The role of exotic species in homogenizing the North American flora

Exotic species have begun to homogenize the global biota, yet few data are available to assess the extent of this process or factors that constrain its advance at global or continental scales. We evaluate homogenization of vascular plants across America north of Mexico by comparing similarity in the complete native and exotic floras between states and provinces of the USA and Canada. Compared with native species, exotic plants are distributed haphazardly among areas but spread more widely, producing differentiation of floras among neighbouring areas but homogenization at greater distance. The number of exotic species is more closely associated with the size of the human population than with ecological conditions, as in the case of native species, and their distributions are less influenced by climate than those of native species.     

Spatial phylogenetics of the North American flora

North America is a large continent with extensive climatic, geological, soil, and biological diversity. As biota faces threat from habitat destruction and climate change, making a quantitative assessment of biodiversity becomes critically important. Rapid digitization of plant specimen records and accumulation of DNA sequence data enable a much‐needed broad synthesis of species occurrences with phylogenetic data. In this study, the first such synthesis of a flora from such a large and diverse part of the world is attempted, all seed plants from the North American continent (here defined to include Canada, United States, and Mexico), with a focus on examining phylogenetic diversity and endemism. We collected digitized plant specimen records and chose a coarse grain for analysis, recognizing that this grain is currently necessary for reasonable completeness per sampling unit. We found that raw richness and endemism patterns largely support previous hypotheses of biodiversity hotspots. The application of phylogenetic metrics and a randomization test revealed novel results, including a significant phylogenetic clustering across the continent, a striking east–west geographical difference in the distribution of branch lengths, and the discovery of centers of neo‐ and paleoendemism in Mexico, the southwestern USA, and the southeastern USA. Finally, our examination of phylogenetic beta diversity provides a new approach to compare centers of endemism. We discuss the empirical challenges of working at the continental scale and the need for more sampling across large parts of the continent, for both DNA data for terminal taxa and spatial data for poorly understood regions, to confirm and extend these results.     

The role of immigrants in the assembly of the South American rainforest tree flora

The Amazon lowland rainforest flora is conventionally viewed as comprising lineages that evolved in biogeographic isolation after the split of west Gondwana (ca. 100 Myr ago). Recent molecular phylogenies, however, identify immigrant lineages that arrived in South America during its period of oceanic isolation (ca. 100-3 Myr ago). Long-distance sweepstakes dispersal across oceans played an important and possibly predominant role. Stepping-stone migration from Africa and North America through hypothesized Late Cretaceous and Tertiary island chains may have facilitated immigration. An analysis of inventory plot data suggests that immigrant lineages comprise ca. 20% of both the species and individuals of an Amazon tree community in Ecuador. This is more than an order of magnitude higher than previous estimates. We also present data on the community-level similarity between South American and palaeotropical rainforests, and suggest that most taxonomic similarity derives from trans-oceanic dispersal, rather than a shared Gondwanan history.     

The role of land plants,phosphorus weathering and fire in the rise and regulation of atmospheric oxygen

The evolution of vascular plants and their spread across the land surface, beginning ～420 Ma, progressively increased the rate of weathering of phosphorus from rocks. This phosphorus supply promoted terrestrial and marine productivity and the burial of organic carbon, which has been the major source of O₂ over geological timescales. Hence, it is predicted that the rise of plants led to an increase in the O₂ content of the atmosphere from ～12 vol %, 570–400 Ma to its present level of ～21 vol % by ～340 Ma. Previous modelling studies suggest that O₂ then rose to ～35 vol % ～300 Ma. Such high concentrations are difficult to reconcile with the known persistence of forests, because rising O₂ increases the frequency and intensity of vegetation fires, tending to decrease biomass and cause ecological shifts toward faster regenerating ecosystems. Rising O₂ also directly inhibits C3 photosynthetic carbon assimilation and increases the production of toxic reactive oxygen species in cells. These effects suppress plant‐induced phosphorus weathering and hence organic carbon burial, providing a sensitive negative feedback on O₂. A revised model predicts that this mechanism could have regulated atmospheric O₂ within the range 15–25 vol % for the last 350 million years.     

Absence of post-Miocene Red Sea land bridges: biogeographic implications

In a large number of studies concerned with species movements between Africa and Eurasia, including the migrations of hominids out of Africa, a frequently‐cited dispersal route is across a hypothetical land bridge in the southern Red Sea, which is suggested to have emerged during glacial sea‐level lowstands. This paper, however, unequivocally demonstrates that palaeoceanographic and palaeoecological data are incompatible with the existence of Red Sea land bridges since the Miocene. The case is made by presenting the first quantitative history of water depth above the Red Sea sill for the last 470,000 years, a time period that includes the four most recent glacial–interglacial cycles, and by discussing the predictable consequences of any land bridge formation on the Red Sea sedimentary and microfossil records. The absence of post‐Miocene Red Sea land bridges has extensive implications for biogeographic models in the Afro‐Arabian region. Genetic, morphometric and palaeontological patterns reported in the literature cannot be related to dispersals over a land bridge, or in the case of marine organisms, separation of the Red Sea from the Indian Ocean by a land bridge. If such patterns in terrestrial species are only congruent with a southern Red Sea dispersal route, then they need to be considered in terms of sweepstake rafting, anthropogenic introduction, or in the particular case of the Out‐of‐Africa migration by modern humans, seafaring. The constraints imposed by our palaeoenvironmental record on biogeographic reconstructions within and around the Red Sea will hopefully encourage both the review of previous works and the preference for multidisciplinary approaches in future studies.     

Spread of North American wind-dispersed trees in future environments

Despite ample research, understanding plant spread and predicting their ability to track projected climate changes remain a formidable challenge to be confronted. We modelled the spread of North American wind-dispersed trees in current and future (c. 2060) conditions, accounting for variation in 10 key dispersal, demographic and environmental factors affecting population spread. Predicted spread rates vary substantially among 12 study species, primarily due to inter-specific variation in maturation age, fecundity and seed terminal velocity. Future spread is predicted to be faster if atmospheric CO(2) enrichment would increase fecundity and advance maturation, irrespective of the projected changes in mean surface windspeed. Yet, for only a few species, predicted wind-driven spread will match future climate changes, conditioned on seed abscission occurring only in strong winds and environmental conditions favouring high survival of the farthest-dispersed seeds. Because such conditions are unlikely, North American wind-dispersed trees are expected to lag behind the projected climate range shift.     

The influence of seasonal migration on range size in temperate North American passerines

Seasonal migration has been alternately proposed to promote geographic range size in some contexts and to constrain it in others, but it remains unclear if migratory behavior has a general effect on range size. Because migration involves movement, most hypotheses about the relationship between migration and range size invoke an influence of migration on the process of dispersal-mediated range expansion. Intuitively, a positive relationship between migratory behavior and dispersal ability could bolster range expansion among migratory species, yet some biogeographic patterns suggest that long-distance migration may instead impede range expansion, especially in the temperate zone. We conducted a comparative analysis of the relationship between migratory behavior and range size by testing the effect of migratory status, migration distance and morphological dispersal ability on breeding range size among all temperate North American passerines. Further, we assessed whether these traits affect range expansion into suitable habitat by analyzing their relationship with range filling (the proportion of climatically-suitable area occupied, or ‘filled’ by a species). Contrary to previous studies, we found migration and dispersal ability to be poor predictors of range size and range filling in North America. Rather, most variation in range size is explained by latitude. Our results suggest that migratory behavior does not affect range size within the scale of a continent, and furthermore, that temperate North American passerines’ breeding ranges are not influenced by their dispersal abilities. To better understand why migratory behavior appears to promote range size in some contexts and constrain it in others, future studies should investigate how migratory behavior affects dispersal at the individual level, as well as the relationship between the evolution of migratory behavior and the breadth of species’ climatic niches.     

The stock structure and migrations of plaice populations on the west coast of England and Wales

Plaice Pleuronectes platessa populations on the west coast of England and Wales are currently managed as two stocks: in ICES Division VIIa (Irish Sea, Cardigan Bay and St George's Channel), and ICES Divisions VIIf&g (Bristol Channel and Celtic Sea). A total of 13,784 plaice were fitted with Petersen tags and released in these areas during 1979–1980 and 1993–1996. Analysis of the 2788 recaptures received by June 2000 confirmed known spawning and feeding grounds in the region. It showed also that plaice >25 cm L _T tended to undertake extensive spatial movements. At this size, female plaice were likely to be mature or maturing for the first time, whilst males were probably mature. Tag recaptures indicated resident sub-stocks of plaice in the north-east Irish Sea, the south-east Irish Sea, Cardigan Bay and Bristol Channel, a contingent of plaice in all areas that undertook permanent dispersal to other areas, and a contingent which originated in the south-east Irish Sea and migrated to spawn in the Bristol Channel. Plaice originating in the Bristol Channel rarely moved north into ICES Vila. A general hypothesis of plaice population structure in the region is presented and discussed in relation to stock assessment.     

Phytochrome-mediated development in land plants: red light sensing evolves to meet the challenges of changing light environments

Phytochromes are photoreceptors that provide plants with circadian, seasonal, and positional information critical for the control of germination, seedling development, shade avoidance, reproduction, dormancy, and sleep movements. Phytochromes are unique among photoreceptors in their capacity to interconvert between a red-absorbing form (absorption maximum of approximately 660 nm) and a far-red absorbing form (absorption maximum of approximately 730 nm), which occur in a dynamic equilibrium within plant cells, corresponding to the proportions of red and far-red energy in ambient light. Because pigments in stems and leaves absorb wavelengths below about 700 nm, this provides plants with an elegant system for detecting their position relative to other plants, with which the plants compete for light. Certain aspects of phytochrome-mediated development outside of flowering plants are strikingly similar to those that have been characterized in Arabidopsis thaliana and other angiosperms. However, early diverging land plants have fewer distinct phytochrome gene lineages, suggesting that both diversification and subfunctionalization have been important in the evolution of the phytochrome gene family. There is evidence that subfunctionalization proceeded by the partitioning among paralogues of photosensory specificity, physiological response modes, and light-regulated gene expression and protein stability. Parallel events of duplication and functional divergence may have coincided with the evolution of canopy shade and the increasing complexity of the light environment. Within angiosperms, patterns of functional divergence are clade-specific and the roles of phytochromes in A. thaliana change across environments, attesting to the evolutionary flexibility and contemporaneous plasticity of phytochrome signalling in the control of development.     

Polygyrid land snail phylogeny: external sperm exchange, early North American biogeography, iterative shell evolution

A fresh assessment of reproductive behaviour and anatomy, combined with new allozyme data, results in a phylogenetic hypothesis for the 23 polygyrid genera that differs substantially from previous attempts. Analyses based on this phylogeny suggest that (a) evolutionary transition from internal to external sperm exchange occurred only once in polygyrids, with unusual functional intermediates still extant; (b) polygyrid biogeographic history paralleled that of plethodontid salamanders, with hypothesized vicariance events at about 145, 120, 65 and 40 MA, and, dispersal events at about 55 and 40 MA; and (c) iterative shell evolution occurred despite a phylogenetic constraint on ontogenetic whorl-expansion rate.     

Changes in the distribution of alien plants along roadsides in relation to adjacent land use over the course of 40 years

Roads have become one of the main corridors supporting the dispersal of alien plants and their penetration and integration into native vegetation communities in new areas. The aim of this study was to use data sampled in 1970, 1994, and 2010 in order to check for changes in the spread of alien species along roadsides in relation to the adjacent land use. The results show that nutrient influxes and mechanical disturbance associated with the onset of intensive farming had a significant impact on the spread of the plant species in this study. In general, a significant increase was documented in the spread of species of invasive status. A different trend in the spread of archaeophytes and neophytes was observed in cases in which a road was adjacent to the meadow. Most of the archaeophytes in these habitats spread significantly in the first 20 years, and the distribution of neophytes did not show an increasing tendency. The highest rate of expansion was observed for plants propagating only by seed and in the built-up area of municipalities. Plants exhibiting both seed and vegetative propagation prevailed in the vicinity of meadows and forest vegetation.     

The role of land cover in bioclimatic models depends on spatial resolution

Aim We explored the importance of climate and land cover in bird species distribution models on multiple spatial scales. In particular, we tested whether the integration of land cover data improves the performance of pure bioclimatic models. Location Finland, northern Europe. Methods The data of the bird atlas survey carried out in 1986–89 using a 10 × 10 km uniform grid system in Finland were employed in the analyses. Land cover and climatic variables were compiled using the same grid system. The dependent and explanatory variables were resampled to 20‐km, 40‐km and 80‐km resolutions. Generalized additive models (GAM) were constructed for each of the 88 land bird species studied in order to estimate the probability of occurrence as a function of (1) climate and (2) climate and land cover variables. Model accuracy was measured by a cross‐validation approach using the area under the curve (AUC) of a receiver operating characteristic (ROC) plot. Results In general, the accuracies of the 88 bird–climate models were good at all studied resolutions. However, the inclusion of land cover increased the performance of 79 and 78 of the 88 bioclimatic models at 10‐km and 20‐km resolutions, respectively. There was no significant improvement at the 40‐km resolution. In contrast to the finer resolutions, the inclusion of land cover variables decreased the modelling accuracy at 80km resolution. Main conclusions Our results suggest that the determinants of bird species distributions are hierarchically structured: climatic variables are large‐scale determinants, followed by land cover at finer resolutions. The majority of the land bird species in Finland are rather clearly correlated with climate, and bioclimate envelope models can provide useful tools for identifying the relationships between these species and the environment at resolutions ranging from 10 km to 80 km. However, the notable contribution of land cover to the accuracy of bioclimatic models at 10–20‐km resolutions indicates that the integration of climate and land cover information can improve our understanding and model predictions of biogeographical patterns under global change.     

Horizontal gene transfer in the innovation and adaptation of land plants

Horizontal gene transfer (HGT) has been well documented in prokaryotes and unicellular eukaryotes, but its role in plants and animals remains elusive. In a recent study, we showed that at least 57 families of nuclear genes in the moss Physcomitrella patens were acquired from prokaryotes, fungi or viruses and that HGT played a critical role in plant colonization of land. In this paper, we categorize all acquired genes based on their putative functions and biological processes, and further address the importance of HGT in plant innovation and evolution.     

华北平原土地利用/覆盖对CO空间分布的调控作用

CO不仅是中国主要的空气污染物之一,还是温室效应的贡献者。农业用地每年消耗了大量的CO通量,土地利用/覆盖格局对于调控CO空间分布发挥了较大的作用。针对土地利用/覆盖调控CO空间分布开展研究,以华北平原为例揭示人类活动对CO空间异质性的影响。研究发现2010至2020年华北平原CO排放量由4964×10⁴ t降低至2683×10⁴ t,大部分耕地CO浓度由90 t/km²下降至45 t/km²以下。CO浓度空间集聚程度呈现先降低后升高趋势,Moran′s I指数由0.25增加至0.41。经济发展迅速的地区CO污染较为严重,北京和周边城市形成了CO污染高-高集聚区,周口和淮北等城市则形成了低-低集聚区。总体来看,CO浓度呈低-低集聚分布的区域不断扩大,反映出CO减排措施已经初见效果。研究表明土地利用/覆盖在类型与结构方面的差异影响了CO的排放、扩散以及氧化消耗,增加了大气CO收支的不确定性,对CO空间分布具有一定的调控作用。通过分析土地利用/覆盖与CO空间分布的关联性,探究土地利用/覆盖及景观格局对区...     

The ecological status of the carob-tree (Ceratonia siliqua, Leguminosae) in the Mediterranean

The present distribution of the carob-tree ( Ceratonia siliqua L.) throughout the coastal regions of the Mediterranean, the route followed from its possible place of origin in southern Arabia and the Horn of Africa, and the possible circumstances of the tree's domestication are discussed in the light of botanical, archaeological, historical and philological evidence. It is shown that the genus Ceratonia formed part of the wild flora of western Europe in preglacial times, that C. siliqua was present in ancient times in the Middle East and that its spread to the western Mediterranean area took place progressively, possibly beginning in the second millennium bc . From the fact that, except in the case of Greece and southern Italy, most of the names applied to the tree today in European languages are linked to Arabic, it is inferred that today's cultivars were probably selected by Muslims in the Middle Ages.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 144 , 431–436.