A latitudinal gradient of beta diversity for exotic vascular plant species in North America

Determining relationships between the ranges of introduced species and geographical and environmental factors is an important step in understanding the mechanisms and processes of the spread of introduced species. In this study, I examined the beta diversity and latitude relationship for all naturalized exotic species of vascular plants in North America at a continental scale. Beta diversity was calculated as the absolute value of the slope of the relationship between the natural logarithm of the Simpson index of similarity (lnS) and spatial distance between pairs of state‐level exotic floras within four latitudinal zones examined. Relative contributions of spatial distance and environmental difference to species turnover between exotic floras were examined. I found that beta diversity decreased monotonically from low to high latitudes: beta diversity for the southernmost zone was shallower than that for the northernmost zone by a factor of 2.6. Regression models of lnS in relation to spatial distance and environmental (climatic and topographical) difference for each latitudinal zone demonstrated that the explanatory power of these variables diminishes monotonically with latitude: the explained variance in lnS is 70.4%, 62.1%, 53.9%, and 33.9%, respectively, for the four latitudinal zones from south to north. For the southernmost zone, 58.3% of the variance in lnS is explained by climate variables and topography, and spatial distance explains only 2.3% of the variance. In contrast, for the northernmost zone, more than half the amount (22.5%) of the explained variance in lnS is attributable to spatial distance, and the remaining (18.9%) of the explained variance is attributable to climate variables and topography.     

Weak latitudinal gradients in insect herbivory for dominant rangeland grasses of North America

Patterns of insect herbivory may follow predictable geographical gradients, with greater herbivory at low latitudes. However, biogeographic studies of insect herbivory often do not account for multiple abiotic factors (e.g., precipitation and soil nutrients) that could underlie gradients. We tested for latitudinal clines in insect herbivory as well as climatic, edaphic, and trait‐based drivers of herbivory. We quantified herbivory on five dominant grass species over 23 sites across the Great Plains, USA. We examined the importance of climate, edaphic factors, and traits as correlates of herbivory. Herbivory increased at low latitudes when all grass species were analyzed together and for two grass species individually, while two other grasses trended in this direction. Higher precipitation was related to more herbivory for two species but less herbivory for a different species, while higher specific root length was related to more herbivory for one species and less herbivory for a different species. Taken together, results highlight that climate and trait‐based correlates of herbivory can be highly contextual and species‐specific. Patterns of insect herbivory on dominant grasses support the hypothesis that herbivory increases toward lower latitudes, though weakly, and indicates that climate change may have species‐specific effects on plant–herbivore interactions.     

The latitudinal gradient of species diversity among North American grasshoppers (Acrididae) within a single habitat: a test of the spatial heterogeneity hypothesis

Abstract. The spatial heterogeneity hypothesis predicts a positive relationship between habitat complexity and species diversity: the greater the heterogeneity of a habitat, the greater the number of species in that habitat. On a regional scale, this hypothesis has been proposed to explain the increases in species diversity from the poles to the tropics: the tropics are more diverse because they contain more habitats. On the local scale, the spatial heterogeneity hypothesis suggests that the tropics are more diverse because they contain more microhabitats. The positive relationship between habitat heterogeneity and species diversity, on the local scale, is well documented. In this paper, we test whether habitat heterogeneity on the local scale can explain the latitudinal gradient of species diversity on the regional scale. We determined the latitudinal gradient of species diversity of 305 species of North American grasshoppers using published distribution maps. We compared the slope of this multihabitat (regional-scale) gradient with the slope of a within-habitat (local-scale) gradient in the prairie grasslands. Our results show no significant difference between the slopes at the two scales. We tested the generality of our results by comparing multi- and within-habitat latitudinal gradients of species diversity for ants, scorpions and mammals using data from the literature. These results are in accordance with those from grasshoppers. We can therefore reject the local-scale spatial heterogeneity hypothesis as a mechanism explaining the regional-scale latitudinal gradient of species diversity. We discuss alternative mechanisms that produce this gradient.     

海南霸王岭热带雨林常见植物丛枝菌根真菌调查

对海南霸王岭热带雨林的12科16种常见植物的丛枝菌根状况进行了调查,用碱解离-酸性品红染色法进行了真菌鉴定。结果表明,13种植物形成典型的丛枝菌根,占所调查植物的81%;3种植物没有形成丛枝菌根,占所调查植物的19%。用湿筛沉淀法从这些植物根际土壤中共分离鉴定出了3属11种丛枝菌根真菌(AMF),即无梗囊霉属(Acaulos-pora)3种,球囊霉属(Glomus)7种,巨孢囊霉属(Gigaspora)1种;其中,球囊霉属是样地的优势属。在AMF中,孔窝无梗囊霉(A.foveata)分离频率最高,在14种植物的根际土中都有发现;此外,大果球囊霉(G.macrocarpum)的相对多度最大,为59%,具有最强的产孢能力。同时,在11种植物的根中发现了深色有隔内生真菌(DSE),占调查植物的69%;其中,11种植物同时被DSE和AMF感染。     

Biogeography of parasite abundance: latitudinal gradient and distance decay of similarity in the abundance of fleas and mites,parasitic on small mammals in the Palearctic,at three spatial scales

We tested whether biogeographic patterns characteristic for biological communities can also apply to populations and investigated geographic patterns of variation in abundance of ectoparasites (fleas and mites) collected from bodies of their small mammalian hosts (rodents and shrews) in the Palearctic at continental, regional and local scales. We asked whether (i) there is a relationship between latitude and abundance and (ii) similarity in abundance follows a distance decay pattern or it is better explained by variation in extrinsic biotic and abiotic factors. We analysed the effect of latitude on mean intraspecific abundance using general linear models including proportional abundance of its principal host as an additional predictor variable. Then, we examined the relative effect of geographic distance, biotic and abiotic dissimilarities among regions, subregions or localities on the intraspecific dissimilarity in abundance among regions, subregions or localities using Generalized Dissimilarity Modelling. We found no relationship between latitude and intraspecific flea or mite abundance. In both taxa, environmental dissimilarity explained the largest part of the deviance of spatial variation in abundance, whereas the effect of the dissimilarity in the principal host abundance was of secondary importance and the effect of geographic distance was minor. These patterns were generally consistent across the three spatial scales, although environmental variation and dissimilarity in principal host abundance were equally important at the local scale in fleas but not in mites. We conclude that biogeographic patterns related to latitude and geographic distance do not apply to spatial variation of ectoparasite abundance. Instead, the geographic distribution of abundance in arthropod ectoparasites depends on their responses, mainly to the off-host environment and to a lesser extent the abundance of their principal hosts.     

Arbuscular mycorrhiza and fungal root endophytes of weeds in an altitudinal gradient in the Pamir Alai Mountains of Central Asia

Arbuscular mycorrhiza and fungal root endophytes of three weeds, Galium tricornutum, Lycopsis orientalis and Scandix pecten-veneris, were studied in an altitudinal gradient of the Pamir Alai Mountains. Colonisation by arbuscular mycorrhizal fungi (AMF) was found in all species. Only in the case of G. tricornutum was there a rise in mycorrhizal parameters values found for the medium altitude range. Similar tendencies were observed in the case of the AMF colonisation potential assessment. This suggests that plant species' identity, dependency on symbiosis and interactions with soil properties determine root colonisation and the abundance of AMF in soils at the elevations in question. Four AMF species, Claroideoglomus claroideum, Funneliformis mosseae, Scutellospora dipurpurescens and Septoglomus constrictum, were isolated from trap cultures established on soil taken from under the weeds. Dark septate endophytes (DSE) accompanied the AMF in the roots of G. tricornutum and S. pecten-veneris; however, they were neither frequently occurring nor abundant. The sporangia of Olpidium spp. were observed with low frequency occurrence in G. tricornutum and S. pecten-veneris and more often in the roots of L. orientalis. However, in both cases, they were low in abundance. No differences were found for the presence of DSE and Olpidium in the altitudinal gradient.     

Angiosperm symbioses with non‐mycorrhizal fungal partners enhance N acquisition from ancient organic matter in a warming maritime Antarctic

In contrast to the situation in plants inhabiting most of the world’s ecosystems, mycorrhizal fungi are usually absent from roots of the only two native vascular plant species of maritime Antarctica, Deschampsia antarctica and Colobanthus quitensis. Instead, a range of ascomycete fungi, termed dark septate endophytes (DSEs), frequently colonise the roots of these plant species. We demonstrate that colonisation of Antarctic vascular plants by DSEs facilitates not only the acquisition of organic nitrogen as early protein breakdown products, but also as non‐proteinaceous d ‐amino acids and their short peptides, accumulated in slowly‐decomposing organic matter, such as moss peat. Our findings suggest that, in a warming maritime Antarctic, this symbiosis has a key role in accelerating the replacement of formerly dominant moss communities by vascular plants, and in increasing the rate at which ancient carbon stores laid down as moss peat over centuries or millennia are returned to the atmosphere as CO₂.     

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.     

松萎蔫病发生区和未发生区油松根部真菌群落研究

植物根部真菌群落结构和多样性与植物的抗病性和病害的危害程度相互影响。为揭示松萎蔫病与松树根部真菌群落的相互作用,该研究对陕西省商洛市柞水县松萎蔫病发生区和未发生区油松的根尖活性、根部外生菌根真菌(ECMF)和深色有隔内生真菌(DSE)的侵染率进行分析,并通过油松根部可培养真菌的分离和鉴定,分析了两地油松根部真菌的群落结构及多样性。结果显示:(1)松萎蔫病未发生区油松根部的活性根尖比、菌根根尖比和ECMF的侵染率均显著高于发生区,而DSE的侵染率和微菌核密度却低于松萎蔫病发生区,ECMF的侵染率在两个样区油松根部都显著高于DSE。(2)从两个样区油松根部共分离到131个菌株,根据形态和分子学特征最终鉴定为23种真菌,其中DSE占绝对优势,且Phialocephala fortinii和Cryptosporiopsis ericae为油松根部分离真菌的优势种。(3)两个样区真菌的群落组成存在明显差异,共有真菌仅5种。(4)松萎蔫病未发生区真菌群落的丰富度(17)和多样性(2.012 0)、以及ECMF的相对丰度(8%)都高于松萎蔫病发生区(分别为11、1.197 9和1.6%),而DSE的相对丰度(70%)却明显低于发生区(82.7%)。研究表明,松萎蔫病的发生影响了油松根部的活性、菌根的形成、ECMF和DSE的侵染,以及根部真菌的群落组成和多样性。该文首次报道了DSE与松萎蔫病的关系,但分离真菌对油松松萎蔫病抗性的影响有待进一步研究。     

西北旱区甘草深色有隔内生真菌物种多样性及空间分布

为探明西北旱区甘草Glycyrrhiza uralensis根系深色有隔内生真菌（dark septate endophytes,DSE）生态分布和定殖状况,于2018年7月分别从甘肃安西、民勤和宁夏沙坡头地区采集甘草不同灌丛范围0-10cm和20-30cm土壤和根系样品,系统研究不同样地甘草灌丛内外DSE生态分布及其与土壤因子的相关性。结果表明,不同样地甘草均能被DSE高度侵染,形成典型深色有隔菌丝和微菌核结构。不同样地DSE定殖率差异显著,安西DSE总定殖率（43.34%）显著低于民勤（90%）和沙坡头（88.34%）样地。相关性分析表明,DSE定殖率主要与土壤速效磷、有机碳和碱性磷酸酶显著相关。共分离鉴定11属13种DSE,即Acrocalymma vagum、Alternaria longissima、Alternaria chlamydospora、Alternaria chlamydosporigena、Paraphoma chrysanthemicola、Darksidea alpha、Niesslia aemula、Tricharina ochroleuca、Acremonium nepalense、Fusarium solani、Preussia sp.、Leptosphaeria oraemaris和Ulocladium sp.。其中Acrocalymma vagum是甘草根系DSE优势菌种,为民勤和沙坡头共有种,而安西样地DSE物种多样性最高,共7种。主成分分析表明,安西DSE物种组成在0-10cm和20-30cm不同灌丛范围存在显著差异;单因素方差分析显示,安西和沙坡头DSE菌丝定殖率在距主干0-10cm显著高于20-30cm,说明荒漠环境灌丛覆盖对DSE真菌群落存在显著影响。方差分解结果表明,DSE定殖受样地空间分布、灌丛覆盖和土壤因子共同影响（74.91%）,而DSE种类组成更多依赖于样地异质性（84.46%）和土壤养分（87.82%）的作用。研究不同荒漠环境DSE定殖和群落组成差异,有助于充分理解DSE在旱区植物生长和植被恢复中的功能和意义。     

西北荒漠带细枝岩黄耆AM真菌与DSE真菌时空分布研究

为探明细枝岩黄耆Hedysarum scoparium根系丛枝菌根真菌（arbuscular mycorrhizae,AM）和深色有隔内生真菌（dark septate endophytes,DSE）定殖特征及其生态地理分布,充分理解菌根共生体在植物生长和植被恢复中的功能,本研究连续3年采集我国西北荒漠带不同样地细枝岩黄耆0-30cm土层土壤样品和根样,不同样地细枝岩黄耆均能被AM和DSE侵染,形成AM典型结构菌丝、泡囊和丛枝,DSE典型结构深色有隔菌丝和微菌核。细枝岩黄耆根系AM真菌定殖高于DSE定殖,但极端干旱条件下DSE定殖优于AM真菌定殖。AM真菌定殖率不同年际间表现为2016年最高,同一年份不同样地,除乌海、沙坡头样地,菌丝定殖率自东向西呈降低趋势。DSE真菌定殖率,在同一样地不同年份：乌海样地2016年定殖率显著高于2015年和2017年,在同一年份不同样地：2015年沙坡头样地DSE菌丝定殖率、总定殖率显著高于其他样地,而2016、2017年鄂尔多斯样地最高。NMDS分析结果显示,AM和DSE真菌定殖不同年际间差异显著。相关性分析表明,AM真菌定殖率与DSE定殖率显著正相关;土壤温度与AM定殖显著负相关;有机碳、速效磷、磷酸酶、湿度与AM定殖显著正相关;DSE菌丝定殖率、定殖强度仅与酸性磷酸酶正相关。本研究比较分析西北荒漠带不同样地AM和DSE定殖与土壤因子的相关性,有助于充分理解菌根共生体在植物生长和植被恢复中的功能和意义。     

The latitudinal gradient of beta diversity in relation to climate and topography for mammals in North America

Aim Spatial turnover of species, or beta diversity, varies in relation to geographical distance and environmental conditions, as well as spatial scale. We evaluated the explanatory power of distance, climate and topography on beta diversity of mammalian faunas of North America in relation to latitude. Location North America north of Mexico. Methods The study area was divided into 313 equal‐area quadrats (241 × 241 km). Faunal data for all continental mammals were compiled for these quadrats, which were divided among five latitudinal zones. These zones were comparable in terms of latitudinal and longitudinal span, climatic gradients and elevational gradients. We used the natural logarithm of the Jaccard index (lnJ) to measure species turnover between pairs of quadrats within each latitudinal zone. The slope of lnJ in relation to distance was compared among latitudinal zones. We used partial regression to partition the variance in lnJ into the components uniquely explained by distance and by environmental differences, as well as jointly by distance and environmental differences. Results Mammalian faunas of North America differ more from each other at lower latitudes than at higher latitudes. Regression models of lnJ in relation to distance, climatic difference and topographic difference for each zone demonstrated that these variables have high explanatory power that diminishes with latitude. Beta diversity is higher for zones with higher mean annual temperature, lower seasonality of temperature and greater topographic complexity. For each latitudinal zone, distance and environmental differences explain a greater proportion of the variance in lnJ than distance, climate or topography does separately. Main conclusions The latitudinal gradient in beta diversity of North American mammals corresponds to a macroclimatic gradient of decreasing mean annual temperature and increasing seasonality of temperature from south to north. Most of the variance in spatial turnover is explained by distance and environmental differences jointly rather than distance, climate or topography separately. The high predictive power of geographical distance, climatic conditions and topography on spatial turnover could result from the direct effects of physical limiting factors or from ecological and evolutionary processes that are also influenced by the geographical template.     

Effect of weather on the reproductive rate of Rock Ptarmigan Lagopus muta in the eastern Pyrenees

Understanding the effects of climate on avian life history traits is essential if we wish to predict the demographic consequences of expected climatic changes. We investigated the influence of weather conditions on the reproductive success of Rock Ptarmigan Lagopus muta in the eastern French Pyrenees, one of the southernmost areas inhabited by the species. Reproductive success was estimated in early August between 1997 and 2006 by counting adults and well-grown chicks with pointing dogs. The number of young per adult varied from 0.08 to 0.72. Using Poisson regression and Akaike's information criterion, we selected the best model explaining the effect of weather (date of snowmelt and, for both laying/incubation and post-hatching periods, mean minimum and maximum temperatures, monthly rainfall and number of days with rain) on the proportion of young in August. Reproductive success was positively associated with early appearance of snow-free ground, and date of snowmelt alone was the model that best explained annual variation in reproductive success. Other models, which included a negative effect of rainfall, particularly after hatching, also had some support. Hence, both pre-laying and post-hatching weather conditions influenced reproductive success of Rock Ptarmigan in the eastern French Pyrenees. On a continental scale, reproductive success of alpine populations of Rock Ptarmigan is consistently lower than that of northern populations. This difference in productivity may be partly correlated with climatic conditions observed along an arctic–alpine gradient, the amount and variation of rainfall being greater in southern alpine areas than elsewhere in the species' range.     

Biogeography and microhabitat variation in temperate algal-invertebrate symbioses: zooxanthellae and zoochlorellae in two Pacific intertidal sea anemones, Anthopleura elegantissima and A. xanthogrammica

Abstract. Temperate sea anemones in the genus Anthopleura are unique among cnidarians in harboring two phylogenetically distinct symbiotic algae, zooxanthellae (golden-brown dinophytes, Symbiodinium ) and zoochlorellae (green chlorophytes). To determine whether their physiological differences generate patterns in anemone habitat and biogeographic distribution, we sampled symbiotic algae in the small clonal A. elegantissima and the large solitary A. xanthogrammica at 8 field sites (and the other large solitary Anthopleura species at one site) spanning 18° of latitude along 2500 km of the Pacific coast of North America. We found that zoochlorellae predominate in low intertidal habitats and northerly latitudes and in A. xanthogrammica , while zooxanthellae constitute the majority of symbionts in high intertidal habitats and more southerly latitudes and in A. elegantissima. These data are consistent with published predictions based on photosynthetic efficiency of the two algae under varied temperature and light regimes in the laboratory. This anemone-algal system provides a potential biological signal of benthic intertidal communities' responses to El Niño events and long-term climate changes in the Pacific.     

Into and out of the tropics: global diversification patterns in a hyperdiverse clade of ectomycorrhizal fungi

Ectomycorrhizal (ECM) fungi, symbiotic mutualists of many dominant tree and shrub species, exhibit a biogeographic pattern counter to the established latitudinal diversity gradient of most macroflora and fauna. However, an evolutionary basis for this pattern has not been explicitly tested in a diverse lineage. In this study, we reconstructed a mega‐phylogeny of a cosmopolitan and hyperdiverse genus of ECM fungi, Russula, sampling from annotated collections and utilizing publically available sequences deposited in GenBank. Metadata from molecular operational taxonomic unit cluster sets were examined to infer the distribution and plant association of the genus. This allowed us to test for differences in patterns of diversification between tropical and extratropical taxa, as well as how their associations with different plant lineages may be a driver of diversification. Results show that Russula is most species‐rich at temperate latitudes and ancestral state reconstruction shows that the genus initially diversified in temperate areas. Migration into and out of the tropics characterizes the early evolution of the genus, and these transitions have been frequent since this time. We propose the ‘generalized diversification rate’ hypothesis to explain the reversed latitudinal diversity gradient pattern in Russula as we detect a higher net diversification rate in extratropical lineages. Patterns of diversification with plant associates support host switching and host expansion as driving diversification, with a higher diversification rate in lineages associated with Pinaceae and frequent transitions to association with angiosperms.     

Climatic drivers of hemispheric asymmetry in global patterns of ant species richness

Although many taxa show a latitudinal gradient in richness, the relationship between latitude and species richness is often asymmetrical between the northern and southern hemispheres. Here we examine the latitudinal pattern of species richness across 1003 local ant assemblages. We find latitudinal asymmetry, with southern hemisphere sites being more diverse than northern hemisphere sites. Most of this asymmetry could be explained statistically by differences in contemporary climate. Local ant species richness was positively associated with temperature, but negatively (although weakly) associated with temperature range and precipitation. After contemporary climate was accounted for, a modest difference in diversity between hemispheres persisted, suggesting that factors other than contemporary climate contributed to the hemispherical asymmetry. The most parsimonious explanation for this remaining asymmetry is that greater climate change since the Eocene in the northern than in the southern hemisphere has led to more extinctions in the northern hemisphere with consequent effects on local ant species richness.