Greenish Warbler Research Articles

Изменение ареала западной зелёной пеночки (Phylloscopus trochiloides viridanus Blyth, 1843) в Украине и на прилежащих территориях

The aim of the work is to analyze the distribution of the Greenish Warbler of the subspecies viridanus in Ukraine and to determine the status of the species in various regions of the country. We used the analysis of the 3 – layer GIS map of the distribution areas of the Greenish Warbler for the period 1936–2022 in the DIVA-GIS program: 1st layer – the first registrations of the species (1936–1974); 2 – bird sightings at the end of the migration period (1979–2022); 3 – registrations in the nesting period. 77 GIS coordinates were used to build maps: author’s data, collection’s data of the Zoological Museum of the NNPM NAS of Ukraine, reference’s data, photo’s databases. In 1936–1974, the Greenish Warbler showed 2 foci of flights: 1 – in the south (in the Crimea, Nikolaev and Odessa regions), 2 – in the northeast – in the Belgorod region. In the northeastern region, the territory of distribution of the Greenish Warbler has increased significantly by 2022, but not in the south. The analysis performed indicates that the southern border of the Greenish Warbler habitat has shifted even more to the south and passes through the northern and northeastern regions of Ukraine. There is a tendency for the species to move further through Central Ukraine to the south of the country. In the south, registrations of a species with an unclear status at the end of spring migration and the beginning of the nesting period are typical. In the northeast, the Greenish Warbler nests. For Chernihiv, Kyiv and Ternopil regions, we assume the possibility of nesting. The species was not recorded in the southeastern and southwestern regions of Ukraine. In the northeastern regions, the first appearance of birds actually coincided with the beginning of their nesting, but the species has remained rare for about 30 years, breeding sporadically. In the southern regions, birds appeared and then disappeared for a rather long period, and after a while they are recorded more often and over a larger area. In Ukraine, the Greenish Warbler inhabits urbanized biotopes and is noted in 3 natural-geographical zones: forest, forest-steppe and steppe. It is possible that the Greenish Warbler does not nest in the south of Ukraine due to significant differences in the habitat conditions of the steppe zone from the forests in which the species has evolved. We believe that the successful resettlement of the Greenish Warbler is associated with a complex of factors: another wave of increase in the number of birds, favorable for the species climatic changes in the territories adjacent to the southern border of the range, the synanthropizations of the Greenish Warbler, transformation of the steppe zone of Ukraine due to the creation of tree plantations on its territory.

Avian Haemosporidian (Plasmodium and Haemoproteus) Status in Two Bird Groups (Old-World Flycatchers and Thrushes) of India and Their Phylogenetic Relationships with Other Lineages of the World.

Avian haemosporidian may affect the host from body damage to the extinction of a population. Knowledge of their status may help in future avifauna conservation plans. Hence, their status in two bird groups of India and their phylogenetic relationships with other known lineages of the world were examined. Cytochrome b gene sequences (479bp) generated from India and available at MalAvi database were used to study the avian haemosporidian prevalence and phylogenetic analysis of lineages at local and world levels. One common (COLL2) and only once in the study (CYOPOL01, CHD01, CYORUB01, EUMTHA01, GEOCIT01) haemosporidian lineages were discovered. 5.88% prevalence of haemosporidian infection was found in 102 samples belonging to 6 host species. Haemoproteus prevalence was 4.90% across five host species (Phylloscopus trochiloides, Cyornis poliogenys, C. hainanus dialilaemus, C. rubeculoides, Eumiyas thalassinus) and Plasmodium prevalence was 0.98% in Geokichla citrina. Spatial phylogeny at the global level showed that COLL2 lineage, found in C. poliogenys in India, was genetically identical to H. pallidus lineages (COLL2) in parts of Africa, Europe, North America, Malaysia, and the Philippines. The Plasmodium lineage (GEOCIT01) was related to PADOM16 in Egypt, but the sequences were only 93.89% alike. Four new lineages of Haemoproteus and one of Plasmodium were reported. COLL2 similarity with other H. pallidus lineages may suggest their hosts as possible infection sources.

The Indo-European flyway of migrating songbirds: Crossing the arid plains of central Eurasia

The arid belt of Central Asia is a major barrier for many migrating songbirds. It has to be crossed by passerines that breed in Siberia and winter in Africa, but also by the species that breed in eastern Europe and winter in southern and south-eastern Asia. Many passerine migrants breeding in Siberia and wintering in Africa avoid crossing the deserts in autumn; instead, they make a detour to the north and northwest and fly north of the Caspian Sea. Here we show that some, but not all, European-Indian migrants (e.g. scarlet rosefinches and greenish warblers) in autumn also make a detour and fly towards the east north of the arid belt before crossing in its central or eastern part. Other species, which include e.g. red-breasted flycatchers, Blyth's reed warblers and possibly booted warblers, take the shortest route between their (north)east European breeding grounds and Indian winter quarters.

Особенности фауны и летнего населения птиц Ашинского природного биологического заказника (Челябинская область)

Based on the results of ornithological research conducted in the Ashinsky State Biological Reserve during several nesting seasons during the period 1990–2021, a preliminary list of bird species was compiled. It includes 107 species, the vast majority of which nest or are expected to nest. To study the bird population, the main types of habitats in the southeastern and southwestern parts of the reserve were examined. The highest indicators of species diversity (42 species) and population density (568.0 ind./km²) were found in avian associations of dark coniferousdeciduous forests. The communities of upland meadows were found to be the most impoverished (16 species and 227.5 ind./km²). Based on these indices, avian associations of floodplain habitats of the Biyanka River occupied an intermediate position (34 species and 385.5 ind./km²).). In the communities of the forest biotopes of the reserve, the chaffinch, redwing, tree pipit, willow tit, white wagtail, garden warbler, common rosefinch and greenish warbler prevailed. In the associations of upland meadows, the skylark, tree pipit, whinchat and yellowhammer dominated. Almost half (43 %) of the nesting species were representatives of the European fauna; the proportions of species of the Euro-Chinese, Siberian and Nomadic types are 19, 15 and 10 %, respectively

Зв’язки чужорідних видів птахів з адвентивними рослинами насаджень парків і ботанічних садів

Introduction. In urban conditions, alien species of biota have become an integral part of the cultural landscape. Today, an overall assessment of the influence of alien species on the functioning of ecosystems of their secondary range as is relevant. Such an assessment requires knowledge of the connections formed by alien species in the secondary habitat. The purpose of the study was to find the connections of alien bird species with alien plant species in the parks and botanical gardens of Kyiv. Methods. Assessment was carried out in 10 forest parks, 3 botanical gardens, and 14 urban parks. In parks and botanical gardens, there is a wide range of plants alien to Kyiv Region, in contrast to forest parks. The number and distribution of birds were determined using the method of transect counts. The total area under study was about 370 hectares. Principal Component Analysis of the characteristics of habitats on which the number of alien birds may depend has been carried out. In the research, α-diversity indices of bird communities; number of people (individuals/km); number of pets (individuals/km); park’s area (ha); part of the territory; under the trees (%); part of alien species on plants communities (%) were analyzed. Results. Parus major, Turdus merula, Erithacus rubecula, Fringilla сoelebs dominate in all communities. Columba palumbus, Ficedula albicollis, Turdus pilaris, Columba livia, Apus apus, Sturnus vulgaris, Passer domesticus sometimes dominate in bird communities in parks and botanical gardens. There are no alien species in forest parks. 4 alien species nest in parks and botanical gardens: Streptopelia decaocto, Dendrocopos syriacus, Phoenicurus ochruros, Serinus serinus (from the last century). Phylloscopus trochiloides was observed for the first time. Nesting of Ph. trochiloides was not confirmed. Alien birds are not evenly distributed (0–3 species). Nest density is low: S. decaocto 0.013±0.01–0.021±0.01, D. syriacus 0.031±0.01–0.043±0.04, Ph. ochruros 0–0.034±0.02, S. serinus 0.013±0.01–0.017±0.01. We assume that alien bird species is an element that replaces the species that were eliminated from the community. Their nesting in forest parks is an indicator of a disruption of the functioning of the forest ecosystem as a result of anthropogenic transformation of the forest. The presence of alien species of birds in modern parks and botanical gardens is normal. Their biotopes were created on the sites of destroyed landscapes and with using alien plant species. Conclusion. In parks and botanical gardens, a specific structure of the plant community has developed due to the introduction of alien plant species, with a tree height of 3–5 m. As a consequence, alien birds find nesting stations in communities of nesting birds, which were not occupied by native species due to the absence of many species of tree canopy nesters and ground nesters birds. Alien species of birds also get access to vacant food resources. Alien birds use vacant resources. It was found that the area of parks has the most profound positive impact on the number of species of alien birds (+0.517), as well as the ratio of alien birds (+0.227). Other important correlations observed were the following: the number of species of alien birds in the bird communities – a part of alien species in plant communities (+0.084), the ratio of alien birds – part of alien species in plant communities (+0.041). The strongest negative connection is as follows: the number of species of alien birds in the bird communities – the number of pets (-0.213), the ratio of alien birds – the number of pets (-0.384).

Greenish Warbler (Phylloscopus trochiloides viridanus): An overlooked indicator of old-growth forest?

Effective bioindicators of old-growth forest are important for conservation. The Greenish Warbler (Phylloscopus trochiloides viridanus), a forest-dwelling passerine, has been recorded in old-growth forests; however, its precise habitat preferences are poorly studied. We used opportunistic observations collected by citizen scientists and stand descriptions from a forestry database to analyse its habitat preferences in Estonia, with a focus on the characteristics of old-growth forests. The Greenish Warbler preferred productive spruce and black alder stands but also favoured rare broad-leaved stands. Forest stands were older, less drained and contained more standing and fallen dead trees in warbler sites than in control sites. Positive effects of stand age and soil fertility exhibited the highest average relative importance in generalized linear models, drainage was of intermediate importance and the occurrence of dead wood was least important. The terrain at warbler sites was also more often uneven than that at control sites. The preference for old-growth forests observed in our study makes the Greenish Warbler, despite occupying various forest stands suggestive of plasticity, a good candidate for inclusion in a suite of old-growth forest indicators.

Male competition drives song divergence along an ecological gradient in an avian ring species.

Sexual selection operates via female choice and male competition, which can act independently, in concert, or in opposition. Female choice is typically considered the stronger selective force, but how these two processes interact to shape phenotypic divergence is poorly understood. I tested the hypothesis that variation in sexual selection in different habitats drives song divergence in the greenish warbler ring species. I evaluated the strength, direction, and targets of female choice and male competition in three populations spanning 2400km of latitude. Average song length increased with latitude, concomitant with a decline in population density. Within populations, males sang longer songs when females were fertile and shorter songs during territory establishment. Females consistently preferred males with longer songs and larger song repertoires. By contrast, playback experiments showed that males used short songs in territory defense. Songs were shortest at high densities, and in the highest density population only, song traits preferred by females correlated with male territoriality. Stronger male competition at high population densities likely constrains maximum song length, whereas weaker competition at low densities allows expression of female choice for long songs. Interactions between male competition and ecology may be a crucial but oft-overlooked component of phenotypic divergence and speciation.

Reexamining Phylloscopus trochiloides complex as a ring species: a refugial counter‐hypothesis

The idea of ring species has been viewed as a demonstration of the potential for species‐level differentiation produced by isolation by distance in otherwise continuous populations. Although the concept is attractive, the list of empirical examples has narrowed significantly as detailed studies have been carried out. One of the few examples still cited among birds is the warbler species complex Phylloscopus trochiloides, which comprises P. trochiloides sensu stricto, P. plumbeitarsus, and P. nitidus. The ring comprises a series of populations surrounding the Tibetan Plateau in which a species‐level break is apparent at the north end of the ring. Although recent theoretical treatments have indicated that such differentiation is possible in theory, recent genomic analyses indicated multiple differentiated populations around the ring unlikely to have resulted from isolation by distance. Here, we complement the genomic studies to date with paleodistributional projections of ecological niche models that provide further evidence for multiple, isolated refugia around the ring during and since the Late Pleistocene. As such, this group should not be interpreted as exemplifying an isolation‐by‐distance mechanism of speciation, and should no longer be considered as a ring species: genomic and geographic evidence coincide in indicating that its differentiation took place in allopatry.

Geographical variation in male territory defence strategies in an avian ring species

Interactions between sexual selection and ecology can drive phenotypic divergence between populations. Geographical variation in female preferences has been linked to ecology in several studies, but much less is known about patterns of geographical variation in male competition. I asked whether male aggressive territorial behaviour varied among three breeding populations of a ring species, the greenish warbler, Phylloscopus trochiloides. I measured aggressive response to playbacks of conspecific song at multiple time points to determine how territorial behaviour varied throughout the breeding season both within and between populations. Differences in the abundance and timing of resources necessary for raising offspring can shape male competitive strategies, and competition may consequently vary as a function of resource availability. I therefore combined assays of temporal variation in aggressive behaviour with season-long measures of food abundance, population density and parental provisioning rates. I found that the populations differed in intensity of aggressive response, the seasonal pattern of territoriality and the traits used in territorial responses. Overall intensity of aggression was lowest but most prolonged in the population with the lowest food abundance and highest population density, and males responded to playback primarily by singing. By contrast, birds in the two populations that experienced high food abundance and low population density exhibited a burst of aggressive display behaviour only when females were fertile. The results suggest that territorial strategies vary geographically and respond to limited resources, switching in function from season-long food defence where food is scarce to mate guarding where mates are scarce. Interactions between sexual selection and ecology across large geographical scales may ultimately lead to population divergence. The geographical variation in territorial behaviour observed in the greenish warbler implies that male competition may be an important diversifying force in this system.

Recurrent selection explains parallel evolution of genomic regions of high relative but low absolute differentiation in a ring species.

Recent technological developments allow investigation of the repeatability of evolution at the genomic level. Such investigation is particularly powerful when applied to a ring species, in which spatial variation represents changes during the evolution of two species from one. We examined genomic variation among three subspecies of the greenish warbler ring species, using genotypes at 13013950 nucleotide sites along a new greenish warbler consensus genome assembly. Genomic regions of low within-group variation are remarkably consistent between the three populations. These regions show high relative differentiation but low absolute differentiation between populations. Comparisons with outgroup species show the locations of these peaks of relative differentiation are not well explained by phylogenetically conserved variation in recombination rates or selection. These patterns are consistent with a model in which selection in an ancestral form has reduced variation at some parts of the genome, and those same regions experience recurrent selection that subsequently reduces variation within each subspecies. The degree of heterogeneity in nucleotide diversity is greater than explained by models of background selection, but is consistent with selective sweeps. Given the evidence that greenish warblers have had both population differentiation for a long period of time and periods of gene flow between those populations, we propose that some genomic regions underwent selective sweeps over a broad geographic area followed by within-population selection-induced reductions in variation. An important implication of this 'sweep-before-differentiation' model is that genomic regions of high relative differentiation may have moved among populations more recently than other genomic regions.

Wherefore and Whither the Ring Species?

Ring species are widely recognized as one of the best natural illustrations of species formation. A ring species is a circular arrangement of populations with one boundary characterized by reproductive isolation, but intergradation among populations elsewhere. They form when populations disperse around a central barrier and form a secondary contact characterized by reproductive isolation. Ring species are often presented as a taxonomic conundrum, because the presence of a single boundary exhibiting reproductive isolation leaves the ring of populations uncomfortably situated between one and two species. Here we review the ring species concept, with a focus on the salamander Ensatina eschscholtzii and the Greenish Warbler, Phylloscopus trochiloides. We argue that ring species demonstrate the gradual nature of species formation, and thereby illustrate the model of species formation originally put forth by Darwin. We also argue that ring species have become overly idealized, with a focus on strict criteria to...

A Spatial Framework for Understanding Population Structure and Admixture.

Geographic patterns of genetic variation within modern populations, produced by complex histories of migration, can be difficult to infer and visually summarize. A general consequence of geographically limited dispersal is that samples from nearby locations tend to be more closely related than samples from distant locations, and so genetic covariance often recapitulates geographic proximity. We use genome-wide polymorphism data to build “geogenetic maps,” which, when applied to stationary populations, produces a map of the geographic positions of the populations, but with distances distorted to reflect historical rates of gene flow. In the underlying model, allele frequency covariance is a decreasing function of geogenetic distance, and nonlocal gene flow such as admixture can be identified as anomalously strong covariance over long distances. This admixture is explicitly co-estimated and depicted as arrows, from the source of admixture to the recipient, on the geogenetic map. We demonstrate the utility of this method on a circum-Tibetan sampling of the greenish warbler (Phylloscopus trochiloides), in which we find evidence for gene flow between the adjacent, terminal populations of the ring species. We also analyze a global sampling of human populations, for which we largely recover the geography of the sampling, with support for significant histories of admixture in many samples. This new tool for understanding and visualizing patterns of population structure is implemented in a Bayesian framework in the program SpaceMix.

天売島におけるヤナギムシクイ<i>Phylloscopus plumbeitarsus</i>の北海道初記録

天売島におけるヤナギムシクイ<i>Phylloscopus plumbeitarsus</i>の北海道初記録

Seasonal and diurnal changes in the weight and fat reserves of the greenish warbler in the western Moscow region

Greenish warblers try to maintain their weight at the same level during the whole period that they spend in their nesting habitat. The average weight of these birds gradually increases from the morning to the afternoon and evening. Weight fluctuations follow diurnal changes in the locomotor activity. Fluctuations of the fat reserves in greenish warblers follow weight changes. When greenish warblers leave their nesting habitat, their body weight and fat reserves are lower than those they arrive with.

Genomic divergence in a ring species complex.

Ring species provide particularly clear demonstrations of how one species can gradually evolve into two, but are rare in nature. In the greenish warbler (Phylloscopus trochiloides) species complex, a ring of populations wraps around Tibet. Two reproductively isolated forms co-exist in central Siberia, with a gradient of genetic and phenotypic characteristics through the southern chain of populations connecting them. Previous genetic evidence has proven inconclusive, however, regarding whether species divergence took place in the face of continuous gene flow and whether hybridization between the terminal forms of the ring ever occurred. Here we use genome-wide analyses to show that, although spatial patterns of genetic variation are currently mostly as expected of a ring species, historical breaks in gene flow have existed at more than one location around the ring, and the two Siberian forms have occasionally interbred. Substantial periods of geographical isolation occurred not only in the north but also in the western Himalayas, where there is now an extensive hybrid zone between genetically divergent forms. Limited asymmetric introgression has occurred directly between the Siberian forms, although it has not caused a blending of those forms, suggesting selection against introgressed genes in the novel genetic background. Levels of reproductive isolation and genetic introgression are consistent with levels of phenotypic divergence around the ring, with phenotypic similarity and extensive interbreeding across the southwestern contact zone and strong phenotypic divergence and nearly complete reproductive isolation across the northern contact zone. These results cast doubt on the hypothesis that the greenish warbler should be viewed as a rare example of speciation by distance, but demonstrate that the greenish warbler displays a continuum from slightly divergent neighbouring populations to almost fully reproductively isolated species.

Song structure variability in passerine birds: Random variation or direct informative changes

The variability of the fine song structure was studied in the wood warbler (Phylloscopus sibilatrix), willow warbler (Ph. trochilus), greenish warbler (Ph. throchiloides viridanus), chaffinch (Fringilla coelebs), and gray shrike thrush (Colluricincla harmonica). The increase in the number of similar elements per phrase is shown to be related to the conspecific and heterospecific male-male song interactions in these birds. The responses of wood warbler males to playback conspecific songs with standard and prolonged (in the number of similar elements) second phrases differ significantly. The initial phrases of willow warbler songs become significantly longer in the populations with a high density as compared to those in populations of low density. The increase in the variability of both phrase combinations and song duration is shown to be related also to the song interaction with conspecific males for the willow warbler, greenish warbler, chaffinch, and gray shrike thrush. The within-song type variations turned out to play an important role during male-male interactions of different species. The results obtained suggest that similar ways of song responses may be quite widespread among passerine birds and reflect the general principles of changes in the song structure during acoustic interactions.

Ecological features of migrating passerines (analysis with molecular biology techniques involved)

The adaptation mechanisms in Phylloscopus warblers to habitat conditions associated with their reproduction, namely, the sex ratio, family structure, duration of sexual activity, etc., have been studied. The brood sex ratio is established to be about 1: 1 among juveniles, but males begin to predominate with time. In the reproductive period, some males remain unmated for a long time or even over the whole season. On the other hand, nesting males create pairs with second females. Visual observations and the results of a family structure analysis by means of molecular-genetic methods have shown that female “adultery” and/or forcible copulations with alien males occur from time to time, which leads to the appearance of extra-pair paternity. A PCR analysis revealed a high level of genetic diversity within the local populations of all the Phylloscopus warbler species, but the diversity for wood and greenish warblers (new species for the region) was lower than that for chiff-chaffs and willow warblers (species native to the region).

Evolution and stability of ring species

Neutral models, in which genetic change arises through random variation without fitness differences, have proven remarkably successful in describing observed patterns of biodiversity, despite the manifest role of selection in evolution. Here we investigate the effect of barriers on biodiversity by simulating the expansion of a population around a barrier to form a ring species, in which the two ends of the population are reproductively isolated despite ongoing gene flow around the ring. We compare the spatial and genetic properties of a neutral agent-based population model to the greenish warblers' complex, a well-documented example of an actual ring species in nature. Our results match the distribution of subspecies, the principal components of genetic diversity, and the linear spatial-genetic correlation of the observed data, even though selection is expected to be important for traits of this species. We find that ring species are often unstable to speciation or mixing but can persist for extended times depending on species and landscape features. For the greenish warblers, our analysis implies that the expanded area near the point of secondary contact is important for extending the duration of the ring, and thus, for the opportunity to observe this ring species. Nevertheless it also suggests the ring will break up into multiple species in 10,000 to 50,000 y. These results imply that simulations can be used to accurately describe empirical data for complex spatial-genetic traits of an individual species.

Variation of song and plumage in the western (Phylloscopus trochiloides viridanus) and eastern (Phylloscopus trochiloides plumbeitarsus) forms of the greenish warbler in a sympatry zone: Is the hypothesis of ring speciation true?

The Greenish Warbler is a classical example of ring speciation in birds. Typical ring species are supposed to form a chain of intergrading populations encircling a geographic barrier, and the terminal forms in the secondary contact coexist without interbreeding. The Western (Phylloscous trochiloides viridanus) and Eastern (Phylloscous trochiloides plumbeitarsus) forms are considered to be a terminal taxa that come into secondary contact. The morphology and song characteristics of these forms in the zone of sympatry in southern Siberia were studied. The vocalization of 133 males from 13 localities was studied. In the zone of sympatry, the population of the Greenish Warbler is polymorphic. Only 30 of 66 birds were typical plumbeitarsus. The phenotypes of the other birds appeared to be intermediate between two taxa. No break of vocal characteristics in the sympatry zone was found. Thirty-one males had a typical “east” song. Vocalization of the other 12 males corresponded to a greater extent to the “west” singing. Both phonetic and syntactic features of the Greenish Warbler’s songs in the zone of sympatry show the presence of gradual and smooth transition in vocalization between two forms. Playbacks of viridanus never elicited a response within the allopatric plumbeitarsus populations, whereas playbacks of viridanus brought on strong or medium responses of some plumbeitarsus in the zone of sympatry. In the zone of sympatry, the convergence of viridanus and plumbeitarsus according to morphological and acoustic characteristics takes place. The data obtained do not confirm the concept of ring speciation in the Greenish Warbler.

Ring distributions leading to species formation: a global topographic analysis of geographic barriers associated with ring species

BackgroundIn the mid 20th century, Ernst Mayr and Theodosius Dobzhansky championed the significance of circular overlaps or ring species as the perfect demonstration of speciation, yet in the over 50 years since, only a handful of such taxa are known. We developed a topographic model to evaluate whether the geographic barriers that favor processes leading to ring species are common or rare, and to predict where other candidate ring barriers might be found.ResultsOf the 952,147 geographic barriers identified on the planet, only about 1% are topographically similar to barriers associated with known ring taxa, with most of the likely candidates occurring in under-studied parts of the world (for example, marine environments, tropical latitudes). Predicted barriers separate into two distinct categories: (i) single cohesive barriers (< 50,000 km2), associated with taxa that differentiate at smaller spatial scales (salamander: Ensatina eschscholtzii; tree: Acacia karroo); and (ii) composite barriers - formed by groups of barriers (each 184,000 to 1.7 million km2) in close geographic proximity (totaling 1.9 to 2.3 million km2) - associated with taxa that differentiate at larger spatial scales (birds: Phylloscopus trochiloides and Larus (sp. argentatus and fuscus)). When evaluated globally, we find a large number of cohesive barriers that are topographically similar to those associated with known ring taxa. Yet, compared to cohesive barriers, an order of magnitude fewer composite barriers are similar to those that favor ring divergence in species with higher dispersal.ConclusionsWhile these findings confirm that the topographic conditions that favor evolutionary processes leading to ring speciation are, in fact, rare, they also suggest that many understudied natural systems could provide valuable demonstrations of continuous divergence towards the formation of new species. Distinct advantages of the model are that it (i) requires no a priori information on the relative importance of features that define barriers, (ii) can be replicated using any kind of continuously distributed environmental variable, and (iii) generates spatially explicit hypotheses of geographic species formation. The methods developed here - combined with study of the geographical ecology and genetics of taxa in their environments - should enable recognition of ring species phenomena throughout the world.