Natural fragmentation in river networks as a driver of speciation for freshwater fishes

Although habitat fragmentation fosters extinctions, it also increases the probability of speciation by promoting and maintaining divergence among isolated populations. Here we test for the effects of two isolation factors that may reduce population dispersal within river networks as potential drivers of freshwater fish speciation: 1) the position of subdrainages along the longitudinal river gradient, and 2) the level of fragmentation within subdrainages caused by natural waterfalls. The occurrence of native freshwater fish species from 26 subdrainages of the Orinoco drainage basin (South America) was used to identify those species that presumably arose from in‐situ cladogenetic speciation (i.e. neo‐endemic species; two or more endemic species from the same genus) within each subdrainage. We related subdrainages fish diversity (i.e. total, endemic and neo‐endemic species richness) and an index of speciation to our two isolation factors while controlling for subdrainages size and energy availability. The longitudinal position of subdrainages was unrelated to any of our diversity measures, a result potentially explained by the spatial grain we used and/or the contemporary connection between Orinoco and Amazon basins via the upstream Casiquiare region. However, we found higher neo‐endemic species richness and higher speciation index values in highly fragmented subdrainages. These results suggest that habitat fragmentation generated by natural waterfalls drives cladogenetic speciation in fragmented subdrainages. More generally, our results emphasize the role of history and natural waterfalls as biogeographic barriers promoting freshwater biodiversity in river drainage basins.     

Global imprint of historical connectivity on freshwater fish biodiversity

The relative importance of contemporary and historical processes is central for understanding biodiversity patterns. While several studies show that past conditions can partly explain the current biodiversity patterns, the role of history remains elusive. We reconstructed palaeo‐drainage basins under lower sea level conditions (Last Glacial Maximum) to test whether the historical connectivity between basins left an imprint on the global patterns of freshwater fish biodiversity. After controlling for contemporary and past environmental conditions, we found that palaeo‐connected basins displayed greater species richness but lower levels of endemism and beta diversity than did palaeo‐disconnected basins. Palaeo‐connected basins exhibited shallower distance decay of compositional similarity, suggesting that palaeo‐river connections favoured the exchange of fish species. Finally, we found that a longer period of palaeo‐connection resulted in lower levels of beta diversity. These findings reveal the first unambiguous results of the role played by history in explaining the global contemporary patterns of biodiversity.     

Contrasting patterns of diversification in a bird family (Aves: Gruiformes: Rallidae) are revealed by analysis of geospatial distribution of species and phylogenetic diversity

Geospatial patterns in the distribution of regional biodiversity reflect the composite processes that underpin evolution: speciation, dispersal and extinction. The spatial distribution and phylogeny of a globally widespread and species rich bird family (Rallidae) were used to help assess the role of large‐scale biogeographical processes in diversity and diversification. Here, we examine how different geostatistical diversity metrics enhance our understanding of species distribution by linking occurrence records of rail species to corresponding species level phylogeny. Tropical regions and temperate zones contained a large proportion of rail species richness and phylogenetic diversity whilst small islands in Australian, Oceanian and Oriental regions held the highest weighted and phylogenetic endemism. Our results suggest that habitat connectivity and dispersal were important ecological features in rail evolution and distribution. Spatial isolation was a significant driver of diversification where islands in Oceania were centres of neo‐endemism with recent multiple and independent speciation events and could be considered as nurseries of biodiversity. Palaeo‐endemism was mostly associated with older stable regions, so despite extensive long distance range shifting these areas retain their own ancient and distinct character. Madagascar was the major area of palaeo‐endemism associated with the oldest rail lineages and could be considered a museum of rail diversity. This implies a mixture of processes determine the current distribution and diversity of rail clades with some areas dominated by recent ‘in situ’ speciation while others harbour old diversity with ecological traits that have stood the test of time.     

Pattern and process in the distribution of North American freshwater fish

Published species lists were analysed to determine the contributions of dispersal, habitat preference, river channel size, body size, and glacial history to large‐scale patterns in freshwater fish species richness in North America, north of central Mexico. Total species richness declines to the north and west but the pattern for endemics differs from that of widespread species. Mississippi Basin regions are more species rich than more isolated, coastal, regions. Richness declines more rapidly with increasing latitude in riverine specialist than in habitat generalist species. Levels of endemism are greatest in species found in small‐ to medium‐sized river channels. The strong Rapoport effect, more marked in migratory than resident species, is correlated with habitat preference, channel size, and glacial history. Body size increases with latitude, largely as a result of a trend from small resident to large migrant species. In unglaciated regions, ancestral species survived in large habitats because these are longer‐lived, more extensive, less isolated and more stable than headwaters, permitting larger populations and lower extinction levels. Reduced levels of gene flow in small, peripheral, channels isolated by larger downstream habitats have resulted in the production of many, small range, small‐bodied species. The latitudinal richness gradient is a consequence of speciation and extinction events in unglaciated faunas and an increasing domination of faunas by generalist, large bodied, large channel, recolonizing species in more northern regions. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 46–61.     

Historical biogeography of South American freshwater fishes

Aim To investigate biogeographical patterns of the obligate freshwater fish order Characiformes. Location South America. Methods Parsimony analysis of endemicity, likelihood analysis of congruent geographical distribution, and partition Bremer support were used. Results Areas of endemism are deduced from parsimony analysis of endemicity, and putative dispersal routes from a separate analysis of discordant patterns of distribution. Main conclusions Our results demonstrate the occurrence of 11 major areas of endemism and support a preferential eastern–western differentiation of the characiforms in the Amazonian region, contrasting with the southern–northern differentiation of terrestrial organisms. The areas of endemism identified seem to be deeply influenced by the distribution of the emerged land during the 100‐m marine highstand that occurred during the late Miocene and allow us to hypothesize the existence of eight aquatic freshwater refuges at that time. The raw distribution of non‐endemic species supports nine patterns of species distribution across the 11 areas of endemism, two of which support a southern–northern differentiation in the eastern part of the Amazon. This result shows that the main channel of the Amazon limited dispersal between tributaries from each bank of the river. The levels of endemism further demonstrate that the aquatic freshwater refuges promoted allopatric speciation and later allowed the colonization of the lowlands. By contrast, the biogeographical pattern found in the western part of the Amazon is identified as a result of the Miocene Andean foreland dynamic and the uplift of the palaeoarches that promoted allopatric divergence across several sedimentary basins by the establishment of disconnected floodplains. The assessment of conflicting species distributions also shows the presence of seven putative dispersal routes between the Amazon, Orinoco and Paraná rivers. Our findings suggest that, rather than there being a single predominant process, the establishment of the modern South American freshwater fish biotas is the result of an interaction between marine incursions, uplift of the palaeoarches, and historical connections allowing cross‐drainage dispersal.     

Biogeography of mammals on tropical Pacific islands

Aim We examine the influence of geography on species richness and endemism of mammals on tropical Pacific archipelagos to determine the importance of intra‐ and inter‐archipelago speciation in promoting local and regional species richness. Location Thirty tropical Pacific archipelagos. Methods A distributional list of mammals on 30 archipelagos was compiled, and values for 10 geographical variables were estimated for each archipelago. Mammal species were placed in three different categories (continental, Pacific and endemic) based on their distribution. The total number of species and numbers of species within each category were related to the geographical variables using Poisson regression analysis. Results Species richness was related positively to variables describing land area, numbers of large islands and elevation; and negatively to variables describing isolation. Levels of endemism did not differ between volant and non‐volant species, but differed between mega‐ and microchiropterans. Main conclusions Variation in species richness of mammals in the tropical Pacific region can be accounted for by a combination of intra‐archipelago speciation within archipelagos composed of large islands, and inter‐archipelago speciation, particularly among more isolated archipelagos. Mammals were less widely distributed throughout the study area than previously found for butterflies, skinks or birds. However, the level of endemism was similar to that of skinks and birds on the same archipelagos, and was higher than that of butterflies.     

Recent origin,active speciation and dispersal for the lichen genus Nephroma (Peltigerales) in Macaronesia

Aim We reconstructed the phylogeny of the lichen genus Nephroma (Peltigerales) to assess the relationships of species endemic to Macaronesia. We estimated dates of divergences to test the hypothesis that the species arose in Macaronesia (neo‐endemism) versus the oceanic archipelagos serving as refugia for formerly widespread taxa (palaeo‐endemism). Location Cosmopolitan with a special focus on the archipelagos of the Azores, Madeira and the Canary Islands. Methods DNA sequences were obtained from 18 species for three loci and analysed using maximum parsimony, maximum likelihood and Bayesian inferences. Divergence dates were estimated for the internal transcribed spacer (ITS)‐based phylogeny using a relaxed molecular clock. Reconstruction of the ancestral geographical range was conducted using the Bayesian 50% majority rule consensus tree under a parsimony method. Results The backbone phylogenetic tree was fully supported, with Nephroma plumbeum as sister to all other species. Four strongly supported clades were detected: the Nephroma helveticum, the N. bellum, the N. laevigatum and the N. parile clades. The latter two share a common ancestor and each includes a widespread Holarctic species (N. laevigatum and N. parile, respectively) and all species endemic to Macaronesia. The data suggest a neo‐endemic origin of Macaronesian taxa, a recent range expansion from Macaronesia of both widespread species, a range expansion limited to the Mediteranean Basin and south‐western Europe for another taxon, and a long dispersal event that resulted in a speciation event in the western parts of North America. Main conclusions The Macaronesian endemic species belong to two sister clades and originated from a most recent common ancestor (MRCA) shared with one widely distributed taxon, either N. parile or N. laevigatum. Estimates of the mean divergence dates suggest that the endemics originated in the archipelagos after the rise of the volcanic islands, along with the ancestor to the now widespread species, which probably expanded their range beyond Macaronesia via long‐distance dispersal. This study provides the first phylogenetic evidence of Macaronesian neo‐endemism in lichenized fungi and provides support for the hypothesis that oceanic islands may serve as a source for the colonization of continents. However, further data are needed to properly assess the alternative hypothesis, namely colonization from western North America.     

Patterns in species richness and endemism of European freshwater fish

Aim  To analyse the patterns in species richness and endemism of the native European riverine fish fauna, in the light of the Messinian salinity crisis and the Last Glacial Maximum (LGM).
Location  European continent.
Methods  After gathering native fish faunistic lists of 406 hydrographical networks, we defined large biogeographical regions with homogenous fish fauna, based on a hierarchical cluster analysis. Then we analysed and compared the patterns in species richness and endemism among these regions, as well as species–area relationships.
Results  Among the 233 native species present in the data set, the Cyprinidae family was strongly dominant (> 50% of the total number of species). Seven biogeographical regions were defined: Western Peri-Mediterranea, Central Peri-Mediterranea, Eastern Peri-Mediterranea, Ponto-Caspian Europe, Northern Europe, Central Europe and Western Europe. The highest regional species richness was observed for Central Peri-Mediterranea and Ponto-Caspian Europe. The highest endemic richness was found in Central Peri-Mediterranea. Species–area relationships were characterized by high slope values for Peri-Mediterranean Europe and low values for Central and Western Europe.
Main conclusions  The results were in agreement with the 'Lago Mare' hypothesis explaining the specificity of Peri-Mediterranean fish fauna, as well as with the history of recolonization of Central and Western Europe from Ponto-Caspian Europe following the LGM. The results also agreed with the mechanisms of speciation and extinction influencing fish diversity in hydrographical networks. We advise the use of the seven biogeographical regions for further studies, and suggest considering Peri-Mediterranean Europe and Ponto-Caspian Europe as 'biodiversity hotspots' for European riverine fish.     

Patterns of endemism in riverine fish of the Northern Hemisphere

Loss of endemic species represents a symptom of general degrading ecosystem conditions that is the indirect result of biodiversity alteration. Here, we developed a predictive model relating species richness of endemic riverine fishes to measured biological, climatic, and historical variables using data from 118 rivers distributed all over the Northern Hemisphere. In a minimally adequate multiple general least square model, total riverine fish species richness, historical biogeography (Pleistocene glaciations), and comtemporary climate accounted for 63% of the variability in endemic species richness; the strongest correlate being riverine fish species richness. Our findings suggest that (i) endemism and richness patterns are generally similar (fish diversity "hot-spots" areas sustain higher endemic species richness); (ii) glaciation in the Pleistocene have had a significant negative influence on endemic species richness in the more septentrional areas; and (iii) certain basins situated in desertic areas (subtropical dry-zone of deserts) have unusually high numbers of endemics. These last areas should not be overshadowed when setting conservation priorities.     

Contrasting patterns and mechanisms of spatial turnover for native and exotic freshwater fish in Europe

Aim We compare the distribution patterns of native and exotic freshwater fish in Europe, and test whether the same mechanisms (environmental filtering and/or dispersal limitation) govern patterns of decrease in similarity of native and exotic species composition over geographical distance (spatial species turnover). Locations Major river basins of Europe. Methods Data related to geography, habitat diversity, regional climate and species composition of native and exotic freshwater fish were collated for 26 major European river basins. We explored the degree of nestedness in native and exotic species composition, and quantified compositional similarity between river basins according to the beta‐sim (independent of richness gradient) and Jaccard (dependent of richness gradient) indices of similarity. Multiple regression on distance matrices and variation‐partitioning approaches were used to quantify the relative roles of environmental filtering and dispersal limitation in shaping patterns of decreasing compositional similarity over geographical distance. Results Native and exotic species exhibited significant nested patterns of species composition, indicating that differences in fish species composition between river basins are primarily the result of species loss, rather than species replacement. Both native and exotic compositional similarity decreased significantly with increasing geographical distance between river basins. However, gradual changes in species composition with geographical distance were found only for exotic species. In addition, exotic species displayed a higher rate of similarity decay (higher species turnover rate) with geographical distance, compared with native species. Lastly, the majority of explained variation in exotic compositional similarity was uniquely related to geography, whereas native compositional similarity was either uniquely explained by geography or jointly explained by environment and geography. Main conclusions Our study suggests that large‐scale patterns of spatial turnover for exotic freshwater fish in Europe are generated by human‐mediated dispersal limitation, whereas patterns of spatial turnover for native fish result from both dispersal limitation relative to historical events (isolation by mountain ranges, glacial history) and environmental filtering.     

Environmental heterogeneity,dispersal mode,and co‐occurrence in stream macroinvertebrates

Both environmental heterogeneity and mode of dispersal may affect species co‐occurrence in metacommunities. Aquatic invertebrates were sampled in 20–30 streams in each of three drainage basins, differing considerably in environmental heterogeneity. Each drainage basin was further divided into two equally sized sets of sites, again differing profoundly in environmental heterogeneity. Benthic invertebrate data were divided into three groups of taxa based on overland dispersal modes: passive dispersers with aquatic adults, passive dispersers with terrestrial winged adults, and active dispersers with terrestrial winged adults. The co‐occurrence of taxa in each dispersal mode group, drainage basin, and heterogeneity site subset was measured using the C‐score and its standardized effect size. The probability of finding high levels of species segregation tended to increase with environmental heterogeneity across the drainage basins. These patterns were, however, contingent on both dispersal mode and drainage basin. It thus appears that environmental heterogeneity and dispersal mode interact in affecting co‐occurrence in metacommunities, with passive dispersers with aquatic adults showing random patterns irrespective of environmental heterogeneity, and active dispersers with terrestrial winged adults showing increasing segregation with increasing environmental heterogeneity.     

BIODIVERSITY RESEARCH: Native and introduced fish species richness in Mediterranean streams: the role of multiple landscape influences

Aim To examine the role of multiple landscape factors on the species richness patterns of native and introduced freshwater fish. Location Mediterranean streams, south‐western Iberian Peninsula, Europe (c. 87,000 km²). Methods We used a dataset of fish occurrences from 436 stream sites. We quantified the incremental explanatory power of multiple landscape factors in native, introduced, and overall local species richness using regression analysis. First, we related variation in local species richness across river basins to regional species richness (here, the basin species pool), area and factors of climate and topography. Second, we related within‐river basin local species richness to site’s climate and topography, and spatial structure derived from Principal Coordinates of Neighbour Matrices approach, after testing for species richness spatial autocorrelation; predicted local richness was mapped. Results Patterns of local species richness across river basins were strongly associated with regional species richness for overall, native and introduced species; annual rainfall showed a significant incremental contribution to variation in introduced species richness only. Within river basins, environmental factors were associated with local richness for the three species groups, though their contributions to the total explained variation were inferior to those of spatial factors; rainfall seasonality and stream slope were the most consistent environmental correlates for all species groups, while the influence of spatial factors was most prevalent for native species. Main conclusions Landscape factors operating among and within river basins seem to play a relevant role in shaping local species richness of both native and introduced species, and may be contingent on basin‐specific contexts. Nevertheless, local factors, such as habitat characteristics and biotic interactions and human‐induced disturbances may also be at play. Multiscale approaches incorporating a multitude of factors are strongly encouraged to facilitate a deeper understanding of the biodiversity patterns of Mediterranean streams, and to promote more effective conservation and management strategies.     

Evidence of history in explaining diversity patterns in tropical riverine fish

Aim Documentation of the ongoing effect of rain forest refuges at the last glacial maximum (LGM) on patterns of tropical freshwater fish diversity. Location Tropical South and Central America, and West Africa. Methods LGM rain forest regions and species richness by drainage were compiled from published data. GIS mapping was applied to compile drainage area and contemporary primary productivity. We used multiple regression analyses, applied separately for Tropical South America, Central America and West Africa, to assess differences in species richness between drainages that were connected and disconnected to rain forest refuge zones during the LGM. Spatial autocorrelation of the residuals was tested using Moran's I statistic. We added an intercontinental comparison to our analyses to see if a historical signal would persist even when a regional historical effect (climate at the LGM) had already been accounted for. Results Both area and history (contact with LGM rain forest refuge) explained the greatest proportions of variance in the geographical pattern of riverine species richness. In the three examined regions, we found highest richness in drainages that were connected to the rain forest refuges. No significant residual spatial autocorrelation was detected after considering area, primary productivity and LGM rain forest refuges. These results show that past climatic events still affect West African and Latin American regional and continental freshwater fish richness. At the continental scale, we found South American rivers more species‐rich than expected on the basis of their area, productivity and connectedness to rain forest refuge. Conversely, Central American rivers were less species‐diverse than expected by the grouped model. African rivers were intermediate. Therefore, a historical signal persists even when a regional historical effect (climate at the LGM) had already been accounted for. Main conclusions It has been hypothesized that past climatic events have limited impact on species richness because species have tracked environmental changes through range shifts. However, when considering organisms with physically constrained dispersal (such as freshwater fish), past events leave a perceptible imprint on present species diversity. Furthermore, we considered regions that have comparable contemporary climatic and environmental characteristics, explaining the absence of a productivity effect. From the LGM to the present day (a time scale of 18,000 years), extinction processes should have played a predominant role in shaping the current diversity pattern. By contrast, the continental effects could reflect historical contingencies explained by differences in speciation and extinction rates between continents at higher time scales (millions of years).     

Centres of plant endemism in China: places for survival or for speciation?

Aim This study aimed to identify the ‘centres of endemism’ of the Chinese spermatophyte flora in order to indirectly detect the locations of past glacial refugia. The role of these areas as places for plant survival (‘plant museums’) and/or areas for plant evolution and speciation (‘plant cradles’) was also assessed. Location China. Methods Distribution patterns of 555 plant endemic taxa, taken as a representative sample of the Chinese endemic flora, were mapped on a 1° × 1° latitude/longitude grid. For each grid cell, species richness (total count of species) and weighted richness (down‐weighting each species by the inverse of its range) were calculated. Grid cells within the top 5% of highest values of weighted richness were considered centres of endemism. Based on available information, all plant taxa included in this study were classified into palaeoendemics and neoendemics, and their distributional patterns were represented separately. Results Twenty areas of endemism were identified in central and southern China, roughly corresponding to mountain ranges, including the Hengduan and Daxue Mountains, the Yungui Plateau, central China Mountains, the Nanling Mountains, eastern China Mountains, and Hainan and Taiwan. Although almost all centres of endemism contained both palaeoendemic and neoendemic taxa, considerable differences in their respective numbers were recorded, with the majority of neoendemics on the eastern fringe of the Tibetan Plateau (Hengduan Mountains sensu lato) but more palaeoendemics towards the east. Main conclusions Owing to their varied topography, the mountainous regions of central and southern China have provided long‐term stable habitats, which allowed palaeoendemics to persist and facilitated the process of speciation. Contrasting patterns between the palaeoendemics and neoendemics within refugia might be attributable to the geological and tectonic history of specific areas. The eastern fringe of the Tibetan Plateau clearly constitutes the ‘evolutionary front’ of China, probably as a result of the uninterrupted uplift of the plateau since the late Neogene. In contrast, the tectonic stability of central and southern China during the Tertiary may have facilitated the persistence of relict plant lineages.     

Evolutionary history of the flora of Mexico: Dry forests cradles and museums of endemism

Mexico is considered an exceptional biogeographic area with a varied endemic flora, however spatial phylogenetic measures of biodiversity have not yet been estimated to understand how its flora assembled to form the current vegetation. Patterns of species richness, endemism, phylogenetic diversity, phylogenetic endemism and centers of neo‐ and paleo‐endemism were determined to examine differences and congruence among these measures, and their implications for conservation. Of 24 360 vascular plant species 10 235 (42%) are endemic. Areas of endemism and phylogenetic endemism were associated with dry forests in zones of topographic complexity in mountain systems, in deserts, and in isolated xeric vegetation. Every single locality where seasonally tropical dry forests have been reported in Mexico was identified as an area of endemism. Significant phylogenetic diversity was the most restricted and occurred in the Trans‐Mexican Volcanic Belt and in the Sierra de Chiapas. Notably, the highest degree of phylogenetic clustering comprising neo‐, paleo‐, and super‐endemism was identified in southernmost Mexico. Most vascular plant lineages diverged in the Miocene (5–20 mya) when arid environments expanded across the world. The location of Mexico between two very large landmasses and the fact that more than fifty percent of its surface is arid favored the establishment of tropical lineages adapted to extreme seasonality and aridity. These lineages were able to migrate from both North and South America across Central America presumably during the Miocene and to diversify, illustrating the signature of the flora of Mexico of areas of endemism with a mixture of neo‐ and paleo‐endemism.     

An assessment of endemism and species richness patterns in the Australian Anura

Aim To assemble a continental‐scale data set of all available anuran records and investigate trends in endemism and species richness for the Anura. Location Continental Australia. Methods 97,338 records were assembled, covering 75% of the continent. A neighbourhood analysis was applied to recorded locations for each species to measure richness and endemism for each half‐degree grid square (c. 50 km) in the continent. This analysis was performed for all anurans, and also for each of the three main anuran families found in Australia. A Monte Carlo simulation was used to test a null hypothesis that observed centres of endemism could result simply from an unstructured overlapping of species ranges of different sizes. Results Eleven main centres of anuran endemism were identified, the most important being the Wet Tropics and the south‐west near Bunbury‐Augusta and near Walpole. With the exception of south‐western Australia, all of the identified significant endemic centres are in the northern half of the continent. The regions identified as significant for endemism differed from those identified for species richness and are more localized. Species richness is greatest in the Wet Tropics and the Border Ranges. High species richness also occurs in several areas not previously identified along the east and northern coasts. Main conclusions Weighted endemism provides a new approach for determining significant areas for anuran conservation in Australia and areas can be identified that could be targeted for beneficial conservation gains. Patterns in endemism were found to vary markedly between the three main anuran families, and south‐eastern Australia was found to be far less significant than indicated by previous studies. The need for further survey work in inland Australia is highlighted and several priority areas suggested. Our results for species richness remain broadly consistent with trends previously observed for the Australian Anura.     

Biodiversity and biogeography of southern temperate and polar bryozoans

Aim To describe the distribution of biodiversity and endemism of bryozoans in southern temperate and polar waters. We hypothesized that we would find: (1) no strong latitudinal richness gradient; (2) striking contrasts in richness and endemism between clades and between regions; and (3) that faunal similarity of regions would cluster geographically around each southern continent. Location South Atlantic, Indian and Pacific Oceans and the Southern Ocean. Methods We constructed a data base from known literature, regional data bases and recent finds. We regionalized each southern continent, calculated levels of richness and endemism for each region and continent, and used primer 5 to perform multivariate statistical analysis. Results A third (1681) of global bryozoan species described occur south of 30° S, of which c. 87% were cheilostomes. In richness we found no latitudinal cline and change across longitude was stronger. New Zealand was richest and had the most (60%) endemic species, followed by Antarctica at 57%. There were striking contrasts in regional richness and endemism between clades but the highest levels of between‐region similarity were around Antarctica. The timing of past continent connectivity was reflected. Main conclusions Bryozoans show strong hemispherical asymmetry in richness and, like molluscs and corals, decrease away from Australasia rather than with latitude. Species endemism is much lower in Antarctic bryozoans than previously thought, and as this taxon is not particularly dispersive and is now amongst the best studied regionally, maybe Antarctic endemism in general is lower and Antarctica less cut‐off to species dispersal than previously thought. However, Antarctic generic endemism is double the level previously calculated and regional faunal similarities are much higher than around other continents – both reflecting long‐term isolation. Bryozoans, in contrast to the paradigm of Antarctic fauna, may be fairly robust to predicted climate change. Paradoxically, they may also be one of the best taxa to monitor to sensitively detect marine benthic responses.     

Desert salt flats as oases for the spider Saltonia incerta Banks (Araneae: Dictynidae)

The deserts of southwestern North America have undergone dramatic changes over their recent geological history including large changes in size and connectivity during the Pleistocene glaciopluvial cycles. This study examines the population history of the rare spider Saltonia incerta, once thought to be extinct, to determine the role of past climatological events in shaping the structure of the species. This species is restricted to salt crusts of intermittent or dry lakes, streams or rivers in the desert southwest, a region that was much wetter during glacial periods. We examine the distribution and genetic variability of populations to test whether there is recent dispersal throughout the range of the species. Analyses of mitochondrial and nuclear DNA indicate significant population structure, with one major clade comprising New Mexico localities and one comprising California‐northern Baja California localities. Finer‐scale structure is evident within the California clade, although not all of the subclades are reciprocally monophyletic. However, isolation with migration analysis suggests that migration is very low to non‐existent. These results extend the known distribution of Saltonia, provide genetic evidence of strong isolation among localities within drainage basins and between drainage basins and provide a mechanistic understanding of population connectivity after the aridification of the American southwest. The implication is that although the species' distribution has been fragmented, populations have persisted throughout this area, suggesting that desert salt flats may have served as refugia for at least some terrestrial species.     

A revision of the bioregionalisation of freshwater fish communities in the Australian Monsoonal Tropics

The Australian freshwater fish fauna is very unique, but poorly understood. In the Australian Monsoonal Tropics (AMT) biome of northern Australia, the number of described and candidate species has nearly doubled since the last attempt to analyse freshwater fish species composition patterns and determine a bioregionalisation scheme. Here, we utilise the most complete database of catchment‐scale freshwater fish distributions from the AMT to date to: (a) reanalyze spatial patterns of species richness, endemism and turnover of freshwater fishes; (b) propose a biogeographic regionalisation based on species turnover; (c) assess the relationship between species turnover and patterns of environmental change and historic drainage connectivity; and (d) identify sampling gaps. Biogeographic provinces were identified using an agglomerative cluster analysis of a Simpson's beta (β_sim) dissimilarity matrix. A generalised dissimilarity model incorporating eighteen environmental variables was used to investigate the environmental correlates of species turnover. Observed and estimated species richness and endemism were calculated and inventory completeness was estimated based on the ratio of observed to estimated species richness. Three major freshwater fish biogeographic provinces and 14 subprovinces are proposed. These differ substantially from the current bioregionalisation scheme. Species turnover was most strongly influenced by environmental variables that are interpreted to reflect changes in terrain (catchment relief and confinement), geology and climate (runoff perenniality, stream density), and biotic responses to climate (net primary productivity). Past connectivity between rivers during low sea‐level events is also influential highlighting the importance of historical processes in explaining contemporary patterns of biodiversity in the AMT. The inclusion of 49 newly discovered species and candidate species only reinforced known focal points of species richness and endemism in the AMT. However, a number of key sampling gaps remain that need to be filled to fully characterise the proposed bioregionalisation.