Geographical variation and environmental correlates of functional trait distributions in palms (Arecaceae) across the New World

Functional traits play a key role in driving biodiversity effects on ecosystem functioning. Here, we examine the geographical distributions of three key functional traits in New World palms (Arecaceae), an ecologically important plant group, and their relationships with current climate, soil and glacial–interglacial climate change. We combined range maps for the New World (N = 541 palm species) with data on traits (leaf size, stem height and fruit size), representing the leaf–height–seed plant strategy scheme of Westoby, to estimate median trait values for palm species assemblages in 110 × 110‐km grid cells. Spatial and non‐spatial multi‐predictor regressions were used with the Akaike Information Criterion to identify minimum adequate models. Present‐day seasonality in temperature and precipitation played a major role in explaining geographical variation of all traits. Mean annual temperature and annual precipitation were additionally important for median leaf size. Glacial–interglacial temperature change was the most important predictor for median fruit size. Large‐scale soil gradients played only a minor role overall. These results suggest that current climate (larger median trait values with increasing seasonality) and glacial–interglacial temperature change (larger median fruit size with increasing Quaternary temperature anomaly) are important drivers for functional trait distributions of New World palms. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 179 , 602–617.     

High tropical net diversification drives the New World latitudinal gradient in palm (Arecaceae) species richness

Aim Species richness exhibits striking geographical variation, but the processes that drive this variation are unresolved. We investigated the relative importance of two hypothesized evolutionary causes for the variation in palm species richness across the New World: time for diversification and evolutionary (net diversification) rate. Palms have a long history in the region, with the major clades diversifying during the Tertiary (65–2 Ma). Location Tropical and subtropical America (34° N–34° S; 33–120° W). Methods Using range maps, palm species richness was estimated in a 1° × 1° grid. Mean lineage net diversification was estimated by the mean phylogenetic root distance (MRD), the average number of nodes separating a species from the base of the palm phylogeny for the species in each grid cell. If evolutionary rate limits richness, then richness should increase with MRD. If time limits richness, then old, relict species (with low root distance) should predominantly occur in long‐inhabited and therefore species‐rich areas. Hence, richness should decrease with MRD. To determine the influence of net diversification across different time frames, MRD was computed for subtribe, genus and species levels within the phylogeny, and supplemented with the purely tip‐level measure, mean number of species per genus (MS/G). Correlations and regressions, in combination with eigenvector‐based spatial filtering, were used to assess the relationship between species richness, the net diversification measures, and potential environmental and geographical drivers. Results Species richness increased with all net diversification measures. The regression models showed that richness and the net diversification measures increased with decreasing (absolute) latitude and, less strongly, with increasing energy/temperature and water availability. These patterns therefore reflect net diversification at both deep and shallow levels in the phylogeny. Richness also increased with range in elevation, but this was only reflected in the MS/G pattern and therefore reflects recent diversification. Main conclusions The geographical patterns in palm species richness appear to be predominantly the result of elevated net diversification rates towards the equator and in warm, wet climates, sustained throughout most of the Tertiary. Late‐Tertiary orogeny has caused localized increases in net diversification rates that have also made a mark on the richness pattern.     

A macroecological perspective of diversity patterns in the freshwater realm

1. The aim of this paper is to review literature on species diversity patterns of freshwater organisms and underlying mechanisms at large spatial scales. 2. Some freshwater taxa (e.g. dragonflies, fish and frogs) follow the classical latitudinal decline in regional species richness (RSR), supporting the patterns found for major terrestrial and marine organism groups. However, the mechanisms causing this cline in most freshwater taxa are inadequately understood, although research on fish suggests that energy and history are major factors underlying the patterns in total species and endemic species richness. Recent research also suggests that not all freshwater taxa comply with the decline of species richness with latitude (e.g. stoneflies, caddisflies and salamanders), but many taxa show more complex geographical patterns in across‐regions analyses. These complexities are even more profound when studies of global, continental and regional extents are compared. For example, clear latitudinal gradients may be present in regional studies but absent in global studies (e.g. macrophytes). 3. Latitudinal gradients are often especially weak in the across‐ecosystems analyses, which may be attributed to local factors overriding the effects of large‐scale factors on local communities. Nevertheless, local species richness (LSR) is typically linearly related to RSR (suggesting regional effects on local diversity), although saturating relationships have also been found in some occasions (suggesting strong local effects on diversity). Nestedness has often been found to be significant in freshwater studies, yet this pattern is highly variable and generally weak, suggesting also a strong beta diversity component in freshwater systems. 4. Both geographical location and local environmental factors contribute to variation in alpha diversity, nestedness and beta diversity in the freshwater realm, although the relative importance of these two groups of explanatory variables may be contingent on the spatial extent of the study. The mechanisms associated with spatial and environmental control of community structure have also been inferred in a number of studies, and most support has been found for species sorting (possibly because many freshwater studies have species sorting as their starting point), although also dispersal limitation and mass effects may be contributing to the patterns found. 5. The lack of latitudinal gradients in some freshwater taxa begs for further explanations. Such explanations may not be gained for most freshwater taxa in the near future, however, because we lack species‐level information, floristic and faunistic knowledge, and standardised surveys along extensive latitudinal gradients. A challenge for macroecology is thus to use the best possible species‐level information on well‐understood groups (e.g. fish) or use surrogates for species‐level patterns (e.g. families) and then develop hypotheses for further testing in the freshwater realm. An additional research challenge concerns understanding patterns and mechanisms associated with the relationships between alpha, beta and gamma components of species diversity. 6. Understanding the mechanistic basis of species diversity patterns should preferably be based on a combination of large‐scale macroecological and landscape‐scale metacommunity research. Such a research approach will help in elucidating patterns of species diversity across regional and local scales in the freshwater realm.     

Phylogenetic utility of the nuclear gene malate synthase in the palm family (Arecaceae)

There is currently a shortage of DNA regions known to be useful for phylogenetic research in palms (Arecaceae). We report the development and use of primers for amplifying and sequencing regions of the nuclear gene malate synthase. In palms the gene appears to be single-copy, with exon regions that are phylogenetically informative within the family. We constructed a phylogeny of 45 palms and five outgroup taxa using 428 bp of malate synthase exon regions. We found that some major clades within the family were recovered, but there was a lack of resolution among the genera in subfamilies Arecoideae, Ceroxyloideae, Coryphoideae, and Phytelephantoideae. In a second analysis, malate synthase exon regions totaling 1002 bp were sequenced for 16 palms and two outgroup taxa. There was increased bootstrap support for some groups and for the placement of the monotypic genus Nypa as sister to the rest of the family. A comparison with data sets from noncoding regions of the chloroplast genome indicates that malate synthase sequences are more variable and potentially contain more phylogenetic information. We found no evidence of multiple copies of the malate synthase gene in palm genomes.     

Ice age legacies in the geographical distribution of tree species richness in Europe

Aim This study uses a high‐resolution simulation of the Last Glacial Maximum (LGM) climate to assess: (1) whether LGM climate still affects the geographical species richness patterns in the European tree flora and (2) the relative importance of modern and LGM climate as controls of tree species richness in Europe. Location The parts of Europe that were unglaciated during the LGM. Methods Atlas data on the distributions of 55 tree species were linked with data on modern and LGM climate and climatic heterogeneity in a geographical information system with a 60‐km grid. Four measures of species richness were computed: total richness, and richness of the 18 most restricted species, 19 species of medium incidence (intermediate species) and 18 most widespread species. We used ordinary least‐squares regression and spatial autoregressive modelling to test and estimate the richness–climate relationships. Results LGM climate constituted the best single set of explanatory variables for richness of restricted species, while modern climate and climatic heterogeneity was best for total and widespread species richness and richness of intermediate species, respectively. The autoregressive model with all climatic predictors was supported for all richness measures using an information‐theoretic approach, albeit only weakly so for total species richness. Among the strongest relationships were increases in total and intermediate richness with climatic heterogeneity and in restricted richness with LGM growing‐degree‐days. Partial regression showed that climatic heterogeneity accounted for the largest unique variation fraction for intermediate richness, while LGM climate was particularly important for restricted richness. Main conclusions LGM climate appears to still affect geographical patterns of tree species richness in Europe, albeit the relative importance of modern and LGM climate depends on range size. Notably, LGM climate is a strong richness control for species with a restricted range, which appear to still be associated with their glacial refugia.     

Investigation of genetic and morphological variation in the sago palm (Metroxylon sagu; Arecaceae) in Papua New Guinea

BACKGROUND AND AIMS: The genetic and morphological variation in the sago palm (Metroxylon sagu, Arecaceae) in Papua New Guinea (PNG) was investigated. METHODS: Amplified fragment length polymorphism (AFLP) was used to investigate the genetic structure of 76 accessions of M. sagu, collected in seven wild and semi-wild stands in PNG. KEY RESULTS: An analysis of ten quantitative morphological variables revealed that most of these were mutually correlated. Principal component analyses of the same morphological variables showed that neither armature (presence or absence of spines) nor geographical separation was reflected clearly in the quantitative morphological variation. Similarity matrices of genetic, quantitative morphological, geographical and armature data were tested for pair-wise correlations, using Mantel's test. The results only showed a significant correlation between genetic and geographical distances. Visual inspection of principal component analyses plots and a neighbour-joining dendrogram based on genetic distances supported this trend, whereas armature showed no relation with genetic distances. CONCLUSIONS: Geographical distribution defines some weak patterns in the genetic variation, whereas the genetic variation does not reflect any patterns in the morphological variation, including armature. The present study supports the accepted taxonomy of M. sagu, recognizing only one species of M. sagu in PNG.     

Landscape genetics, historical isolation and cross-Andean gene flow in the wax palm, Ceroxylon echinulatum (Arecaceae)

Knowledge of the role of landscapes in shaping genetic connectivity and divergence is essential for understanding patterns of biogeography and diversity. This is particularly relevant for the Andes region, a major biodiversity hotspot of relatively recent origin. We examined the phylogeography and landscape genetics of the Andean wax palm Ceroxylon echinulatum (Arecaceae) that occurs in two narrow bands of montane forests on each side of the Andes in Ecuador and northeastern Peru. First, we tested the hypothesis of C. echinulatum being a geographic cline species crossing the Andes in the Amotape–Huancabamba zone (AHZ) of southern Ecuador/northern Peru, as indicated by observations on fruit morphology. Second, we assessed the timeframe of cross-Andean divergence, and third, we investigated the impact of contemporary and historical landscape features on observed spatio-genetic patterns. Individual-based Bayesian clustering (BC) identified a northeastern, southeastern, southwestern, and northwestern cluster, with areas of genetic discontinuity coinciding with the Andes and the Giron–Paute deflection. F -statistics derived from BC suggested an east-to-west dispersal history. Population-based analyses revealed strong genetic structuring at both small and large geographic scales. Interpopulation relationships and Mantel tests strongly supported the cline model with cross-Andean dispersal in the AHZ. Along the cline, gene flow measured as F _ST was mainly limited by distance, with less but significant impact of climatic friction. Coalescent analysis revealed that cross-Andean divergence took place during the Quaternary. Significant historical isolation ( R _ST >  F _ST) was found in the southwestern population. The current study illustrates a joint effect of founder dynamics, divergence by distance and historical isolation on patterns of Andean diversity and distribution.     

Elevational patterns of functional diversity and trait of Delphinium (Ranunculaceae) in Hengduan Mountains,China

Elevational patterns of trait occurrence and functional diversity provide an important perspective for understanding biodiversity. However, previous studies have mostly examined functional diversity at the community scale. Here, we examined large-scale patterns of trait occurrence and functional diversity in Delphinium along an elevational gradient from 1000 to 5700 m in the Hengduan Mountains, SW China. Elevational distribution and trait data of 102 Delphinium species were compiled to evaluate the patterns of interspecific traits, species richness, and functional diversity. We found that the distribution of species richness showed a unimodal curve that peaked between 3500 and 4000 m; functional diversity and traits showed different patterns along an elevational gradient. The functional diversity increased at a lower rate along an elevation gradient, whereas species richness continued to increase. Species with large ranges and non-endemic species were most affected by geometric constraints. Richness of species endemic to the Hengduan Mountains peaked at higher elevations, likely due to increased speciation and restricted dispersion under alpine conditions. We conclude that the middle elevation region is not only the functionally richest but also the most functionally stable region for Delphinium, which could be insurance against environmental change. Extreme conditions and strong environmental filters in an alpine environment may cause the convergence of species traits, which could relate to reducing nutrient trait investment and increasing reproductive trait investment. We conclude that large-scale studies are consistent with previous studies at the community scale. This may indicate that the relationship between functional diversity and species richness across different scales is the same.     

中国典型森林生态系统乔木层群落物种多样性的空间分布格局及其影响因素

物种多样性地理分布格局及其成因是生物地理学和宏观生态学研究的核心问题之一,基于中国13个典型森林生态系统乔木层群落植物的调查数据,分析物种多样性随经纬度的变化规律,探讨物种多样性空间分布格局的影响因素。结果表明:(1) 13个典型森林生态系统的4个物种多样性指数均随经纬度上升而下降,其中物种丰富度变化更为显著,而Shannon-Wiener指数、Simpson指数和Pielou指数随经度上升变化不显著;(2)相关性分析结果显示,物种多样性指数与植物特性、能量和水分因子的单因素相关关系并不一致。其中,物种丰富度、Shannon-Wiener指数和Simpson指数与年均温、最冷月均温、温度年较差和潜在蒸散量的相关性最显著(P0.01),Pielou指数与年均温、最冷月均温、实际蒸散量、潜在蒸散量和郁闭度有显著相关关系(P0.05);(3)方差分解结果表明,能量和水分的共同作用对物种多样性指数空间分布格局的解释率最高,达到15%—42%;植物特性、能量和水分因子三者共同作用对物种多样性指数空间分布格局解释率次之,为14%—27%;植物特性与能量因子或水分因子两者之间的共同作用以及植物特性和水分因子独立作用对物种多样性指数空间分布格局的解释率较小,其中能量因子对物种多样性指数空间分布格局的单独解释率高于植物特性或水分因子。研究表明能量和水分共同作用是影响大尺度森林乔木层物种多样性空间分布格局形成的主要因素,但植物特性的差异对物种多样性空间分布格局影响也不可忽视。     

The patterns of genetic diversity in Carpentaria acuminata (Arecaceae), and rainforest history in northern Australia

Carpentaria acuminata occurs in monsoon rainforest and is endemic to the Northern Territory, Australia. The genetic diversity of C. acuminata populations was surveyed across the geographical range of the species using isozyme analysis. Genetic diversity within C. acuminata populations ( H _E = 0.143) was typical of rainforest species and woody angiosperms generally. Genetic diversity was not correlated with rainforest patch size. However, there was significant heterogeneity among populations ( F _ST = 0.379), with infrequent effective gene flow among populations ( Nm = 0.39). Genetic diversity was negatively correlated with increasing distance between neighbouring C. acuminata populations, but geographical distance was not a good predictor of genetic similarity. C. acuminata is a favoured food of mobile frugivores such as Torres Strait pigeons and flying foxes. The decreased diversity with decreasing density of populations indicated that seed dispersal by frugivores has been important for the maintenance of diversity in this species. Populations known to have originated on relatively young, Holocene landforms were not necessarily genetically depauperate. Gene flow by pollen is apparently limited because C. acuminata populations are significantly inbred regardless of genetic diversity ( F = 0.641). The distribution and diversity of rare alleles, i.e. those occurring in few populations, is consistent with the theory of rainforest contraction during the Pleistocene.     

Spatial patterns of disparity and diversity of the Recent cuttlefishes (Cephalopoda) across the Old World

Aim Diversity and disparity metrics of all Recent cuttlefishes are studied at the macroevolutionary scale (1) to establish the geographical biodiversity patterns of these cephalopods at the species level and (2) to explore the relationships between these two metrics. Location Sampling uses what is known about these tropical, subtropical and warm temperate cephalopods of the Old World based on a literature review and on measurements of museum specimens. Some 111 species spread across seventeen biogeographical areas serve as basic units for exploring diversity and disparity metrics in space. Methods Landmarks describe the shape of the cuttlebone (the inner shell of the sepiids) and differences between shapes are quantified using relative warp analyses. Relative warps are thus used as the morphological axis for constructing morphospaces whose characteristics are described by disparity indices: total variance, range, and minimum and maximum of relative warps. These are analysed and then compared with the diversity (species richness) metric. Results Results show no significant latitudinal or longitudinal gradients either for diversity or for disparity. Around the coast of southern Africa, disparity is high regardless of whether diversity (species richness) is high or low. In the ‘East Indies’ area disparity is low despite the high diversity. Main conclusions The relationship between diversity and disparity is clearly not linear and no simple adjustment models seem to fit. The number of species in a given area does not predict its disparity level. The particular pattern of southern Africa may be the result of paleogeographical changes since the Eocene, whereas that of the ‘East Indies’ may indicate that this area could act as a centre of origin. However, the lack of any clear phylogenetical hypothesis precludes the study from providing any explanation of the observed patterns.     

Soil and canopy Pseudoscorpiones (Arthropoda,Arachnida) in a monodominant forest of Attalea phalerata Mart. (Arecaceae) in the Brazilian Pantanal

We studied the occurrence of Pseudoscorpiones in the soil, leaf litter, and in canopies of a monodominant forest of Attalea phalerata at different seasons in the northern region of the Brazilian Pantanal. A total of 1197 pseudoscorpions from nine families and 16 species were sampled. Olpiidae, Chernetidae, and Geogarypidae predominated in soil and leaf litter. Chernetidae was the most abundant family in canopies. Soil and canopy corresponded to distinct habitats in relation to pseudoscorpion abundance and richness, with the canopies being the most diversified environment. These habitats are occupied in different ways by pseudoscorpion populations. Geogarypus sp. occurs in the edaphic environment during receding water and dry season, but can be found in canopies of A. phalerata exclusively during high water. This alternation in the use of the edaphic environments and canopies in the same area by pseudoscorpion species probably happens due to the strong seasonality of the Brazilian Pantanal.     

Genetic diversity and population differentiation of the Chinese soft-shelled turtle (Pelodiscus sinensis) in three geographical populations

The Chinese soft-shelled turtle (Pelodiscus sinensis) is one of the most important economical chelonians in the world. To understand the genetic variations of the Chinese soft-shelled turtle in China, 62 individuals were sampled from three localities and 18 polymorphic microsatellite loci tested were used to detect genetic diversity and population structure. Results showed that the genetic diversity of the wild P. sinensis was high. Except for the Wuhu populations, the majority of microsatellite loci are not deviation from Hardy–Weinberg equilibrium in the other two populations. AMOVA analysis indicated that genetic variations occurred mainly within populations (97.4%) rather than among populations (2.6%). The gene flow estimates (Nm) among three geographic populations demonstrated that strong gene flow existed (Nm > 1, mean 6). The present study supported that different habitats, breed turtles escaped, multiple paternity and long evolutionary history may be responsible for the current genetic diversity and differentiation in the wild Chinese soft-shelled turtle.     

Population genetics of the hispid cotton rat (Sigmodon hispidus): patterns of genetic diversity at the major histocompatibility complex

The hispid cotton rat, Sigmodon hispidus, is a common rodent widely distributed across the southern USA and south into South America. To characterize major histocompatibility complex (MHC) diversity in this species and to elucidate large-scale patterns of genetic partitioning, we examined MHC genetic variability within and among 13 localities, including a disjunct population in Arizona and a population from Costa Rica that may represent an undescribed species. We also tested the hypothesis that populations within the USA are at equilibrium with regard to gene flow and genetic drift, resulting in isolation-by-distance. Using single-strand conformation polymorphism (SSCP) analysis we identified 25 alleles from 246 individuals. Gene diversity within populations ranged from 0.000 to 0.908. Analysis of molecular variance (AMOVA) revealed that 83.7% of observed variation was accounted for by within-population diversity and 16.3% was accounted for by among-population divergence. The disjunct population in Arizona was fixed for a single allele. The Costa Rican population was quite divergent based on allelic composition and was the only population with unique alleles. Within the main portion of the geographical distribution of S. hispidus in the USA there was considerable divergence among some populations; however, there was no significant pattern of isolation-by-distance overall (P = 0.090). Based on the significant divergence of the only sampled population to its east, the Mississippi River appears to represent a substantial barrier to gene flow.     

Latitudinal gradients of associations between beta and gamma diversity of trees in forest communities in the New World

Aims We analyze two continental data sets of forest communities from across the New World to examine the latitudinal gradients of beta diversity after accounting for gamma diversity and the latitudinal gradient of gamma diversity after accounting for beta diversity.Methods Correlation and regression analyses were used to relate beta and gamma diversity to latitude along two latitudinal gradients in the New World (one including 72 forest sites located south of the equator and the other including 79 forest sites located north of the equator).Important findings Beta diversity and gamma diversity were negatively correlated with latitude. Beta diversity was strongly and positively correlated with gamma diversity (Pearson's correlation coefficient: 0.783 for New World North and 0.848 for New World South). When beta diversity was regressed on latitude and gamma diversity, 69.8 and 85.7% of the variation in beta diversity were explained, respectively, for New World North and New World South. When gamma diversity was regressed on latitude and beta diversity, 81.8 and 84.3% of the variation in gamma diversity were explained, respectively, for New World North and New World South. After statistically removing the relationship between beta and gamma diversity, latitude has weak or no relationships with beta and gamma diversity. However, strong positive correlations between beta and gamma diversity may not be considered as evidence of one driving the other along a latitudinal gradient.