The West Indies as a laboratory of biogeography and evolution

Islands have long provided material and inspiration for the study of evolution and ecology. The West Indies are complex historically and geographically, providing a rich backdrop for the analysis of colonization, diversification and extinction of species. They are sufficiently isolated to sustain endemic forms and close enough to sources of colonists to develop a dynamic interaction with surrounding continental regions. The Greater Antilles comprise old fragments of continental crust, some very large; the Lesser Antilles are a more recent volcanic island arc, and the low-lying Bahama Islands are scattered on a shallow oceanic platform. Dating of island lineages using molecular methods indicates over-water dispersal of most inhabitants of the West Indies, although direct connections with what is now southern Mexico in the Early Tertiary, and subsequent land bridges or stepping stone islands linking to Central and South America might also have facilitated colonization. Species-area relationships within the West Indies suggest a strong role for endemic radiations and extinction in shaping patterns of diversity. Diversification is promoted by opportunities for allopatric divergence between islands, or within the large islands of the Greater Antilles, with a classic example provided by the Anolis lizards. The timing of colonization events using molecular clocks permits analysis of colonization-extinction dynamics by means of species accumulation curves. These indicate low rates of colonization and extinction for reptiles and amphibians in the Greater Antilles, with estimated average persistence times of lineages in the West Indies exceeding 30Myr. Even though individual island populations of birds might persist an average of 2Myr on larger islands in the Lesser Antilles, recolonization from within the archipelago appears to maintain avian lineages within the island chain indefinitely. Birds of the Lesser Antilles also provide evidence of a mass extinction event within the past million years, emphasizing the time-heterogeneity of historical processes. Geographical dynamics are matched by ecological changes in the distribution of species within islands over time resulting from adaptive radiation and shifts in habitat, often following repeatable patterns. Although extinction is relatively infrequent under natural conditions, changes in island environments as a result of human activities have exterminated many populations and others--especially old, endemic species--remain vulnerable. Conservation efforts are strengthened by recognition of aesthetic, cultural and scientific values of the unique flora and fauna of the West Indies.     

A global comparison of plant invasions on oceanic islands

Oceanic islands have long been considered to be particularly vulnerable to biotic invasions, and much research has focused on invasive plants on oceanic islands. However, findings from individual islands have rarely been compared between islands within or between biogeographic regions. We present in this study the most comprehensive, standardized dataset to date on the global distribution of invasive plant species in natural areas of oceanic islands. We compiled lists of moderate (5–25% cover) and dominant (>25% cover) invasive plant species for 30 island groups from four oceanic regions (Atlantic, Caribbean, Pacific, and Western Indian Ocean). To assess consistency of plant behaviour across island groups, we also recorded present but not invasive species in each island group.We tested the importance of different factors discussed in the literature in predicting the number of invasive plant species per island group, including island area and isolation, habitat diversity, native species diversity, and human development. Further we investigated whether particular invasive species are consistently and predictably invasive across island archipelagos or whether island-specific factors are more important than species traits in explaining the invasion success of particular species.We found in total 383 non-native spermatophyte plants that were invasive in natural areas on at least one of the 30 studied island groups, with between 3 and 74 invaders per island group. Of these invaders about 50% (181 species) were dominants or co-dominants of a habitat in at least one island group. An extrapolation from species accumulation curves across the 30 island groups indicates that the total current flora of invasive plants on oceanic islands at latitudes between c. 35°N and 35°S may eventually consist of 500–800 spermatophyte species, with 250–350 of these being dominant invaders in at least one island group. The number of invaders per island group was well predicted by a combination of human development (measured by the gross domestic product (GDP) per capita), habitat diversity (number of habitat types), island age, and oceanic region (87% of variation explained). Island area, latitude, isolation from continents, number of present, non-native species with a known invasion history, and native species richness were not retained as significant factors in the multivariate models.Among 259 invaders present in at least five island groups, only 9 species were dominant invaders in at least 50% of island groups where they were present. Most species were invasive only in one to a few island groups although they were typically present in many more island groups. Consequently, similarity between island groups was low for invader floras but considerably higher for introduced (but not necessarily invasive) species – especially in pairs of island groups that are spatially close or similar in latitude. Hence, for invasive plants of natural areas, biotic homogenization among oceanic islands may be driven by the recurrent deliberate human introduction of the same species to different islands, while post-introduction processes during establishment and spread in natural areas tend to reduce similarity in invader composition between oceanic islands. We discuss a number of possible mechanisms, including time lags, propagule pressure, local biotic and abiotic factors, invader community assembly history, and genotypic differences that may explain the inconsistent performance of particular invasive species in different island groups.     

Orchids of the West Indies: predictability of diversity and endemism

Aim We examined phytogeographical patterns of West Indian orchids, and related island area and maximum elevation with orchid species richness and endemism. We expected strong species–area relationships, but that these would differ between low and montane island groups. In so far as maximum island elevation is a surrogate for habitat diversity, we anticipated a strong relationship with maximum elevation and both species richness and endemism for montane islands. Location The West Indies. Methods Our data included 49 islands and 728 species. Islands were classified as either montane (≥ 300 m elevation) or low (< 300 m). Linear and multivariate regression analyses were run to detect relationships between either area or maximum island elevation and species richness or the number of island endemic species. Results For all 49 islands, the species–area relationship was strong, producing a z‐value of 0.47 (slope of the regression line) and explaining 46% of the variation. For 18 relatively homogeneous, low islands we found a non‐significant slope of z = −0.01 that explained only 0.1% of the variation. The 31 montane islands had a highly significant species–area relationship, with z = 0.49 and accounting for 65% of the variation. Species numbers were also strongly related to maximum island elevation. For all islands < 750 km², we found a small‐island effect, which reduced the species–area relationship to a non‐significant z = 0.16, with only 5% of the variation explained by the model. Species–area relationships for montane islands of at least 750 km² were strong and significant, but maximum elevation was the best predictor of species richness and accounted for 79% of the variation. The frequency of single‐island endemics was high (42%) but nearly all occurred on just nine montane islands (300 species). The taxonomic distribution of endemics was also skewed, suggesting that seed dispersability, while remarkable in some taxa, is very limited in others. Montane island endemics showed strong species–area and species–elevation relationships. Main conclusions Area and elevation are good predictors of orchid species diversity and endemism in the West Indies, but these associations are driven by the extraordinarily strong relationships of large, montane islands. The species richness of low islands showed no significant relationship with either variable. A small‐island effect exists, but the montane islands had a significant relationship between species diversity and maximum elevation. Thus, patterns of Caribbean orchid diversity are dependent on an interplay between area and topographic diversity.     

A phylogenetic approach towards understanding the drivers of plant invasiveness on Robben Island,South Africa

Invasive plant species are a considerable threat to ecosystems globally and on islands in particular where species diversity can be relatively low. In this study, we examined the phylogenetic basis of invasion success on Robben Island in South Africa. The flora of the island was sampled extensively and the phylogeny of the local community was reconstructed using the two core DNA barcode regions, rbcLa and matK. By analysing the phylogenetic patterns of native and invasive floras at two different scales, we found that invasive alien species are more distantly related to native species, a confirmation of Darwin's naturalization hypothesis. However, this pattern also holds even for randomly generated communities, therefore discounting the explanatory power of Darwin's naturalization hypothesis as the unique driver of invasion success on the island. These findings suggest that the drivers of invasion success on the island may be linked to species traits rather than their evolutionary history alone, or to the combination thereof. This result also has implications for the invasion management programmes currently being implemented to rehabilitate the native diversity on Robben Island. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 172 , 142–152.     

山东省外来植物的区系特征及空间分布

外来植物及其生态入侵对当地生物多样性保护和生态系统产生的不利影响,是目前生态学研究的热点之一。本文在文献查阅和野外调查基础上,建立了山东省外来植物数据库,并对其组成、地理区系、空间分布等进行统计分析,结果表明:1)山东省现有外来植物共827种,隶属122科,416属,其中境外外来种348种;2)外来植物比例高,占山东植物区系的39.03%,且优势科和表征科明显;3)外来植物属的地理分布多样,温带成分占优势(52.51%),热带成分丰富(44.06%);4)外来植物来源地和分布地相对集中,反映了环境因子和人类活动在入侵因素中的共同影响;5)温带气候带来源的植物较易入侵山东。     

Phylogeography of the parthenogenic ant Platythyrea punctata: highly successful colonization of the West Indies by a poor disperser

Aim We investigated the spatio‐temporal patterns of genetic diversity in West Indian and mainland populations of a widespread parthenogenic ant (Platythyrea punctata F. Smith) to infer source populations and subsequent colonizations across its geographic range. Location Central America, Texas and the West Indies (Florida, the Bahamas, Greater and Lesser Antilles). Methods We employed phylogeographic reconstruction based on 1451 bp of mitochondrial DNA (cytochrome c oxidase subunits I and II) sequenced from 91 individuals of P. punctata. We employed standard population genetic analyses, Bayesian phylogenetic analyses, haplotype networks and molecular dating methods as performed by beast . We also employed phylogenetic analysis using two nuclear markers (970 bp) to understand the placement of P. punctata in the globally distributed genus Platythyrea. Results Based on highly reduced haplotypic variation and temporal estimates, rapid expansion and dispersal from Central America best explains the observed distribution of haplotypes. Platythyrea punctata successfully invaded the West Indies very few times. One haplotype occurred on every island surveyed from the Bahamas and Florida in the north to Barbados at the southern edge of its range. Haplotype diversity in the West Indies is quite low, despite a larger sample size relative to the mainland. Most mainland colonies collected each possessed a unique haplotype, whereas only Florida and the larger islands (the Dominican Republic, Puerto Rico and Guadeloupe) contained more than one haplotype. Island haplotypes were most similar to haplotypes collected in northern Mexico and southern Texas, but genetic distances were nevertheless high. The putative sister species of P. punctata appears to be an endemic of Hispaniola (P. strenua Wheeler & Mann), even though older, mainland populations of P. punctata are sympatric with at least two other congenerics. Main conclusions Dispersal seems very limited on the mainland, with well‐defined clades corresponding to geographical regions. Colonization of the islands from the mainland was extremely rare, but once successful there were very few barriers to expansion to nearly every island in the West Indies. We hypothesize that this invasion occurred during the late Pleistocene as the climate became warmer and less arid.     

厦门近岸海域无居民海岛植物区系和物种组成相似性

为摸清厦门近岸无居民海岛的主要植物群落类型, 于2017年10月调查了12个无居民海岛的植物组成, 共记录到维管束植物360种, 其中乔木78种, 小乔木或灌木109种, 藤本23种, 草本150种; 包含外来入侵植物49种, 其中恶性入侵种10种。植物区系分析表明, 厦门周边12个无居民海岛植物主要由泛热带分布种及其变型组成, 以热带、亚热带成分占主导地位, 符合其亚热带地理分布特点。总体上, 维管束植物物种相似性较高, 物种丰富度受海岛面积的影响较大, 与海岛面积存在显著的对数和幂函数关系。此外, 岸线长度、高程、周长/面积比等空间参数也对海岛物种丰富度产生一定的影响。岛屿间维管束植物物种相似性受生境多样性和岛屿边缘效应的影响, 仅吾屿可能存在小岛屿效应。     

Dimorphism and divergence in island and mainland Anoles

Relative to the West Indies, the ecology and evolution of anoles inhabiting islands off Central and South America have received little attention. The paucity of studies on continental islands has limited our ability to generalize and extend results based on the West Indian paradigm, as well as our understanding of the profound differences between the adaptive radiations of continental vs. Greater Antillean anoles. Here we compare the morphological, ecological, behavioural and genetic divergence between Anolis nebulosus populations inhabiting a small island in the Bay of Chamela, Mexico, and a nearby mainland forest. Notably, the two populations exhibit intra‐sexual dimorphism with respect to head and limb sizes, the first such polymorphism documented for an Anolis species. We also compare the shape of island and mainland A. nebulosus with each other, the six West Indian ecomorphs and a hypothetical generalist species. Finally, we address the generalist convergence hypothesis for anoles on single species islands. We conclude that convergence on a generalist morphology is widespread among solitary anoles in the West Indies. We present data on a limited sample of solitary anoles with mainland ancestors that suggest a parallel convergence on a similar generalist morphology, probably due to similar adaptive landscapes shaped by selective forces common to small island environments.     

Determinants of bird species richness,endemism, and island network roles in Wallacea and the West Indies: is geography sufficient or does current and historical climate matter?

Island biogeography has greatly contributed to our understanding of the processes determining species' distributions. Previous research has focused on the effects of island geography (i.e., island area, elevation, and isolation) and current climate as drivers of island species richness and endemism. Here, we evaluate the potential additional effects of historical climate on breeding land bird richness and endemism in Wallacea and the West Indies. Furthermore, on the basis of species distributions, we identify island biogeographical network roles and examine their association with geography, current and historical climate, and bird richness/endemism. We found that island geography, especially island area but also isolation and elevation, largely explained the variation in island species richness and endemism. Current and historical climate only added marginally to our understanding of the distribution of species on islands, and this was idiosyncratic to each archipelago. In the West Indies, endemic richness was slightly reduced on islands with historically unstable climates; weak support for the opposite was found in Wallacea. In both archipelagos, large islands with many endemics and situated far from other large islands had high importance for the linkage within modules, indicating that these islands potentially act as speciation pumps and source islands for surrounding smaller islands within the module and, thus, define the biogeographical modules. Large islands situated far from the mainland and/or with a high number of nonendemics acted as links between modules. Additionally, in Wallacea, but not in the West Indies, climatically unstable islands tended to interlink biogeographical modules. The weak and idiosyncratic effect of historical climate on island richness, endemism, and network roles indicates that historical climate had little effects on extinction‐immigration dynamics. This is in contrast to the strong effect of historical climate observed on the mainland, possibly because surrounding oceans buffer against strong climate oscillations and because geography is a strong determinant of island richness, endemism and network roles.     

Geographical ecology of dry forest tree communities in the West Indies

Aim

Seasonally dry tropical forest (SDTF) of the Caribbean Islands (primarily West Indies) is floristically distinct from Neotropical SDTF in Central and South America. We evaluate whether tree species composition was associated with climatic gradients or geographical distance. Turnover (dissimilarity) in species composition of different islands or among more distant sites would suggest communities structured by speciation and dispersal limitations. A nested pattern would be consistent with a steep resource gradient. Correlation of species composition with climatic variation would suggest communities structured by broad‐scale environmental filtering.

Location

The West Indies (The Bahamas, Cuba, Hispaniola, Jamaica, Puerto Rico, US Virgin Islands, Guadeloupe, Martinique, St. Lucia), Providencia (Colombia), south Florida (USA) and Florida Keys (USA).

Taxon

Seed plants—woody taxa (primarily trees).

Methods

We compiled 572 plots from 23 surveys conducted between 1969 and 2016. Hierarchical clustering of species in plots, and indicator species analysis for the resulting groups of sites, identified geographical patterns of turnover in species composition. Nonparametric analysis of variance, applied to principal components of bioclimatic variables, determined the degree of covariation in climate with location. Nestedness versus turnover in species composition was evaluated using beta diversity partitioning. Generalized dissimilarity modelling partitioned the effect of climate versus geographical distance on species composition.

Results

Despite a set of commonly occurring species, SDTF tree community composition was distinct among islands and was characterized by spatial turnover on climatic gradients that covaried with geographical gradients. Greater Antillean islands were characterized by endemic indicator species. Northern subtropical areas supported distinct, rather than nested, SDTF communities in spite of low levels of endemism.

Main conclusions

The SDTF species composition was correlated with climatic variation. SDTF on large Greater Antillean islands (Hispaniola, Jamaica and Cuba) was characterized by endemic species, consistent with their geological history and the biogeography of plant lineages. These results suggest that both environmental filtering and speciation shape Caribbean SDTF tree communities.     

Biogeographical modules and island roles: a comparison of Wallacea and the West Indies

Aim In order to advance our understanding of the assembly of communities on islands and to elucidate the function of different islands in creating regional and subregional distribution patterns, we identify island biogeographical roles on the basis of the distribution of the islands’ biota within the archipelago. We explore which island characteristics determine island biogeographical roles. Furthermore, we identify biogeographical subregions, termed modules. Location Wallacea in Indonesia, and the West Indies in the Caribbean Sea. Methods We use a network approach to detect island biogeographical roles and avian biogeographical modules. To designate the biogeographical role of an island, each island is assigned two coordinates, l and r. The position of an island in l–r space characterizes its role, namely as peripheral, connector, module hub, or network hub. Island characteristics are tested as predictors of l and r. Results Both Wallacea and the West Indies were found to be significantly modular and divided into four biogeographical modules. The four modules identified within Wallacea each contain all existing island roles, whereas no module in the West Indies represents all possible roles. Island area and elevation appeared to be the most important determinants of an island’s l score, while measurements of isolation essentially determined the r score. Main conclusions In both Wallacea and the West Indies, the geographic structuring into biogeographical modules corresponds well with our knowledge of past connections and contemporary factors. In both archipelagos, large, mountainous islands are identified as hubs and are thus responsible for faunal coherence within modules (module hubs) and across the entire archipelago (network hubs). We thus interpret these as source islands for the surrounding islands in their module (module hubs) or for the entire archipelago (network hubs). Islands positioned marginally in their module and distant from the mainland are identified as connectors or network hubs, behaving as sinks and stepping stones for dispersing species. Modularity and predictors of biogeographical roles are similar for Wallacea and the West Indies, whereas the build‐up of biogeographical modules and the assortment of roles depend on the spatial constellation of islands in each archipelago.     

THE RELEVANCE OF GENE FLOW IN METAPOPULATION DYNAMICS OF AN OCEANIC ISLAND ENDEMIC,OLEA EUROPAEA SUBSP. GUANCHICA

Theoretical and empirical studies suggest that geographical isolation and extinction–recolonization dynamics are two factors causing strong genetic structure in metapopulations, but their consequences in species with high dispersal abilities have not been tested at large scales. Here, we investigated the effect of population age structure and isolation by distance in the patterns of genetic diversity in a wind‐pollinated, zoochorous tree (Olea europaea subsp. guanchica) sporadically affected by volcanic events across the Canarian archipelago. Genetic variation was assessed at six nuclear microsatellites (nDNA) and six chloroplast fragments (cpDNA) in nine subpopulations sampled on four oceanic islands. Subpopulations occurring on more recent substrates were more differentiated than those on older substrates, but within‐subpopulation genetic diversity was not significantly different between age groups for any type of marker. Isolation‐by‐distance differentiation was observed for nDNA but not for cpDNA, in agreement with other metapopulation studies. Contrary to the general trend for island systems, between‐island differentiation was extremely low, and lower than differentiation between subpopulations on the same island. The pollen‐to‐seed ratio was close to one, two orders of magnitude lower than the average estimated for other wind‐pollinated, animal‐dispersed plants. Our results showed that population turnover and geographical isolation increased genetic differentiation relative to an island model at equilibrium, but overall genetic structure was unexpectedly weak for a species distributed among islands. This empirical study shows that extensive gene flow, particularly mediated by seeds, can ameliorate population subdivision resulting from extinction–recolonization dynamics and isolation by distance.     

Plant invasions on small Mediterranean islands: An overview

Biological invasions have become one of the main drivers of habitat degradation and a leading cause of biodiversity loss in island ecosystems worldwide. The spread of invasive species poses a particular environmental threat on the islands of the Mediterranean Basin, which are hot spots of biodiversity and contain rare habitats and endemic species, especially on small islands, which are highly vulnerable to biodiversity loss. Following a recent survey, in this paper we aim to provide an overview of the present-day non-native vascular flora of small Mediterranean islands based on a sample of 37 islands located in the middle of the Mediterranean Sea, off the coast of Italy. By comparing the current data with those gathered during a previous survey conducted in the same study area, we also aim to highlight the main changes that have occurred in non-native plant species diversity, establishment and distribution in recent years and to present a first general overview of the most prominent plant taxa in the island’s introduced flora, focusing on those most responsible for these changes and those that pose the greatest environmental threats. We recorded 203 non-native plant species, 147 of which have established on at least one of the islands investigated. Overall, we detected a sharp increase in the number of species, in their levels of establishment and in the extent of their distribution within the study area in recent years. This may be explained by the intensification of research on plant invasions, as well as to new introduction, escape, establishment and invasion events on the islands in recent decades. The most remarkable plants detected include acacias and succulents, two groups that appear to be emerging very rapidly and to be posing new threats to the conservation of the islands’ natural environment, especially the genus Carpobrotus, whose spread into natural habitats containing rare and endemic taxa is seriously threatening biodiversity on both a local and global scale. On the whole, our results show that the plant invasion phenomenon in the study area has in recent years intensified considerably. As this process seems likely to continue, we should expect more establishment events in the future and the further spread of species that are already present. This is of particular conservation concern on the islands investigated in this survey, which are rich in endemisms, but have been facing deep socio-economic and environmental transformations in these last decades as a consequence of the abandonment of traditional management practices and the development of tourism. Our study thus confirms that plant invasions on Mediterranean islands are a serious environmental problem that threatens biodiversity conservation not only in the Mediterranean biogeographic region, but also on the global scale, and highlights the need to further increase efforts aimed at preventing, controlling or mitigating the effects of plant invasions in island ecosystems.     

Determinants of alpha and beta vascular plant diversity in Mediterranean island systems: the Ionian islands,Greece

The Ionian archipelago is the second largest Greek archipelago after the Aegean, but the factors driving plant species diversity in the Ionian islands are still barely known. We used stepwise multiple regressions to investigate the factors affecting plant species diversity in 17 Ionian islands. Generalized dissimilarity modelling was applied to examine variation in the magnitude and rate of species turnover along environmental gradients, as well as to assess the relative importance of geographical and climatic factors in explaining species turnover. The values of the residuals from the ISAR log₁₀‐transfomed models of native and endemic taxa were used as a measure of island floristic diversity. Area was confirmed to be the most powerful single explanatory predictor of all diversity metrics. Mean annual precipitation and temperature, as well as shortest distance to the nearest island are also significant predictors of vascular plant diversity. The island of Kalamos constitutes an important plant diversity hotspot in the Ionian archipelago. The recent formation of the islands, the close proximity to the mainland source and the relatively low dispersal filtering of the Ionian archipelago has resulted in islands with a flora principally comprising common species and a low proportion of endemics. Small islands keep a key role in conservation of plant priority sites.     

A mesoscale analysis of floristic patterns in the south-west Finnish Archipelago

Aim To identify the ecological gradients based on the flora on a mesoscale in an archipelago. To interpret the results of the ordination and the classification of a grid cell‐based botanical data set, with several environmental and geographical attributes. To compare the mesoscale distribution patterns of vascular plants with patterns previously observed on an island scale, and to develop a floristic zonation of the study area. Location The south‐west Finnish Archipelago. Methods Vascular plant species‐lists from over 1500 localities were assigned to 5 × 5 km grid cells. The grid cell‐based floristic data were subjected to both unconstrained [detrended correspondence analysis (DCA)] and constrained [detrended canonical correspondence analysis (DCCA)] gradient analyses. The results of DCA were interpreted with calculated weighted averages of Ellenberg's indicator values for vascular plants, the number of occurring taxa and indices for the strength of human influence and the occurrence of limestone. The results of DCCA were interpreted with geographical attributes of the grid cells and the occurrence of limestone. The grid cells were clustered using two‐way indicator species analysis (twinspan ). Results Both the unconstrained and the constrained ordinations gave consistent and interpretable results. The main ecological gradient runs from the grid cells containing species‐rich islands with high human impact to grid cells containing species‐poor islands with low human impact. This gradient also represents the continuum from areas with large islands near the mainland, to the outermost areas at the edge of the open sea. The secondary gradient was shown to be a gradient of soil reaction. twinspan gave a clustering primarily based on the location of the grid cells on an inner–outer archipelago gradient, but the occurrence of limestone also influenced the classification. The archipelago was divided into five non‐homogeneous areas based on the twinspan clusters. The detected gradients correspond well with the gradients detected in a similar island‐level analysis. Main conclusions The two major ecological gradients in the study area seem to be robust, which is indicated by the similar results obtained both on an island and on a mesoscale. A shift from local and regional processes to broader geographical gradients probably starts to occur at the applied scale. The distribution patterns are strongly affected by the inner–outer archipelago gradient and the occurrence of limestone.     

Out of Cuba: overwater dispersal and speciation among lizards in the Anolis carolinensis subgroup

Overwater dispersal and subsequent allopatric speciation contribute importantly to the species diversity of West Indian Anolis lizards and many other island radiations. Here we use molecular phylogenetic analyses to assess the contribution of overwater dispersal to diversification of the Anolis carolinensis subgroup, a clade comprising nine canopy-dwelling species distributed across the northern Caribbean. Although this clade includes some of the most successful dispersers and colonists in the anole radiation, the taxonomic status and origin of many endemic populations have been ambiguous. New mitochondrial and nuclear DNA sequences from four species occurring on small islands or island banks (Anolis brunneus, Anolis longiceps, Anolis maynardi, Anolis smaragdinus) and one species from the continental United States (A. carolinensis) are presented and analysed with homologous sequences sampled from related species on Cuba (Anolis allisoni and Anolis porcatus). Our analyses confirm that all five non-Cuban species included in our study represent distinct, independently evolving lineages that warrant continued species recognition. Moreover, our results support Ernest Williams's hypothesis that all of these species originated by overseas colonization from Cuban source populations. However, contrary to Williams's hypothesis of Pleistocene dispersal, most colonization events leading to speciation apparently occurred earlier, in the late Miocene-Pliocene. These patterns suggest that overwater dispersal among geologically distinct islands and island banks is relatively infrequent in anoles and has contributed to allopatric speciation. Finally, our results suggest that large Greater Antillean islands serve as centres of origin for regional species diversity.     

A biogeographical perspective on ecological systems: some personal reflections

During my graduate studies, I characterized patterns of geographical distribution and taxonomic differentiation in birds of the West Indies, which suggested that species undergo phases of expansion and contraction similar to the taxon cycles that E. O. Wilson had described for Melanesian ants. Fieldwork in the early 1970s with George Cox confirmed that these phases were associated with variation in habitat distribution and abundance on individual islands, tying together local ecology and biogeography. Because taxon‐cycle stage was independent of taxonomic or ecological relationships among birds of the West Indies, George and I postulated that whether a species was in a phase of expansion or contraction reflected the outcome of coevolved relationships with antagonists, including pathogens. The taxon cycle concept had a cool reception initially, but subsequent phylogeographical analyses, beginning in the early 1990s with Eldredge Bermingham, provided a time scale that confirmed the relationship between taxon cycle stage and the relative age of the most recent population expansion. The discrete nature of islands allows one to visualize taxon cycles in island systems, but the principle should apply in a continental biota as well. The absence of strong phylogenetic effects in distribution and abundance is consistent with evolutionary lability caused by coevolutionary outcomes with specialized antagonists. Related species appear to compete for resources on a more‐or‐less equal footing across a broad range of environments, and their distribution at any particular time is likely to be determined primarily by their relationships with pathogens, among other antagonists. This model of distribution and abundance within a regional community is consistent with much of what we know about the interactions between pathogens and their host populations, but testing the model will require the development of a new research programme focused on endemic pathogen effects in natural communities.     

Arthropod diversity and allochthonous-based food webs on tiny oceanic islands

Very small islands, on the order of a few hundred square metres in area, have rarely been the focus of ecological investigations. I sampled nine such islands in the central Exumas, Bahamas for arthropod species abundance and diversity using a combination of pitfall traps, pan traps and sticky traps. Three islands had no terrestrial vegetation, three islands contained only Sesuvium portulacastrum L., a salt‐tolerant perennial that had been experimentally introduced 10 years ago, and three islands supported one or two naturally occurring plant species. A relatively diverse arthropod assemblage was discovered, including representatives of 10 different orders of Crustacea and Insecta. Land hermit crabs were the most abundant crustaceans, and dipterans were the most abundant and speciose insects. Two of the most common insects were previously undescribed species. Measures of arthropod species abundance and diversity were not significantly different for vegetated vs. non‐vegetated islands. All 10 orders were present on bare islands, and nine of them were present on vegetated islands. Measures of arthropod species abundance and diversity were positively associated with island area, and negatively associated with distance from the nearest large island. Hypothesized food webs consist of several trophic levels and have strong allochthonous inputs. Tiny islands such as these hold insights into early successional processes and the base of insular food webs.     

Evolution on oceanic islands: molecular phylogenetic approaches to understanding pattern and process

By their very nature oceanic island ecosystems offer great opportunities for the study of evolution and have for a long time been recognized as natural laboratories for studying evolution owing to their discrete geographical nature and diversity of species and habitats. The development of molecular genetic methods for phylogenetic reconstruction has been a significant advance for evolutionary biologists, providing a tool for answering questions about the diversity among the flora and fauna on such islands. These questions relate to both the origin and causes of species diversity both within an archipelago and on individual islands. Within a phylogenetic framework one can answer fundamental questions such as whether ecologically and/or morphologically similar species on different islands are the result of island colonization or convergent evolution. Testing hypotheses about ages of the individual species groups or entire community assemblages is also possible within a phylogenetic framework. Evolutionary biologists and ecologists are increasingly turning to molecular phylogenetics for studying oceanic island plant and animal communities and it is important to review what has been attempted and achieved so far, with some cautionary notes about interpreting phylogeographical pattern on oceanic islands.     

The Linnean shortfall in oceanic island biogeography: a case study in the Azores

Aim Speciation processes on islands are still poorly understood. Previous studies based on the analysis of distribution data from checklists found that the flora of the Azores archipelago differs from other island floras in the exceptionally low number of radiations and the low number of single‐island endemics. The general mechanism(s) responsible for these apparently unique patterns remained unclear. One possible explanation for the distinctiveness of the Azorean endemic flora is the lack of a consistent and critical taxonomic framework for the floras of the Atlantic archipelagos. In this study, molecular variation within a range of Azorean endemic plant lineages was analysed to determine whether inadequacies in the current taxonomy of endemics might be an explanation for the unusual diversity patterns observed in the endemic flora of the Azores. Location Azores archipelago. Method Sixty‐nine populations of eight endemic species or subspecies belonging to five genetic lineages were sampled from all Azorean islands but one. Nuclear and plastid DNA regions were sequenced, and relationships among internal transcribed spacer (ITS) region ribotypes established using statistical parsimony. Results Molecular diversity patterns differ from current taxonomic groupings, with all lineages comprising previously overlooked genetic entities. Main conclusions Recognition as distinct taxa of the genetically distinct entities discovered in this study would drastically change the diversity patterns and make them more similar to those of other Atlantic archipelagos. The results serve to highlight that current knowledge of endemic diversity on oceanic islands may be far from complete, even in relatively well‐known groups such as angiosperms. This limitation is rarely considered in macroecological and evolutionary studies that make use of data from taxonomic checklists to draw inferences about oceanic island biogeographic processes.