Global flows of insect transport and establishment: The role of biogeography,trade and regulations

Aim

Non-native species are part of almost every biological community worldwide, yet numbers of species establishments have an uneven global distribution. Asymmetrical exchanges of species between regions are likely influenced by a range of mechanisms, including propagule pressure, native species pools, environmental conditions and biosecurity. While the importance of different mechanisms is likely to vary among invasion stages, those occurring prior to establishment (transport and introduction) are difficult to account for. We used records of unintentional insect introductions to test (1) whether insects from some biogeographic regions are more likely to be successful invaders, (2) whether the intensity of trade flows between regions determines how many species are intercepted and how many successfully establish, and (3) whether the variables driving successful transport and successful establishment differ.

Location

Canada, mainland USA, Hawaii, Japan, Australia, New Zealand, Great Britain, South Korea, South Africa.

Methods

To disentangle processes occurring during the transport and establishment stages, we analysed border interceptions of 8199 insect species as a proxy for transported species flows, and lists of 2076 established non-native insect species in eight areas. We investigated the influence of biogeographic variables, socio-economic variables and biosecurity regulations on the size of species flows between regions.

Results

During transport, the largest species flows generally originated from the Nearctic, Panamanian and Neotropical regions. Insects native to 8 of 12 biogeographic regions were able to establish, with the largest flows of established species on average coming from the Western Palearctic, Neotropical and Australasian/Oceanian regions. Both the biogeographic region of origin and trade intensity significantly influenced the size of species flows between regions during transport and establishment. The transported species richness increased with Gross National Income in the source country, and decreased with geographic distance. More species were able to establish when introduced within their native biogeographic region.

Main Conclusions

Our results suggest that accounting for processes occurring prior to establishment is crucial for understanding invasion asymmetry in insects, and for quantifying regional biosecurity risks.     

Estimating potential global sources and secondary spread of freshwater invasions under historical and future climates

Aim

We employed a climate-matching method to evaluate potential source regions of freshwater invasive species to an introduced region and their potential secondary spread under historical and future climates.

Location

Global source regions, with primary introductions to the Laurentian Great Lakes and secondary introductions throughout North America.

Methods

We conducted a climate-match analysis using the CLIMATE algorithm to estimate global source freshwater ecoregions under historical and future climates with an ensemble of global climate models for climate-change scenario SSP5-8.5. Given existing research, we use a climate match of ≥71.7% between ecoregions to indicate climatic conditions that will not inhibit the survival of introduced freshwater organisms. Further, we estimate the secondary spread of freshwater invaders to the ecoregions of North America under historical and future climates.

Results

We identified 54 global freshwater ecoregions with a climate match ≥71.7% to the recipient Laurentian Great Lakes under historical climatic conditions, and 11 additional ecoregions were predicted to exceed the threshold under climate change. Three of the 11 ecoregions were located in South America, a continent where no matches existed under historical climates and eight were located in the southern United States, southern Europe, Japan and New Zealand. Further, we identify 34 North American ecoregions of potential secondary spread of freshwater invasions from the Great Lakes under historical climatic conditions, and five ecoregions were predicted to exceed the threshold under climate change.

Main Conclusion

We provide a climate-match method that can be employed to assess the sources and spread of freshwater invasions under historical and future climate scenarios. Our climate-match method predicted increases in climate match between the recipient region and several potential source regions, and changes in areas of potential spread under climate change. The identified ecoregions are candidates for detailed biosecurity risk assessments and related management actions.     

Characteristics of the introduced fish fauna of Israel

Fishes have been introduced worldwide with deleterious effects on various native ecosystems. To gain insight into this phenomenon in Israel, we studied the introduced ichthyofauna. There are 27 species of introduced fishes in the freshwater habitats of Israel, a large number for a nation this size. Ten of these species reproduce in the wild. Most of these fishes were introduced for aquaculture; some are constantly restocked. The proportion of restocked versus established species in Israel is high compared to other regions. New fish introductions continue in recent decades, unlike the global trend. In Israel these species are found in the Jordan Basin, Lake Kinneret (Sea of Galilee), and the coastal plain rivers. A few species are widespread, and most are found in Lake Kinneret. Harmful effects of introduced fishes have been suspected and in several cases demonstrated. We encourage further caution when new introductions are contemplated; in some regions eradication should be attempted.     

Transport pathways shape the biogeography of alien freshwater fishes in Australia

Aim

Changing preferences regarding which species humans have transported to new regions can have major consequences for the potential distribution of alien taxa, but the mechanisms shaping these patterns are poorly understood. We assessed the extent to which changes in human preferences for transporting and introducing alien freshwater fishes have altered their biogeography.

Location

Australia.

Methods

We compiled an up‐to‐date database of alien freshwater fishes established in drainages in Australia before and after the number of established alien fish species doubled (pre‐1970 and post‐1970, respectively). Using metacommunity models, we analysed the influence of species traits and drainage features on the distribution of alien fishes that established pre‐ and post‐1970.

Results

Alien fishes in Australia were introduced via four main transport pathways: acclimatization, aquaculture, biocontrol and ornamental trade. The relative importance of each pathway changed substantially between the two periods, accompanied by changes in the distribution of alien fishes and the variables predicting their distribution. Pre‐1970, most species (64%) were introduced by acclimatization societies for purposes such as angling and biocontrol, and these fish have established in inland drainages more heavily impacted by human activities. In contrast, most of the post‐1970 introductions (69%) were ornamental fishes, with most species established in small, north‐eastern, tropical and subtropical coastal drainages.

Main conclusions

Substantial changes in introduction preferences and transport pathways over time have altered both the patterns and underlying processes shaping the biogeography of alien fishes in Australia. Our findings highlight the need for caution when using historical data to infer potential future distributions of alien species. The continuing spread of alien species means traditional biogeographical units may no longer be identifiable in the foreseeable future.

     

Freshwater fish introductions in mediterranean‐climate regions: are there commonalities in the conservation problem?

Aim To compare patterns and drivers of freshwater fish introductions across five climatically similar regions and evaluate similarities and differences in the non‐native species introduced. Location Five mediterranean‐climate regions: California (USA), central Chile, south‐western Australia, the Iberian peninsula (Spain and Portugal) and the south‐western Cape (South Africa). Methods Species presence–absence for native and non‐native fishes were collated across the regions, and patterns of faunal change were examined using univariate and multivariate statistical approaches. Taxonomic patterns in freshwater fish introductions were evaluated by comparing the number of species introduced by order to the numbers expected from binomial probabilities. Factors influencing multiple introductions of freshwater fish species in mediterranean regions were determined using generalized linear modelling. Results High levels of endemism (70–90%) were revealed for south‐western Cape, south‐western Australia and Chile. Despite their high rates of endemism, all regions currently have more non‐native species than endemic species. Taxonomic selection was found for five orders, although this was only significant for Salmoniformes across regions. The average increase in regional compositional similarity of fish faunas resulting from non‐native fish introductions was 8.0%. Important factors predicting multiple introductions of a species include previous introduction success and mean latitude of its distribution Main conclusions The mediterranean‐climate regions of the world, separated by vast distances, originally had a few fish species in common but are now more similar, owing to species introductions, illustrating the extent and importance of taxonomic homogenization. Introductions are largely driven by taxonomically biased human interests in recreational fisheries, aquaculture and ornamental pet species.     

A global assessment of freshwater fish introductions in mediterranean-climate regions

Mediterranean-climate regions (med-regions) are global hotspots of endemism facing mounting environmental threats associated with human-related activities, including the ecological impacts associated with non-native species introductions. We review freshwater fish introductions across med-regions to evaluate the influences of non-native fishes on the biogeography of taxonomic and functional diversity. Our synthesis revealed that 136 freshwater fish species (26 families, 13 orders) have been introduced into med-regions globally. These introductions, and local extirpations, have increased taxonomic and functional faunal similarity among regions by an average of 7.5% (4.6–11.4%; Jaccard) and 7.2% (1.4–14.0%; Bray–Curtis), respectively. Faunal homogenisation was highest in Chile and the western Med Basin, whereas sw Cape and the Aegean Sea drainages showed slight differentiation (decrease in faunal similarity) over time. At present, fish faunas of different med-regions have widespread species in common (e.g. Gambusia holbrooki, Cyprinus carpio, Oncorhynchus mykiss, Carassius auratus, and Micropterus salmoides) which are typically large-bodied, non-migratory, have higher physiological tolerance, and display fast population growth rates. Our findings suggest that intentional and accidental introductions of freshwater fish have dissolved dispersal barriers and significantly changed the present-day biogeography of med-regions across the globe. Conservation challenges in med-regions include understanding the ecosystem consequences of non-native species introductions at macro-ecological scales.     

Non-native fish in aquaculture and sport fishing in Brazil: economic benefits versus risks to fish diversity in the upper River Paraná Basin

Brazil has a highly diverse freshwater fish fauna and their freshwaters provide valuable provisioning ecosystem services in aquaculture and sport angling, especially in the developed regions in the south. Non-native fish now comprise a substantial proportion of the total aquaculture production and value, contributing at least $US 250?million in 2008 (63% of the total value of freshwater fish aquaculture) according to the Fish and Agriculture Organisation. Much of this aquaculture activity is centred in Central and Southern Brazil, such as impounded sections of the upper River Paraná. The non-native fishes used tend to feed at relatively low trophic levels, with the most prominently species being Cyprinus carpio and Oreochromis niloticus. Ecological risk assessment suggests these species are potentially highly invasive and deleterious to the native fish diversity of invaded water bodies. Fishes introduced for the creation of sport fisheries tend feed higher trophic levels through piscivory, such as the peacock basses (Cichla species) from Amazonia. Their introductions have generally resulted in establishment and invasion, which tends to be followed by significant and rapid declines in native fish diversity as a consequence of increased predation pressure. Thus, whilst non-native fish in the upper Paraná River support provisioning ecosystem services of substantial economic value, the principal species used represent high risks to fish diversity and conservation. It is recommended local management should concentrate on reducing these risks through use of more appropriate species in these ecosystem services, with these decisions derived using risk assessment and precautionary principles.     

Global patterns of phylogenetic relatedness of invasive flowering plants

Aim

The ability of predicting which naturalized non-native species are likely to become invasive can help manage and prevent species invasions. The goal of this study is to test whether invasive angiosperm (flowering plant) species are a phylogenetically clustered subset of naturalized species at global, continental and regional scales, and to assess the relationships of phylogenetic relatedness of invasive species with climate condition (temperature and precipitation).

Location

Global.

Time period

Current.

Taxon

Angiosperms (flowering plants).

Methods

The globe is divided into 290 regions, which are grouped into seven biogeographic (continental) regions. Two phylogenetic metrics (net relatedness index and nearest taxon index), which represent different evolutionary depths, are used to quantify phylogenetic relatedness of invasive angiosperms, with respect to different tailor-made species pools. Phylogenetic relatedness of invasive angiosperms is related to climatic variables.

Results

The global assemblage of invasive angiosperm species is a strongly phylogenetically clustered subset of the species of the entire global angiosperm flora. Most invasive angiosperm assemblages are a phylogenetically clustered subset of their respective naturalized species pools, and phylogenetic clustering reflecting shallow evolutionary history is greater than that reflecting deep evolutionary history. In general, the phylogenetic relatedness of invasive species is greater in regions with lower temperature and precipitation across the world.

Main conclusions

The finding that invasive angiosperm assemblages across the globe are, in general, phylogenetically clustered subsets of their respective naturalized species pools has significant implications in biological conservation, particularly in predicting and controlling invasive species based on phylogenetic relatedness among naturalized species.     

Seventy years of stream‐fish collections reveal invasions and native range contractions in an Appalachian (USA) watershed

Aim

Knowledge of expanding and contracting ranges is critical for monitoring invasions and assessing conservation status, yet reliable data on distributional trends are lacking for most freshwater species. We developed a quantitative technique to detect the sign (expansion or contraction) and functional form of range‐size changes for freshwater species based on collections data, while accounting for possible biases due to variable collection effort. We applied this technique to quantify stream‐fish range expansions and contractions in a highly invaded river system.

Location

Upper and middle New River (UMNR) basin, Appalachian Mountains, USA.

Methods

We compiled a 77‐year stream‐fish collections dataset partitioned into ten time periods. To account for variable collection effort among time periods, we aggregated the collections into 100 watersheds and expressed a species’ range size as detections per watershed (HUC) sampled (DPHS). We regressed DPHS against time by species and used an information‐theoretic approach to compare linear and nonlinear functional forms fitted to the data points and to classify each species as spreader, stable or decliner.

Results

We analysed changes in range size for 74 UMNR fishes, including 35 native and 39 established introduced species. We classified the majority (51%) of introduced species as spreaders, compared to 31% of natives. An exponential functional form fits best for 84% of spreaders. Three natives were among the most rapid spreaders. All four decliners were New River natives.

Main conclusions

Our DPHS‐based approach facilitated quantitative analyses of distributional trends for stream fishes based on collections data. Partitioning the dataset into multiple time periods allowed us to distinguish long‐term trends from population fluctuations and to examine nonlinear forms of spread. Our framework sets the stage for further study of drivers of stream‐fish invasions and declines in the UMNR and is widely transferable to other freshwater taxa and geographic regions.

     

Characteristics of Australia's alien flora vary with invasion stage

Aim

Directly or indirectly, humans select the plants that they transport and introduce outside of species native ranges. Plants that have become invasive may therefore reflect which species had the chance to invade, rather than which species would become invasive given the chance. We examine characteristics of failed introductions, along with invasion successes, by investigating (a) variation in plant characteristics across invasion stages, and (b) how observed characteristics predict the likelihood of species moving through invasion stages.

Location

Australia.

Time period

1770s to present.

Major taxa studied

34,650 plant species, across 424 families.

Methods

We used a comprehensive list of 34,650 plant species that are known to have been introduced to Australia, 4,081 of which are classified as naturalized and 428 as invasive. We represent plant characteristics with categorical growth forms, three functional traits (plant height, seed mass, and specific leaf area) and three factors related to species introduction histories (native regions, purpose, and minimum residence times).

Results

(a) The types of species introduced determine the types of species that naturalize and become invasive; (b) species introduction histories predict the likelihood of species moving through invasion stages; and (c) the numbers of species naturalizing (~15%) and becoming invasive (~15%) slightly exceeds expectation from the “tens rule”, which expects that 10% of introduced species naturalize and 10% become invasive.

Main conclusions

Our findings are significant for global biosecurity, indicating that functional traits alone cannot be used to predict a species' risk of becoming invasive. Rather, evidence suggests that characteristics of species introductions—specifically, a longer time-lag since first introduction and more pathways of introduction—define the relative risks of species moving through invasion stages. This is important for assessing future invasion risks, as future introductions may differ from those of the past. Our work highlights the need to reduce the number of species introduced.     

Estimates of niche position and breadth vary across spatial scales for native and alien inland fishes

Aim

We estimate and compare niche position, marginality and breadth of Iberian inland fishes at three geographical extents (regional, restricted to the species’ range and global) to understand the effect of spatial scale on niche metrics. Furthermore, we investigate differences in niche metrics between native and alien fish, and test for associations with introduction date of alien species and niche characterization to better understand their invasion process.

Location

Iberian Peninsula and global.

Time period

2000–2020.

Major taxa studied

Fifty-one native and 17 alien inland fish species from the Iberian Peninsula.

Methods

Outlying mean index (OMI) analyses were used to estimate the niche position, marginality and breadth of Iberian inland fishes. Climatic OMI analyses were computed at three different scales (regional, restricted to the species’ range and global). Permutational analyses of variance (PERMANOVAs) were used to test for differences in niche position, marginality and breath among native and alien species.

Results

Niche metrics differed depending on the geographical extent of the investigation, as well as with respect to species origin (native versus alien). Differences in climatic niche position between native and alien species observed at the global scale were non-existent at the regional scale. The niche breadth of widely distributed alien species was highly underestimated when only considering the invaded region, and further influenced by the first date of of species introduction.

Main conclusions

Estimating niches of freshwater species, especially of alien invaders, should carefully consider the geographical extent of the investigation. We suggest that analyses that jointly consider regional and global scales will improve the estimation of niche metrics of widely distributed organisms, particularly regarding species climatic niche, and the assessment of the invasive potential of species.     

Predicting global ascidian invasions

Aim

Many species of ascidians are invasive and can cause both ecological and economic losses. Here, we describe risk assessment for nineteen ascidian species and predict coastal regions that are more vulnerable to arrival and expansion.

Location

Global.

Methods

We used ensemble niche modelling with three algorithms (Random Forest, Support Vector Machine and MaxEnt) to predict ecologically suitable areas and evaluated our predictions using independent (area under the curve—AUC) and dependent thresholds (true skill statistics—TSS). Environmental variables were maximum and the range of sea surface temperature, mean salinity and maximum chlorophyll. We used our niche modelling results and a modified invasibility index to compare invasion risk among 15 coastal regions.

Results

Currently, the most invaded regions are in temperate latitudes of the Northern Hemisphere and Temperate Australasia, which are regions most prone for new invasions. In the tropics, the West and Central Indo‐Pacific are two regions of strong concern, the former with high risk of primary invasion by Botryllus schlosseri and Didemnum perlucidum. In the Southern Hemisphere, the Southwest and Southeast Atlantic are most at risk, both subject to invasion by Botrylloides violaceus, Didemnum vexillum, Molgula manhattensis and Styela clava among others. Regions most at risk of expansion of established invasive species are the Central Indo‐Pacific, Northwest Pacific, Mediterranean and West Indo‐Pacific.

Main conclusions

All regions studied have areas that are suitable and connected to receive new ascidian introductions or that may permit the spread of already established species. Risk comparison of primary introductions and expansion of established introduced ascidians among regions will allow managers to prioritize species of concern for each region both for monitoring future introductions or to enforce control actions towards established species to decrease the risk of regional expansion.

     

Patterns of species richness and turnover in endemic amphibians of the Guineo-Congolian rain forest

Aim

The African Guineo-Congolian (GC) region is a global biodiversity hotspot with high species endemism, bioclimatic heterogeneity, complex landscape features, and multiple biogeographic barriers. Bioclimatic and geographic variables influence global patterns of species richness and endemism, but their relative importance varies across taxa and regions and is poorly understood for many faunas. Here, we test the hypothesis that turnover in endemic amphibians of the GC biodiversity hotspot is influenced mainly by the geographic distance between grid cells and secondarily by rainfall- and temperature-related variables.

Location

West and Central Africa.

Major Taxa Studied

Amphibians.

Methods

We compiled species-occurrence records via field sampling, online databases, and taxonomic literature. Our study used 1205 unique georeferenced records of 222 amphibian species endemic to the GC region. Patterns of species richness were mapped onto a grid with a spatial resolution of 0.5° × 0.5°. We estimated weighted endemism and tested whether endemism was higher than the expected species richness (randomization test). We quantified species turnover using generalized dissimilarity modelling to evaluate the processes underlying observed patterns of species richness in GC endemic amphibians. We explored bioregionalization using agglomerative hierarchical clustering based on the unweighted pair group method with arithmetic averages.

Results

We identified seven areas within the lower GC region – forests in Cameroon, Gabon, Southern Nigeria, Equatorial Guinea, Republic of Congo, Democratic Republic of Congo, and Cote d'Ivoire – as having high species richness of endemic amphibians. The randomization test returned four major areas of significant weighted endemism: Nigeria-Cameroon mountains, forest regions of the Democratic Republic of Congo, Cote d'Ivoire, and Ghana. Our analysis revealed five bioregions for amphibian endemism, four of which were located within the lower Guineo-Congolian forest. Species turnover was strongly related to the geographic distance between grid cells; contributing bioclimatic variables included precipitation of the warmest quarter, mean temperature of the wettest quarter, and mean diurnal temperature range.

Main Conclusions

Our results indicate that geographic distance between grid cells is the primary determinant of turnover in GC endemic amphibians, with secondary but significant effects of rainfall- and temperature-related variables. Our study identifies key areas of endemic amphibian richness that could be prioritized for conservation actions.     

Do trophic subsidies affect the outcome of introductions of a non‐native freshwater fish?

相似文献   

Freshwater fish diversity in Algeria with emphasis on alien species

Little is known about freshwater fish diversity in Algeria, especially after the broad national program of introduction of exotic species applied for over 20 years. This paper is an attempt to describe the current situation emphasizing the characteristics of the various introductions of non-autochthonous species, their current status and their possible impacts. The freshwater fish fauna of Algeria is composed of 48 species belonging to 15 families. Twenty-one species are autochthonous, of which, three are endemic (Haplochromis desfontainii, Aphanius saourensis, Aphanius apodus), two are endangered (H. desfontainii, Aphanius iberus), and one is critically endangered (Anguilla anguilla). Twenty-seven species were introduced, of which, 18 never became established and 9 are established. Four species are reported for the first time: Abramis brama, Aspius aspius, Carassius carassius, Perca fluviatilis. Since 1860, 303 introduction events have been recorded at almost 107 different sites in Algeria. The number of introduction events per site was between 1 and 10. Most of the introduced fish are found in Oubéïra Lake (seven species). Aquaculture development was the main reason for fish introductions (37.0%). The five most often introduced species were Cyprinus carpio (86 records), Hypophthalmichthys molitrix (65 records), Aristichthys nobilis (51 records), Oreochromis niloticus niloticus (33 records), and Ctenopharyngodon idella (18 records). Since the adverse effects of introduced fish are risky and demonstrated in several countries, the adoption of the precautionary principle is recommended when new introductions are planned. It is important, therefore, to adopt regulations and procedures which will minimize the risks arising from introductions.     

Species invasions and the changing biogeography of Australian freshwater fishes

Aim By dissolving natural physical barriers to movement, human‐mediated species introductions have dramatically reshuffled the present‐day biogeography of freshwater fishes. The present study investigates whether the antiquity of Australia's freshwater ichthyofauna has been altered by the widespread invasion of non‐indigenous fish species. Location Australia. Methods Using fish presence–absence data for historical and present‐day species pools, we quantified changes in faunal similarity among major Australian drainage divisions and among river basins of north‐eastern Australia according to the Sørensen index, and related these changes to major factors of catchment disturbance that significantly alter river processes. Results Human‐mediated fish introductions have increased faunal similarity among primary drainages by an average of 3.0% (from 17.1% to 20.1% similarity). Over three‐quarters of the pairwise changes in drainage similarity were positive, indicating a strong tendency for taxonomic homogenization caused primarily by the widespread introduction of Carassius auratus, Gambusia holbrooki, Oncorhynchus mykiss and Poecilia reticulata. Faunal homogenization was highest in drainages subjected to the greatest degree of disturbance associated with human settlement, infrastructure and change in land use. Scenarios of future species invasions and extinctions indicate the continued homogenization of Australian drainages. In contrast, highly idiosyncratic introductions of species in river basins of north‐eastern Australia have decreased fish faunal similarity by an average of 1.4%. Main conclusions We found that invasive species have significantly changed the present‐day biogeography of fish by homogenizing Australian drainages and differentiating north‐eastern river basins. Decreased faunal similarity at smaller spatial scales is a result of high historical similarity in this region and reflects the dynamic nature of the homogenization process whereby sporadic introductions of new species initially decrease faunal similarity across basins. Our study points to the importance of understanding the role of invasive species in defining patterns of present‐day biogeography and preserving the antiquity of Australia's freshwater biodiversity.     

Importance of geographic origin for invasion success: A case study of the North and Baltic Seas versus the Great Lakes–St. Lawrence River region

Recently, several studies indicated that species from the Ponto‐Caspian region may be evolutionarily predisposed to become nonindigenous species (NIS); however, origin of NIS established in different regions has rarely been compared to confirm these statements. More importantly, if species from certain area/s are proven to be better colonizers, management strategies to control transport vectors coming from those areas must be more stringent, as prevention of new introductions is a cheaper and more effective strategy than eradication or control of established NIS populations. To determine whether species evolved in certain areas have inherent advantages over other species in colonizing new habitats, we explored NIS established in the North and Baltic Seas and Great Lakes–St. Lawrence River regions—two areas intensively studied in concern to NIS, highly invaded by Ponto‐Caspian species and with different salinity patterns (marine vs. freshwater). We compared observed numbers of NIS in these two regions to expected numbers of NIS from major donor regions. The expected numbers were calculated based on the available species pool from donor regions, frequency of shipping transit, and an environmental match between donor and recipient regions. A total of 281 NIS established in the North and Baltic Seas and 188 in the Great Lakes–St. Lawrence River. Ponto‐Caspian taxa colonized both types of habitats, saltwater areas of the North and Baltic Seas and freshwater of the Great Lakes–St. Lawrence River, in much higher numbers than expected. Propagule pressure (i.e., number of introduced individuals or introduction effort) is of great importance for establishment success of NIS; however in our study, either shipping vector or environmental match between regions did not clarify the high numbers of Ponto‐Caspian taxa in our study areas. Although we cannot exclude the influence of other transport vectors, our findings suggest that the origin of the species plays an important role for the predisposition of successful invaders.     

Elevational Gradients in Fish Diversity in the Himalaya: Water Discharge Is the Key Driver of Distribution Patterns

Background

Studying diversity and distribution patterns of species along elevational gradients and understanding drivers behind these patterns is central to macroecology and conservation biology. A number of studies on biogeographic gradients are available for terrestrial ecosystems, but freshwater ecosystems remain largely neglected. In particular, we know very little about the species richness gradients and their drivers in the Himalaya, a global biodiversity hotspot.

Methodology/Principal Findings

We collated taxonomic and distribution data of fish species from 16 freshwater Himalayan rivers and carried out empirical studies on environmental drivers and fish diversity and distribution in the Teesta river (Eastern Himalaya). We examined patterns of fish species richness along the Himalayan elevational gradients (50–3800 m) and sought to understand the drivers behind the emerging patterns. We used generalized linear models (GLM) and generalized additive models (GAM) to examine the richness patterns; GLM was used to investigate relationship between fish species richness and various environmental variables. Regression modelling involved stepwise procedures, including elimination of collinear variables, best model selection, based on the least Akaike’s information criterion (AIC) and the highest percentage of deviance explained (D²). This maiden study on the Himalayan fishes revealed that total and non-endemic fish species richness monotonously decrease with increasing elevation, while endemics peaked around mid elevations (700–1500 m). The best explanatory model (synthetic model) indicated that water discharge is the best predictor of fish species richness patterns in the Himalayan rivers.

Conclusions/Significance

This study, carried out along one of the longest bioclimatic elevation gradients of the world, lends support to Rapoport’s elevational rule as opposed to mid domain effect hypothesis. We propose a species-discharge model and contradict species-area model in predicting fish species richness. We suggest that drivers of richness gradients in terrestrial and aquatic ecosystems are likely to be different. These studies are crucial in context of the impacts of unprecedented on-going river regulation on fish diversity and distribution in the Himalaya.     

Fish fauna, biogeography and conservation of freshwater fish in Poyang Lake Basin, China

A checklist of the fish of Poyang Lake Basin based on an extensive survey and literature review is presented. A total of 220 species and subspecies belonging to12 orders, 27 families and 100 genera, have been recorded. Of these, 131 species are endemic to China. Based on cluster analysis with presence-absence data, freshwater ecosystems in Jiangxi Province are divided into two regions, the Xunwushui River region and the region of Poyang Lake. The Xunwushui River flows into the Pearl River, whereas the region of Poyang Lake flows into the Yangtze River. The fish fauna and evolution of the fish fauna in Poyang Lake Basin owes much to geological events and belongs to the Oriental Region, South-east Asiatic sub-region and East China area. Anthropogenic activities including habitat alteration, overfishing, pollution and soil erosion have severely reduced the fish biodiversity in Poyang Lake Basin. River modifications (i.e. dam construction and sand excavation) and heavy metal pollution are the most significant threats to fish diversity and ecosystem functioning in the majority of the river systems in the province. To protect fish diversity and fisheries more effectively in Poyang Lake Basin, law enforcement should be strengthened, and the following measures could be introduced: restocking economically important fish species; establishing fish sanctuaries and freshwater protected areas, ordering a close season and developing sustainable aquaculture.     

Hidden cargo: The impact of historical shipping trade on the recent-past and contemporary non-native flora of northeastern United States

Premise

Understanding establishment and spread of non-native plants is important in the face of a homogenizing global flora. While many studies focus on successful, invasive species, fewer have studied failed plant introductions. Until the early 1900s, large quantities of ship ballast, often containing foreign plant propagules, were deposited in New Jersey (USA). The resulting ballast flora is documented in extensive herbarium records, providing us a unique opportunity to analyze successes and failures of novel plant species introductions.

Methods

We used digitized specimens from 75 herbaria to study 264 non-native species introduced into New Jersey through 19th century ballast deposition. We used spatial (density-based clustering; HDBSCAN) and temporal analyses of species retention and geographic spread to quantify disappearance rate, survival, and dispersion through time and define trajectory groups.

Results

Four distinct trajectory groups were identified: waif (only present during import; 32% of species), short-term (disappeared quickly; 20%), established–limited spread (survives locally, 30%), and established–widespread (widespread, 18%). Species disappearance rate was highest during ballast deposition and decreased soon after deposition stopped around 1900. Spatial patterns showed a strong association with 19th century railroads for inland dispersal from ports. The disappearance rate and spatial analyses are robust to herbarium collection bias.

Conclusions

This study using New Jersey as a model is one of the few documenting multispecies successes and failures in inadvertent plant introductions. Results reveal distinct trends in species establishment and geographic spread and highlight the utility of herbarium specimens in answering questions that span large time scales.