One haploid parent contributes 100% of the gene pool for a widespread species in northwest North America

The monoicous peatmoss Sphagnum subnitens has a tripartite distribution that includes disjunct population systems in Europe (including the Azores), northwestern North America and New Zealand. Regional genetic diversity was highest in European S. subnitens but in northwestern North America, a single microsatellite‐based multilocus haploid genotype was detected across 16 sites ranging from Coos County, Oregon, to Kavalga Island in the Western Aleutians (a distance of some 4115 km). Two multilocus haploid genotypes were detected across 14 sites on South Island, New Zealand. The microsatellite‐based regional genetic diversity detected in New Zealand and North American S. subnitens is the lowest reported for any Sphagnum. The low genetic diversity detected in both of these regions most likely resulted from a founder event associated with vegetative propagation and complete selfing, with one founding haploid plant in northwest North America and two in New Zealand. Thus, one plant appears to have contributed 100% of the gene pool for the population systems of S. subnitens occurring in northwest North America, and this is arguably the most genetically uniform group of plants having a widespread distribution yet detected. Although having a distribution spanning 12.5° of latitude and 56° of longitude, there was no evidence of any genetic diversification in S. subnitens in northwest North America. No genetic structure was detected among the three regions, and it appears that European plants of S. subnitens provided the source for New Zealand and northwest North American populations.     

Mammalian turnover and community structure in the Paleocene of North America

The effects of faunal turnover on mammalian community structure are evaluated for 17 faunal zones of the North American Paleocene through early Eocene land mammal ages (Puercan through early Wasatchian). Generic disappearances were significantly high at the end of the Puercan, Torrejonian, and Tiffanian land mammal ages, but appearances were significantly high only during the early Puercan. Generic richness rose rapidly in the early Puercan, remained stable throughout most of the Paleocene, and increased from the late Paleocene into the early Eocene. The null hypothesis that generic turnover clustered preferentially according to dentally defined trophic or body size categories could be rejected or attributed to sampling problems for all but the early (Pu0) and late Paleocene (Ti5‐Cf2). Early Paleocene change in community structure most probably represented endemic radiation of mammals into previously unoccupied niches. Community restructuring in the late Paleocene reflected a complex of causes, including climatic wanning, intercontinental dispersal, and competition.     

Distribution and systematics of the freshwater red algal family Thoreaceae in North America

North American populations and type specimens of Thorea and Nemalionopsis were compared using multivariate morphometrics and image analysis. We continue to recognise the separation of the two genera based on spore-bearing branch-to-assimilatory filament length ratio and assimilatory filament density (≤0·3 and loose for Thorea and ≥0·6 and compressed for Nemalionopsis, respectively). Four species of Thorea were distinguished worldwide: T. hispida (syn. T. andina, T. lehmannii, T. ramosissima), T. violacea (syn. T. bachmannii, T. brodensis, T. gaudichaudii, T. okadae, T. prowsei and T. riekei), T. clavata and T. zollingeri. The former two species have variable branched, non-clavate assimilatory filaments, whereas the latter two have unbranched, clavate assimilatory filaments. Thorea hispida has copious secondary branches while T. violacea is sparsely branched. Thorea clavata is differentiated from T. zollingeri by having fewer monosporangia per cluster. Two of these species were found in North America: T. hispida in Mexico, Grenada and Jamaica, and T. violacea in Texas and Mexico. Two species of Nemalionopsis were differentiated: N. shawii with long assimilatory filaments composed of barrel-shaped cells and n. tortuosa (syn. N. shawii f. caroliniana) with short assimilatory filaments having cylindrical cells. Only N. tortuosa has been collected on the continent, from Florida, Louisiana and North Carolina.     

Bryozoan provinces and patterns of generic evolution and extinction in the Late Ordovician of North America

The Late Ordovician bryozoan genera of central and southeastern North America are geographically distributed in three biotic provinces, separated by boundaries reflecting major lithofacies differences. The central Cincinnati Province contains most of the North American endemic genera, and represents a narrow ecological zone separating the clastic wedges of the marginal Reedsville-Lorraine Province from the cratonic carbonate platform of the Red River-Stony Mountain Province. The provinces provided major life zones, or biomes, for each of the five bryozoan orders. Genera comprising the provinces differed as well in morphologic complexity, geochronologic survivorship, tiering, endemism and eurytopy. Regions on either side of the Cincinnati Province were dominated by inferred immigrants from Baltoscandia. Al-logenic provincial succession produced time-averaged mixed faunas in regions near the provincial boundaries. Although most generic originations took place within the Cincinnati Province, evolutionary novelties are associated with the Reedsville-Lorraine Province. The loss of the diverse Cincinnati Province, connected with global cooling and a eustatic lowering of sea level, may have been a chief factor in the Late Ordovician extinction of bryozoan genera. Genera from the Red River-Stony Mountain Province differentially survived into the Silurian.     

Of glaciers and refugia: a decade of study sheds new light on the phylogeography of northwestern North America

Glacial cycles have played a dominant role in shaping the genetic structure and distribution of biota in northwestern North America. The two major ice age refugia of Beringia and the Pacific Northwest were connected by major mountain chains and bordered by the Pacific Ocean. As a result, numerous refugial options were available for the regions taxa during glacial advances. We reviewed the importance of glaciations and refugia in shaping northwestern North America’s phylogeographic history. We also tested whether ecological variables were associated with refugial history. The recurrent phylogeographic patterns that emerged were the following: (i) additional complexity, i.e. refugia within refugia, in both Beringia and the Pacific Northwest; and (ii) strong evidence for cryptic refugia in the Alexander Archipelago and Haida Gwaii, the Canadian Arctic and within the ice‐sheets. Species with contemporary ranges that covered multiple refugia, or those with high dispersal ability, were significantly more likely to have resided in multiple refugia. Most of the shared phylogeographic patterns can be attributed to multiple refugial locales during the last glacial maximum or major physiographic barriers like rivers and glaciers. However, some of the observed patterns are much older and appear connected to the orogeny of the Cascade‐Sierra chain or allopatric differentiation during historic glacial advances. The emergent patterns from this review suggest we should refine the classic Beringian‐southern refugial paradigm for northwestern North American biota and highlight the ecological and evolutionary consequences of colonization from multiple refugia.     

Taxonomy and biogeography of the fiddler crabs (Ocypodidae: Genus Uca) of the Atlantic and Gulf coasts of eastern North America

Fifteen species of fiddler crabs are reported for eastern North America between Massachusetts and Quintana Roo, Mexico. Thirteen occur in the United States and 11 in Mexico, with eight in common to the two countries. Of 13 species in the Gulf of Mexico, five are endemic and a sixth is restricted largely to the peninsulas of Florida and Yucatan. The status of U. rapax in the northern Gulf remains to be resolved. Range limits of most species approximate one or the other of two sets of intersecting thermal and geological boundaries that subdivide the Gulf of Mexico along north-south and east-west axes. Species belonging to subgenus Minuca tend to replace one another at the thermally-controlled Carolinian-Caribbean marine biotic boundary across the Florida peninsula and northern Gulf. However, only U. minax of all the North American fiddler crabs exhibits the classical disjunct Carolinian distribution, and this appears basically to reflect the discontinuous distribution of temperate salt marshes that are the habitat of the species. Distributions of species belonging to subgenus Celuca adhere for the most part to the subdivision of the Gulf into western terrigenous and eastern carbonate sedimentary provinces. The northern transition occurs in the vicinity of Apalachee Bay and the southern at Laguna de Terminos. A third distributional pattern is shown by U. subcylindrica , a specialized endemic species of the hypersaline Laguna Madre system of the western Gulf. The level of endemism in the fiddler crabs is relatively high in comparison with that of other marine groups within the Gulf of Mexico. This may be a consequence of the adaptations of fiddler crabs as specialized deposit feeders to regional differences in climatic and edaphic characteristics of a marginally marine upper shore habitat. The distributional patterns of the endemics could prove useful in reconstructing palaeoecological events of evolutionary significance within the Gulf of Mexico.     

The Aristida pansa complex and a key to the Divaricatae group of North America (Gramineae: Aristideae)

Variation in lateral awn length and pulvini development is described for A. pansa and A. gypsophila. The two species are distinguished by lateral awn development. Within each species, forms are based on pulvini development. Three new forms are described (A. pansa f. contracta; A. gypsophila f. gypsophiloides and f. diffusa), A. dissita is reduced to a form of A. pansa, and A. tehuacanensis is considered synonymous with A. pansa f. dissita. Keys, illustrations, and maps are provided.     

北美东部8种温带树种向北分布的限制气候因子

利用分布于北美东部的 8种温带落叶树种为研究材料 ,应用反映热量和降水状况的 11个变量为气候指标 ,用标准差分析方法分析了这 8个树种的分布北界与气候因子之间的关系。结果表明 ,在所使用的气候指标中 ,同一树种不同地点的温暖指数或年生物温度的标准差最小 ,说明积温是限制这些树种向北分布的主要气候因子 ;温暖指数和寒冷指数随着年降水量的增大而减小 ,寒冷指数随着年较差的增加而增加 ,温暖指数随着水热综合指数的增加表现出减小的趋势。表明 ,除了生长季节的积温之外 ,降水和大陆性等气候条件对温带树种向北分布也起着重要作用     

北美东部8种温带树种向北分布的限制气候因子

利用分布于北美东部的8种温带落叶树种为研究材料,应用反映热量和降水状况的11个变量为气候指标,用标准差分析方法分析了这8个树种的分布北界与气候因子之间的关系.结果表明,在所使用的气候指标中,同一树种不同地点的温暖指数或年生物温度的标准差最小,说明积温是限制这些树种向北分布的主要气候因子;温暖指数和寒冷指数随着年降水量的增大而减小,寒冷指数随着年较差的增加而增加,温暖指数随着水热综合指数的增加表现出减小的趋势.表明,除了生长季节的积温之外,降水和大陆性等气候条件对温带树种向北分布也起着重要作用.     

Potential Changes in the Distributions of Western North America Tree and Shrub Taxa under Future Climate Scenarios

Increases in atmospheric greenhouse gases are driving significant changes in global climate. To project potential vegetation response to future climate change, this study uses response surfaces to describe the relationship between bioclimatic variables and the distribution of tree and shrub taxa in western North America. The response surfaces illustrate the probability of the occurrence of a taxon at particular points in climate space. Climate space was defined using three bioclimatic variables: mean temperature of the coldest month, growing degree days, and a moisture index. Species distributions were simulated under present climate using observed data (1951–80, 30-year mean) and under future climate (2090–99, 10-year mean) using scenarios generated by three general circulation models—HADCM2, CGCM1, and CSIRO. The scenarios assume a 1% per year compound increase in greenhouse gases and changes in sulfate (SO₄) aerosols based on the Intergovernmental Panel on Climate Change (IPCC) IS92a scenario. The results indicate that under future climate conditions, potential range changes could be large for many tree and shrub taxa. Shifts in the potential ranges of species are simulated to occur not only northward but in all directions, including southward of the existing ranges of certain species. The simulated potential distributions of some species become increasingly fragmented under the future climate scenarios, while the simulated potential distributions of other species expand. The magnitudes of the simulated range changes imply significant impacts to ecosystems and shifts in patterns of species diversity in western North America. Received 12 May 2000; accepted 20 December 2000.     

Pears and persimmons: A comparison of temperate forests in Europe and eastern North America

Major dimensions of ecological segregation of tree species in cool temperate Europe and E North America appear related to (a) soil pH, (b) large scale ‘succession’ including topographic sequences of changing moisture stress, and (c) intolerance versus tolerance of canopy competition as involved in ‘gap-phase’ dynamics. Genera tend to have similar average positions along these dimensions in the two subcontinents. E North American genera that were probably never present in Europe, and the few opposites, tend to be southern and are concentrated on dry or basic soil. The cause of this trend may involve the isolated expansions of dry climatic areas since the early Tertiary. E North American genera that became extinct in Europe after the mid-Pliocene are typical of habitat intermediate between dry-acid and moist-basic, though generally more moist-acid than dry-basic. These genera also have few species and little overall habitat width. Severe restrictions of their habitats may have occurred. Also, difficulties of migration to and from refugia are suggested by the generally heavier seed of extinet genera and those with strongly southern ranges in Europe or with few species compared to E North America. This relationship is apparent within small winged, medium fleshy and large nutty fruit classes. However, there is little difference in geographic restriction between these classes. Carpinus, Alnus, Corylus, Taxus, Pyrus and Sorbus reach 100–1000% greater height in Europe. There are no opposing differences of this magnitude. These trees may be ecological substitutes for extinct Liriodendron, Liquidambar, Carya, Tsuga + Thuja, Diospyros, and a group with smaller fleshy fruits, respectively. There are other intrageneric differences in height, seed weight, niche width, longevity, etc., that deserve further attention.     

The distribution of deer biomass in North America supports the hypothesis of exploitation ecosystems

The hypothesis of exploitation ecosystems (EEH) predicts that, along a productivity gradient in terrestrial environments, predators will regulate herbivores at a relatively constant density whenever primary productivity exceeds 700 g m⁻² y⁻¹; under this threshold, or if predators are absent, forage production determines herbivore density. I tested EEH using the pattern of deer biomass distribution over North America, the dominant family of large herbivores. Deer biomass increased from the High Arctic to the north of the boreal forest and remained in the same range southward within the gray wolf range; for the same latitude, deer biomass increased by a factor of 5 in the absence of wolves. South of the wolf range, there existed a clear relationship between actual evapotranspiration, a proxy of primary productivity, and deer biomass. Highest deer densities occurred in the south-east of the continent where only white-tailed deer are present. The observed pattern lends support to EEH and suggests that the removal of large predators in southern North America may have imposed an unprecedented pressure on plants eaten by deer.     

Paleoceanography of the Late Cretaceous (Maastrichtian) Western Interior Seaway of North America: evidence from Sr and O isotopes

Well-preserved fossils of the Late Cretaceous Western Interior Seaway (WIS) of North America have been analyzed for Sr concentration and Sr and O isotopes in order to decipher paleosalinities and paleotemperatures. The samples are from four biofacies within the Seaway (late Maastrichtian): offshore Interior (Pierre Shale), nearshore Interior (Fox Hills Formation), brackish (reduced salinity; Fox Hills Formation) and freshwater (Hell Creek Formation). Samples were also obtained from the Severn Formation of Maryland (considered to be representative of the open ocean). All biofacies (except the freshwater) are demonstrably within the Jeletzkytes nebrascensis ammonite zone (<1 Ma duration). The ⁸⁷Sr/⁸⁶Sr ratios show significant and systematic decreases from marine (mean±1 S.D.=0.707839±0.000024) to brackish facies (mean±1 S.D.=0.707677±0.000036), consistent with dilution by freshwater with a lower ⁸⁷Sr/⁸⁶Sr ratio than seawater. Such variation disallows using the ⁸⁷Sr/⁸⁶Sr ratios of fossil shell material to assign ages to fossils from the Late Cretaceous WIS without knowledge of the salinity in which the organism grew. The Sr isotope ratios for scaphitid ammonites within a single biofacies are similar to each other and different from those for scaphites in other biofacies, implying that these organisms are restricted in their distribution during life. The ⁸⁷Sr/⁸⁶Sr values of freshwater unionid mussels range widely and are not compatible with the freshwater endmember ⁸⁷Sr/⁸⁶Sr ratio required by the trend in ⁸⁷Sr/⁸⁶Sr vs. biofacies established from the other samples. Paleosalinities for the biofacies are estimated to range from 35‰ in the open marine to a minimum of 20‰ in the brackish, based on the presence of cephalopods in all four facies and the known salinity tolerance of modern cephalopods. Producing reasonable ⁸⁷Sr/⁸⁶Sr values for the freshwater endmember of a ⁸⁷Sr/⁸⁶Sr vs. 1/[Sr] plot requires a Sr concentration 0.2-0.5 that of seawater for the dominant freshwater input to the WIS. Such high Sr concentrations (relative to seawater) are not observed in modern rivers, and we suggest that the brackish environment in the WIS arose through the mixing of freshwater and seawater in a nearshore aquifer system. Reactions of the solution with aquifer solids in this ‘subterranean estuary’ [Moore, Mar. Chem. 65 (1999) 111-125] produced brackish water with the Sr concentration and isotopic composition recorded in the brackish biofacies. δ¹⁸O values of the fossils show decreases from the marine to brackish biofacies consistent with increasing temperatures (from ∼13 to 23°C) or, if temperatures were relatively constant, to a decrease in the δ¹⁸O of the water in which the shell formed. The latter interpretation is consistent with less-than-fully marine salinities in the nearshore biofacies, but both changes in temperature and the isotopic composition of the water may have occurred in this environment.     

First record of the mygalomorph spider family Paratropididae (Arachnida,Araneae) in North America with the description of a new species of Paratropis Simon from Mexico,and with new ultramorphological data for the family

A new species of the genus Paratropis is described from North America: Paratropis tuxtlensissp. n., from a tropical rainforest in Veracruz, Mexico. This is the fifth Paratropis and the tenth paratropidid species described and the first North American record of this Neotropical family. The species is described based on adult males and females, and juveniles. The juveniles show ontogenetic variation in the number of cuspules on the labium and endites, and in the number and position of leg trichobothria. This is the second Paratropis species, and the third paratropidid known from both sexes. The scanning electron photographs (SEM) reveal new morphological data and contribute to the knowledge of the family.     

Yearly maps of summer temperatures in Western Europe from A.D. 1750 to 1975 and Western North America from 1600 to 1982:

The primary purpose of this publication is to make available two series of historical maps showing summer (April–September mean) temperatures over western Europe from A.D. 1750 and western North America from A.D. 1600. These maps have been reconstructed using networks of temperature-sensitive tree-ring chronologies as part of a continuing collaboration between the Swiss Federal Institute for Forest, Snow and Landscape Research (FSL) at Birmensdorf, Switzerland and the Climatic Research Unit (CRU) at the University of East Anglia, Norwich, U.K. The maps were reconstructed using relatively long maximum latewood density chronologies selected from the extensive networks of tree-ring data produced at the FSL. The reconstructions were produced using a spatial regression technique developed at CRU.The basis for the reconstructions are wood samples from various conifers growing at cool-moist sites close to the alpine or boreal timberlines. This material was analysed by x-ray densitometry and the resulting maximum latewood density chronologies were calibrated against meteorological data over a 100-year calibration period.These results emphasize the value of dendroclimatological research which can provide continentalscale reconstructions of past climate which represent a potential resource for climatologists, biologists, and historians with an interest in the spatial variability of summer temperatures over the middle to high latitudes.     

Revision of the larvae of Leptus Latreille (Acarina: Erythraeidae) of Europe and North America, with descriptions of post-larval instars

The larvae of Leptus Latreille, 1796 (Acarina: Erythraeidae) of Europe and North America are comprehensively revised. Of those described since 1900 a total of 34 species is considered recognizable and capable of being keyed; no species described before 1900 is considered recognizable. The nominal type of the genus, Acarus phalangii de Geer, 1778 is rejected as an illegitimate name. Eighteen European and 17 North American species are described and keyed, of which 17 are new to science. One new subspecies from North America, of a species previously known from Europe, is described and keyed. Standard metric data are given for each species or subspecies from available specimens (except two North American species, L. ariel Southcott and L. clarki Southcott, recently described elsewhere; for these last-named two additional metric data are given). Larvae have been recorded from April to September, with the greatest number found being for July and August.
Protonymphs are described for two North American species ( L. ghiradellae sp. nov. and L. welbourni sp. nov. ), and deutonymphs for two North American species ( L. calix sp. nov. and L. ghiradellae ). Keys are given to separate the reared protonymphs, and three described deutonymphs (the two preceding and the European L. galerucae Feider). Data on the duration of the protonymphal instar suggest that in North America and Europe there are two modes: one lasting 3–4 weeks, the other 5–7 months. Developmental abnormalities are recorded systematically.     

Brachiopod community paleoecology, paleobiogeography, and depositional topography of the Devonian Onondaga Limestone and correlative strata in eastern North America

The Emsian? through early Eifelian Onondaga Limestone of the Appalachian Basin was deposited in a topographic basin and on the carbonate platform which surrounded the basin on the west, north, and northeast. Onondaga strata thin from the platform into the basin. Two sedimentary cycles are present in the sub-Tioga Onondaga of eastern North America. The Edgecliff-Amherstburg represents an interval of transgression, in which epeiric seas spread over much of eastern North America. During the Nedrow-Lucas regression, the interior of the carbonate platform became restricted, resulting in the deposition of evaporites. The Moorehouse-Anderdon transgression continued through the deposition of the Tioga Bentonite, followed by the pre-Speeds-Dundee regression from the craton. Early Eifelian Appalachian Basin Onondaga brachiopod communities, arranged from nearshore to offshore, include the Atrypid-Megakozlowskiella, Atrypid-Levenea, Chonetid, Atlanticocoelia, Ambocoeliid, and Truncalosia Communities. The Onondaga-age Eastern Americas Realm is divided into the Appohimchi Province in the Appalachian Basin and the Michigan Basin-Hudson Bay Lowland Province in the Midwest. The provincial assignment of the James Bay region of Ontario is uncertain; the Eastern Townships of Quebec are near the boundaries both of the two provinces of the Eastern Americas Realm, and of the Eastern Americas Realm and the Old World Realm, the latter realm being probably in the Canadian Maritime Provinces.     

Biogeography and systematics of Hildenbrandia (Rhodophyta,Hildenbrandiales) in North America: inferences from morphometrics and rbcL and 18S rRNA gene sequence analyses

Morphometric analysis and phylogenetic analysis of sequences of the rbcL chloroplast gene (which codes for the large subunit of the ribulose-1,5-bisphosphate carboxylase/oxygenase enzyme) and the nuclear 18S ribosomal RNA (rRNA) gene were carried out on 26 specimens of marine and freshwater Hildenbrandia from North America. Nineteen marine specimens were collected from Alaska to Costa Rica on the Pacific coast and from Newfoundland to Connecticut on the Atlantic coast. Seven freshwater samples were collected from Texas, Costa Rica, St Lucia and Puerto Rico. Three groups of samples were distinguished by morphometric analysis: one containing all freshwater samples (H. angolensis Welwitsch ex West et West), one consisting of a marine sample with parallel tetrasporangial divisions (H. occidentalis Setchell ex Gardner) and one group with non-parallel tetrasporangial divisions (H. rubra (Sommerfelt) Meneghini. These groupings were partially incongruent with those obtained by analyses of the molecular data. Parsimony and distance analyses of the rbcL gene resulted in trees in which Atlantic and Pacific clades were largely resolved. However, an Alaskan sample was included in the Atlantic group, which may indicate a trans-Arctic invasion event. The freshwater samples were paraphyletic for the rbcL gene, among the marine collections, which supports the concept of multiple invasions establishing the freshwater populations in North America. The 18S rRNA gene sequence data indicate that the freshwater samples are monophyletic with the exception of the unresolved position of the H. occidentalis sample. The freshwater samples form a monophyletic clade when multiple outgroups are used. The rbcL data appear to be mutationally saturated above approximately 17% divergence, which makes interpretation of phylogenetic signal among distant groups difficult. This may be a result of the asexual reproduction of the alga.