Stepping Stone Islands Research Articles

A historical stepping-stone path for an island-colonizing cactus across a submerged "bridge" archipelago.

Here we use population genomic data (ddRAD-Seq) and ecological niche modeling to test biogeographic hypotheses for the divergence of the island-endemic cactus species Cereus insularis Hemsl. (Cereeae; Cactaceae) from its sister species C. fernambucensis Lem. The Cereus insularis grows in the Fernando de Noronha Islands (FNI), a Neotropical archipelago located 350 km off the Brazilian Atlantic Forest (BAF) coast. Phylogeographic reconstructions support a northward expansion by the common ancestor of C. insularis and C. fernambucensis along the mainland BAF coast, with C. insularis diverging from the widespread mainland taxon C. fernambucensis after colonizing FNI in the late Pleistocene. The morphologically distinct C. insularis is monophyletic and nested within C. fernambucensis, as expected from a progenitor-derivative speciation model. We tested alternative biogeographic and demographic hypotheses for the colonization of the FNI using Approximate Bayesian Computation. We found the greatest support for a stepping-stone path that emerged during periods of decreased sea level (the "bridge" hypothesis), in congruence with historical ecological niche modeling that shows highly suitable habitats on stepping-stone islands during glacial periods. The outlier analyses reveal signatures of selection in C. insularis, suggesting a putative role of adaptation driving rapid anagenic differentiation of this species in FNI.

Alone on an island: The reassessment of an enigmatic species of Handmaiden Moth (Lepidoptera, Erebidae) endemic to Mauritius

AbstractMaculonaclia florida (de Joannis, 1906) has been one of the most mysterious moths of Mauritius, a small volcanic island located some 900 km east from Madagascar. Here, we reviewed its generic placement, phylogenetic relationships and the potential evolutionary scenarios leading to the current distribution of this unique Mauritian member of Syntomini. The species, known previously only from a few old museum specimens, is redescribed based on newly collected material including both sexes and eggs. The generic affiliation to the Palaearctic Dysauxes is confirmed based on morphological and molecular data. A hypothesis is presented on the colonization of Mauritius by the ancestor of D. florida from Madagascar through the now submerged stepping stone islands of the Mascarene ridge. Behavioural data and environment preferences of D. florida are assessed for the first time. The species prefers shrubby vegetation with a humid understory, and presence of endemic shrub Ixora parviflora seems to play a role in selecting the suitable microhabitat. Additionally, based on IUCN criteria, a CR threat category is proposed, highlighting the major risk factors affecting the species. The significant variation in wing venation of D. florida is noted and provisionally correlated with environmental stress, which is the consequence of human‐caused habitat degradation. Finally, the study provides further evidence for the significant role of Madagascar in the diversification of continental biota, indicating a Malagasy origin of the African syntomine Pseudonaclia puella.

Mouse management on Ōtamahua/Quail Island—lessons learned

ABSTRACTŌtamahua/Quail Island is an 85 ha Recreation Reserve in Lyttelton Harbour, New Zealand. It is being ecologically restored and cats, hedgehogs, rabbits, mustelids and rats have been eradicated. However, the house mouse (Mus musculus) survived two eradication attempts, a bait station operation in 2002 and an aerial operation in 2009. Data on aerial bait deposition, bait degradation, mouse resurgence and non-target mortalities were collected. Brodifacoum bait deposition in many areas was considerably lower than the prescribed rate of 8 kg/ha. Mouse sign was simultaneously detected at seven sites around the island 6 months after the aerial operation. Tails were collected from trapped mice on Quail Island, the adjacent mainland and on the stepping-stone island (King Billy) to undertake DNA analysis. Little genetic discrimination was observed between samples obtained after the 2009 aerial bait operation, and samples from before or outside of the bait drop. By contrast, samples taken from a location 15 km distant were genetically distinguishable. Intensive trapping was also trialled in a 2 ha area as a possible strategy to regulate the mouse density using two trap designs and three bait types. Mouse trapping data indicated that abundance was highest in May and lowest in January. The results are discussed in terms of mouse eradication and management.

Analysing the importance of stepping-stone islands in maintaining structural connectivity and endemicity

We analysed the species–area relationship and structural connectivity among islands of La Maddalena Archipelago (Italy), a numerous group of small islands very close to Sardinia. We related species richness (amphibians and reptiles) to several environmental factors (area; number of unique habitats; topographical variables; and distances of each island to Sardinia, to the nearest island and to the nearest large island) using generalized additive models and connectivity analysis by graph theory and the software Conefor 2.6. Using each method, we performed several comparisons: considering all species; excluding species with a high exchange rate (‘in transit’); including only autochthonous species; and including species present on large islands. We also excluded, in turn, all amphibians; all Scincidae; all Gekkonidae; all Lacertidae; all Colubridae; and one species in turn. Except in the case of species present on large islands, all models selected the same variables: ruggedness standard deviation, area, number of unique habitats, and mean and maximal elevation. When excluding Sardinia, the highest connectivity value corresponded to the largest islands. Species richness is related to island complexity (habitat diversity and topographical complexity) and not simply to area. Network connectivity is dominated by the internal connectivity of the largest islands, but small islands are essential to maintain the network connectivity and endemicity.

Native plant species richness on Eastern Polynesia’s remote atolls

Which abiotic factors influence the number of native plant species on remote atolls is an important question to understand better the spatial pattern of the species observed on these low and vulnerable coral islands. However, this issue is still very poorly documented, often due to human degradation, partial botanical surveys or the difficult geographic access of remote atolls for researchers. The remote atolls of Eastern Polynesia, which are among the most isolated in the world, are of great interest for studies of native species’ distribution due to their isolation, low human density and urbanisation. In this study, we selected 49 remote atolls of Eastern Polynesia with complete botanical surveys to test the relative influence of eight abiotic factors on native plant species richness (i.e. indigenous and endemic species). Abiotic factors used as potential predictors included atoll area (km2), shoreline length (km), atoll elevation (m) and index of isolation (UNEP), but also the coastal index of the atoll ( Ic), the distance to the nearest similar atoll (km), the distance to the nearest large volcanic island ≥ 1000 km2 (here, Tahiti as a potential stepping-stone island) and the distance to the nearest raised atoll ≥ 15 m a.s.l. (here, Makatea or Henderson as a potential refugium during sea-level highstands). Spearman’s rank correlation, linear regression analysis and frequency diagrams were used to assess the relative influence of these factors on native species richness. No relationship was found between the species richness and the index of isolation or the distance to the nearest similar atoll. Atoll area and distance to the nearest raised atoll of Makatea explained 47.1% and 40%, respectively, of the native species richness variation observed on the remote atolls. The distance to the volcanic island of Tahiti and the coastal index explained 36.9% and 27.3% of the variation, while elevation and shoreline length explained 23.3% and 18.4% of the variation, respectively. Native species richness on the atolls surveyed increased with the increasing atoll area, elevation and shoreline length, but decreased with the increasing distance to the nearest raised atoll of Makatea and the large volcanic island of Tahiti. This supports the view that the spatial pattern of native species richness observed on the remote atolls was strongly influenced by (i) atoll area but also by (ii) the distance to the raised atoll of Makatea, and (iii) the distance to the volcanic island of Tahiti. This finding suggests that the raised atoll may be viewed as a refugium during sea-level highstands while the large volcanic island played the role of stepping-stone island, both islands influencing the dispersal of native species on remote atolls and attenuating the isolation effect in the study area.

The Canaries: an important biogeographical meeting place

The Canaries: an important biogeographical meeting place

Tracing the colonization history of the Indian Ocean scops-owls (Strigiformes: Otus) with further insight into the spatio-temporal origin of the Malagasy avifauna

BackgroundThe island of Madagascar and surrounding volcanic and coralline islands are considered to form a biodiversity hotspot with large numbers of unique taxa. The origin of this endemic fauna can be explained by two different factors: vicariance or over-water-dispersal. Deciphering which factor explains the current distributional pattern of a given taxonomic group requires robust phylogenies as well as estimates of divergence times. The lineage of Indian Ocean scops-owls (Otus: Strigidae) includes six or seven species that are endemic to Madagascar and portions of the Comoros and Seychelles archipelagos; little is known about the species limits, biogeographic affinities and relationships to each other. In the present study, using DNA sequence data gathered from six loci, we examine the biogeographic history of the Indian Ocean scops-owls. We also compare the pattern and timing of colonization of the Indian Ocean islands by scops-owls with divergence times already proposed for other bird taxa.ResultsOur analyses revealed that Indian Ocean islands scops-owls do not form a monophyletic assemblage: the Seychelles Otus insularis is genetically closer to the South-East Asian endemic O. sunia than to species from the Comoros and Madagascar. The Pemba Scops-owls O. pembaensis, often considered closely related to, if not conspecific with O. rutilus of Madagascar, is instead closely related to the African mainland O. senegalensis. Relationships among the Indian Ocean taxa from the Comoros and Madagascar are unresolved, despite the analysis of over 4000 bp, suggesting a diversification burst after the initial colonization event. We also highlight one case of putative back-colonization to the Asian mainland from an island ancestor (O. sunia). Our divergence date estimates, using a Bayesian relaxed clock method, suggest that all these events occurred during the last 3.6 myr; albeit colonization of the Indian Ocean islands were not synchronous, O. pembaensis diverged from O. senegalensis about 1.7 mya while species from Madagascar and the Comoro diverged from their continental sister-group about 3.6 mya. We highlight that our estimates coincide with estimates of diversification from other bird lineages.ConclusionOur analyses revealed the occurrence of multiple synchronous colonization events of the Indian Ocean islands by scops-owls, at a time when faunistic exchanges involving Madagascar was common as a result of lowered sea-level that would have allowed the formation of stepping-stone islands. Patterns of diversification that emerged from the scops-owls data are: 1) a star-like pattern concerning the order of colonization of the Indian Ocean islands and 2) the high genetic distinctiveness among all Indian Ocean taxa, reinforcing their recognition as distinct species.

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.

The Prehistory of Buka: A Stepping Stone Island in the Northern Solomons (review)

Reviewed by: The Prehistory of Buka: A Stepping Stone Island in the Northern Solomons Simon Holdaway The Prehistory of Buka: A Stepping Stone Island in the Northern Solomons. Stephen Wickler. Terra Australis 16. Canberra: Department of Archaeology and Natural History and Centre for Archaeological Research, The Australian National University, 2001. xix + 360 pp., 68 figs., 40 plates, 175 tables, bibliography. Paperback. ISBN 0-7315-5500-7. This work reports on archaeological fieldwork conducted on the small offshore islands of Sohano and Pororan over eight months in 1987, which formed the basis of Wickler's doctoral dissertation. As is spelled out in Chapter 1, "Introduction and Research Design," Wickler sets out to test the ceramic sequence proposed by Jim Specht in his 1969 doctoral dissertation, examine the temporal relationships between the pottery styles that Specht proposed, and document more fully the rather insubstantial evidence for Lapita occupation that Specht discovered. In addition, Wickler seeks to provide both a more detailed understanding of occupation and settlement before Lapita through the analysis of nonceramic artifacts and faunal remains. Wickler's discovery on Buka of pre-ceramic occupations dating well back into the Pleistocene at Kilu Cave is by now well known, but in the book full details of the excavation are provided together with an analysis of the artifacts and fauna. Details are also provided for excavations at Palandraku Cave, where a brief pre-Lapita occupation, dated to approximately 5000 B.P., is inferred. Both caves also provided faunal evidence. However, to document the ceramic sequence, Wickler turned away from the caves, concentrating instead on a series of coastal sites with limited occupation spans. Significantly, some of the sites used are reef deposits, not a site type investigated by Specht, but targeted because of discoveries in similar situations on Nissan and in the Bismarcks. Ceramics from these sites are analyzed using attributes that relate to temper and paste, as well as vessel form and decoration. Analyses aimed at determining the nature of exchange and interaction during and after Lapita are partly based on these pottery studies, but also are based on an analysis of obsidian artifacts. In studying these materials, Wickler is concerned with isolating long-term trends in the movement of pottery and obsidian, and similar long-term patterns are sought in the faunal evidence, particularly information related to the shift from hunting and gathering to agriculture. The Prehistory of Buka is organized in a way similar to other regionally based Pacific archaeology studies. Chapter 2 backgrounds the natural and cultural environments, while Chapter 3 provides details of the site survey and excavations at a series of sites. Rather than attempt a wide-ranging survey, Wickler targeted the coastal portion of the raised Sohano formation within the Lonaha and Soraken land systems as areas in which suitable places to excavate might be [End Page 153] found. The sites studied are broken into two groups: the reef sites that provide most of the evidence for Lapita occupation, and excavated sites on land. The reef sites consist of scatters of pottery and stone artifacts distributed across the intertidal reef flats at three locations. Four of the excavated sites are beach deposits while the other three occur in caves or rockshelters. Full descriptions are provided for each of the excavations to a generally high standard, although the reproduction of photographs is poor. A section at the end of the chapter summarizes chronological information based on a sample of 16 radiocarbon determinations, nine of these obtained from the pre-ceramic levels at Kilu Cave and a further two from the preceramic deposits at Palandraku Cave. This leaves only six determinations for the excavated ceramic sites. Chapter 4 deals with Lapita pottery design and analysis, comparing assemblages from three reef sites, one each on Sohano Island, Buka Island, and Nissan Island. The chapter reports on the analysis of more than 42,000 sherds (the vast majority from one site), although only a much smaller sample (around 15 percent) of diagnostic sherds: those that are either shaped, decorated, or both, are subjected to the full range of analyses. Analysis involves a consideration of vessel morphology, manufacturing and finishing techniques, paste, composition, and decoration and is aimed at answering...

How important were stepping stones in the colonization of Krakatau?

In theory, one factor determining the rate and nature of the assembly of island biotas is the presence or absence of stepping stone islands, yet no field studies have demonstrated stepping stone function in practice. Krakatau, in Sunda Strait, is about equidistant from Java and Sumatra. Sebesi lies about half way between Krakatau and Sumatra, but no island intervenes between Krakatau and the nearest coast of Java. We assess the evidence that Sebesi has acted as an important stepping stone for Krakatau's recolonization since the devastating 1883 volcanic eruption. About a quarter of Krakatau's resident land birds, two-fifths of its reptiles, bats and land molluscs, and about two-thirds of its termites, pteridophytes, butterflies and spermatophytes are unknown on Sebesi, evidently having colonized without stepping stone involvement. Identifiable Sumatran taxa do not outnumber identifiable Javan ones on Krakatau, nor do historical distribution records indicate movement from Sebesi to Krakatau in animal groups. Krakatau's biota is not a subset of Sebesi's in predominantly anemochorous or thallassochorous plant groups, butterflies, reptiles or bats, and is only marginally so in termites. It is a subset in predominantly zoochorous spermatophyte groups, except Ficus species, and in birds and land molluscs. Comparison with a weaker stepping stone candidate, Panaitan, provides no evidence for a stepping stone role for Sebesi in butterflies or termites. We discuss the dispersal and establishment constraints on colonization by the groups involved, and conclude that, overall, Sebesi had little impact as a stepping stone. Instead, it is more probable that divergence of the environments of the two islands has led to an increasingly independent recolonization of Krakatau.

Peninsular Diversity Patterns

Previous articleNext article No AccessNotes and CommentsPeninsular Diversity PatternsMichael E. GilpinMichael E. Gilpin Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The American Naturalist Volume 118, Number 2Aug., 1981 Published for The American Society of Naturalists Article DOIhttps://doi.org/10.1086/283822 Views: 4Total views on this site Citations: 11Citations are reported from Crossref Copyright 1981 The University of ChicagoPDF download Crossref reports the following articles citing this article:Yeong-Seok Jo, Richard D. Stevens, John T. Baccus Peninsula effect and species richness gradient in terrestrial mammals on the Korean Peninsula and other peninsulas, Mammal Review 47, no.44 (Jun 2017): 266–276.https://doi.org/10.1111/mam.12094C. Battisti Peninsular patterns in biological diversity: historical arrangement, methodological approaches and causal processes, Journal of Natural History 48, no.43-4443-44 (Jun 2014): 2701–2732.https://doi.org/10.1080/00222933.2014.925599 References, (Apr 2013): 249–280.https://doi.org/10.1201/b14057-9Anna Traveset, Anna Jakobsson Ecology of Plant Reproduction, (Dec 2009).https://doi.org/10.1201/9781420007626.ch17Walter Harwood, Ralph Mac Nally Geometry of Large Woodland Remnants and its Influence on Avifaunal Distributions, Landscape Ecology 20, no.44 (May 2005): 401–416.https://doi.org/10.1007/s10980-004-3163-xSei-Woong Choi Trends in butterfly species richness in response to the peninsular effect in South Korea, Journal of Biogeography 31, no.44 (Mar 2004): 587–592.https://doi.org/10.1046/j.1365-2699.2003.01007.xJohn F. Fox Size and sex allocation in monoecious woody plants, Oecologia 94, no.11 (Jan 1993): 110–113.https://doi.org/10.1007/BF00317310Thomas Caraco, Thomas S. Whittam Immigration-extinction competition on islands: Associations among three species, Journal of Theoretical Biology 110, no.22 (Sep 1984): 241–252.https://doi.org/10.1016/S0022-5193(84)80056-9 Stephen D. Busack , and S. Blair Hedges Is the Peninsular Effect a Red Herring?, The American Naturalist 123, no.22 (Oct 2015): 266–275.https://doi.org/10.1086/284201 Timothy E. Lawlor The Peninsular Effect on Mammalian Species Diversity in Baja California, The American Naturalist 121, no.33 (Oct 2015): 432–439.https://doi.org/10.1086/284071Michael E. Gilpin The role of stepping-stone islands, Theoretical Population Biology 17, no.22 (Apr 1980): 247–253.https://doi.org/10.1016/0040-5809(80)90009-X

The role of stepping-stone islands

Equilibrium island biogeography is used to assess the importance of stepping stone islands in the colonization of more distant islands. The effect of a single stepping-stone island is relatively small, as it chiefly serves to increase the colonization rate of species that should be successful colonists in any case. A chain of stepping stones boosts colonization more than a single, centrally located stepping stone of the same total area.

: The Distribution of Compound Fishhook Types as a Gauge of Population Interaction in the Solomon Islands . Henry Cummings. ; A Style Analysis of Pottery Sherds from Nissan Island, Papua New Guinea: An Inquiry Into the Prehistory of a Stepping Stone Island and Its Role in Regulating Trade and Population Interaction between the Solomons and the Bismarck Archipelago .

Book reviewed in this article: Archaeology: The Distribution of Compound Fishhook Types as a Gauge of Population Interaction in the Solomon Islands. Henry Cummings Archaeology: A Style Analysis of Pottery Sherds from Nissan Island, Papua New Guinea: An Inquiry into the Prehistory of a Stepping Stone Island and its Role in Regulating Trade and Population Interaction between the Solomons and the Bismarck Archipelago. Susan Kaplan