Biotic Boundaries Research Articles

An analytically derived delineation of the West African Coastal Province based on bivalves

AbstractAimTo assess the pattern of biotic regions (BR) and their boundaries, to detect chorotypes and to relate these patterns to key environmental factors.LocationEastern Atlantic Ocean.Time periodRecent.Taxon studiedBivalvia.MethodsDistributions were scored for 595 species. Operational geographical units are classified hierarchically using Baroni‐Urbani & Buser similarity index, clusters were assessed for statistical significance with the ‘RMacoqui 1.0’ software using G tests of independence, and chorotypes were inferred likewise from similarity between species distributions.ResultsThree strong biotic boundaries delimit four BR: (1) European Atlantic and Mediterranean; (2) West African, from western Sahara to southern Angola; (3) Baia dos Tigres/Namibia; and (4) Saint Helena/Ascension. The West African BR is subdivided by two weak boundaries into three subordinate BR: the tropical region proper, the north‐western African transition zone and the cluster (southern Angola/São Tomé/Cape Verde Islands). Of the 429 species present in West Africa, 261 (60.7%) are endemic, and 19 genera (7.2%) are endemic. Sixteen chorotypes were identified; the European BR is correlated with chorotypes C5 (149 species mostly European and Mediterranean) and C3 (38 species mostly in northern Europe), whereas the West African BR is mainly characterized by chorotype C6 (221 species). Some discontinuous distribution patterns of tropical West African species were identified as chorotypes, but subordinate to chorotype C6. The West African BR is mainly characterized by sea surface temperature and chlorophyll; characterization without the islands also involved the extensive sandy coast. The north‐western African transition region is characterized by an arid climate and few rivers and influenced by seasonal upwelling. The cluster of southern Angola, Sao Tomé and Cape Verdes contrasts with the remainder of West Africa in having a predominantly rocky shore.Main conclusionsThe present analyses provide an objective regionalization based on species occurrences, which supports the traditional recognition of West Africa as a major biotic region with a high level of endemism. Attention is called on that the unique endemic component is insufficiently represented in current marine protected areas.

How do hedgerows influence soil organic carbon stock in livestock‐grazed pasture?

AbstractHedgerows have the potential to influence ecosystem function in livestock‐grazed pasture. Despite this, they are often ignored when quantifying farmland ecosystem service delivery. In this study, we assess the contribution of hedgerows to the ecosystem function of carbon (C) storage, with a particular emphasis on soil organic carbon (SOC). We measured SOC stock (kg C m−2), on an equivalent soil mass basis, at 0–0.15 m depth in pasture adjacent to 38 hedgerows (biotic) and 16 stone walls or fences (abiotic controls) across ten farms in the county of Conwy, Wales, UK. Pasture SOC stock (~7 kg C m−2) was similar adjacent to biotic and abiotic field boundaries, positively associated with soil moisture and negatively with soil bulk density (BD). For biotic boundaries, two further variables were significantly associated with SOC stock, distance from hedgerow (decrease in SOC stock) and slope orientation (upslope SOC stock greater than downslope). For pasture adjacent to hedgerows, a model combining the aforementioned variables (BD, soil moisture, distance from hedgerow, slope orientation) explained 78% of variation in SOC stock. This study demonstrates that whilst hedgerows do have subtle positive effects on SOC stock in adjacent pasture, SOC storage adjacent to field boundaries is influenced more by soil moisture content and BD than field boundary type.

P‐removal for restoration ofNardusgrasslands on former agricultural land: cutting traditions

AbstractPast intensive land use complicates the successful restoration of oligotrophic species‐rich grassland types. One of the major bottlenecks are the elevated nutrient levels due to fertilization, especially residual phosphorus (P). Aiming to deplete nutrients, managers often reintroduce traditional haymaking management, sometimes combined with grazing. Here, we evaluate whether this technique restores the abiotic and biotic boundary conditions for restoration ofNardusgrassland. Seven grasslands were selected in Flanders, Belgium, which had elevated nutrient levels after the cessation of intensive agriculture 16–24 years ago, and which have been mown and grazed since. We compared soil and vegetation data of these postfertilization grasslands with 34 well‐developed oligotrophicNardusgrasslands. Mowing and grazing did not cause community composition to resemble that ofNardusgrassland. Furthermore, bioavailable P‐concentrations were significantly higher in the postfertilization grasslands and P‐limitation was not obtained. Restoring P‐poor soil conditions through continued mowing and grazing management would take at least decades. Phosphorus‐mining can shorten the restoration time by increased P‐removal. Given our results, we propose a decision framework to aid planners and managers in their choice of interventions. Cost‐effective efforts for restoration should be well‐prepared, including measurements of important initial soil characteristics. This allows for an evaluation of “distance to target” and the selection of an effective restoration technique. These techniques may involve cutting the mowing tradition, and utilizing P‐mining or topsoil removal instead.

Amphibian and reptilian distribution patterns in the transitional zone between the Euro-Siberian and Central Asia Subrealms

There exist some controversies over the larger zoogeographic divisions of the arid areas of Central Asia, whose characteristics include complex ecological environments, complex fauna origins and unique patterns of animal distribution. The aim of this study was to determine, using quantitative analysis, the distribution patterns of amphibians and reptiles in the arid areas of Central Asia, whose various physiographical regions were divided into 17 Operative Geographical Units (OGUs). Based on the presence or absence of 52 amphibian and reptile genera in the 17 OGUs, and by making use of the Czekanowski Similarity Index, the Baroni-Urbani and Buser’s Similarity Index, and the strong and weak boundary test, we studied the biotic boundaries within these contested regions. In accordance with our results, the classification dendrogram was divided into two main branches. One branch is composed of the northern OGUs of the Altai Mountains which are a part of the Euro-Siberian Subrealm. The other branch includes all of the OGUs south of the Altai Mountains, which belong to the Central Asia Subrealm. There is a significantly weak biotic boundary (DW>0, GW>GS, P<0.01) between the Euro-Siberian Subrealm and the Central Asia Subrealm that corresponded to the transitional zones. The boundary between the two subrealms runs along the Altai Mountains, the Sayan Mountains, the Hangai Mountains and the Mongolian Dagurr Mountains. The boundaries between the main branches in the Central Asia Subrealm are weak, reflecting the widespread existence of transitional zones in the arid areas of Central Asia. The Tianshan Mountains should be elevated to form its own separate region, “the Middle Asian Mountain Region”, which, due to its special fauna and environment, would be classified at the same level as the Mongolia-Xinjiang Region. With the approach of creating a cluster analysis dendogram based upon the genera of amphibians and reptiles, the relationship of these higher level zoogeographical divisions was successfully resolved and the error of long-branch attraction was also avoided. With our clustering dendrogram as the foundation, the independence test was applied to strong and weak boundaries, and this resolved the problem of where to attribute the transition areas and revealed as well the barrier effect that physical, geographic boundaries have upon amphibians and reptiles. The approach of combining genera clustering analysis with a statistical boundary test should be applicable not only to the distribution patterns of other animal groups, but also to delineating large-scale zoogeographical divisions.

Saltmarsh boundary modulates dispersal of mangrove propagules: implications for mangrove migration with sea-level rise.

Few studies have empirically examined the suite of mechanisms that underlie the distributional shifts displayed by organisms in response to changing climatic condition. Mangrove forests are expected to move inland as sea-level rises, encroaching on saltmarsh plants inhabiting higher elevations. Mangrove propagules are transported by tidal waters and propagule dispersal is likely modified upon encountering the mangrove-saltmarsh ecotone, the implications of which are poorly known. Here, using an experimental approach, we record landward and seaward dispersal and subsequent establishment of mangrove propagules that encounter biotic boundaries composed of two types of saltmarsh taxa: succulents and grasses. Our findings revealed that propagules emplaced within saltmarsh vegetation immediately landward of the extant mangrove fringe boundary frequently dispersed in the seaward direction. However, propagules moved seaward less frequently and over shorter distances upon encountering boundaries composed of saltmarsh grasses versus succulents. We uniquely confirmed that the small subset of propagules dispersing landward displayed proportionately higher establishment success than those transported seaward. Although impacts of ecotones on plant dispersal have rarely been investigated in situ, our experimental results indicate that the interplay between tidal transport and physical attributes of saltmarsh vegetation influence boundary permeability to propagules, thereby directing the initial phase of shifting mangrove distributions. The incorporation of tidal inundation information and detailed data on landscape features, such as the structure of saltmarsh vegetation at mangrove boundaries, should improve the accuracy of models that are being developed to forecast mangrove distributional shifts in response to sea-level rise.

Genome-wide analysis of Sphingomonas wittichii RW1 behaviour during inoculation and growth in contaminated sand.

The efficacy of inoculation of single pure bacterial cultures into complex microbiomes, for example, in order to achieve increased pollutant degradation rates in contaminated material (that is, bioaugmentation), has been frustrated by insufficient knowledge on the behaviour of the inoculated bacteria under the specific abiotic and biotic boundary conditions. Here we present a comprehensive analysis of genome-wide gene expression of the bacterium Sphingomonas wittichii RW1 in contaminated non-sterile sand, compared with regular suspended batch growth in liquid culture. RW1 is a well-known bacterium capable of mineralizing dibenzodioxins and dibenzofurans. We tested the reactions of the cells both during the immediate transition phase from liquid culture to sand with or without dibenzofuran, as well as during growth and stationary phase in sand. Cells during transition show stationary phase characteristics, evidence for stress and for nutrient scavenging, and adjust their primary metabolism if they were not precultured on the same contaminant as found in the soil. Cells growing and surviving in sand degrade dibenzofuran but display a very different transcriptome signature as in liquid or in liquid culture exposed to chemicals inducing drought stress, and we obtain evidence for numerous ‘soil-specific' expressed genes. Studies focusing on inoculation efficacy should test behaviour under conditions as closely as possible mimicking the intended microbiome conditions.

Common distribution patterns of marsupials related to physiographical diversity in Venezuela.

The aim of this study is to identify significant biotic regions (groups of areas with similar biotas) and biotic elements (groups of taxa with similar distributions) for the marsupial fauna in a part of northern South America using physiographical areas as Operational Geographical Units (OGUs). We considered Venezuela a good model to elucidate this issue because of its high diversity in landscapes and the relatively vast amount of information available on the geographical distribution of marsupial species. Based on the presence-absence of 33 species in 15 physiographical sub-regions (OGUs) we identified Operational Biogeographical Units (OBUs) and chorotypes using a quantitative analysis that tested statistical significance of the resulting groups. Altitudinal and/or climatic trends in the OBUs and chorotypes were studied using a redundancy analysis. The classification method revealed four OBUs. Strong biotic boundaries separated: i) the xerophytic zone of the Continental coast (OBU I); ii) the sub-regions north of the Orinoco River (OBU III and IV); and those south to the river (OBU II). Eleven chorotypes were identified, four of which included a single species with a restricted geographic distribution. As for the other chorotypes, three main common distribution patterns have been inferred: i) species from the Llanos and/or distributed south of the Orinoco River; ii) species exclusively from the Andes; and iii) species that either occur exclusively north of the Orinoco River or that show a wide distribution throughout Venezuela. Mean altitude, evapotranspiration and precipitation of the driest month, and temperature range allowed us to characterize environmentally most of the OBUs and chorotypes obtained.

Twelve new Demospongiae (Porifera) from Chilean fjords, with remarks upon sponge-derived biogeographic compartments in the SE Pacific.

This article reports on 12 new species originating from the Chilean fjords region, namely Clathria (Microciona) mytilifila sp. nov., Haliclona (Reniera) caduca sp. nov., Latrunculia (L.) ciruela sp. nov., Latrunculia (L.) copihuensis sp. nov., Latrunculia (L.) verenae sp. nov., Latrunculia (L.) yepayek sp. nov., Myxilla (Burtonanchora) araucana sp. nov., Neopodospongia tupecomareni sp. nov., Oceanapia guaiteca sp. nov., Oceanapia spinisphaera sp. nov., Suberites cranium sp. nov. and Tethya melinka sp. nov. The material studied was collected between 5 and 30 m depth at latitudes comprised between 42º and 50ºS, and is part of a large collection of Chilean sponges gathered by an international team in a series of expeditions. Identification keys are provided for SE Pacific Suberites and Latrunculia, and the known species of Myxilla (Burtonanchora) and Neopodospongia. A trans-Pacific link to the New Zealand fauna was retrieved for the latter genus. Distribution ranges apparent from the materials studied here are judged too preliminary to allow any inference on biotic boundaries in the SE Pacific. A revision of earlier assertions about these biogeographic units and their boundaries concluded that very little support remains other than for existence of a Magellanic fauna. This is in part a consequence of revising the taxonomy of sponge species originally deemed to underpin these areas. Specifically, the former proposal of a Central to Southern Chile biogeographic unit (33-56ºS) has been markedly undone.

Temporal Geobiotic Mapping: a conceptual mapping technique toward visualising geobiotic areas in cross-section

Geobiota are defined by taxic assemblages (i.e., biota) and their defining abiotic breaks, which are mapped in cross-section to reveal past and future biotic boundaries. We term this conceptual approach Temporal Geobiotic Mapping (TGM) and offer it as a conceptual approach for biogeography. TGM is based on geological cross-sectioning, which creates maps based on the distribution of biota and known abiotic factors that drive their distribution, such as climate, topography, soil chemistry and underlying geology. However, the availability of abiotic data is limited for many areas. Unlike other approaches, TGM can be used when there is minimal data available. In order to demonstrate TGM, we use the well-known area in the Blue Mountains, New South Wales (NSW), south-eastern Australia and show how surface processes such as weathering and erosion affect the future distribution of a Moist Basalt Forest taxic assemblage. Biotic areas are best represented visually as maps, which can show transgressions and regressions of biota and abiota over time. Using such maps, a biogeographer can directly compare animal and plant distributions with features in the abiotic environment and may identify significant geographical barriers or pathways that explain biotic distributions.

Effect of the East Siberian barrier on the echinoderm dispersal in the Arctic Ocean

The distributional patterns were analyzed for 43 species and 33 genera of echinoderms in the Laptev and East Siberian seas and for 59 species and 35 genera of the asteroid species in the Arctic Ocean. The probable colonization route through the Arctic was suggested for each species based on (1) the distributional patterns of the Arctic species, (2) the distributional patterns of the closely related species, and (3) the location of the center of the diversity of the species belonging to a certain genus. The species of the Pacific origin prevailed in the asteroid fauna of the Arctic seas. The asteroid species diversity and the ratio of the species of Pacific origin decreased from the Barents towards the Laptev Sea and increased, respectively, in the East Siberian and the Chukchee seas. The species range limits were found for 19 species in the East Siberian Sea compared to only 3 species in the Laptev Sea. The East Siberian Sea was a limiting area for the dispersal of four species groups: (1) invaders from the North Pacific dispersing along the Asian coast of the Arctic (shallow-water stenobathic species), (2) invaders from the North Pacific dispersing along the American coast of the Arctic and further on back into the Arctic along the Eurasian coast (secondarily Atlantic species); (3) originally invaders from the Northern Atlantic; (4) representatives of the Arctic autochthonous fauna. A great width of the biotic boundaries (i.e., the zones of the species range boundaries crowding) was typical for the Arctic Basin, which was a sign of their young geological age.

Including Riparian Vegetation in the Definition of Morphologic Reference Conditions for Large Rivers: A Case Study for Europe’s Western Plains

Methods for defining and retrieving reference conditions for large rivers were explored with emphasis on hydromorphologic and biologic quality indicators. For a set of four large rivers in the European Western Plains ecoregion, i.e., the rivers Meuse, Loire, Allier, and Dordogne, reference reaches were selected based on geomorphologic characteristics. A survey of riparian land use, vegetation, and bed geometry was done for the selected reaches. Responses of the riparian landscape to hydromorphologic conditions were determined with a set of existing and newly developed measures of riparian dynamics and forest development. Strong correlations were observed at the reach and local levels between the ratios of width to depth and embankment and the developed measures of riparian dynamics and forest. Boundary conditions for riparian forest development were determined for the hydromorphologic and biologic indicators of riparian dynamics and vegetation structure. These conditions also proved useful for determining the presence of sustainable populations of Populus nigra and Salix purpurea. From this agreement between abiotic and biotic boundary conditions, a set of useful reference conditions was determined, and a framework for the definition of reference and good status conditions subsequently evolved. Finally, a proposal for assessment and monitoring the proposed indicators is discussed for its applicability.

The Canaries: an important biogeographical meeting place

The Canaries: an important biogeographical meeting place

Some Biogeographic Aspects of Hydrobiology

The issues of interrelation between hydrosphere biogeography and hydrobiology are considered. The peculiarities of usage of hydrobiological data in biogeography are discussed, in particular, in connection with the insular nature of inland water bodies and the discontinuity of species areas. The conceptual models of forming biotic boundaries between biotas and biotic groups are offered. Some topics of hydrobiology, solution of which may promote mutual enrichment of hydrosphere biogeography and hydrobiology, are considered.

Biogeographical boundaries and Monmonier’s algorithm: a case study in the northern Neotropics

AbstractAim To use Monmonier’s algorithm, a spatially explicit technique, to elucidate positions of biogeographical boundaries in the northern Neotropics.Location The northern Neotropics (Isthmus of Tehuantepec, Mexico, south to trans‐Andean Colombia).Methods We compiled avifaunal lists for 36 forested sites from the literature, museum records, field notes, and web sources. We constructed distance matrices as inverse Jaccard’s similarity, used Monmonier’s algorithm to place biogeographical boundaries, and created bootstrap matrices to determine the relative strength of boundaries.Results Biogeographical boundaries with the best support separated lowland (&lt; 1000 m) and montane sites and areas with a distinct historical background, such as seaways, suture zones, volcanic peaks, and former islands.Main conclusions Monmonier’s algorithm used with distance (dissimilarity) data effectively identified biogeographical boundaries consistent with historical processes and with past research. Montane sites tended to be circumscribed by sharp boundaries, emphasizing their isolation and higher endemism. Lowland sites, by contrast, tended to be homogeneous, suggesting that dispersal has played a much larger role at low elevations. Former seaways, as in the Nicaraguan Depression and extended Bay of Urabá, yielded boundaries, but typically for highland avifauna only. In addition to providing a rigorous (bootstrap support) and heuristic (direct mapping) means of locating biotic boundaries, Monmonier’s algorithm can be a valuable tool for conservation planning.

Centers of marine fauna redistribution

The concepts of centers of biota origin and centers of biota accumulation are usually regarded as mutually exclusive. In this paper, they are analyzed within the framework of a unified concept of centers of biota redistribution. Such a center is a biogeographic unit that has three developmental stages: accumulation, diversification, and dispersal. At the accumulation stage, the taxonomic capacity of the corresponding biogeographic district drastically increases and its species richness becomes higher owing to in-migration of species from other regions. At the diversification stage, the species richness continues to increase owing to speciation, and a unified succession system develops. At the dispersal stage, the biotic boundaries of the region act as efficient barriers to species invasion, and the species of the redistribution center gain an advantage over the species of adjacent regions when colonizing new habitats. In the Neogene, the main shallow-water centers of marine fauna redistribution were located in the Indo-Malayan triangle, the western Atlantic, and the northern Pacific. The role of redistribution centers in deep-ocean areas belonged to the Antarctic and the western Pacific. The possibility of using an ecosystem approach to the study of redistribution centers is discussed.

Root Border-Like Cells of Arabidopsis. Microscopical Characterization and Role in the Interaction with Rhizobacteria

Plant roots of many species produce thousands of cells that are released daily into the rhizosphere. These cells are commonly termed border cells because of their major role in constituting a biotic boundary layer between the root surface and the soil. In this study, we investigated the occurrence and ultrastructure of such cells in Arabidopsis (Arabidopsis thaliana) using light and electron microscopy coupled to high-pressure freezing. The secretion of cell wall molecules including pectic polysaccharides and arabinogalactan-proteins (AGPs) was examined also using immunofluorescence microscopy and a set of anticarbohydrate antibodies. We show that root tips of Arabidopsis seedlings released cell layers in an organized pattern that differs from the rather randomly dispersed release observed in other plant species studied to date. Therefore, we termed such cells border-like cells (BLC). Electron microscopical results revealed that BLC are rich in mitochondria, Golgi stacks, and Golgi-derived vesicles, suggesting that these cells are actively engaged in secretion of materials to their cell walls. Immunocytochemical data demonstrated that pectins as well as AGPs are among secreted material as revealed by the high level of expression of AGP-epitopes. In particular, the JIM13-AGP epitope was found exclusively associated with BLC and peripheral cells in the root cap region. In addition, we investigated the function of BLC and root cap cell AGPs in the interaction with rhizobacteria using AGP-disrupting agents and a strain of Rhizobium sp. expressing a green fluorescent protein. Our findings demonstrate that alteration of AGPs significantly inhibits the attachment of the bacteria to the surface of BLC and root tip.

Spatial analysis of taxonomic and genetic patterns and their potential for understanding evolutionary histories

AbstractAim The aim of this research is to develop and investigate methods for the spatial analysis of diversity based on genetic and taxonomic units of difference. We use monophyletic groups of species to assess the potential for these diversity indices to elucidate the geographical components of macro‐scaled evolutionary processes.Location The range occupied byPultenaeaspecies in temperate and sub‐tropical eastern Australia, extending from western South Australia (133° E–32° S) to Tasmania (146° E–43° S) to coastal central Queensland (148° E–20° S).Methods We applied a series of both spatially explicit and spatially implicit analyses to explore the nature of diversity patterns in the genusPultenaea, Fabaceae. We first analysed the eastern species as a whole and then the phylogenetic groups within them. We delineated patterns of endemism and biotic (taxon) regions that have been traditionally circumscribed in biogeographical studies of taxa. Centres of endemism were calculated using corrected weighted endemism at a range of spatial scales. Biotic regions were defined by comparing the similarity of species assemblages of grid cells using the Jaccard index and clustering similar cells using hierarchical clustering. On the basis that genetically coherent areas were likely to be more evolutionary informative than species patterns, genetic indices of similarity and difference were derived. A matrix of similarity distances between taxa was generated based on the number of shared informative characters of two sections oftrnL‐FandndhFchloroplast nuclear regions. To identify genetically similar areas, we clustered cells using the mean genetic similarities of the species contained within each pair of cells. Measures of the mean genetic similarity of species in areas were delineated using a geographically local multi‐scalar approach. Resultant patterns of genetic diversity are interpreted in relation to theories of the evolutionary relationships between species and species groups.Results Centres ofPultenaeaendemism were defined, those of clades 1 congruent with the spatially separated centres of clades 2 and 3. The taxonomic classification analysis defined cells with shared groups of species, which in some cases clustered when plotted in geographic space, defining biotic regions. In some instances the distribution of biotic regions was congruent with centres of endemism, however larger scale groupings were also apparent. In clade 1 one set of species was replaced by another along the extent of the range, with some connectivity between some geographically disjunct regions due to the presence of widespread species. In the combined analysis of clade 2 and 3 species the major biotic (taxonomic) groups with geographic coherence were defined by species in the respective clades, representing the geographic separation of these clades. However distinctive biotic regions within these main groupings of clades 2 and 3 were also apparent. Clustering cells using the mean genetic similarities of the species contained within each pair of cells indicated that some of the taxonomically defined biotic boundaries were the result of changes in composition of closely related species. This was most apparent in clades 1 and 2 where most cells were highly genetically similar. In clade 3 genetically distinct groups remained and were in part defined by sister taxa with disjunct distributions. Gradients in mean genetic similarity became more apparent from small to larger scales of analysis. At larger scales of analysis, regions of different levels of genetic diversity were delineated. Regions with highest diversity levels (lowest level of similarity) often represented regions where the ranges of phylogenetically distinctive species intergraded.Main conclusions The combined analysis of diversity, phylogeny and geography has potential to reveal macro‐scaled evolutionary patterns from which evolutionary processes may be inferred. The spatial genetic diversity indices developed in this study contribute new methods for identifying coherent evolutionary units in the landscape, which overcome some of the limitations of using taxonomic data, and from which the role of geography in evolutionary processes can be tested. We also conclude that a multiple‐index approach to diversity pattern analysis is useful, especially where patterns may be the result of a long history of different environmental changes and related evolutionary events. The analysis contributes to the knowledge of large‐scale diversity patterns ofPultenaeawhich has relevance for the assessment of the conservation status of the genus.

A biogeographical analysis of the genera Audouinella (Rhodophyta), Cystoseira (Phaeophyceae) and Cladophora (Chlorophyta) in the western Mediterranean Sea and Adriatic Sea

We carried out a biogeographical analysis of the genera Audouinella (Rhodophyta), Cystoseira (Phaeophyceae) and Cladophora (Chlorophyta), as well as the species in the three genera pooled together, in the western Mediterranean Sea and Adriatic Sea. For this purpose, the continental shelves close to 13 hydrographical watersheds were used as operational geographical units. The analysis was performed in accordance with a hypothetical–deductive approach. Four weak boundaries and five biotic regions were obtained for Audouinella; one strong and two weak boundaries, separating four biotic regions, were found for Cystoseira; two weak boundaries delimiting three biotic regions were obtained for Cladophora. The species of the three genera pooled together allowed us to separate three biotic regions delimited by two weak boundaries. The environmental factors that can explain the presence of the boundaries between biotic regions were run-off, distance of a given region from the Strait of Gibraltar following the course of the main current of the Mediterranean Sea, current flow, and salinity. The characterization of each biotic region and the relationships with the environmental factors that could explain the biotic boundaries are discussed.

Use of a latitudinal gradient in bald cypress (Taxodium distichum) production to examine physiological controls of biotic boundaries and potential responses to environmental change

ABSTRACTAim Predictions of vegetation change with global warming require models that accurately reflect physiological processes underlying growth limitations and species distributions. However, information about environmental controls on physiology and consequent effects on species boundaries and ecosystem functions such as production is limited, especially for forested wetlands that are potentially important carbon sinks.Location The bald cypress (Taxodium distichum) region of the south‐eastern United States was studied to examine how production of an important forested wetland varies with latitude and temperature as well as local hydrology.Methods We used published data to analyse litter production across a latitudinal gradient from 26.2 to 37.8° N to determine how bald cypress swamps might respond to alternate climate conditions and what changes might occur throughout the distributional range.Results Litterfall rates followed a bell shaped curve, indicating that production was more limited at the distributional boundaries (c. 225 g/m2 year−1) compared to the mid‐range (795–1126 g/m2 year−1). This pattern suggests that conditions are suboptimal near both boundaries and that the absence of populations outside this latitudinal range may be largely due to physiological constraints on the carbon balance of dominant species. While dispersal limitations cannot be totally discounted, competition with other wetland types at the extremes of the range does not seem likely to be important because the relative basal area of bald cypress does not decrease near the edges of the range. Impaired hydrology depressed production across the entire range, but more in the south than the north.Main conclusions Our findings suggest that (1) physiological limitations constrain biotic boundaries of bald cypress swamps; (2) future changes in global temperature would affect litter production in a nonlinear manner across the distributional range; (3) local changes in hydrology may interact with climate to further reduce litter production, particularly at lower latitudes; and (4) southernmost forests could be extirpated if environmental conditions compromise carbon balance and water‐use efficiency of trees.

Relaciones biogeográficas de los sistemas montañosos de la Península Ibérica: el caso de los micromamíferos

Biogeographical relationships of the Iberian mountain ranges: the case of micromammals In the present paper we analyse the biogeographical relationship between the 12 mountain ranges surrounding the western Mediterranean basin, according to their micromammal fauna (70 species belonging to the orders Erinaceomorpha, Soricomorpha and Rodentia). Using an area classification analysis, we performed a biogeographical regionalization of the study area, and later we characterised the biotic boundaries detected. We also identified the interchanges of species that could have happened between the mountain ranges considered. A strong boundary exists between the European and African faunas, which is characterised by a higher energy availability in the south. For non-rodents micromammals there is also a week boundary between the exclusively-Iberian mountain ranges and the northern ones, which is characterised by a higher simultaneous availability of water and energy in the north. Finally, we suggest the existence of a main interchange of species between Europe and the Iberian Peninsula.