Corridor Hypothesis Research Articles

Molecular phylogenetics of the Ophiocordyceps sinensis-species complex lineage (Ascomycota, Hypocreales), with the discovery of new species and predictions of species distribution

Ophiocordyceps sinensis is a famous traditional Chinese medicine adapted to the alpine environment of the Qinghai-Tibet Plateau and adjacent regions. Clarification of the species diversity of Ophiocordyceps sinensis and its relatives could expand the traditional medicinal resources and provide insights into the speciation and adaptation. The study is prompted by the discovery of a new species, O. megala, described here from a biodiversity hotspot in the Hengduan Mountains, China. Combined morphological, ecological, and phylogenetic evidence supports its distinctiveness from O. sinensis, O. xuefengensis, and O. macroacicularis. Additionally, based on the phylogenetic construction of Ophiocordyceps, a special clade was focused phylogenetically on the more closely related O. sinensis complex, which was defined as the O. sinensis- species complex lineage. A total of 10 species were currently confirmed in this lineage. We made a comprehensive comparison of the sexual/asexual morphological structures among this species complex, distinguishing their common and distinctive features. Furthermore, using the method of species distribution modelling, we studied the species ocurrences in relation to climatic, edaphic, and altitudinal variables for the eight species in the O. sinensis-species complex, and determined that their potential distribution could extend from the southeastern Qinghai-Tibet Plateau to the Xuefeng Mountains without isolating barrier. Thus, the biodiversity corridor hypothesis was proposed around the O. sinensis-species complex. Our study highlights the phylogeny, species diversity, and suitable distribution of the O. sinensis-species complex lineage, which should have a positive implication for the resource discovery and adaptive evolution of this unique and valuable group.

Management diversity begets biodiversity in production forest landscapes

How to manage forest for biodiversity conservation is an ongoing debate. We argue that maximizing biodiversity in managed forest landscapes requires a diversity of forest management regimes in space and time. This will generate high levels of habitat heterogeneity at a landscape scale, which in turn will support various groups of forest species. Based on concepts from landscape ecology, we formulate five hypotheses on how management diversity, i.e. combining various management approaches can benefit overall biodiversity across a production forest landscape. First, management diversity will increase habitat diversity and, therefore, beta diversity (the habitat diversity hypothesis). Second, asynchrony in management timing will enhance long-term availability of different habitat types (the spatio-temporal heterogeneity hypothesis). Third, management to create spatial adjacency or proximity of stands with different management or successional stages will increase biodiversity by providing simultaneous access to multiple resources (the interspersion hypothesis). Fourth, heterogeneous unmanaged set-aside forests, interspersed with managed forests, are needed for complete biodiversity conservation (the natural forest hypothesis). Fifth, management diversity will create functional landscape connectivity between protected forests for multiple species through time (the temporary corridor hypothesis). Although strongly grounded in landscape and forest ecology, these five hypotheses remain largely under-investigated, and we suggest methods for how they can be tested. In the meantime, we suggest that increasing forest management diversity represents a risk-spreading approach for adaptation to global change, and therefore is likely a reasonable objective for sustainable forestry moving forward.

The role of Sahara highlands in the diversification and desert colonization of the Bosc's fringe‐toed lizard

AbstractAimThe biogeographic history of the Sahara‐Sahel desert is tightly linked to its extreme and fluctuating palaeoclimate and diverse topography. For the mesic species inhabiting the region, coastal areas and the Nile Valley are perceived as the main pathways to disperse through desert habitats, but past connections may have also occurred throughout currently isolated mountain regions. Herein, we test the trans‐Sahara mountain corridor hypothesis (i.e., mesic connectivity across Central Sahara highlands) and its role in the diversification of a small terrestrial vertebrate.LocationNorth Africa and Arabia.TaxonAcanthodactylus boskianus (Squamata: Lacertidae).MethodsWe integrated multi‐locus mitochondrial and nuclear phylogenies with species’ climate‐niche modelling, including palaeo‐projections. Genetic analyses aimed to assess the species’ genetic structure, identify its main mitochondrial lineages and nuclear diversity, and reconstruct its ancestral biogeography. Species’ climate‐niche stability was modelled independently for the Late Pleistocene‐Holocene and the Plio‐Pleistocene, to infer historical climatic refugia and dispersal corridors.ResultsFour spatially structured mitochondrial lineages, integrating several parapatric sub‐lineages, originated during the Plio‐Pleistocene. Nuclear data revealed nine potential candidate species. Climatic refugia were located in mountains and desert fringes, remaining consistent for the Late Pleistocene‐Holocene and the Plio‐Pleistocene. Recurrent North‐South climatic corridors were located along the desert periphery, while others less frequent were found across Central Sahara. Ancestral biogeography analyses recovered a recent Pleistocene colonization of the Sahel throughout eastern Sahara and either Sahara or Sahel origin for Central Sahara populations.Main conclusionsSpecies’ diversification was triggered by a combination of Plio‐Pleistocene climatic cycles across a complex topographic region, where mountains acted as the main diversification hotspots. The historical role of Central Sahara highlands as main non‐peripheral mesic refugia was corroborated. In addition, intermittent climatic connections linked Mediterranean and Sahel ecoregions with Central Sahara refugia, suggesting the existence of alternative trans‐Sahara dispersal routes to the putative coastal and Nile corridors.

Nouveaux assemblages du Paléolithique supérieur ancien en Hongrie du nord dans le contexte de l’hypothèse du Couloir danubien

Linking southeastern Europe and central Europe, the Danube Valley plays a key role in the models of the first colonization of Europe by anatomically modern humans about 40 thousand years ago (Danube Corridor hypothesis). The middle course of the river, the Carpathian Basin occupies a fundamental place in the search for archaeological evidences of the expansion of modern humans. Surveys carried out in northern Hungary in the last two decades have discovered numerous open-air sites whose lithic material can be attributed to the period concerned. Our excavations carried out in the region of Eger demonstrated the presence of the Aurignacian but also allowed the recognition of a macrolaminar industry of the Initial Upper Palaeolithic. The lithic material collected on the surface of the Andornaktálya 2 site provided rich assemblages of these two industries. The macrolaminar industry has techno-morphological connections with the leptolithic tools of Sokyrnytsia and Korolevo in Transcarpathian Ukraine. The Aurignacian industry has several characteristics in common with those of Košice-Barca and Seňa in southeastern Slovakia. Unfortunately, the chronological position of the macrolaminar and Aurignacian industries cannot be specified at the sites of the Eger region, although their age of Interpleniglacial seems evident from the stratigraphic considerations and the dating of the sediments. Despite these chronological inaccuracies, our results support the model, published by J.K. Kozłowski in 2010, of two waves of the immigration of modern humans across the Danube Corridor.

Species distribution modelling supports “nectar corridor” hypothesis for migratory nectarivorous bats and conservation of tropical dry forest

AbstractAimThe Mexican long‐tongued bat (Choeronycteris mexicana), Mexican long‐nosed bat (Leptonycteris nivalis) and lesser long‐nosed bat (Leptonycteris yerbabuenae) (Phyllostomidae: Glossophaginae) undertake long‐distance migrations from south‐central Mexico to the south‐western United States. It is proposed that these bats migrate along a nectar corridor of columnar cacti and Agave species, but this has not been tested with independent data and the spatiotemporal nature of this relationship is poorly understood. Our goal was to test this nectar corridor hypothesis and determine the relative importance of food plant and abiotic variables to the distribution and seasonal movements of these migratory nectarivores.LocationMexico and the south‐western United States.MethodsWe generated species distribution models (SDMs) of documented food plants for these bats. We then created SDMs for each bat following a model selection approach, using food plant and abiotic predictor variables. We modelled migration pathways for C. mexicana and L. yerbabuenae using circuit theory and seasonal SDMs based on seasonally available food plants.Main conclusionsFood plants were more important than climatic and topographic variables in shaping the distribution of these bats. The most important predictors of distribution were Agave, columnar cacti and species richness of food plants. Species richness of food plants was the most consistently important variable, but the components of this diversity varied by bat species: Choeronycteris mexicana was influenced by Agave and cacti; Leptonycteris nivalis was influenced solely by Agave; Leptonycteris yerbabuenae was influenced more generally by cacti, Agave and C3 plants. Migration models for C. mexicana and L. yerbabuenae provided independent support for the nectar corridor hypothesis and indicate shifts in relative importance of specific food plants throughout the year. These results suggest that conservation of these bats should focus more broadly on management for species richness of food plants, especially in tropical dry forests.

The Danube Corridor Hypothesis and the Carpathian Basin: Geological, Environmental and Archaeological Approaches to Characterizing Aurignacian Dynamics

Early Upper Paleolithic sites in the Danube catchment have been put forward as evidence that the river was an important conduit for modern humans during their initial settlement of Europe. Central to this model is the Carpathian Basin, a region covering most of the Middle Danube. As the archaeological record of this region is still poorly understood, this paper aims to provide a contextual assessment of the Carpathian Basin’s geological and paleoenvironmental archives, starting with the late Upper Pleistocene. Subsequently, it compiles early Upper Paleolithic data from the region to provide a synchronic appraisal of the Aurignacian archaeological evidence. It then uses this data to test whether the relative absence of early Upper Paleolithic sites is obscured by a taphonomic bias. Finally, it reviews current knowledge of the Carpathian Basin’s archaeological record and concludes that, while it cannot reject the Danube corridor hypothesis, further (geo)archaeological work is required to understand the link between the Carpathian Basin and Central and Southeastern Europe.

Testing the savannah corridor hypothesis during MIS2: The Boh Dambang hyena site in southern Cambodia

The Boh Dambang karstic site in southern Cambodia, Kampot province, is a mammal bone-rich deposit in a hyena site. Very few hyena sites have been recovered in the Pleistocene of Southeast Asia, thus little information is known about the foraging abilities of hyenas during that period and their decline in the region, while the other hypercarnivores (tiger, leopard, and dhole) persisted until present day.To constrain the site we applied luminescence (red TL and single-grain OSL), ESR and U/Th dating methods to the sediments and faunal teeth, respectively. The resulting age estimatessuggest that the site represents an accumulation of a young deposit with faunal teeth in the range of 25–18 ka that was last exposed to sunlight between 8 and 7 ka, and an older deposit containing older teeth (∼100–80 ka) that have been eroded from the upper caves in the system and incorporated into the younger deposit. Thus, the faunal age of 25–18 ka (MIS2), provides the best estimate for the age of the hyena site during LGM (26.5–19 ka).We analysed the assemblage of isolated teeth in terms of taxonomic diversity and abundance. The role of bone accumulators, either carnivores or rodents, has been precised through a taphonomic analysis. Diet was reconstructed through measurement of δ13C values of tooth enamel. The taphonomic analysis reveals that the hyenas were the main bone accumulators at Boh Dambang. Porcupines were aslo a factor in the accumulation of remains. The results show that the spotted hyenas hunted large-sized herbivores (>600 kg), in a mixed environment dominated by grassland.These data along with evidence from other Pleistocene faunas from Southeast Asian mainland, in terms of prey preference of hyenas (“rhinoceroses versus large bovines”) also reveal marked differences in relation to habitat type. Possible causes of the decline of the spotted hyena in the Indochinese sub-region (hypercarnivory, high trophic level, comparable foraging strategies with hunters-gatherers, and climatic changes) are tentatively proposed at this point.

How did bonobos come to range south of the congo river? Reconsideration of the divergence of Pan paniscus from other Pan populations.

While investigating the genetic structure in wild bonobos,(1) we realized that the widely accepted scenario positing that the Pleistocene appearance of the Congo River separated the common ancestor of chimpanzees (Pan troglodytes) and bonobos (P. paniscus) into two species is not supported by recent geographical knowledge about the formation of the Congo River. We explored the origin of bonobos using a broader biogeographical perspective by examining local faunas in the central African region. The submarine Congo River sediments and paleotopography of central Africa show that the Congo River has functioned as a geographical barrier for the last 34 million years. This evidence allows us to hypothesize that when the river was first formed, the ancestor of bonobos did not inhabit the current range of the species on the left bank of the Congo River but that, during rare times when the Congo River discharge decreased during the Pleistocene, one or more founder populations of ancestral Pan paniscus crossed the river to its left bank. The proposed scenario for formation of the Congo River and the corridor hypothesis for an ancestral bonobo population is key to understanding the distribution of great apes and their evolution.

New chronology for Ksâr ‘Akil (Lebanon) supports Levantine route of modern human dispersal into Europe

Modern human dispersal into Europe is thought to have occurred with the start of the Upper Paleolithic around 50,000-40,000 y ago. The Levantine corridor hypothesis suggests that modern humans from Africa spread into Europe via the Levant. Ksâr 'Akil (Lebanon), with its deeply stratified Initial (IUP) and Early (EUP) Upper Paleolithic sequence containing modern human remains, has played an important part in the debate. The latest chronology for the site, based on AMS radiocarbon dates of shell ornaments, suggests that the appearance of the Levantine IUP is later than the start of the first Upper Paleolithic in Europe, thus questioning the Levantine corridor hypothesis. Here we report a series of AMS radiocarbon dates on the marine gastropod Phorcus turbinatus associated with modern human remains and IUP and EUP stone tools from Ksâr 'Akil. Our results, supported by an evaluation of individual sample integrity, place the EUP layer containing the skeleton known as "Egbert" between 43,200 and 42,900 cal B.P. and the IUP-associated modern human maxilla known as "Ethelruda" before ∼ 45,900 cal B.P. This chronology is in line with those of other Levantine IUP and EUP sites and demonstrates that the presence of modern humans associated with Upper Paleolithic toolkits in the Levant predates all modern human fossils from Europe. The age of the IUP-associated Ethelruda fossil is significant for the spread of modern humans carrying the IUP into Europe and suggests a rapid initial colonization of Europe by our species.

The open-air site of Tolbor 16 (Northern Mongolia): Preliminary results and perspectives

Numerous questions remain regarding the timing and the context of Upper Paleolithic emergence in Northeast Asia. Available data allow the recognition of a form of Initial Upper Paleolithic (IUP) documented in the Altai circa 45–40 ka 14C BP, and in the Cis- and Transbaikal around −37 ka 14C BP. In Northern Mongolia, a series of assemblages show intriguing similarities with IUP laminar assemblages from South Siberia and suggest long distance contact/movements of population during the first half of MIS3. These contacts are potentially enabled by the main river that drains into Lake Baikal, the Selenga. By cutting through the Sayan and the Yablonovy mountain ranges, the Selenga drainage system provides a potential corridor connecting South Siberia with the plains of Mongolia. The Tolbor 16 site (Ikh Tulberiin Gol, Northern Mongolia) is located circa 13 km from the confluence with the Selenga. The first results presented here suggest that the lithic assemblage and the ornaments discovered at Tolbor 16 document the early appearance of Upper Paleolithic in the region. This newly discovered site offers the possibility to generate high-resolution contextual data on the first appearance of the blade assemblages in Mongolia and to test the ‘Selenga corridor hypothesis’.

Road verges as invasion corridors? A spatial hierarchical test in an arid ecosystem

Disturbed habitats are often swiftly colonized by alien plant species. Human inhabited areas may act as sources from which such aliens disperse, while road verges have been suggested as corridors facilitating their dispersal. We therefore hypothesized that (i) houses and urban areas are propagule sources from which aliens disperse, and that (ii) road verges act as corridors for their dispersal. We sampled presence and cover of aliens in 20 plots (6 × 25 m) per road at 5-km intervals for four roads, nested within three localities around cities (n = 240). Plots consisted of three adjacent nested transects. Houses (n = 3,349) were mapped within a 5-km radius from plots using topographical maps. Environmental processes as predictors of alien composition differed across spatial levels. At the broadest scale road-surface type, soil type, and competition from indigenous plants were the strongest predictors of alien composition. Within localities disturbance-related variables such as distance from dwellings and urban areas were associated with alien composition, but their effect differed between localities. Within roads, density and proximity of houses was related to higher alien species richness. Plot distance from urban areas, however, was not a significant predictor of alien richness or cover at any of the spatial levels, refuting the corridor hypothesis. Verges hosted but did not facilitate the spread of alien species. The scale dependence and multiplicity of mechanisms explaining alien plant communities found here highlight the importance of considering regional climatic gradients, landscape context and road-verge properties themselves when managing verges.

Habitat corridors function as both drift fences and movement conduits for dispersing flies

Corridors connect otherwise isolated habitat patches and can direct movement of animals among such patches. In eight experimental landscapes, we tested two hypotheses of how corridors might affect dispersal behavior. The Traditional Corridor hypothesis posits that animals preferentially leave patches via corridors, following them into adjacent patches. The Drift Fence hypothesis posits that animals dispersing through matrix habitat are diverted into patches with corridors because they follow corridors when encountered. House flies (Musca domestica L.), a species that prefers the habitat of our patches and corridors, were released in a central patch (100x100 m) and recaptured in peripheral patches that were or were not connected by a corridor. Flies were captured more frequently in connected than unconnected patches, thereby supporting the Traditional Corridor hypothesis. The Drift Fence hypothesis was also supported, as flies were captured more frequently in unconnected patches with blind (dead end) corridors than in unconnected patches of equal area without blind corridors. A second experiment tested whether these results might be dependent on the type of patch-matrix boundary encountered by dispersing flies and whether edge-following behavior might be the mechanism underlying the observed corridor effect in the first experiment. We recorded dispersal patterns of flies released along forest edges with dense undergrowth in the forest ("closed" edges) and along edges with little forest understory ("open" edges). Flies were less likely to cross and more likely to follow closed edges than open edges, indicating that when patch and corridor edges are pronounced, edge-following behavior of flies may direct them along corridors into connected patches. Because edges in the first experiment were open, these results also suggest that corridor effects for flies in that experiment would have been even stronger if the edges around the source patches and corridors had been more closed. Taken together, our results suggest that corridors can affect dispersal of organisms in unappreciated ways (i.e., as drift fences) and that edge type can alter dispersal behavior.

AN EXPERIMENTAL TEST OF WHETHER HABITAT CORRIDORS AFFECT POLLEN TRANSFER

Negative effects of habitat fragmentation are thought to be diminished when habitat patches are joined by a corridor. A key assumption is that corridors facilitate ex- change rates of organisms between otherwise isolated patches. If the organisms are pol- linators, corridors may be important for maintaining genetically viable populations of the plants that they pollinate. We tested the hypothesis that corridors increase the movement of insect pollinators into patches of habitat and thereby increase pollen transfer for two species of plants, one pollinated by butterflies (Lantana camara) and the other by bees and wasps (Rudbeckia hirta). We worked in an experimental landscape consisting of 40 --1- ha patches of early-successional habitat in a matrix of forest. Within each of eight exper- imental units, two patches were connected by a corridor (150 x 25 m), and three were not. Patch shape varied to control for the area added by the presence of a corridor. Differences in patch shape also allowed us to test alternative hypotheses of how corridors might function. The Traditional Corridor Hypothesis posits that corridors increase immigration and emi- gration by functioning as movement conduits between patches. The Drift Fence Hypothesis posits that corridors function by capturing organisms dispersing through the matrix, redirecting them into associated habitat patches. Using fluorescent powder to track pollen, we found that pollen transfer by butterflies between patches connected by a corridor was significantly higher than between unconnected patches (all values mean ? 1 SE: 59% ? 9.2% vs. 25% ? 5.2% of flowers receiving pollen). Likewise, pollen transfer by bees and wasps was significantly higher between connected patches than between unconnected patch- es (30% ? 4.2% vs. 14.5% ? 2.2%). These results support the Traditional Corridor Hy- pothesis. There was little support, however, for the Drift Fence Hypothesis. To generalize our results to a larger scale, we measured the probability of pollen transfer by butterflies as a function of distance along a 2000 x 75 m corridor. Pollen transfer probability expo- nentially declined with respect to distance and successfully predicted pollen transfer prob- ability on the scale of our previous experiment. These results suggest that corridors facilitate pollen transfer in fragmented landscapes.

Unexpectedly recent dates for human remains from Vogelherd.

The human skeletal remains from the Vogelherd cave in the Swabian Jura of southwestern Germany are at present seen as the best evidence that modern humans produced the artefacts of the early Aurignacian. Radiocarbon measurements from all the key fossils from Vogelherd show that these human remains actually date to the late Neolithic, between 3,900 and 5,000 radiocarbon years before present (bp). Although many questions remain unresolved, these results weaken the arguments for the Danube Corridor hypothesis--that there was an early migration of modern humans into the Upper Danube drainage--and strengthen the view that Neanderthals may have contributed significantly to the development of Upper Palaeolithic cultural traits independent of the arrival of modern humans.

Testing the usefulness of habitat corridors in mitigating the negative effects of fragmentation: the soil faunal community as a model system

The corridor hypothesis predicts that habitat corridors should attenuate the negative effects of fragmentation on populations or communities by enhancing the dispersal of organisms between the habitat fragments (the ‘rescue effect’). In the present 12-month mesocosm experiment, this hypothesis was tested using the soil micro- and mesofaunal community in humus patches—either connected or unconnected with humus corridors to each other—as a model system. Of particular interest was to explore whether faunal groups with differing life strategies (e.g. in trophic position and dispersal capacity) would differ in their responses to the corridors. The results showed that enchytraeid worms were the only faunal group affected by the corridors: population growth of the worms was promoted by the presence of the corridors. The lack of corridor effects on other soil fauna, such as microarthropods, is likely to be due to unexpected increases in the populations and species richness of this fauna in the humus patches, thus providing no grounds for the rescue effect to operate. The results of the experiment indicate that the faunal groups studied are not sensitive to fragmentation-induced changes in their landscape. It is suggested that the high heterogeneity and availability of resources (including space) even in a small volume of soil render the use of corridors by this soil fauna ineffective.

Molecular Phylogeny and Evolution of the Freshwater Eel, Genus Anguilla

A molecular phylogenetic analysis was conducted on all of the known catadromous eel species of the genus Anguilla to assess their relationships and evolutionary history. The analyses of a total of 1427 bp of the mitochondrial 16S ribosomal RNA and 1140 bp of the complete cytochrome b gene sequences suggested that the genus Anguilla was monophyletic in origin, with A. borneensis as the most basal species. Four clades/species groups that correspond to their geographical ranges were indicated, Indo-Atlantic (three species), Oceania (two species), tropical Pacific (two species), and Indo-Pacific (five species), with ambiguous positions for A. japonica and A. reinhardti. This grouping conflicts with that of a previous morphological study, since the broad undivided maxillary and short-fin type, which were thought to be phylogenetically important, were paraphyletic in the molecular analysis. However, the molecular phylogeny and the present geographic distribution of species suggested historical dispersion of the genus Anguilla according to the Tethys corridor hypothesis, which proposed that anguillid eels originated near present-day Indonesia and dispersed westward along paleo-circumglobal equatorial currents. The westward-moving strain entered the paleo-Atlantic thyough the Tethys Sea and was ancestral to present-day European and American species.

Countercyclical versus Passive Monetary Policy in a Medium-Run Macro Model

A macro model of an inflationary economy incorporating the government budget constraint is set up to analyze two alternative monetary policy regimes: a passive policy and an active countercyclical policy. It is found that the policy is potentially unstable, especially when monetarist parameter values prevail, whereas the local stability of fullemployment equilibrium can always be ensured by choosing an appropriate countercyclical feedback rule for the monetary growth rate. An active monetary policy can also smooth out the business cycle in the neighborhood of equilibrium, but in accordance with Leijonhufvud's corridor hypothesis, instability may occur when output is pushed sufficiently far below its full-employment level.