Trait differences between grass species along a climatic gradient in South and North America

Question: Are trait differences between grasses along a gradient related to climatic variables and/or photosynthetic pathway? Location: Temperate grassland areas of South and North America. Methods: In a common garden experiment, we cultivated C₃ and C₄ grasses from grasslands under different climatic conditions, and we measured a set of 12 plant traits related to size and resource capture and utilization. We described (1) interspecific plant trait differences along a climatic gradient defined by the precipitation and temperature at the location where each species is dominant and (2) the association between those plant trait differences and the photosynthetic pathway of the species. Results: Trait differences between grasses were related to the precipitation at the area where each species is dominant, and to the photosynthetic pathway of the species. Leaf length, leaf width, plant height, leaf area per tiller, specific leaf area, leaf δ¹³C ratio, and nitrogen resorption efficiency increased while leaf dry matter content and nitrogen concentration in senesced leaves decreased as precipitation increased. A proportion of these changes along the gradient was related to the photosynthetic pathway because dominant grass species in cold areas with low precipitation are mainly C₃ and those from warm and wet areas are C₄. Conclusions: A previous worldwide analysis showed that traits of graminoid species measured in situ changed slightly along climatic gradients (< 10% variance explained). In contrast, under a common environment we observed that (1) grass traits changed strongly along a climatic gradient (30‐85% variance explained) and, (2) a proportion of those changes were related to the association between photosynthetic pathway of the species and precipitation.     

Geographical distributions of spiny pocket mice in South America: insights from predictive models

Aim Predictive models of species’ distributions use occurrence records and environmental data to produce a model of the species’ requirements and a map of its potential distribution. To determine regions of suitable environmental conditions and assess biogeographical questions regarding their ranges, we modelled the potential geographical distributions of two spiny pocket mice (Rodentia: Heteromyidae) in north‐western South America. Location North‐western South America. Methods We used the Genetic Algorithm for Rule‐Set Prediction (GARP), environmental data from GIS maps and georeferenced collection localities from a recent systematic review of Heteromys australis and H. anomalus to produce the models. Results GARP models indicate the potential presence of H. australis throughout mesic montane regions of north‐western South America, as well as in some lowland regions of moderately high precipitation. In contrast, H. anomalus is predicted to occur primarily in drier areas of the Caribbean coast and rain‐shadowed valleys of the Andes. Conclusions The models support the disjunct status of the population of H. australis in the Cordillera de Mérida, but predict a continuous distribution between known populations of H. anomalus in the upper Magdalena Valley and the Caribbean coast. Regions of suitable environmental conditions exist disjunct from known distributional areas for both species, suggesting possible historical restrictions to their ranges. This technique holds wide application to other study systems.     

Continental and regional ranges of North American mammals: Rapoport's rule in real and null worlds

Aim To assess the relationship between species richness and distribution within regions arranged along a latitudinal gradient we use the North American mammalian fauna as a study case for testing theoretical models. Location North America. Methods We propose a conceptual framework based on a fully stochastic mid‐domain model to explore geographical patterns of range size and species richness that emerge when the size and position of species ranges along a one‐dimensional latitudinal gradient are randomly generated. We also analyse patterns for the mammal fauna of North America by comparing empirical results from a biogeographical data base with predictions based on randomization null models. Results We confirmed the validity of Rapoport's rule for the mammals of North America by documenting gradients in the size of the continental ranges of species. Additionally, we demonstrated gradients of mean regional range size that parallel those of continental range. Our data also demonstrated that mean range size, measured both as a continental or a regional variable, is significantly correlated with the geographical pattern in species richness. All these patterns deviated sharply from null models. Main conclusions Rapoport's statement of an areographic relationship between species distribution and richness is highly relevant in modern discussions about ecological patterns at the geographical scale.     

Small rainfall events: An ecological role in semiarid regions

Summary Small precipitation events account for a large proportion of the precipitation received in semiarid regions, and their potential ecological importance has previously been ignored. We investigated the effect of a small rainfall event (5 mm) upon Bouteloua gracilis, the dominant grass species of the central and southern Great Plains of North America. An effect of a small event on leaf water potential and leaf conductance to water vapor was observed in less than 12 h and lasted for up to two days.The remarkable short response time of Bouteloua gracilis to a rainfall stimulus enables this species to utilize small events and, therefore, may influence its persistence as a dominant species in the steppe region.We proposed response times to be one of the major species characteristics determining capacity for utilizing different portions of the water resource of the region. We suggest that small precipitation events are ecologically significant and a qualitatively distinct resource for ecosystems in semiarid regions.     

Spatial Pattern of Vascular Plant Diversity in North America North of Mexico and its Floristic Relationship with Eurasia

This paper reports: (1) patterns of taxonomic richness of vascularplants in North America (north of Mexico), an area accountingfor 16.6% of the total world land, in relation to latitudinaland longitudinal gradients; (2) floristic relationships betweendifferent latitudinal zones, longitudinal zones, and geographicregions of North America; and (3) floristic relationships betweenNorth America and Eurasia at various geographic scales. NorthAmerica was geographically divided into twelve regions, whichwere latitudinally grouped into four zones, each with threeregions, and longitudinally grouped into three zones, each withfour regions. The native vascular flora of North America consistsof 162 orders, 280 families, 1904 genera and 15352 species.Along the latitudinal gradient, species richness shows a strikingincrease with decreasing latitude (e.g. the northernmost latitudinalzone has only 11.7% of the number of species in the southernmostlatitudinal zone). However, about 63% of the species of thenorthernmost latitudinal zone are also present in the southernmostlatitudinal zone of North America. Among the three longitudinalzones, the zone on the Pacific coast has 1.48 and 1.64-timesas many species as the zones in the interior and on the Atlanticcoast, respectively. About 36% of the species in the zone ofthe Atlantic coast also occur in the Pacific coast zone. However,each of over 40% of the species in North America occupies lessthan 10% of the total land area of North America. Some 48% ofthe genera and 6.5% of the species of North America are alsonative to Eurasia. In general, the number of genera common toNorth America and Eurasia increased from the north to the southand from the west to the east of North America, whereas thenumber of species common to the two continents decreased alongthe same two geographic gradients.Copyright 1999 Annals of BotanyCompany Asia, biodiversity, Europe, floristic similarity, latitudinal and longitudinal gradients, North America, taxonomic richness.     

Invasion of Old World Phragmites australis in the New World: precipitation and temperature patterns combined with human influences redesign the invasive niche

After its introduction into North America, Euro‐Asian Phragmites australis became an aggressive invasive wetland grass along the Atlantic coast of North America. Its distribution range has since expanded to the middle, south and southwest of North America, where invasive P. australis has replaced millions of hectares of native plants in inland and tidal wetlands. Another P. australis invasion from the Mediterranean region is simultaneously occurring in the Gulf region of the United States and some countries in South America. Here, we analysed the occurrence records of the two Old World invasive lineages of P. australis (Haplotype M and Med) in both their native and introduced ranges using environmental niche models (ENMs) to assess (i) whether a niche shift accompanied the invasions in the New World; (ii) the role of biologically relevant climatic variables and human influence in the process of invasion; and (iii) the current potential distribution of these two lineages. We detected local niche shifts along the East Coast of North America and the Gulf Coast of the United States for Haplotype M and around the Mississippi Delta and Florida of the United States for Med. The new niche of the introduced Haplotype M accounts for temperature fluctuations and increased precipitation. The introduced Med lineage has enlarged its original subtropical niche to the tropics‐subtropics, invading regions with a high annual mean temperature (> ca. 10 °C) and high precipitation in the driest period. Human influence is an important factor for both niches. We suggest that an increase in precipitation in the 20th century, global warming and human‐made habitats have shaped the invasive niches of the two lineages in the New World. However, as the invasions are ongoing and human and natural disturbances occur concomitantly, the future distribution ranges of the two lineages may diverge from the potential distribution ranges detected in this study.     

A tale of North and South America: time and mode of dispersal of the amphitropical genus Munroa (Poaceae,Chloridoideae)

Plant disjunctions have provided some of the most intriguing distribution patterns historically addressed by biogeographers. We evaluated the three hypotheses that have been postulated to explain these patterns [vicariance, stepping‐stone dispersal and long‐distance dispersal (LDD)] using Munroa, an American genus of grasses with six species and a disjunct distribution between the desert regions of North and South America. The ages of clades, cytology, ancestral characters and areas of distribution were investigated in order to establish relationships among species, to determine the time of divergence of the genus and its main lineages, and to understand further the biogeographical and evolutionary history of this genus. Bayesian inference recovered the North American M. pulchella as sister species to the rest. Molecular dating and ancestral area analyses suggest that Munroa originated in North America in the late Miocene–Pliocene (7.2 Mya; 8.2–6.5 Mya). Based on these results, we postulate that two dispersal events modelled the current distribution patterns of Munroa: the first from North to South America (7.2 Mya; 8.2–6.5 Mya) and the second (1.8 Mya; 2–0.8 Mya) from South to North America. Arid conditions of the late Miocene–Pliocene in the Neogene and Quaternary climatic oscillations in North America and South America were probably advantageous for the establishment of populations of Munroa. We did not find any relationship between ploidy and dispersal events, and our ancestral character analyses suggest that shifts associated with dispersal and seedling establishment, such as habit, reproductive system, disarticulation of rachilla, and shape and texture of the glume, have been important in these species reaching new areas. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 179 , 110–125.     

Latitudinal patterns of mammalian species richness in the New World: the effects of sampling method and faunal group

Abstract. Although the latitudinal gradient of species richness for mammals in North America is well documented, few investigators have quantified the relationship in South America. We examined the pattern in North and South America, at two spatial scales (2.5° and 5°) for each of two sampling methods (quadrats and latitudinal bands). A scale effect was evident for quadrats but not for bands. Significant linear relationships between species richness and latitude were found for three faunal groups: all mammals, nonvolant species, and bats. Effects of area confound the latitudinal relationship. By statistically removing such effects, we found that the latitudinal gradient is not an artifact of the species-area relationship, and that the latitudinal gradients for North and South America were statistically indistinguishable. Our data suggest that both faunal subgroups, nonvolant species and bats, contributed substantially to the overall mammalian pattern. Further, multiple regression analyses showed that only latitude is a necessary variable to explain bat richness; for nonvolant species, in addition to latitude, area and longitude may be important.     

GIS analysis of the biogeography of beetles of the subgenus Anisodactylus (Insecta: Coleoptera: Carabidae: genus Anisodactylus)

The advent of GIS technology and the World Wide Web, respectively, facilitate analysing geographical relationships and electronically storing and exchanging biogeographic data. This paper illustrates GIS technology with a study of the subgenus Anisodactylus Dejean (Insecta: Coleoptera: Carabidae: genus Anisodactylus). Species are concentrated in three centres of biodiversity in North America and in four in lands near the western Mediterranean. These centres largely correspond to current areas of wetlands. Eurasia has fewer species than expected based on its area, probably because large portions have habitats unfavourable for the subgenus and/or are poorly collected for Carabidae. Members of the subgenus are primarily adapted to areas with January temperatures between ?10 and 10 °C, July temperatures from 10 to 30 °C and mean annual precipitation from 20 to 200 mm. Cold is apparently a major limiting factor because it typically occurs during several consecutive months of winter and is difficult to escape except by hibernation. Heat is less of a stress when moisture is sufficient. The size of geographical ranges is often larger in the North than in the South and correlates with the latitude of the centre of ranges at r =0.42 (level of significance=0.05). Geographic ranges are often smaller in western North America and in the western Mediterranean than elsewhere in the Northern Hemisphere. Explanations for the smaller sizes include portions of western North America having unfavourable desert or montane habitats, the Rocky Mountains and deserts barring eastward dispersal of species, and the smaller size and more patchy distribution of climatic zones and habitats. In North America geographical ranges west of the Rocky Mountains are north–south elongated because they track primarily north–south orientated climatic zones and because mountains and deserts bar eastward extension. Ranges in north-eastern and north-central North America tend to extend east–west along temperature isotherms. In Eurasia many ranges are stretched east–west because of the shape of the continent and because many northern and southern areas lack suitable habitats. Species with relatively high numbers of apomorphic character states cluster in western Eurasia and to a lesser extent in western North America. The North American centres of biodiversity are post-Wisconsin phenomena while those near the western Mediterranean probably date from the Oligocene or Miocene.     

Convergence and contingency in production–precipitation relationships in North American and South African C4 grasslands

Mesic grasslands in North America and South Africa share many structural attributes, but less is known of their functional similarities. We assessed the control of a key ecosystem process, aboveground net primary production (ANPP), by interannual variation in precipitation amount and pattern via analysis of data sets (15- and 24-year periods) from long-term research programs on each continent. Both sites were dominated by C₄ grasses and had similar growing season climates; thus, we expected convergence in precipitation–ANPP relationships. Lack of convergence, however, would support an alternative hypothesis—that differences in evolutionary history and purportedly greater climatic variability in South Africa fundamentally alter the functioning of southern versus northern hemisphere grasslands. Neither mean annual precipitation nor mean ANPP differed between the South African and North American sites (838 vs. 857 mm/year, 423.5 vs. 461.4 g/m² respectively) and growing season precipitation–ANPP relationships were similar. Despite overall convergence, there were differences between sites in how the seasonal timing of precipitation affected ANPP. In particular, interannual variability in precipitation that fell during the first half of the growing season strongly affected annual ANPP in South Africa (P < 0.01), but was not related to ANPP in North America (P = 0.098). Both sites were affected similarly by late season precipitation. Divergence in the seasonal course of available soil moisture (chronically low in the winter and early spring in the South African site vs. high in the North American site) is proposed as a key contingent factor explaining differential sensitivity in ANPP to early season precipitation in these two grasslands. These long-term data sets provided no support for greater rainfall, temperature or ANPP variability in the South African versus the North American site. However, greater sensitivity of ANPP to early season precipitation in the South African grassland suggests that future patterns of productivity may be more responsive to seasonal changes in climate compared with the North American site.     

Present and potential distribution of invasive garlic mustard (Alliaria petiolata) in North America

Abstract. This paper demonstrates the use of a bioclimatic model mapped over geographical regions as a tool for spatially refined risk assessment for the establishment of non-indigenous plants with invasive behaviour. Drawing on the relationship between plant distribution and climate, the approach uses gridded spatial interpolated monthly means of temperature and precipitation linked with accurate maps of general native distribution ranges to predict the long-term potential of a plant species to invade a certain region. The ascertained potential for establishment is illustrated by the example of garlic mustard ( Alliaria petiolata [M. Bieb.] Cavara & Grande) in North America. The first step is to calculate and visualize the number of populated grid cells along climatic gradients in frequency diagrams for the general native distribution range. Interpretations of the response curves recorded are used for assessing apparent climatic range boundaries. Modelling was gradually optimized based on the results of experience-based interpretations and by examining omission and over-representation errors. The obtained climatic model of the range of A. petiolata shows considerable congruencies with its mapped, native Eurasian range. Degrees of climatic similarity between North America and the native range of A. petiolata were calculated with the help of GIS methodology and were used to assess the regionally different likelihood of establishment in North America of the invasive species under consideration.     

Neutral and functionally important genes shed light on phylogeography and the history of high‐altitude colonization in a widespread New World duck

Phylogeographic studies often infer historical demographic processes underlying species distributions based on patterns of neutral genetic variation, but spatial variation in functionally important genes can provide additional insights about biogeographic history allowing for inferences about the potential role of adaptation in geographic range evolution. Integrating data from neutral markers and genes involved in oxygen (O₂)‐transport physiology, we test historical hypotheses about colonization and gene flow across low‐ and high‐altitude regions in the Ruddy Duck (Oxyura jamaicensis), a widely distributed species in the New World. Using multilocus analyses that for the first time include populations from the Colombian Andes, we also examined the hypothesis that Ruddy Duck populations from northern South America are of hybrid origin. We found that neutral and functional genes appear to have moved into the Colombian Andes from both North America and southern South America, and that high‐altitude Colombian populations do not exhibit evidence of adaptation to hypoxia in hemoglobin genes. Therefore, the biogeographic history of Ruddy Ducks is likely more complex than previously inferred. Our new data raise questions about the hypothesis that adaptation via natural selection to high‐altitude conditions through amino acid replacements in the hemoglobin protein allowed Ruddy Ducks to disperse south along the high Andes into southern South America. The existence of shared genetic variation with populations from both North America and southern South America as well as private alleles suggests that the Colombian population of Ruddy Ducks may be of old hybrid origin. This study illustrates the breadth of inferences one can make by combining data from nuclear and functionally important loci in phylogeography, and underscores the importance of complete range‐wide sampling to study species history in complex landscapes.     

Species distribution modelling as a macroecological tool: a case study using New World amphibians

Although species distribution modelling (SDM) is widely accepted among the scientific community and is increasingly used in ecology, conservation biology and biogeography, methodological limitations generate potential problems for its application in macroecology. Using amphibian species richness in North and South America, we compare species richness patterns derived from SDM maps and ‘expert’ maps to evaluate if: 1) richness patterns derived from SDM are biased toward climate‐based explanations for diversity when compared to expert maps, since SDM methods are typically based on climatic variables; and 2) SDM is a reliable tool for generating richness maps in hyperrich regions where point occurrence data are limited for many species. We found that although three widely used SDM methods overestimated amphibian species richness in grid cells when compared to expert richness maps in both North and South America due to systematic overestimation of range sizes, diversity gradients were reasonably robust at broad scales. Further, climatic variables statistically explained patterns of richness at similar levels among the different richness sources, although climatic relationships were stronger in the much better known North America than in South America. We conclude that in the face of the high deforestation rates coupled with incomplete data on species distributions, especially in the tropics, SDM represents a useful macroecological tool for investigating broad‐scale richness patterns and the dynamics between species richness and climate.     

Allotetraploids in Patagonia with Affinities to Western North American Diploids: Did Dispersal or Genome Doubling Occur First?

Amphitropical disjunct distributions between western North America and western South America have intrigued botanists for over a century. Here, specific examples of migration and speciation are investigated using herbaceous species from the phlox family (Polemoniaceae) as a model for considering the timing of dispersal relative to speciation. Comparative DNA sequencing reveals that, in Collomia and Navarretia, the South American species are allopolyploids, suggesting either two dispersals prior to the allopolyploidization event for each species with subsequent extirpation of the diploid progenitors from South America, or allopolyploid formation prior to dispersal with extirpation of these polyploids from North America. Divergence time estimates support a Pliestocene dispersal hypothesis and sequence data indicate that, at least in Collomia, hybridization of the diploid progenitors occurred in South America.     

The biogeography and filtering of woody plant functional diversity in North and South America

Aim In recent years evidence has accumulated that plant species are differentially sorted from regional assemblages into local assemblages along local‐scale environmental gradients on the basis of their function and abiotic filtering. The favourability hypothesis in biogeography proposes that in climatically difficult regions abiotic filtering should produce a regional assemblage that is less functionally diverse than that expected given the species richness and the global pool of traits. Thus it seems likely that differential filtering of plant traits along local‐scale gradients may scale up to explain the distribution, diversity and filtering of plant traits in regional‐scale assemblages across continents. The present work aims to address this prediction. Location North and South America. Methods We combine a dataset comprising over 5.5 million georeferenced plant occurrence records with several large plant functional trait databases in order to: (1) quantify how several critical traits associated with plant performance and ecology vary across environmental gradients; and (2) provide the first test of whether the woody plants found within 1° and 5° map grid cells are more or less functionally diverse than expected, given their species richness, across broad gradients. Results The results show that, for many of the traits studied, the overall distribution of functional traits in tropical regions often exceeds the expectations of random sampling given the species richness. Conversely, temperate regions often had narrower functional trait distributions than their smaller species pools would suggest. Main conclusion The results show that the overall distribution of function does increase towards the equator, but the functional diversity within regional‐scale tropical assemblages is higher than that expected given their species richness. These results are consistent with the hypothesis that abiotic filtering constrains the overall distribution of function in temperate assemblages, but tropical assemblages are not as tightly constrained.     

The biogeography of Hoffmannseggia (Leguminosae, Caesalpinioideae, Caesalpinieae): a tale of many travels

Aim The flowering plant genus Hoffmannseggia consists of 21 species distributed amphitropically between the arid regions of the south‐western United States and adjacent Mexico, and west‐central South America. This pattern of geographical disjunction is shared by numerous other angiosperm genera and has been the subject of discussions for more than a century with various authors advocating a northern origin for particular taxa and others advocating a southern origin. This study uses a well‐supported phylogeny of a genus with numerous species in each area to address the issues of a northern or southern origin and the facility with which organisms move between the two continents. Location South‐western United States and northern Mexico, northern Chile and Argentina, southern Bolivia, and western Peru. Methods Using DNA sequence data from the nuclear and chloroplast genomes, we generated a phylogenetic hypothesis for all species of Hoffmannseggia rooted with Zuccagnia and Balsamocarpon. Geographical data were optimized on the resultant tree to assess the probable continent of origin for the genus, the pattern of disjunctions between North and South America, and species radiations within the genus. Main conclusions Hoffmannseggia arose in South America and initially split into a suffrutescent (somewhat woody) and an herbaceous clade. Within each of these major clades, there have been at least two exchanges between North and South America. There are no data to support an ancestral pan‐American range for Hoffmannseggia and we therefore ascribe the amphitropical disjunctions to long‐distance dispersal. The phylogeny clearly shows that all dispersals were from South to North America and they occurred at different times and thus the pattern is not the result of a single simultaneous set of dispersals.     

Biogeography and macroecology of phorid flies that attack fire ants in south-eastern Brazil and Argentina

Aim Saevissima group fire ants, Solenopsis richteri and S. invicta, have become serious pests when introduced from Argentina and Brazil to other continents. In South America, Solenopsis are distributed across a great variety of habitats and climates. In North America, S. invicta, introduced free of phorids, now ranges from coast to coast in the south. Success in introducing particular Pseudacteon as agents for the biological control of fire ants has varied across climatic zones. We aimed at assembling all the information about fire ant phorids from Argentina and Brazil, to estimate their richness and geographical ranges, to perform a climatic analysis for these distributions, to define groups and climate‐based communities, and to test and elucidate Rapoport's biogeographical rule. Location Argentina and Brazil (South America). Methods From field and museum collections and historical records, we developed a database of fire ant‐specific phorids throughout their known geographical range. A total of 123 sites with values for 15 climatic variables were mapped between 10° and 38° SL and between 35° and 65° C WL for the presence/absence of phorids. We calculated species richness across all sites combined, and for each phytogeographical region, using rarefaction curves, and ICE and Mmean estimators. We calculated mid‐latitudinal points, geographical ranges and areas for each species. The correlation between mid‐latitudinal point and ranges/areas was tested against a null model generated from the randomization of the raw distributional data. We used several types of multivariate analyses to distinguish groups of phorids by phytogeographical regions, hosts and climate, to find gradients of climate throughout the studied area, to define phorid communities in terms of their relationships with gradients of climate, and to test a mechanism for Rapoport's rule. Results Richness estimations using ICE and Mmean estimators were similar or higher than the observed values depending on the phytogeographical region. Cluster multivariate analyses based on climatic, phytogeographic and host data revealed distinct groupings of Pseudacton. The ‘cerrado’ group was confined to tropical savanna areas. A more ‘widespread’ group included ‘Chaco’ and ‘Maritime’ subgroups defined by their respective association with extreme temperatures or precipitation. Ordination multivariate analyses showed (1) two climatic gradients throughout the study area: one of temperature and the other of precipitation, and (2) that climatic variables significantly explained the observed assemblages of phorids. Positive and negative signs of the eigenvalues from the main axes of a canonical correspondence analysis allowed us to define eight communities whose geographical distribution resembled that of phytogeographical regions. We found a significant and positive correlation between geographical areas and mid latitudinal points, and furthermore, the Mantel test based on climatic variables suggested a mechanism for Rapoport's rule applying in the case of Pseudacteon. Main conclusions Pseudacteon species with greater mid‐latitudinal points occupy broader geographical areas and confront more stressful environmental conditions. Because the composition of Pseudacteon communities is largely determined by climatic variables, the correspondence between climates at sites of origin vs. sites of release should be an important consideration in choosing specific phorids for biocontrol efforts.     

Patterns of species turnover in plant‐pollinator communities along a precipitation gradient in Patagonia (Argentina)

Recent studies have assessed the influence of different types of gradients (e.g. altitudinal, latitudinal and temporal, among others) on the structure and function of community‐level plant‐pollinator webs. Although the importance of humidity as a major driver of species‐richness gradients worldwide has been stressed by recent reviews, no studies have been specifically designed to address the influence of precipitation gradients on pollination webs. In the present paper we describe for the first time the turnover of species of plants and their associated flower visitors between eight communities located along a steep precipitation gradient in north‐west Patagonia, Argentina. Our results show that: (i) there is a high spatial turnover of plant communities and their associated pollinators; (ii) this turnover is strongly related to precipitation changes across the region; and (iii) the turnover rate is similar for plants and pollinators. Our results support the view that the precipitation gradient is a significant factor associated with the regional turnover of plants and their pollinators in the temperate forests of southern South America.     

Phylogenetic structure of angiosperm trees in local forest communities along latitudinal and elevational gradients in eastern North America

Latitudinal and elevational gradients both represent thermal gradients. Assessing the consistency of the relationships between phylogenetic structure and climate between latitudinal and elevational gradients can provide insight into the mechanisms driving assembly of species from regional pools into local assemblages. The aim of this study is to compare patterns of phylogenetic structure measures for angiosperm tree species between latitudinal and elevational gradients, using a dataset of angiosperm tree species in 14 092 forest plots in eastern North America. We assessed whether these two gradients produce similar relationships between climate and phylogenetic structure, hypothesizing that they should differ in magnitude but not direction. We used correlation and regression analyses to assess the relation of measures of phylogenetic structure to elevation, latitude and climatic variables, which included minimum temperature, temperature seasonality, annual precipitation and precipitation seasonality. We found that 1) phylogenetic relatedness of angiosperm trees increases with decreasing temperature along both latitudinal and elevational gradients but the relationship between phylogenetic relatedness and temperature is steeper for elevational gradients than for latitudinal gradients; 2) the tip-weighted metric of phylogenetic relatedness (nearest taxon index) is more strongly correlated with climatic variables than the basal-weighted metric of phylogenetic relatedness (net relatedness index); 3) winter cold temperature exerts a stronger effect on community assembly of angiosperm trees than does temperature seasonality. These results suggest that winter cold temperature, rather than temperature seasonality, drives phylogenetic structure of plants in local forest communities, and that species distributions along elevational gradients are more in equilibrium with temperature, compared with those along latitudinal gradients.     

Species diversity and endemism in the Daphnia of Argentina: a genetic investigation

Although the temperate regions of South America are known to have a diverse daphniid fauna, there has been no genetic evaluation of the existing taxonomic system or of the affinities between the North and South American faunas. The present study analyses mitochondrial DNA sequences and allozyme variation to investigate species diversity in 176 Daphnia populations from Argentina. This work established the presence of at least 15 species in Argentina, six of which are either undescribed or are currently misidentified and two of which represent range extensions of North American taxa. Eleven of the Argentine species appear endemic to South America, while the remaining four also occur in North America. In the latter cases, the close genetic similarity between populations from North and South America indicates the recent exchange of propagules between the continents. While biological interactions and habitat availability have undoubtedly contributed to the observed species distributions, chance dispersal has apparently played a dominant role in structuring large-scale biogeographical patterns in this genus and probably in other passively-dispersed organisms.  © 2004 The Linnean Society of London, Zoological Journal of the Linnean Society , 2004, 140 , 171−205.