an archipelago’s species richness.

A trait‐based approach to marine island biogeography

AbstractAimThe Island Biogeography Theory (IBT) and its multiple extensions explain species diversity patterns in insular systems. However, how these theories can predict the functional diversity patterns in island systems remains challenging. Here, we evaluated the predictions of the IBT, the General Dynamic Theory of Oceanic Island Biogeography (GDM) and the Glacial‐sensitive model of Island Biogeography (GSM) considering the functional diversity of reef fishes on islands.LocationTropical oceanic islands.TaxonActinopterygii.MethodWe combined literature data and online repositories to gather occurrence data and traits of reef fish species for 72 tropical oceanic islands. We then calculated five functional diversity indices (functional richness ‘FRic’, functional evenness ‘FEve’, functional divergence ‘FDiv’, functional over‐redundancy ‘FOR’ and functional vulnerability ‘FVul’). We used generalized additive mixed models to explore relationships among species richness and functional indices. Furthermore, we built Bayesian models to evaluate relationships between the functional diversity indices and several island features (isolation from the nearest reef, past and present reef area, and geological age) and two metrics that reflect the potential influence of Quaternary climatic changes (isolation from Quaternary refugia) and historical contingency (isolation from biodiversity centres).ResultsWe observed higher levels of FRic, FDiv and FOR on the Indo‐Pacific islands, whereas FEve and FVul showed higher values on the Atlantic and Eastern Pacific islands. We identified positive relationships between FRic, FDiv and FOR with species richness but negative relationships with FEve and FVul. We found that past and present reef areas best explained the variation in functional diversity among islands.Main ConclusionsThe functional diversity of reef fishes on oceanic islands showed a longitudinal gradient, which can be explained by differences in the evolutionary history among marine regions. Furthermore, past and present reef areas were found to be the best predictors of reef fish functional diversity on oceanic islands, extending the IBT, GDM and GSM for marine organisms within a trait‐based framework.

Can we ignore trait-dependent colonization and diversification in island biogeography?

The application of state-dependent speciation and extinction models to phylogenetic trees has shown an important role for traits in diversification. However, this role remains comparatively unexplored on islands, which can include multiple independent clades resulting from different colonization events. To explore whether assuming no dependence on traits leads to bias in inference on island dynamics, we extend an island biodiversity model, DAISIE (Dynamic Assembly of Islands through Speciation, Immigration, and Extinction) to include trait-dependent diversification simulations, and evaluate the robustness of the inference model which ignores this trait-dependence. Our results indicate that when the differences between colonization, extinction, and speciation rates between trait states are moderate, the model shows negligible error for a variety of island diversity metrics, suggesting that island diversity dynamics can be accurately estimated without the need to explicitly model trait dependence. We conclude that for many biologically realistic scenarios with trait-dependent diversification and colonization, this simple trait-less inference model is informative and robust to trait effects on colonization, speciation, and extinction. Nonetheless, our new simulation model may provide a useful tool for studying patterns of trait variation.

Testing Geology with Biology: Plate Tectonics and the Diversification of Microhylid Frogs in the Papuan Region.

Studies of the Papuan region have provided fundamental insights into the evolutionary processes generating its exceptional biodiversity, but the influence of geological processes merits further study. Lying at the junction of five tectonic plates, this region has experienced a turbulent geological history that has not only produced towering mountains allowing elevational specialization and island archipelagos with varying degrees of isolation promoting vicariance, but also active margins where land masses have collided and been subsequently rifted apart creating a mosaic of intermixed terranes with vastly different geological histories. Asterophryine frogs are a hyperdiverse clade representing half the world's microhylid diversity (over 360 species) centered on New Guinea and its satellite islands. We show that vicariance facilitated by geological history explains this far and wide distribution of a clade that should have poor dispersal abilities. We recovered a mainland tectonic unit, the East Papua Composite Terrane (EPCT), as the center of origin for Asterophryinae and no fewer than 71 instances of what appear to be long-distance dispersal events, 29 of which are between mainland regions, with 42 from the mainland to the islands, some presently as far as 200km away from source populations over open ocean. Furthermore, we find strong support for a "Slow and Steady" hypothesis for the formation of the northern margin of New Guinea by many separate accretion events during the Miocene, over other major geological alternatives, consistent with the 20M year age of the clade and arrival via the EPCT. In addition, the historical biogeography of our frogs strongly supports an affiliation of the Louisiade Archipelago and Woodlark Island with the Owen Stanley Range on the EPCT, and the recent proximity of the large New Britain Island. Our results show that Asterophryinae did not have to repeatedly and independently disperse across large ocean barriers to the offshore islands, against the predictions of island biogeography theory, but that the current distribution can be explained through vicariance and short-distance oceanic dispersal as historical land connections disappeared and islands slowly became separated from each other. We show that islands have a life history, changing in distance from other land masses, with consequent opportunities for dispersal, isolation, and cladogenesis of their biotas. More broadly, we can begin to see how the geological history of the Papuan region can result in the rapid accumulation and staggering number of extant species.

Do Geographically Isolated Grasslands Follow the Principle of Island Biogeography in a Landscape Scale? Taking Poyang Lake Grassland as an Example

As one of the basic theories of biodiversity conservation, island biogeography has been widely accepted in the past decades. Originally, island biogeography was put forward and applied in oceanic environments. But later on, it was found out that the application was not only limited to oceanic islands, but also in terrestrial environments with relatively isolated conditions. In terms of biodiversity level, island biogeography generally focuses on a small scale, such as species diversity and genetic diversity. The studies of biodiversity on a large-scale based on island biogeography, such as ecosystem and landscape scales, were seldomly conducted. Taking Poyang Lake, the largest fresh water lake in China as case study area, 30 grasslands were randomly selected to study whether island biogeography can be applied to grasslands at a landscape level from three island attributes (area, distance and shape), and the most important ecological variable (flooding) in Poyang Lake. The results showed that in general, grasslands have the property of an island, and follow the basic principle of island biogeography. We found the area and flooding duration were the two most important determinants of landscape diversity. There was a significant positive correlation between the grassland area and the landscape diversity, which could be well expressed by logarithmic function model (R2 = 0.73). There was a negative correlation between flooding duration and landscape diversity, which could be described by an inverse model (R2 = 0.206). The distance to mainland and the shape of grassland were correlated with landscape diversity, but the fitting result of the models was not as good as expected. The possible reason could be that Poyang Lake is a seasonal lake, the water level varies with hydrological conditions, so that the grasslands are not strongly isolated and their shape is not stable enough required by island biogeography. Furthermore, it indicates that besides area, distance and shape attributes, flooding strongly affects the biodiversity of grassland vegetation, and should not be ignored when applying island biogeography theory to Poyang Lake. This study is expected to be a supplement for island biogeography in terrestrial environments, and the results are expected to benefit for the biodiversity conservation in Poyang Lake.

Biogeographic and environmental drivers of reef fish diversity in coastal islands of the Gulf of Thailand

Islands, critical environments for marine biodiversity, have endorsed several classical ecological theories. However, most studies on marine communities in islands are restricted to oceanic settings; whether premises of island biogeography apply to coastal islands is still unknown. In the Gulf of Thailand (GoT), coral reefs occur in nearshore coastal islands, subject to a wide range of environmental conditions, diverging from the most-studied oceanic counterparts. We investigated fish communities of 51 reefs at 10 sites spanning ~1500 km of the GoT coast, to answer whether diversity and species composition were (1) more influenced by area and isolation than by local environmental conditions and/or (2) affected by the geographical position. As predicted by island biogeography models, diversity decreased with island isolation, albeit only for rare species; reef area increased diversity but solely for common and dominant species. The effect of the geographical position of reefs within the GoT was negligible. Small-scale differences in local conditions of turbidity and depth affected diversity and composition more than isolation and SST. Within-island variability in these conditions yielded a high local turnover of species, enhancing within-site gamma richness, even when the mean alpha richness per site was low. Trophic group composition was similar among most sites, but extreme conditions of environmental constraints (e.g. very high/low turbidity) rendered changes in the dominant trophic group. Results suggest that island biogeography models apply to the reef fish communities in coastal islands to some extent, but the broader ranges of local conditions are the primary drivers of their diversity and composition.

Island biogeography of soundscapes: Island area shapes spatial patterns of avian acoustic diversity

AbstractAimThe equilibrium theory of island biogeography predicts the positive species–area relationship and the negative species–isolation relationship, resulting in higher species richness on large and close islands. Unlike species richness, soundscape diversity integrates sound from various sources (e.g. biophony, geophony and anthrophony). However, how soundscape diversity varies with island area and isolation still needs to be tested. Here, we explored the island biogeography of bird soundscapes and the determinants of island attributes in shaping bird diversity and soundscape diversity.LocationThousand Island Lake, Zhejiang, China.TaxonBirds.MethodsWe recorded avian soundscapes by audio recorders and censused bird diversity by line transects on 20 land‐bridge islands. We calculated four acoustic indices (acoustic complexity index, bioacoustic index, acoustic evenness index and acoustic entropy index) to assess acoustic richness, evenness and heterogeneity to explore the soundscape diversity of birds. We used multiple linear regressions, spatial autoregressions and piecewise structural equation models to examine the relationships between bird richness and acoustic diversity, and island attributes.ResultsWe found positive diversity–area relationships for avian soundscapes. Larger islands had more vocal species and higher habitat diversity, which led to an increment in the richness and unevenness of avian soundscapes on large islands. Acoustic evenness decreased with increasing isolation (distance to the mainland).Main ConclusionsSoundscapes on large islands are more diverse than those on small islands. Rich acoustic assemblages and heterogeneous habitats promote increased soundscape diversity on islands. Conversely, the lack of vocal contributors, resulting in a decrement in the communication of acoustic signals, can create a lower soundscape diversity on small and remote islands. Our study emphasizes the necessity of examining both species and habitat diversity in island biogeography for better understanding the underlying mechanisms determining biological soundscapes on islands.

Selective extinction and habitat nestedness are the main drivers of lizard nestedness in the Zhoushan Archipelago.

Nested subset pattern (nestedness) is an important part of the theoretical framework of island biogeography and community ecology. However, most previous studies often used nestedness metrics or randomization algorithms that are vulnerable to type I error. In this study, we investigated the nestedness of lizard assemblages on 37 islands in the Zhoushan Archipelago, China. We used the line-transect method to survey species occurrence, abundance, and habitat types of lizards on 37 islands during 2 breeding seasons in 2021 and 2022. We applied the nested metric WNODF and the conservative rc null model to control for type I error and quantify the significance of nestedness. Spearman rank correlations were used to evaluate the role of 4 habitat variables (island area, 2 isolation indices, and habitat diversity) and 4 ecological traits (body size, geographic range size, clutch size, and minimum area requirement) in generating nestedness. The results of WNODF analyses showed that lizard assemblages were significantly nested. The habitat-by-site matrix estimated by the program NODF was also significantly nested, supporting the habitat nestedness hypothesis. The nestedness of lizard assemblages were significantly correlated with island area, habitat diversity, clutch size, and minimum area requirement. Overall, our results suggest that selective extinction and habitat nestedness were the main drivers of lizard nestedness in our system. In contrast, the nestedness of lizard assemblages was not due to passive sampling or selective colonization. To maximize the number of species preserved, our results indicate that we should protect both large islands with diverse habitats and species with large area requirement and clutch size.

Drivers of contemporary lacustrine fish species richness in the glacial Lake Agassiz basin

AbstractAimBiological communities are the result of a stepwise spatiotemporal filtering process, driven by large‐scale historical and local contemporary determinants. The biogeographical pattern and species richness of North American fishes are predominantly determined by historical processes of past glaciations and postglacial dispersal and by contemporary environmental and ecological processes. We evaluated the effects of postglacial dispersal through glacial Lake Agassiz and habitat heterogeneity, represented by lake surface area, on contemporary freshwater fish species richness patterns of northwestern Ontario lakes.LocationNorthwestern Ontario, Canada.TaxonFreshwater fishes.MethodsApplying the theory of island biogeography and species–area curves, we examined the effects of isolation from the past dispersal corridor of glacial Lake Agassiz and habitat heterogeneity on species richness across 264 contemporary lakes. While controlling for correlations among the predictor variables, generalized linear models were constructed between species richness, as the response variable and the explanatory variables of lake elevation and surface area, and connection to the dispersal corridor.ResultsDifferential cover by glacial Lake Agassiz led to variation in fish species richness across contemporary lakes and it is higher in lakes that were covered by Lake Agassiz relative to basins remaining outside of the boundaries of the glacial lake. Lake surface area is the strongest predictor of species richness, while lake elevation is the strongest factor predicting isolation.Main ConclusionsHabitat heterogeneity and postglacial colonization have led to differences in fish richness within the same geographical region, which increases with lake surface area and decreases with elevation. These are likely driven by greater niche diversity facilitating the assembly of more diverse communities and isostatic rebound and fluctuating levels of Lake Agassiz isolating lakes at high elevations from the dispersal route earlier during the colonization process, respectively. These patterns underscore the importance of incorporating historical and environmental community determinants in biodiversity studies.