Forecasting faunal and floral homogenization associated with human population geography in North America

Human population and urbanization is unprecedented in its rate of growth and geographic scope. With the help of humans, exotic species have piggybacked their way to distant lands, which in combination with the loss of endemic native species, has led to the convergence of biological communities toward common and ubiquitous forms. However, the extent to which this “biotic homogenization” varies along gradients of human population size and urbanization remains mostly unexplored, especially at broad spatial scales. The present paper combines a recent conceptual model of homogenization with estimates of species invasions and extinctions to provide the first estimates of homogenization for five major taxonomic groups - land birds, freshwater fish, terrestrial mammals, plants, and freshwater reptiles and amphibians - at the continental-scale of North America (exclusive of Mexico). On average, the greatest levels of biotic homogenization were predicted for plants (22%) and fishes (14%), followed by reptiles/amphibians (12%), mammals (9%) and birds (8%). Substantial spatial variation in predictions of community similarity exists and emphasize that the outcome of species invasions and extinctions may not only increase community similarity, but may also decrease it (i.e., differentiation). Homogenization is predicted to be greatest for fish in southwestern and northeastern US, highest in eastern North America for plants, greatest for birds and mammals along the west coast of North America, and peak in southern US for reptiles and amphibians. We show that predicted change in community similarity for all taxonomic groups is positively related to human population size and urbanization, thus providing the first quantitative linkage between human population geography and homogenization for a number of major taxonomic groups at the continental-scale of North America. Our study helps identify regional hotspots of biotic homogenization across North America, thus setting the stage for future studies where more directed investigations of biotic homogenization along urban gradients can be conducted.     

Fish introductions in California: History and impact on native fishes

Since 1871, at least 50 species of fish have been successfully introduced into California's inland waters, and numerous transfers of native fishes have been made between isolated drainage systems. Introductions were made of sport fish, commercial fish, forage fish, bait fish, fish for weed and insect control, and aquarium fish. Most of the introductions were authorised, reflecting a dissatisfaction with the native fishes, but in recent years unauthorised introductions have become common. The continuing decline of the native fish fauna seems to be largely the result of habitat change but introduced fishes may have contributed to this decline through competition, predation, and hybridisation. The lack of information on the native and introduced fishes of California, and their interactions, demonstrates the critical need for a statewide natural history survey.     

Decoupling plant-growth from land-use legacies in soil microbial communities

Differences in soil microbial communities between ex-arable and undisturbed soils are often assumed to reflect long-term legacies of agricultural practices. Ex-arable soils, however, are commonly dominated by different plant species than undisturbed soils making it difficult to separate the importance of land-use and plant-growth legacies. In a system where non-native plants dominate ex-arable soils, we decoupled land-use (ex-arable, undisturbed) and plant-growth (native, non-native) effects on soil microbial communities using a factorial sampling design. Soils were removed from 14 sites that formed a 52-year chronosequence of agricultural abandonment. Microbial abundance and composition were measured using whole-soil phospholipid fatty acid analyses and microbial activity was measured in a subset of samples using sole-carbon-source utilization analyses. We found that both non-native-cultivated and ex-arable soils were independently associated with lower microbial abundance and diversity than native and undisturbed soils. We also found a correlation between microbial abundance and age-since-agricultural abandonment in ex-arable/non-native-cultivated soils suggesting that non-native plant effects accumulate over time. Microbial activity was consistent with microbial abundance; microbial communities in non-native-cultivated, ex-arable soils were slow to respire most carbon sources. Our data suggests that agricultural practices create soil conditions that favor non-native plant growth and non-native plants maintain these conditions. Potential mechanisms explaining how non-natives create soils with small microbial communities and how small microbial communities may benefit non-natives are discussed.     

Threats, conservation strategies, and prognosis for suckers (Catostomidae) in North America: insights from regional case studies of a diverse family of non-game fishes

Catostomid fishes are a diverse family of 76+ freshwater species that are distributed across North America in many different habitats. This group of fish is facing a variety of impacts and conservation issues that are somewhat unique relative to more economically valuable and heavily managed fish species. Here, we present a brief series of case studies to highlight the threats such as migration barriers, flow regulation, environmental contamination, habitat degradation, exploitation and impacts from introduced (non-native) species that are facing catostomids in different regions. Collectively, the case studies reveal that individual species usually are not threatened by a single, isolated factor. Instead, species in general face numerous stressors that threaten multiple stages of their life history. Several factors have retarded sucker conservation including widespread inabilities of field workers to distinguish some species, lack of basic natural history and ecological knowledge of life history, and the misconception that suckers are tolerant of degraded conditions and are of little social or ecological value. Without a specific constituent group lobbying for conservation of non-game fishes, all such species, including members of the catostomid family, will continue to face serious risks because of neglect, ignorance, and misunderstanding. We suggest that conservation strategies should incorporate research and education/outreach components. Other conservation strategies that would be effective for protecting suckers include freshwater protected areas for critical habitat, restoration of degraded habitat, and design of catostomid-friendly fish bypass facilities. We believe that the plight of the catostomids is representative of the threats facing many other non-game freshwater fishes with diverse life-history strategies globally.     

Survival of the western pond turtle (Emys marmorata) in an urban California environment

The western pond turtle Emys (formerly Clemmys) marmorata is declining throughout its range, primarily due to loss of habitat via urbanization and conversion to agriculture. Urban waterways present several important challenges to freshwater turtle populations, but they also present an opportunity to maintain declining species in a ubiquitous habitat that has high public visibility. The arboretum waterway on the University of California, Davis campus is an example of an extensively altered urban habitat that supports a relatively large E. marmorata population. Over the last 6 years, we monitored the turtle population inhabiting the arboretum waterway to determine the demographic health of the population, and the challenges and opportunities that urban environments pose for pond turtles. Since 1993, the naturally existing arboretum pond turtle population has declined by approximately 40% and has shown little natural recruitment. During this time, we also introduced 31 headstarted turtles into the arboretum. Headstarting is the process of raising juveniles in captivity until they have outgrown their period of greatest vulnerability to predators, and then releasing them into the wild. Our headstarting results demonstrate that this contentious strategy is a viable option for adding young turtles to the population, although it does not address the causes of decline. Over the course of our study, we encountered nine species of non-native turtles in the waterway, and these appear to be a serious threat to the native species. As more habitat becomes urbanized, it is increasingly important to understand how freshwater turtles, such as E. marmorata, adapt to urban waterways and the impact of non-native turtles on native turtle species. Our strong feeling is that urban waterways can provide habitat for viable populations of freshwater turtles and showcase them to the public, but both the aquatic and terrestrial habitat must be managed according to the biological requirements of individual species.     

Homogenization of ant communities in mediterranean California: The effects of urbanization and invasion

In coastal California, the invasive Argentine ant (Linepithema humile) displaces nearly all above ground foraging native ant species. The loss of native ants following invasion by Argentine ants homogenizes these faunas; natural habitats invaded by L. humile have lower beta diversity compared to comparable uninvaded areas. Argentine ant abundance in the seasonally dry mediterranean environments of this region correlates strongly and positively with soil moisture. For this reason, the displacement of native ants across natural and artificial moisture gradients often resembles an edge effect, the magnitude of which is inversely proportional to the suitability of the physical environment from the perspective of L. humile. The direct effects of Argentine ant invasions in natural environments are therefore amplified by inputs of urban and agricultural run off. Indirect ecological effects of these invasions arise from the loss of large-bodied ants, arid adapted ants, and behavioral repertoires unique to particular native ant species. Further research is needed to quantify how these aspects of functional homogenization affect invaded communities. The close association between L. humile and moist soils suggests that, at least in arid regions, control strategies might be aimed at reducing urban run off in order to maintain functionally diverse communities of native ants.     

Avian assemblages along a gradient of urbanization in a highly fragmented landscape

Our goal was to evaluate how avian assemblages varied along a gradient of urbanization in the highly fragmented landscape of coastal southern California. We measured species richness and abundance of birds within continuous blocks of habitat, within urban habitat fragments that varied in landscape and local habitat variables, and within the urban matrix at different distances from the wildland interface. These comparisons allowed us to characterize patterns of avifaunal response to a gradient of urban fragmentation. At the fragment scale, we found that fragment area was a strong, positive predictor of the total number of breeding species detected per fragment; total bird abundance per point count also increased with fragment size. Tree cover was higher in small fragments, as was the abundance of birds that typically occupy wooded habitats. Comparisons between core, fragment, and urban transects revealed differing patterns of response of individual bird species to urbanization. In unfragmented habitat, we recorded a relatively high diversity of urbanization-sensitive birds. In urban transects, these species were rare, and a relatively few species of non-native and anthropophilic birds were common. These urbanization-enhanced birds were also recorded in previous urban gradient studies in northern California and Ohio. Bird communities along the urban gradient reached their highest richness and abundance in fragments. The marked difference in vegetation structure between urban and natural landscapes in this arid shrubland system likely contributed to this pattern; the presence of native shrubs and exotic trees in fragments enabled both shrub and arboreal nesters to co-occur. As is characteristic of biotic homogenization, urban fragmentation in coastal southern California may increase local diversity but decrease overall regional avifaunal diversity.     

Diverting the Colorado River leads to a dramatic life history shift in an endangered marine fish

Diversion of river water has diminished freshwater flow into many estuaries worldwide, yet the effects of these diversions on marine fisheries, many of which depend on estuaries, are largely unexplored. We document the impact of diverting Colorado River flow from the Gulf of California on the life history of a now-endangered marine fish (Totoaba macdonaldi, Sciaenidae). Growth increments in prehistoric (1000–5000 ybp) otoliths document that pre-dam juveniles grew twice as fast and matured 1–5 years earlier than post-dam fish. Oxygen isotopes link these changes to elimination of estuarine habitat. This study provides evidence that river diversion can have a dramatic effect on life history of marine fishes by slowing growth during the juvenile stage, thus delaying maturation. These findings also provide valuable insight into the relative influence of habitat alteration versus fishing pressure on marine fishes.     

Patterns of fish invasions in the Great Plains of North America

A basic step toward controlling invasive species outbreaks is to predict which assemblages or habitats are most susceptible to invasion and effects of invading species on native communities. However, because predictive models may not work across a wide range of conditions it is important to examine processes associated with fish invasions across different regions. In this study, we use data from 949 sites in Oklahoma and Kansas to examine spatial patterns of species invasions in the Great Plains region of the US. Of these sites, 16 were intensively sampled between 1977 and 1994 and used to evaluate temporal patterns of species introductions. We found a trend of increasing introduced species richness without a decline in native species richness over 18 years. However, total abundance and community structure of native assemblages has changed at several of these sites during this time period. Because some of these changes occurred at sites with few or no introduced species, factors other than interactions with introduced fishes may have been responsible for this pattern. A stepwise multiple regression model that included human population size, native species richness, mean annual precipitation and drainage area explained 43% of the variation in the number of non-native species across all sites. Most introduced species in this region have native ranges within the Mississippi River basin and therefore are presumably adapted to regional environmental conditions. Great Plains streams have, to some extent, resisted invasion by introduced species; however, our analysis shows that proximity to dense human populations and importance to humans has largely structured species introductions and can partly explain spatial patterns of species invasions in this region.     

淡水鱼腹背定向装置设计及试验

针对目前淡水鱼前处理设备主要采用人工进行定向喂料,劳动强度大、效率低,同时鱼体定向整理设备缺乏等问题,该研究以鱼体腹部横截面近似为楔形的典型大宗淡水鱼鲫鱼为研究对象,在鱼体腹背受力挤压力学特性研究的基础上,提出了一种淡水鱼鱼体腹背定向方法,同时分析了鱼体腹背定向机理,设计并试制了淡水鱼鱼体腹背定向试验装置。选取鲫鱼为试验对象,以定向成功率和定向时间为试验指标,对淡水鱼鱼体腹背定向试验装置的主要参数进行了优化。通过单因素试验探究了辊形、对辊间隙、鱼体输送速度、对辊转速等装置主要参数对鱼体腹背定向的影响规律。在单因素试验结果的基础上,进行了正交试验,试验结果表明:各因素间的最优水平组合为:对辊间隙50 mm,对辊转速50 r/min,鱼体输送速度0.6 m/s时,在此最优水平组合下,定向成功率为100%,定向时间为0.55 s,试验装置工作运行参数最佳。该文的研究结果可为淡水鱼鱼体定向设备的研发提供理论依据和技术参考。     

Winners and losers among stream fishes in relation to land use legacies and urban development in the southeastern US

The southeastern United States is a center of aquatic species diversity and endemism in North America, but many taxa are imperiled or in decline. Proactive conservation strategies depend on developing sensitive measures of ecological response to environmental degradation early in the process. In the southern Appalachian highlands, much of the region has reforested following extensive logging and agriculture in the last century, but recently exurban development has surged. Patterns of aquatic ecosystem response to these changes were examined in 36 watersheds along a gradient of forest cover from moderately to heavily forested. A linear combination of watershed-scale measures reflecting the extent contemporary forest cover, the trajectory of forest cover change over time, and building and road density were stronger predictors of fish assemblage composition than topographic features. A measure of biotic homogenization relating the abundance of endemic highland fishes to abundance of broad-ranged fishes was sensitive to the gradient of anthropogenic disturbance. Across the watershed disturbance gradient, cosmopolitan species were clear winners as forms unique to the Appalachian highlands were lost. Similar measures of homogenization may be suitable elsewhere for tracking early warning signs of ecosystem stress, particularly in regions with significant endemism. Quantification of the homogenization process in response to urban development and other stressors is a promising avenue for proactive conservation, land use planning, and sustainable development efforts.     

Rapid decline of California’s native inland fishes: A status assessment

A quantitative protocol was developed to determine conservation status of all 129 freshwater fishes native to California. Seven (5%) were extinct; 33 (26%) were found to be in danger of extinction in the near future (endangered); 33 (26%) were rated as sufficiently threatened to be on a trajectory towards extinction if present trends continue (vulnerable); 34 (26%) were rated as declining species but not in immediate danger of extinction. Only 22 (17%) species were found to be of least concern. Of 31 species officially listed under federal and state endangered species acts (ESAs), 17 (55%) were rated as endangered by our criteria, while 12 (39%) were rated vulnerable. Conversely, of the 33 species that received our endangered rating, only 17 (51%) were officially listed under the ESAs. Among the seven metrics used to assess extinction threat, climate change, area occupied and anthropogenic threats had the largest negative impacts on status. Of 15 categories of causes of decline, those most likely to diminish status were alien species, agriculture, and dams. Overall, 83% of California’s freshwater fishes are extinct or at risk of becoming so, a 16% increase since 1995 and a 21% increase since 1989. The rapid decline of California’s inland fishes is probably typical of declines in other regions that are less well documented, indicating a strong need for improved conservation of freshwater ecosystems.     

淡水鱼产气荚膜梭菌的分离及毒素型的鉴定

为研究产气荚膜梭菌在淡水鱼中的分布及毒素型,随机采取同一水库的鲤鱼、鲢鱼、鲫鱼、鲶鱼、黄鳝等淡水鱼样品420尾,细菌学方法分离肠内容物中的产气荚膜梭菌,PCR方法检测分离菌株的毒素基因确定毒素型,PCR扩增片段克隆后进行核苷酸序列分析并且与Genebank相应基因进行同源性比较。结果：自75份肠内容物样品中分离出产气荚膜梭菌;58株为C型（α、β毒素基因）,13株为A型（α毒素基因）,4株为B型（α、β、ε毒素基因）;三型菌株均能扩增出特异性2条带;检出基因与Genebank相应基因的同源性为98.15－99.29%。在淡水鱼检出产气荚膜梭菌的α、β、ε、β2毒素基因,在B型产气荚膜梭菌中扩增出2毒素基因均属首次,本研究对水体环境的污染及人类的食品安全有一定的指导意义。     

Factors resulting in decline of the endangered Sonoran topminnow Poeciliopsis occidentalis (Atheriniformes: Poeciliidae) in the United States

The endangered Sonoran topminnow Poeciliopsis occidentalis has steadily declined in distribution and abundance in the past several decades, and currently survives in the United States only in several isolated localities in southern Arizona. This reduction is correlated with, and primarily attributed to, habitat destruction, and introduction and establishment of mosquitofish Gambusia affinis and other exotic fishes. Topminnows have characteristically been reduced in number or replaced within a year or two of introduction of non-native fishes. Other native fishes have experienced similar declines after introduction of exotics, and much of the endemic western ichthyofauna may be vulnerable to extirpation in this manner. Predation by introduced fishes on natives appears to be a likely mechanism of replacement.     

广州市典型食用鱼类甲基汞含量及风险评估

通过分析广州市区居民消费量较大的7种淡水鱼和5种海水鱼肌肉中甲基汞（MeHg）含量,评估人体通过食鱼摄入MeHg的暴露风险。结果显示,广州市鱼体肌肉中MeHg含量范围为2.39～349μg·kg-1,平均含量为43.4μg·kg-1。不同食性鱼类MeHg含量水平依次为：肉食性〉杂食性〉草食性,处于食物链不同环节解释了这种含量差异。从生长环境来看,海水鱼肌肉的MeHg含量总体上高于淡水鱼。所有鱼中MeHg含量均低于国内外相关标准限值。与国内其他地区商品鱼相比,广州市商品鱼中MeHg含量相当,但明显低于野生鱼。居民通过食鱼摄入的MeHg范围为0.035～0.087μg·kg-1·d-（1bw）,均值为0.050μg·kg-1·d-（1bw）,远低于美国EPA规定的MeHg暴露参考剂量（RfD）值（1.1μg·kg-·1d-1）,也低于WHO和FAO制定的临时性周可承受摄入量（PTWI）（1.6μg·kg-1）。研究结果表明,广州居民食鱼MeHg暴露风险较小,但儿童等敏感人群食用特定鱼类的量和频次要引起一定注意。     

Distribution of non-native trout in Slovenia and their introgression with native trout populations as observed through microsatellite DNA analysis

In Slovenia, the Adriatic basin inhabited by native marble trout (S. marmoratus), and the Danubian basin inhabited by native Danubian lineage of brown trout (S. trutta) have been intensively affected by stocking with non-native trout strains. In order to assess spread of non-native strains and their introgression with native trout, a population study based on five microsatellite loci was applied across ten marble and ten brown trout populations, ranging from allegedly non-introgressed to heavily managed. On the basis of correspondence analysis, which revealed three clear groupings consisting of the Danubian and Atlantic lineages of brown trout and the marble trout, the alleles, characteristic of each grouping were identified and used for estimating genetic composition of each population according to the three possible origins. Among the wild populations, five marble and one brown trout populations were found to be pure; all the others were introgressed with exotic alleles (Atlantic and marmoratus alleles in the Danubian basin and Atlantic and Danubian in the Adriatic basin) that markedly dominate in intensively managed populations. As revealed by non-significant F_IS values, panmixia between native and introduced fishes has for the most part already been reached. Our research showed that it is not only marble trout whose identity is endangered in Slovenia but also the existence of autochthonous Danubian brown trout is critically compromised, which is new information to be taken into account for local trout conservation.     

Urbanization and homogenization - Comparing the floras of urban and rural areas in Germany

The process of urbanization has resulted in an expansion of alien plant species and declines of native species, in particular already rare species. These processes may cause a greater similarity between different urban regions, i.e. biotic homogenization. We explored the relationship between urban regions and homogenization for plant species in Germany using (i) all plant species, (ii) only native species, (iii) all alien species and only those introduced (iv) before or (v) after 1500, respectively. We used the database FLORKART for species distribution on a 6 min latitude × 10 min longitude (ca. 130 km²) scale. We calculated mean similarities for the 60 “most urbanized” cells. We then resampled 60 randomly drawn “less urbanized” cells and 60 “rural” cells and compared these results to the “most urbanized” cells taking distance effects into account. Urbanization does not have an overall effect on homogenization of all species, but native species as well as pre-1500 alien plant assemblages show effects of homogenization while post-1500 alien plant assemblages show the opposite effect. On a regional scale, urbanization is not unequivocally related to homogenization. This might be different when extending the analysed range across several bioclimatic regions. Specific urban habitats, or what remains of them, require special protection and management if the trend towards homogenization is to be avoided.     

淡水鱼鱼鳞生物结合力与去鳞特性的试验研究

为研究影响淡水鱼去鳞难易程度的因素,以鲤鱼、草鱼、鲫鱼、鳊鱼4种淡水鱼为试验对象,利用TMS-PRO质构仪对鱼鳞与鱼体的生物结合力进行了测量,研究了鱼鳞所处部位、加载速率、死亡时间对鱼鳞生物结合力的影响。同时,测量了淡水鱼单位面积内的鱼鳞数目,淡水鱼的滑动摩擦角,进行了去鳞试验。在此基础上分析并验证了单位面积鱼鳞生物结合力对去鳞的影响,表明淡水鱼单位面积鱼鳞生物结合力越大,去鳞越难,为去鱼鳞设备的研制提供参考。     

Characterization of phospholipid molecular species in the edible parts of bony fish and shellfish

The phospholipid molecular species of freshwater (pangasius, Nile perch, trout), marine fish fillets (horse mackerel, European hake, common sole, European anchovy, European pilchard, Atlantic mackerel) and the edible muscle foot of bivalves (clam, mussel, oyster) commonly available in the Italian market during spring and summer were characterized by means of normal-phase high performance liquid chromatography coupled online with positive electrospray ionization ion-trap tandem mass spectrometry. From principal component analysis (PCA), it was observed that the total fatty acid profile was not suitable to differentiate among the shellfish genera. The fatty acid molecular combinations of phosphatidylcholine, the main phospholipid class, as well as phosphatidylinositol and phosphatidylethanolamine allowed for the differentiation of shellfish from the bony fishes. Phosphatidylserine and phosphatidylethanolamine plasmalogen profile allowed for the discrimination of each bony fish or shellfish genus since PS and pPE classes included a large number of fatty acid combinations that were specific for a fish genus or group.     

Recovery of native plant communities after the control of a dominant invasive plant species, Foeniculum vulgare: Implications for management

The control and/or removal of a dominant invasive species is expected to lead to increases in native species richness and diversity. Small pilot studies were performed on Santa Cruz Island (SCI), California, in the early 1990s to test the efficacy of different methods on the control of Foeniculum vulgare (fennel) and management’s effects on native species recovery. We chose a treatment that showed significant native species recovery, applied it at the landscape scale, and followed its effects on fennel infested plant communities. We tested the hypothesis that results from small-scale studies translate to the landscape level. We found that although the control of fennel translated from the small to landscape scale, decreasing from an average of 60% to less than 3% cover, native species recovery did not occur in the landscape study as it did in the pilot studies. Invasive fennel cover was replaced by non-native grass cover over time. Unexpectedly, fennel cover in untreated fennel plots decreased significantly (though not as drastically) from over 60% cover to just under 40% cover while native species richness in untreated areas increased significantly. The correlation between precipitation and changes in native and non-native species richness and abundance in this study imply that changes in species abundances were highly correlated with environmental fluctuations. The lack of a native seedbank and the accumulation of non-native grass litter likely prevented the recovery of native species in treated areas. Greater vertical complexity found in fennel communities, which increased visitation by frugivorous birds and likely increased native seed dispersal, may have been responsible for the increase in native species richness in the untreated areas. These results suggest that successful invasive species control and native species recovery experiments conducted at small scales may not translate to the landscape level, and active restoration should be an organic component of such large-scale projects.