Search

Exotic annual grass invasion is a widespread threat to the integrity of sagebrush ecosystems in Western North America. Although many predictors of annual grass prevalence and native perennial vegetation have been identified, there remains substantial uncertainty about how regional‐scale and local‐scale predictors interact to determine vegetation heterogeneity, and how associations between vegetation and cattle grazing vary with environmental context. Here, we conducted a regionally extensive, one‐season field survey across burned and unburned, grazed, public lands in Oregon and Idaho, with plots stratified by aspect and distance to water within pastures to capture variation in environmental context and grazing intensity. We analyzed regional‐scale and local‐scale patterns of annual grass, perennial grass, and shrub cover, and examined to what extent plot‐level variation was contingent on pasture‐level predictions of site favorability. Annual grasses were widespread at burned and unburned sites alike, contrary to assumptions of annual grasses depending on fire, and more common at lower elevations and higher temperatures regionally, as well as on warmer slopes locally. Pasture‐level grazing pressure interacted with temperature such that annual grass cover was associated positively with grazing pressure at higher temperatures but associated negatively with grazing pressure at lower temperatures. This suggests that pasture‐level temperature and grazing relationships with annual grass abundance are complex and context dependent, although the causality of this relationship deserves further examination. At the plot‐level within pastures, annual grass cover did not vary with grazing metrics, but perennial cover did; perennial grasses, for example, had lower cover closer to water sources, but higher cover at higher dung counts within a pasture, suggesting contrasting interpretations of these two grazing proxies. Importantly for predictions of ecosystem response to temperature change, we found that pasture‐level and plot‐level favorability interacted: perennial grasses had a higher plot‐level cover on cooler slopes, and this difference across topography was starkest in pastures that were less favorable for perennial grasses regionally. Understanding the mechanisms behind cross‐scale interactions and contingent responses of vegetation to grazing in these increasingly invaded ecosystems will be critical to land management in a changing world. [ABSTRACT FROM AUTHOR]

The present study investigates the ecology and distribution of ostracod species and assemblages from 62 inland waterbodies in the Eastern Cape province of South Africa and tests the influence of two major climatic zones (Arid steppe climate BS and Warm temperate humid climate Cf) and two primary catchments (Kowie and Great Fish Rivers), as well as broad gradients of altitude and several local environmental factors. Distance-based linear models were used to test these species-environment relationships and indicated that eight variables (water temperature, pH, conductivity, waterbody size, habitat type, altitude, hydrological-drainage, climate) individually showed significant correlations with the response ostracod dataset of 35 species. However, owing to substantial collinearity, the most parsimonious model identified only two predicting variables (climatic zone and water pH) which best explained variation in ostracod assemblage composition. The assemblages of the two climatic zones differed significantly, with Plesiocypridopsis newtoni and Sarscypridopsis ochracea being most commonly found in the BS climates, while Sarscypridopsis trigonella and Physocypria capensis occurred most frequently in the Cf climates. Finally, tolerance ranges to water pH and electrical conductivity for 21 ostracod species are provided to facilitate application of ostracods in further biodiversity and water-quality assessments, as well as in palaeo-environmental reconstructions. [ABSTRACT FROM AUTHOR]

Introduction: Microorganisms play a critical role in soil biogeochemical cycles, but it is still debated whether they influence soil biogeochemical processes through community composition and diversity or not. This study aims to investigate variation in bacterial community structure across different soils and its correlation to soil multifunctionality. Soil samples were collected from five typical farmland zones along distinct climatic gradients in China. Methods: The high-throughput sequencing (Illumina MiSeq) of 16S rRNA genes was employed to analyze bacterial community composition in each soil sample. Multivariate analysis was used to determine the difference in soil properties, microbial community and functioning, and their interactions. Results: Cluster and discrimination analysis indicated that bacterial community composition was similar in five tested soil samples, but bacterial richness combined with soil enzyme activities and potential nitrification rate (PNR) contributed most to the differentiations of soil samples. Mantel test analysis revealed that bacterial community composition and richness were more significantly shaped by soil nutrient conditions and edaphic variables than bacterial diversity. As for soil multifunctionality, soil microbial community level physiological profiles were little affected by abiotic and biotic factors, while soil enzymes and PNR were also significantly related to bacterial community composition and richness, in addition to soil N and P availability. Conclusion: Cumulatively, soil enzymes’ activities and PNR were greatly dependent on bacterial community composition and richness not diversity, which in turn were greatly modified by soil N and P availability. Therefore, in the future it should be considered for the role of fertilization in the modification of bacterial community and the consequent control of nutrient cycling in soil. [ABSTRACT FROM AUTHOR]

Species under milder climates (e.g., warm and wet) tend to experience lower variability in temperature and rainfall regimes and might occur in narrower climatic ranges than species that tolerate harsher conditions (e.g., cold or dry climates). Thus, tree species that occur under harsh conditions should have a broader climatic range, being a small subset of the flora. Here, we assess the influence of climate on species distribution of 1138 tree species from the Atlantic Forest biodiversity hotspot. We investigate their range (or niche breadth), and the "center of gravity" index (or niche optima), along with gradients of mean annual temperature and climatic water deficit (CWD). We further identified those species associated with conditions on different ends of temperature and moisture gradients. We found a small subset of species occurring under colder temperatures or under drier conditions, and these species had a wider niche breadth. The warm or wet‐affiliated species had narrower ranges along with the temperature and the CWD gradients, respectively. Moreover, species affiliated to warm and those to moister conditions had greater densities near their occurrence limits, thus they may be more susceptible to climate changes. We conclude that global climate changes will affect the incidence and abundance distribution patterns of tree species along this threatened biodiversity hotspot, mainly those with narrow niches and within the limit of its distribution. Abstract in Portuguese is available with online material [ABSTRACT FROM AUTHOR]

Prior studies on Hemiculter leucisculus, which is a widespread native fish in China, mainly focused on its growth, feeding habits, and individual fecundity, but few have investigated the brain. In this research, we explored the developmental patterns of the Hemiculter leucisculus brain and found the brain showed allometry through sample time points and three age groups. At the same time, we found that the brain varied along climatic gradients. The volumes of the olfactory bulbs, telencephalic lobes, optic tectum, corpus cerebelli, and total brain in the south were larger than those in the north, while the volume of the hypothalamus in the north was larger than in the south. This study provides a view for the in‐depth study of the acclimatized mechanism of the teleost brain, lays a foundation for the further study of evolutionary ecology, and provides a reference for the phenotypic plasticity of the teleost brain. [ABSTRACT FROM AUTHOR]

Abiotic factors are generally assumed to determine whether species can exist at the extreme ends of environmental gradients, for example, at high elevations, whereas the role of biotic interactions is less clear. On temperate mountains, insect‐pollinated plant species with bilaterally symmetrical flowers exhibit a parallel elevational decline in species richness and abundance with bees. This suggests that the lack of mutualistic interaction partners sets the elevational range limits of plants via a reduction in reproductive success. We used the bee‐pollinated mountain plant Clinopodium alpinum (Lamiaceae), which blooms along a continuous 1000‐m elevational gradient and has bilaterally symmetrical flowers, as a model to test the predicted parallel elevational decline in flower visitation and seed production. Although the community of flower visitors changed with elevation, the flower visitation rate by the most frequent visitors, bumble bees (33.8% of legitimate visits), and the overall rate of flower visitation by potential pollinators did not vary significantly with elevation. However, we discovered that nectar robbing by bumble bees and nectar theft by ants, two interactions with potentially negative effects on flowers, sharply increased with elevation. Seed set depended on pollinators across elevations and followed a weak hump‐shaped pattern, peaking at mid‐elevations and decreasing by about 20% toward both elevational range edges. Considering the mid‐ and high elevations, elevational variation in seed production could not be explained by legitimate bee visitation rates but was inversely correlated with the frequency of nectar robbing. Our observations challenge the hypothesis that a decrease in the availability of pollinators limits seed production of bee‐flowered plants at high elevations but suggest that an increase in negative interactions (nectar robbing and larceny) constrains reproductive success. [ABSTRACT FROM AUTHOR]

Abstract Abiotic factors are generally assumed to determine whether species can exist at the extreme ends of environmental gradients, for example, at high elevations, whereas the role of biotic interactions is less clear. On temperate mountains, insect‐pollinated plant species with bilaterally symmetrical flowers exhibit a parallel elevational decline in species richness and abundance with bees. This suggests that the lack of mutualistic interaction partners sets the elevational range limits of plants via a reduction in reproductive success. We used the bee‐pollinated mountain plant Clinopodium alpinum (Lamiaceae), which blooms along a continuous 1000‐m elevational gradient and has bilaterally symmetrical flowers, as a model to test the predicted parallel elevational decline in flower visitation and seed production. Although the community of flower visitors changed with elevation, the flower visitation rate by the most frequent visitors, bumble bees (33.8% of legitimate visits), and the overall rate of flower visitation by potential pollinators did not vary significantly with elevation. However, we discovered that nectar robbing by bumble bees and nectar theft by ants, two interactions with potentially negative effects on flowers, sharply increased with elevation. Seed set depended on pollinators across elevations and followed a weak hump‐shaped pattern, peaking at mid‐elevations and decreasing by about 20% toward both elevational range edges. Considering the mid‐ and high elevations, elevational variation in seed production could not be explained by legitimate bee visitation rates but was inversely correlated with the frequency of nectar robbing. Our observations challenge the hypothesis that a decrease in the availability of pollinators limits seed production of bee‐flowered plants at high elevations but suggest that an increase in negative interactions (nectar robbing and larceny) constrains reproductive success.

Understanding the invasion success of alien species includes developing knowledge on how the biological traits of their populations respond to spatial differences in environmental conditions. For invasive fishes, while the influence of latitudinal and climatic gradients on their biological traits over large spatial scales is well established, there is less certainty in how these vary over smaller scales. Here, we tested the influence of a climatic and geographic gradient on the reproductive traits and body sizes of the invasive mosquitofish Gambusia holbrooki across five climatic regions in Turkey. The results revealed that the environmental conditions across eight sites provided two gradients: a latitudinal gradient (where northern sites were cooler with less rainfall) and a coastal–inland gradient (where changes were apparent from coastal areas and into inland areas). These gradients had marked effects on the traits of both sexes. In sites in coastal and southern areas, males had significantly larger gonopodia and females had greater fecundity than in inland and warmer areas, and with both sexes having body sizes that were smaller. The spatial differences in the male traits were suggested as being driven by differences in selection pressures at the sites that related to differences in their population abundances. The results revealed that environmental conditions across a relatively small spatial scale had some strong influences on the expression of specific biological traits of these mosquitofish populations, but with further work needed to test how these influences affect their invasion success. [ABSTRACT FROM AUTHOR]

Aim: Plant–plant interactions are an important factor in structuring plant biodiversity. However, most studies on the impacts of plant–plant interactions on biodiversity focus on species richness and to a lesser extent on other facets of diversity. When other facets of biodiversity are considered, studies often include a limited set of environmental conditions. We aimed to quantify the impacts of nurse plants on taxonomic, functional and phylogenetic facets of plant biodiversity and how these impacts change across environmental gradients. Location: We report data on 28 alpine and 50 dryland sites, established in 11 countries. Time period: 1998–2019. Major taxa studied: Vascular plants. Methods: We analysed plant–plant interactions using co‐occurrence analyses and obtained information on the functional traits and phylogenetic relationships of the beneficiary species. We calculated the change in taxonomic, functional and phylogenetic diversity caused by the presence of nurse plants and environmental conditions. Results: Nurse plants enhanced taxonomic and phylogenetic diversity in alpine communities and enhanced functional and phylogenetic diversity in dryland communities. However, they had a positive effect on functional and taxonomic diversity only in moderate environments in alpine and dryland communities, respectively. The effects of nurse plants were larger in drylands for functional and phylogenetic diversity and in alpine communities for taxonomic diversity. Interestingly, nurse plants induced nonlinear changes in all facets of biodiversity across environmental gradients, whereas biodiversity tended to increase linearly toward more benign conditions in open interspaces. Main conclusions: Facilitation is important in alpine environments to maximize taxonomic diversity and has a more consistent positive effect on the functional and phylogenetic diversity of drylands. In general, effects of facilitation on biodiversity peak in moderate environmental conditions, which suggests that nurse plants can protect biodiversity from impacts of climate change mostly in those places currently under low environmental stress and that will be likely to experience moderate stress levels in the future. [ABSTRACT FROM AUTHOR]

Many studies have confirmed the impact of the environment on the brain. However, it is still controversial whether the cause of the change is phenotypically plastic or heritable. In this study, we studied morphological variations of the brain among Gambusia affinis obtained from 10 different populations in China. We found that the sizes of total brain and brain regions were affected by climatic gradients. For instance, there was a decrease in the volume of olfactory bulbs, optic tectum, corpus cerebelli, and total brain from north to south. Common‐garden experiments indicated that the variations in the sizes of the hypothalamus and the total brain were heritable, while that of other brain regions were phenotypically plastic. Variation in brain morphology of wild fish supports the mosaic hypothesis. The common‐garden experiments provide a reference for heritability estimates and phenotypic plasticity of brain volumes. In addition, our study has laid the foundation for in‐depth research on the adaptive evolution of the brain of G. affinis. [ABSTRACT FROM AUTHOR]

Aim: Worldwide distribution patterns of living animals are structured in multiple zoogeographical regions, characterized by faunas with homogeneous composition that are separated by sharp boundaries. These zoogeographical regions can differ depending on the considered animal group, probably because they have distinct characteristics such as dispersal, metabolism, or evolutionary history, and thus divergent responses to major biogeographical drivers, such as tectonic movements, abrupt climate transitions and orographic barriers. Here, we tested if the drivers of biogeographical boundaries are different between vertebrate classes with strongly divergent traits and evolutionary history. Location: Global. Time period: Present. Major taxa studied: Amphibians, birds and mammals. Methods: We focused on terrestrial biogeographical boundaries, considering multiple potential drivers: spatial heterogeneity of present‐day climate, altitudinal variation, long‐term tectonic movements and past climate change (temperature). We used spatially explicit regression models and geographically weighted regressions to select and quantify the factors explaining the position of the biogeographical boundaries between vertebrate classes. Results: For mammals, tectonic movements, abrupt climatic transitions and orographic barriers jointly determined extant biogeographical boundaries, with tectonic movements being the most important. For birds, abrupt climatic transitions played the strongest role, while the effect of orographic barriers was weak. For amphibians, biogeographical boundaries mostly corresponded to areas with abrupt climatic transitions. The strongest transitions of amphibian faunas occur in areas with abrupt shifts of temperature and precipitation regimes. Main conclusions: Our analyses confirmed that different drivers have jointly shaped the global vertebrate biogeographical regions, and highlight that taxa with different features show heterogeneous responses across the globe. Eco‐physiological constraints likely increase the importance of spatial heterogeneity of climate, while dispersal limitations magnify the relevance of physical barriers (mountain chains and long‐term tectonic instability). Integrating among‐taxa heterogeneity into analyses thus provides a more complete view of how different processes determine biodiversity variation across the globe. [ABSTRACT FROM AUTHOR]

Premise: Leaf shape and size figure strongly in plants' adaptation to their environments. Among trees, oaks are notoriously variable in leaf morphology. Our study examines the degree to which within‐tree, among‐tree, and among‐site variation contribute to latitudinal variation in leaf shape and size of bur oak (Quercus macrocarpa: Fagaceae), one of North America's most geographically widespread oak species. Methods: Samples were collected from four sites each at northern, central, and southern latitudes of the bur oak range. Ten leaf size traits were measured, and variance in these traits and eight ratios based on these traits was partitioned into tree and population components. Population means were regressed on latitude. We then parameterized a series of leaf collection simulations using empirical covariance among leaves on trees and trees at sites. We used the simulations to assess the efficiency of different collecting strategies for estimating among‐population differences in leaf shape and size. Results: Leaf size was highly responsive to latitude. Site contributed more than tree to total variation in leaf shape and size. Simulations suggest that power to detect among‐site variance in leaf shape and size increases with either more leaves per tree (10–11 leaves from each of 5 trees) or more trees per site (5 leaves from each of 10+ trees). Conclusions: Our study demonstrates the utility of simulating sampling and controlling for variance in sampling for leaf morphology, whether the questions being addressed are ecological, evolutionary, or taxonomic. Simulation code is provided as an R package (traitsPopSim) to help researchers plan morphological sampling strategies. [ABSTRACT FROM AUTHOR]

The Mediterranean climate of North Africa encompasses an interesting variety of sub-climates, from humid and sub-humid to semi-arid and arid. Such variability may provide vital insights into mechanisms that drive species distribution and offered us an ideal opportunity to test phenotypic variations along gradients. We aim in this study to investigate the breeding behaviour of house martin Delichon urbica (Linnaeus, 1758) populations along regional climatic gradients in north-eastern Algeria. During two consecutive breeding seasons (2016–2017), nine field sites (328 active nests) belonging to three different sub-climates: humid, sub-humid, and semi-arid were surveyed regularly from March to August. We used generalized linear models to test the relevance of local climate and several ecological variables on laying reproductive output. Laying dates were positively correlated with climate condition (GOF = 0.42), the semi-arid climate creating appropriate conditions for advancing the laying process, whereas sub-humid and humid climate delayed it. Clutch-size and number of chicks hatched per nest were affected by local climate conditions; they were greater in humid areas than in sub-humid and semi-arid ones. The other non-climatic variables as brood order, laying date, distance to fields, and distance to water were not significant. The spatial analysis around nest sites of house martins also showed that dense vegetation cover and reduced urbanization levels may be potential predictors of breeding behaviour. Nest sites located in humid areas with dense vegetation cover, and low urbanization levels that characterize the surrounding landscape provide high-breeding success rate to this species if compared to sub-humid and semi-arid areas. These findings can be a useful indicator of environmental change in a country that is already experiencing severe drought stresses, uncontrolled urbanization, and high deforestation rates. [ABSTRACT FROM AUTHOR]

Elevational gradients are useful ecological settings for revealing the biotic and abiotic drivers of plant trait variation and plant–insect interactions. However, most work focusing on plant defences has looked at individual traits and few studies have assessed multiple traits simultaneously, their correlated expression patterns, and abiotic factors associated with such patterns across elevations. To address this knowledge gap, we studied elevational variation in direct (phenolic compounds) and indirect (volatile organic compounds) constitutive defences and their inducibility after feeding by a specialist beetle Altica quercetorum in saplings of 18 wild populations of Quercus pyrenaica. We tested for: 1) clines in each defensive trait individually, 2) their patterns of correlated expression and 3) associations between any such clines and climatic factors. We found that constitutive direct defences (lignins and hydrolysable tannins) decreased with increasing elevation. We observed no elevational gradient for constitutive indirect defences (volatile organic compounds) or the inducibility of direct or indirect defensive traits when looking at groups of compounds. However, at individual tree‐level, increased induction of two monoterpenes (α‐fenchene and camphene) at higher elevation was shown. Furthermore, we show a significant pattern of co‐expression of constitutive and induced phenolics across populations, which weakened with increasing elevation. Finally, we found no evidence that climatic factors were associated with either individual or correlated trait expression patterns across elevations. Overall, these findings call for moving beyond elevational clines in individual plant defences, and argue that assessing elevational shifts in trait correlated expression patterns and their underlying mechanisms can increase our understanding of plant defence evolution and plant–herbivore interactions along environmental gradients. [ABSTRACT FROM AUTHOR]

Tropical montane forests (TMFs) play an important role as a carbon reservoir at a global scale. However, there is a lack of a comprehensive understanding on the variation in carbon storage across TMF compartments [namely aboveground biomass (AGB), belowground biomass (BGB), and soil organic matter] along altitudinal and environmental gradients and their potential trade-offs. This study aims to: 1) understand how carbon stocks vary along altitudinal gradients in Andean TMFs, and; 2) determine the influence of climate, particularly precipitation seasonality, on the distribution of carbon stocks across different forest compartments. The study was conducted in sixty 0.1 ha plots along two altitudinal gradients at the Podocarpus National Park (Ecuador) and Río Abiseo National Park (Peru). At each plot, we calculated the amount of carbon in AGB (i.e. aboveground carbon stock, AGC), BGB (i.e. belowground carbon stock, BGC), and soil organic matter (i.e. soil organic carbon stock, SOC). The mean total carbon stock was 244.76 ± 80.38 Mg ha–1 and 211.51 ± 46.95 Mg ha–1 in the Ecuadorian and Peruvian plots, respectively. Although AGC, BGC, and SOC showed different partitioning patterns along the altitudinal gradient both in Ecuador and Peru, total carbon stock did not change with altitude in either site. The combination of annual mean temperature and precipitation seasonality explained differences in the observed patterns of carbon stocks across forest compartments between the two sites. This study suggests that the greater precipitation seasonality of colder, higher altitudes may promote faster turnover rates of organic matter and nutrients and, consequently, less accumulation of SOC but greater AGC and BGC, compared to those sites with lesser precipitation seasonality. Our results demonstrate the capacity of TMFs to store substantial amounts of carbon and suggest the existence of a trade-off in carbon stocks among forest compartments, which could be partly driven by differences in precipitation seasonality, especially under the colder temperatures of high altitudes.

Tropical montane forests (TMFs) play an important role as a carbon reservoir at a global scale. However, there is a lack of a comprehensive understanding on the variation in carbon storage across TMF compartments [namely aboveground biomass (AGB), belowground biomass (BGB), and soil organic matter] along altitudinal and environmental gradients and their potential trade-offs. This study aims to: 1) understand how carbon stocks vary along altitudinal gradients in Andean TMFs, and; 2) determine the influence of climate, particularly precipitation seasonality, on the distribution of carbon stocks across different forest compartments. The study was conducted in sixty 0.1 ha plots along two altitudinal gradients at the Podocarpus National Park (Ecuador) and Río Abiseo National Park (Peru). At each plot, we calculated the amount of carbon in AGB (i.e. aboveground carbon stock, AGC), BGB (i.e. belowground carbon stock, BGC), and soil organic matter (i.e. soil organic carbon stock, SOC). The mean total carbon stock was 244.76 ± 80.38 Mg ha–1 and 211.51 ± 46.95 Mg ha–1 in the Ecuadorian and Peruvian plots, respectively. Although AGC, BGC, and SOC showed different partitioning patterns along the altitudinal gradient both in Ecuador and Peru, total carbon stock did not change with altitude in either site. The combination of annual mean temperature and precipitation seasonality explained differences in the observed patterns of carbon stocks across forest compartments between the two sites. This study suggests that the greater precipitation seasonality of colder, higher altitudes may promote faster turnover rates of organic matter and nutrients and, consequently, less accumulation of SOC but greater AGC and BGC, compared to those sites with lesser precipitation seasonality. Our results demonstrate the capacity of TMFs to store substantial amounts of carbon and suggest the existence of a trade-off in carbon stocks among forest compartments, which could be partly driven by differences in precipitation seasonality, especially under the colder temperatures of high altitudes. [ABSTRACT FROM AUTHOR]

Morphological variation is strongly related to variation in the ecological characteristics and evolutionary history of each taxon. To explore how geographical variation in morphology is related to different climatic gradients and phylogenetic structure, we analyzed the variation of morphological traits (body size, bill, and wing) of 64 species of tyrant flycatchers (Tyrannidae) distributed in Mexico. We measured these morphological traits in specimens from biological collections and related them to the climatic and topographic data of each collection locality. We performed the analyses separately at two levels: (1) the regional level and (2) the assemblage level, which was split into (assemblage I) lowland forests and (assemblage II) highland forests and other vegetation types. We also calculated the phylogenetic structure of flycatchers of each locality in order to explore the influence of climatic variables and the phylogenetic structure on the morphological variation of tyrant flycatchers, by means of linear mixed-effects models. We mapped the spatial variation of the relationship between morphological traits and environmental gradients, taking into account the phylogenetic structure. Important climatic variables explaining the morphological variation were those of temperature ranges (seasonality) and the results suggest that the phylogenetic clustering increases towards the highlands of Sierra Madre Oriental and Sierra Madre del Sur, and the lowlands of Balsas Depression. For the regional level, the spatial distribution of body size showed a pattern coincident with Bergmann’s rule, with increasing in size from south to north. In the tropical lowland forests assemblage, body size tend to increase in seasonally dry forests (western Mexico) and decrease in the humid ones (eastern Mexico). In the assemblage of highland forests and other types of vegetation, morphological trait values increased northeast to southwest. Phylogenetic structure helped to explain the variation of morphology at the assemblage level but not at the regional level. The patterns of trait variation in the lowland and highland assemblages suggest that parts of morphological variation are explained both by the climatic gradients and by the lineage relatedness of communities. Overall, our results suggest that morphological variation is best explained by a varied set of variables, and that regression models representing this variation, as well as integrating phylogenetic patterns at different community levels, provide a new understanding of the mechanisms underlying the links among biodiversity, its geographical setting, and environmental change.

Morphological variation is strongly related to variation in the ecological characteristics and evolutionary history of each taxon. To explore how geographical variation in morphology is related to different climatic gradients and phylogenetic structure, we analyzed the variation of morphological traits (body size, bill, and wing) of 64 species of tyrant flycatchers (Tyrannidae) distributed in Mexico. We measured these morphological traits in specimens from biological collections and related them to the climatic and topographic data of each collection locality. We performed the analyses separately at two levels: (1) the regional level and (2) the assemblage level, which was split into (assemblage I) lowland forests and (assemblage II) highland forests and other vegetation types. We also calculated the phylogenetic structure of flycatchers of each locality in order to explore the influence of climatic variables and the phylogenetic structure on the morphological variation of tyrant flycatchers, by means of linear mixed-effects models. We mapped the spatial variation of the relationship between morphological traits and environmental gradients, taking into account the phylogenetic structure. Important climatic variables explaining the morphological variation were those of temperature ranges (seasonality) and the results suggest that the phylogenetic clustering increases towards the highlands of Sierra Madre Oriental and Sierra Madre del Sur, and the lowlands of Balsas Depression. For the regional level, the spatial distribution of body size showed a pattern coincident with Bergmann’s rule, with increasing in size from south to north. In the tropical lowland forests assemblage, body size tend to increase in seasonally dry forests (western Mexico) and decrease in the humid ones (eastern Mexico). In the assemblage of highland forests and other types of vegetation, morphological trait values increased northeast to southwest. Phylogenetic structure helped to explain the variation of morphology at the assemblage level but not at the regional level. The patterns of trait variation in the lowland and highland assemblages suggest that parts of morphological variation are explained both by the climatic gradients and by the lineage relatedness of communities. Overall, our results suggest that morphological variation is best explained by a varied set of variables, and that regression models representing this variation, as well as integrating phylogenetic patterns at different community levels, provide a new understanding of the mechanisms underlying the links among biodiversity, its geographical setting, and environmental change. [ABSTRACT FROM AUTHOR]

• Plant diversity and productivity are involved in explaining δ15N plant , δ15N soil, and δ15N soil-to-plant in North Tibet. • Precipitation is critical for driving spatial variability of δ15N plant , δ15N soil and δ15N soil-to-plant in North Tibet. • The δ15N plant and δ15N soil-to-plant indicate growth limitation shifts from P in meadows to N in desert-steppes. Nitrogen (N) cycling is a critical pathway by which producer, consumer, and decomposer interact with each other and with environmental circumstances simultaneously. The natural abundance composition of 15N/14N in plants and soils (termed as δ15N plant and δ15N soil), as well as the difference between them (δ15N soil-to-plant = δ15N plant −δ15N soil), is a useful tool for better understanding ecosystem N cycling. However, the drivers and mechanisms of ecosystem N cycling in alpine grasslands on the Tibetan Plateau are mostly unknown, especially across different grassland types at a regional scale. To fill this knowledge gap, we measured δ15N plant (200 samples of top-dominant species) and δ15N soil (85 samples of top-layer soils, 0–20 cm) at nine sites that represent zonal communities of alpine deserts, steppes, and meadows in North Tibet, and calculated the corresponding δ15N soil-to-plant. Our results showed that δ15N plant, δ15N soil, and δ15N soil-to-plant were significantly different among the three zonal grassland types (analysis of differences with non-parametric Kruskal Test, P < 0.05), with the lowest values in meadows and the highest values in deserts. Regression analyses showed that the δ15N plant , δ15N soil, and δ15N soil-to-plant decreased with the increases of growing season precipitation (GSP) and habitat aridity index (Aridity), soil organic carbon (SOC) and soil total nitrogen (STN), plant species richness, Shannon diversity index, and plant community productivity, whereas increased with the increases of accumulated active temperature (AccT) and soil total phosphorus (STP) across alpine grassland types at the regional scale. Multiple linear models with analysis of covariance (ANCOVA) confirmed GSP to be the most critical driver, which alone explained most variances of δ15N plant (56%), δ15N soil (62%), and δ15N soil-to-plant (35%). However, structural equation modeling performed better than multiple linear modeling in predicting δ15N plant (76% vs. 66%) and worse in predicting δ15N soil (79% vs. 84%) and δ15N soil-to-plant (31% vs. 46%), likely due to the exclusion of collinear predictors and the removal of non-significant influencing paths. Overall, this study has highlighted the importance to uncover the complexity of climate, soil nutrients, and vegetation properties in networking to drive the different components of ecosystem N cycling in alpine grasslands on the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

Aim: We analysed elevational and microclimatic drivers of thermal tolerance diversity in a tropical mountain frog clade to test three macrophysiological predictions: less spatial variation in upper than lower thermal limits (Bretts' heat‐invariant hypothesis); narrower thermal tolerance ranges in habitats with less variation in temperature (Janzen's climatic variability hypothesis); and higher level of heat impacts at lower elevations. Location: Forest and open habitats through a 4,230‐m elevational gradient across the tropical Andes of Ecuador. Method: We examined variability in critical thermal limits (CTmax and CTmin) and thermal breadth (TB; CTmax–CTmin) in 21 species of Pristimantis frogs. Additionally, we monitored maximum and minimum temperatures at the local scale (tmax, tmin) and estimated vulnerability to acute thermal stress from heat (CTmax–tmax) and cold (tmin–CTmin), by partitioning thermal diversity into elevational and microclimatic variation. Results: Our results were consistent with Brett's hypothesis: elevation promotes more variation in CTmin and tmin than in CTmax and tmax. Frogs inhabiting thermally variable open habitats have higher CTmax and tmax and greater TBs than species restricted to forest habitats, which show less climatic overlap across the elevational gradient (Janzen's hypothesis). Vulnerability to heat stress was higher in open than forest habitats and did not vary with elevation. Main conclusions: We suggest a mechanistic explanation of thermal tolerance diversity in elevational gradients by including microclimatic thermal variation. We propose that the unfeasibility to buffer minimum temperatures locally may explain the rapid increase in cold tolerance (lower CTmin) with elevation. In contrast, the relative invariability in heat tolerance (CTmax) with elevation may revolve around the organisms' habitat selection of open‐ and canopy‐buffered habitats. Secondly, on the basis of microclimatic estimates, lowland and upland species may be equally vulnerable to temperature increase, which is contrary to the pattern inferred from regional interpolated climate estimators. [ABSTRACT FROM AUTHOR]

Anonychomyrma is a dolichoderine ant genus of cool-temperate Gondwanan origin with a current distribution that extends from the north of southern Australia into the Australasian tropics. Despite its abundance and ecological dominance, little is known of its species diversity and distribution throughout its range. Here, we describe the diversity and distribution of Anonychomyrma in the Australian Wet Tropics bioregion, where only two of the many putative species are described. We hypothesise that the genus in tropical Australia retains a preference for cool wet rainforests reminiscent of the Gondwanan forests that once dominated Australia, but now only exist in upland habitats of the Wet Tropics. Our study was based on extensive recent surveys across five subregions and along elevation and vertical (arboreal) gradients. We integrated genetic (CO1) data with morphology to recognise 22 species among our samples, 20 of which appeared to be undescribed. As predicted, diversity and endemism were concentrated in uplands above 900 m a.s.l. Distribution modelling of the nine commonest species identified maximum temperature of the warmest month, rainfall seasonality, and rainfall of the wettest month as correlates of distributional patterns across subregions. Our study supported the notion that Anonychomyrma radiated from a southern temperate origin into the tropical zone, with a preference for areas of montane rainforest that were stably cool and wet over the late quaternary.

Background: Coastal ecosystems in Mexico remain understudied in spite of their ecological, economic and conservation value and are being impacted by human activities along the coast. Knowledge on spatial patterns of plant species distribution that helps preserve these fragile ecosystems is crucial. Aims: We evaluated differences in species richness, species diversity and species dominance patterns in 16 plant communities as well as the degree to which differences were driven by climatic conditions in sandy dunes in Yucatán. We evaluated the importance of invasive species in mediating patterns of species diversity and species dominance patterns. Results: We found wide variation in plant species richness, species diversity and species dominance patterns among communities that stems from broad climatic differences along dune systems. Invasive plants represent almost one-third of total species richness and seem to be drastically changing the species dominance patterns in these communities. Conclusions: Regional climatic differences along the Yucatán north coast seems to be a major driver of plant diversity and species composition. Our findings suggest that invasive plants have successfully colonised and spread along the coast over the past 30 years. Even though invasive species do not alter spatial patterns of species diversity, they are becoming more dominant with potential detrimental consequences for native plants. [ABSTRACT FROM AUTHOR]

This study examines the distribution patterns of grass subfamilies and their diagnostic silica phytoliths along a transect running approximately at latitude 28° S in South Africa. The transect encompasses 77 surface samples collected along moisture and temperature gradients, across 6 biomes and 39 ecozones, and spanning elevations between near-sea level and over 2253 m. This study tests the relation between the distribution and density of grass subfamilies and the proportions of their diagnostic grass silica short cell phytoliths (GSSCP) representing them, and how these proportions correlate with five climatic variables (mean temperature of the wettest quarter, annual precipitation, precipitation of the wettest quarter, precipitation variability, and the aridity index). The results suggest that C 3 -grass diagnostic GSSCP morphotypes increase with a decline in temperature in the wettest quarter, occurring in areas receiving mostly winter rain or at high elevations in areas of summer rain. Of the C 4 grass subfamilies, the Panicoideae increase with summer precipitation and low precipitation variability, while the Aristidoideae- Stipagrostis the opposite. The distribution of Chloridoideae depends on complex changes in all climatic variables, suggesting aridity gradients only in the eastern half of the transect. In view of the data, this study reviews the usefulness of the phytolith humidity-aridity index (Iph) and the water stress index (Fs) and proposes the Panicoideae index (PI) and Stipagrostis index (SI) as indicator of aridity and high precipitation variability in southern Africa. • Modern surface grasses and their phytoliths vary across bioclimatic gradients. • Stipagrostis phytoliths are indicators of aridity and high precipitation variability. • Panicoideae phytoliths are good indicators of abundant summer precipitation. • The C 3 :C 4 ratio, the Panicoideae index, and the Stipagrostis index are proposed. [ABSTRACT FROM AUTHOR]

Delimiting species is an important, but frequently difficult aspect of systematics that should be addressed using data from multiple sources. Here we combine morphometric analyses and environmental characteristics to delimit species in the South Andean and Patagonian taxonomically difficult species-group composed byMulinum spinosum,M. echinusandM. leptacanthum(Apiaceae-Azorelloideae). Molecular phylogenies have shown that these three species form part of a polytomy together with otherMulinumspecies, and therefore these data are not useful for their delimitation. We include measurements of 25 morphometric variables from 163 herbarium specimens and perform univariate and multivariate principal component analysis (PCA) and discriminant analysis (DA) to establish the limits amongst the three mostly sympatric, morphologically similar, and phylogenetically unresolved species. We also use 19 bioclimatic and three geographic variables from localities of the specimens to infer environmental characteristics of the taxa and test their relation with morphological variation. Morphological evidence supports the inclusion ofM. echinuswithin the morphologically and climatically variableM. spinosum, and rejects its recognition as a distinct taxon at any rank. On the contrary,M. leptacanthumis considered a morphologically distinct species, generally restricted to high altitude areas of the southern Andes with a cooler and wetter climate. Within the widespreadM. spinosum, environmental gradients of precipitation and temperature relate to morphological gradients (e.g., in leaf and inflorescence sizes, in leaf acicularity, and in fruit-wing width). These last results showed that the large morphological variation in vegetative and reproductive characteristics of this species that grows in arid and semiarid habitats are related to regional climatic gradients that have probably been important in the evolution of this species' plasticity, diversification, and differentiation. [ABSTRACT FROM AUTHOR]

The influence of spatial and environmental factors in explaining the structure of large branchiopod assemblages at different spatial scales is still poorly explored. We hypothesized that the extent of actual spatial connectivity, and thus the spatial distribution of a metacommunity, may depend on the environmental conditions as represented by climatic gradients and the structural characteristics of the landscape. To test this hypothesis, the distributional patterns of 14 large branchiopod species in a set of 177 temporary water bodies repeatedly sampled across Tunisia and on its main islands were analysed. Physical, chemical, morphological and climatic characteristics of the studied water bodies were collected as well, and spatial structures were described using distance-based Moran's Eigenvector Maps. Distance-based Redundancy Analysis and variance partitioning explained more than one-half of total variation. Mantel's autocorrelograms demonstrated that species composition was spatially autocorrelated at shorter distances in the Mediterranean part of the country than in the southern, more arid part. These results suggest that both dispersal limitation and species response to spatially structured environmental gradients might be involved in determining large branchiopod distribution in Tunisia and that these patterns may greatly vary on a regional basis. [ABSTRACT FROM AUTHOR]

Introduction: Microorganisms play a critical role in soil biogeochemical cycles, but it is still debated whether they influence soil biogeochemical processes through community composition and diversity or not. This study aims to investigate variation in bacterial community structure across different soils and its correlation to soil multifunctionality. Soil samples were collected from five typical farmland zones along distinct climatic gradients in China., Methods: The high-throughput sequencing (Illumina MiSeq) of 16S rRNA genes was employed to analyze bacterial community composition in each soil sample. Multivariate analysis was used to determine the difference in soil properties, microbial community and functioning, and their interactions., Results: Cluster and discrimination analysis indicated that bacterial community composition was similar in five tested soil samples, but bacterial richness combined with soil enzyme activities and potential nitrification rate (PNR) contributed most to the differentiations of soil samples. Mantel test analysis revealed that bacterial community composition and richness were more significantly shaped by soil nutrient conditions and edaphic variables than bacterial diversity. As for soil multifunctionality, soil microbial community level physiological profiles were little affected by abiotic and biotic factors, while soil enzymes and PNR were also significantly related to bacterial community composition and richness, in addition to soil N and P availability., Conclusion: Cumulatively, soil enzymes' activities and PNR were greatly dependent on bacterial community composition and richness not diversity, which in turn were greatly modified by soil N and P availability. Therefore, in the future it should be considered for the role of fertilization in the modification of bacterial community and the consequent control of nutrient cycling in soil., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Liu, Gul Wazir, Hou, Wang, Rong, Xu, Liu, Li, Liu and Liu.)

Aim: Faced with the dispute regarding spatial gradients of body size in ectotherms, we build upon their long-known allometric relationship with water economy, which scales with thermal and hydric regimes, to revisit and refine the water conservation hypothesis (WCH). We provide a brief description of the WCH, including its physiological basis and geographical predictions for body size clines in terrestrial amphibians, and test it against heat-based hypotheses in four amphibian clades. Location: The Americas. Methods: We employ phylogenetic comparative analyses to examine relationships between body size and both temperature, as a descriptor of the effect of heat alone, and potential evapotranspiration, which describes the water constraint along evaporative gradients. We assess these relationships in four amphibian clades: the subfamily of leaf frogs (Phyllomedusinae), genera of gladiator frogs (Hypsiboas), salamanders (Plethodon) and the family of glass frogs (Centrolenidae). Results: Three clades did not show phylogenetic signals in body size variation. In addition, three clades showed a positive relationship with potential evapotranspiration as predicted, and all of them were unrelated to temperature. When present, however, the explanatory power of evaporative energy on body size variation was relatively weak. Main conclusions: The conservation of water across evaporative gradients is both a more comprehensive explanation and a more pervasive driver of spatial clines in body size among terrestrial amphibians than is the balance of heat alone. However, the relatively low predictive ability of evaporative energy and its dependence on specific climatic configurations both emphasize and elucidate the non-universality of the phenomenon. [ABSTRACT FROM AUTHOR]

Despite their recognized importance in promoting crop yields and soil health, little is known about earthworm species composition and density within the cereal production region of the Inland Pacific Northwest (IPNW). The overall goal of this work was to understand the influence of climatic factors and soil properties on the presence/absence and density of earthworm species found in the region. The IPNW cereal production region includes a steep climatic gradient and can be divided into four agroecological classes (annual cropping, transition crop-fallow, crop-fallow and irrigated) (AECs) according to the dominant cropping systems present. Replicate sites were selected within the annual cropping, transition and crop-fallow AECs and earthworm density, diversity and soil properties were measured. Earthworm diversity was extremely low. Only two of the sampled sites had more than a single species, and these sites were both in the wettest AEC. Aporrectodea trapezoides was the predominant species sampled, and this species was present at every site where earthworms were found. Earthworms were present at all sites within the annual cropping and transition classes, while only 13.3% of sites within the crop-fallow AEC had earthworms. When only sites with earthworms were considered, earthworm metrics were greater in the driest crop-fallow AEC (density = 151.2 individuals m −2 ) compared to 113.8 individuals m −2 in the transition and 86.4 individuals m −2 in annual cropping fields and a significant negative correlation was found with precipitation. The data suggest that while earthworms are largely absent from the driest sites, they can achieve relatively high density and biomass values when local conditions (soil properties and management) are favorable. A clear minimum threshold of mean annual precipitation (MAP) between 330 and 370 mm was observed, with earthworms absent from all fields with MAP values below 330. This value is lower than those previous reported for A. trapezoides and demonstrates the species’ ability to deal with warm, dry conditions. Biomass values (mean of 94.3 g m −2 ) for sites with earthworms were generally above those reported to be necessary to significantly influence crop yields, suggesting that further research focusing on quantification of the impact of earthworm on crop yields in this important agricultural region is warranted. [ABSTRACT FROM AUTHOR]

Aim: To map and analyse range size variation in the terrestrial seed-plant flora of Australia in relation to latitude, habitat availability, climate and soils, and to compare mean range size between biomes and growth forms. Location: Australia. Methods: Range sizes were estimated from herbarium records using alphahulls for 19,227 species and mapped into a set of 0.5° × 0.5° grid cells across Australia. Ordinary-least squares regressions were used to test for relationships between mean range size, latitude and habitat availability. Simultaneous autoregressive models (SAR) with spatial error terms were used in a multi-model framework to assess the role of aridity, mean annual temperature (MAT), soil pH, depth and total P concentration in shaping range size variation. Specieslevel differences between growth forms (graminoids, herbs, trees, shrubs, climbers) and biomes were assessed using one-way analysis of variance (ANOVA). Results: 68% of Australian seed-plant species have ranges which cover < 1% of the continent. Generally, large ranges are characteristic of graminoids and herbs and are associated with arid and grassland biomes. The smallest ranges were found in Mediterranean ecosystems in the SW corner of the continent, and were typically shrub species. Range size peaked at mid-latitudes and was not consistently smaller at lower latitudes (contrary to Rapoport's Rule). Increasing aridity, MAT and soil pH were strong predictors of large range size; however, soil depth and P content had little influence in SAR models. Main conclusions: Aridity and temperature are the primary drivers of range size variation in the Australian flora. Trait syndromes which promote colonization and survival in arid and grassland habitats (e.g. C4 photosynthesis, wind pollination) have allowed grasses and herbs to occupy large areas of the continent. Ranges were not smaller, on average, in the tropics due to the concentration of large-ranged species in the widespread arid biome in the centre of the continent. [ABSTRACT FROM AUTHOR]

[fr] Dans le cadre du projet GLORIA EUROPE on a étudié la diversité floristique, la fréquence et le recouvrement des espèces, par rapport aux principaux gradients écologiques (altitude, exposition), au sein des associations de prés alpins (Primulo-Caricetum curvulae, Oreochloo-Juncetum trifidi) et des buissons subalpins de petite taille (Rhododendro myrtifolii - Vaccinietum), sur quatre sommets dans le massif Pietrosul Mare (Les Carpates Roumaines). La diversité floristique est plus grande chez les associations de plantes des sommets avec des altitudes plus basses (Golgota, Gropile) et elle s'abaisse chez les associations des sommets plus hauts (Buhaiescu, Rebra). Dans le cas où l'altitude des sommets subalpins-alpins est 100 m plus élevée, on a constaté une réduction du nombre desespèces de plantes vascidaires avec 10%. La fréquence et le recouvrement les plus élevées dans ces associations appartiennent aux espèces arctico-alpines (Carex curvida, Juncus trifidus, Hieracium alpinum, Oreochloa disticha etc.) et à une espèce régionale carpato-balkanique (Rhododendron myrtifolium). Dans les aires de versants nord et est, où le recouvrement de la végétation est 15-30% plus bas que sur les versants ensoleillés, et où la température dans le sol est, généralement, 1-3° C plus réduite dans la saison de végétation (juin-août), le nombre des espèces sur un mètre carré est, en moyenne, de 25% plus grand que dans les aires de versants sud et ouest. [es] En el marco del proyecto GLORIA EUROPE hemos estudiado la diversidad florística, la frecuencia y la cobertura de las especies en relación con los principales gradientes ecológicos (altitud, exposición), con las asociaciones de pastos alpinos (Primulo-Caricetum curvulae, Oreochloo-Juncetum trifidi ) y con los matorrales bajos subalpinos (Rhododendro myrtifolii – Vaccinietum), todo ello en cuatro cimas del macizo Pietrosul Mare (Cárpatos Rumanos). La diversidad florística es mayor en las asociaciones de las cimas más bajas (Golgota, Gropile) y menor en las asociaciones de las cimas elevadas (Buhaiescu, Rebra). Cuando el intervalo altitudinal de las cimas subalpinas-alpinas es de 100 m la disminución en el número de plantas vasculares es aproximadamente del 10%. La mayor frecuencia y el más importante recubrimiento corresponden a las especies ártico-alpinas (Carex curvula, Juncus trifidus, Hieracium alpinum, Oreochloa disticha etc.) así como a una especie regional carpato-balcánica (Rhododendron myrtifolium). En las subparcelas de laderas norte y este, donde el recubrimiento vegetal es 15-30% menor que en las laderas soleadas, y donde la temperatura del suelo es generalmente 1-3° C más fría en el período vegetativo (junio-agosto), el número de especies en un metro cuadrado es, por término medio, un 25% mayor que en las subparcelas de las laderas meridionales y occidentales.

ABSTRACT The taxonomy and ecology of the sorediate species of Menegazzia from the southernmost regions of Chile and Argentina and the South Atlantic Islands was recently published, only with sporadic reports from the more northern regions. In the present work the distribution patterns and habitat ecology of the sorediate species are discussed, with emphasis on the area north of 48º S. Eleven species are treated. Menegazzia subpertusa, an epiphyte of sclerophyll scrubs, is recorded from South America for the first time (Chile and Argentina). Menegazzia neozelandica has a disjunct distribution in Chile, with occurrences in Fray Jorge (Fourth Region of Chile) and on Islas Juan Fernández, and along the coast south of latitude 38º S. Menegazzia kawesqarica and M. tenuis are most common in the southernmost part of Chile, but are also found at high altitudes at lower latitudes. Additional treated species are M. chrysogaster, M. fumarprotocetrarica, M. globulifera, M. magellanica, M. norsorediata, M. sanguinascens and M. wandae. Several of the sorediate species are early colonisers of newly developed substrates. They show variable occurrences along light and humidity gradients. Distribution maps and a revised key are presented.Recientemente se han publicado datos sobre la taxonomía y ecología de las especies sorediosas de Menegazzia representadas en las regiones más australes de Chile y Argentina e islas del Atlántico Sur, además de registros esporádicos en zonas ubicadas más al norte en Chile. En este trabajo se discuten los patrones de distribución y la ecología del hábitat de 11 especies sorediosas, con especial enfásis en aquellas que se desarrollan al norte de los 48º S. Menegazzia subpertusa, un epífito de arbustos esclerófilos, se registra por primera vez en América (Chile y Argentina). Menegazzia neozelandica tiene una distribución discontinua en Chile; ha sido recolectada en Fray Jorge (Cuarta Región de Chile), Islas Juan Fernández y en regiones costeras al sur de los 38º S. Menegazzia kawesqarica y M. tenuis son más frecuentes en las zonas más australes de Chile; también se han encontrado en hábitats de altura y bajas latitudes. Se incluyen, además, M. chrysogaster, M. fumarprotocetrarica, M. globulifera, M. magellanica, M. norsorediata, M. sanguinascens y M. wandae. Varias especies sorediosas crecen como pioneras en sustratos jóvenes. Los patrones de distribución a lo largo de gradientes de humedad y de luz son variables. Se presentan mapas de distribución y clave de las especies.

Plant radiations are widespread but their influence on community assembly has rarely been investigated. Theory and some evidence suggest that radiations can allow lineages to monopolize niche space when founding species arrive early into new bioclimatic regions and exploit ecological opportunities. These early radiations may subsequently reduce niche availability and dampen diversification of later arrivals., We tested this hypothesis of time-dependent lineage diversification and community dominance using the alpine flora of New Zealand. We estimated ages of 16 genera from published phylogenies and determined their relative occurrence across climatic and physical gradients in the alpine zone. We used these data to reconstruct occupancy of environmental space through time, integrating palaeoclimatic and palaeogeological changes., Our analysis suggested that earlier-colonizing lineages encountered a greater availability of environmental space, which promoted greater species diversity and occupancy of niche space. Genera that occupied broader niches were subsequently more dominant in local communities. An earlier time of arrival also contributed to greater diversity independently of its influence in accessing niche space., We suggest that plant radiations influence community assembly when they arise early in the occupancy of environmental space, allowing them to exclude later-arriving colonists from ecological communities by niche preemption. [ABSTRACT FROM AUTHOR]

Aim Most studies on latitudinal gradients of biodiversity have focused on gradients of species richness. Here we aim to test whether, on top of these strong diversity gradients, processes of community assembly vary along a latitudinal gradient of more than 33°. Location China, latitude 18.67-51.86° N. Methods We used species abundance distribution ( SAD) data collected in 32 forest tree plots, and fitted a non-neutral model of community assembly to these SADs. We then calculated the fitted deviation from neutrality, δ, and looked for correlations between δ and geographical and environmental data. Results The fitted parameter δ was positive in most plots, and was furthermore positively correlated with latitude and negatively with temperature, indicating a less even abundance distribution and a likely increase in the strength of environmental filtering in regions further from the tropics and with decreasing temperatures. These results imply that on top of reducing the species richness, cold temperature may impact community assembly processes by strengthening local environmental filtering. Main conclusions Our results suggest a latitudinal gradient in tree community assembly process in Chinese forests, in which deviations from neutrality increase with latitude, probably because of an increase in environmental harshness. [ABSTRACT FROM AUTHOR]

The latitudinal herbivory-defense hypothesis (LHDH) posits that herbivory and plant defenses increase toward lower latitudes. Recent studies provide contradictory evidence and suggest alternative explanations for biogeographic patterns in plant-herbivore interactions. Here we test the LHDH by sampling herbivory from multiple generalist and specialist insect herbivores over the entire latitudinal native range of the plant species Oenothera biennis L. (Onagraceae). We sampled 79 populations on a 16° north-south gradient from Ontario and Maine to Alabama and Florida. From each population, we quantified herbivory across feeding guilds by considering leaf herbivory caused by generalist insects, damage by a specialist stem-boring beetle, and flower/seed herbivory by three Lepidoptera that specialize on Oenothera. We also related environmental and population density variables to herbivory. Our results show that latitudinal patterns vary dramatically among herbivore species. While generalist leaf herbivory showed no latitudinal pattern, stem borer damage increased with decreasing latitude. By contrast, the specialist flower/seed herbivores all caused less damage at lower latitudes. Temperature explained slightly more variation in herbivory than latitude, while precipitation and population density were less important. Overall, we show that every pattern of herbivory (positive, negative and no relationship) is possible across a latitudinal gradient, and this variation depends on the insects' degree of specialization and feeding guild. [ABSTRACT FROM AUTHOR]

Aims Understanding how tree growth is influenced by climate is vital for predicting how forests will respond to climate change, yet there have been few studies of tree growth spanning macroclimatic gradients. The aim of this study is to correlate growth of a single lineage of broadleaf evergreen trees with continental-scale variability in climate. Location Australia's temperate mesic eucalypt forests, spanning latitudes from 23 to 43° S and longitudes from 115 to 153° E. Methods We compiled and analysed a dataset containing around half a million measurements of growth in eucalypt tree diameter, collected from 2409 permanent forestry plots. These plots spanned a range of 558-2105 mm mean annual precipitation and 6-22 °C mean annual temperature. Generalized additive models were used to study the relationship between growth in tree diameter and several temperature and water availability variables. Results Tree growth increased with precipitation, but with a diminishing response above a mean annual precipitation of 1400 mm. There was a peaked response to temperature, with maximum growth occurring at a mean annual temperature of 11 °C and maximum temperature of the warmest month of 25-27 °C. Lower temperatures directly constrain growth. High temperatures primarily reduced growth by reducing water availability, but they also appeared to exert a direct negative effect. Our best model, which included maximum temperature of the warmest month and the ratio of precipitation to evaporation, explained 28% of the deviance. Main conclusions The productivity of Australia's temperate eucalypt forests could decline substantially as the climate warms, given that 87% of these forests currently experience a mean annual temperature above 11 °C, where the highest growth rates were observed. This will reduce carbon sequestration and slow recovery after catastrophic disturbances such as wildfire. [ABSTRACT FROM AUTHOR]

Adaptive radiation and reproductive isolation can determine the biogeographic structure of any species. We examine patterns of biotic variation in Embothrium coccineum, a Proteaceae tree that spans 20° of latitude and is both morphologically and genetically highly variable. We aim to (1) explore the correspondence between these biotic patterns and current geographic and climatic gradients, and (2) determine whether and how those patterns are likely to respond to changing climate. We conducted separate principal component analyses on biotic and abiotic sets of variables for 34 populations of Embothrium coccineum, accounting for a large fraction of the total variation in each. We then used canonical correlation analyses to optimise the match of those gradients onto each other. Smaller, rounder leaves and particular alleles typify the colder and drier parts of the range, whereas larger, lanceolate leaves and other alleles typify warmer and moister areas. Finally, we mapped biotic profiles onto a predicted climatic landscape, on the basis of doubling of CO[sub 2] projections. The climatic regime is predicted to shift geographically, but this lineage has successfully responded to repeated and dramatic climatic shifts since the Oligocene, and it should also be able to move and adapt quickly enough to meet the present challenge. More generally, our analytic approach can be extended to analysis of biotic and abiotic patterns in other species facing climatic challenges. Where there is enough biogeographic variation to provide adaptively relevant substrate, and where propagule dispersal is sufficiently extensive to keep up with the pace of spatial climatic shift, such taxa should be able to cope with shifting climate. Covering 20° of latitude in the Patagonian Andes, Embothrium occupies a range of habitats that are moving with climate change. We show that current biotic patterns vary with climate across geography, forecast responses to ongoing climate change, and predict that Embothrium must move, but will persist. Our approach can be used for other species facing similar climatic challenges. [ABSTRACT FROM AUTHOR]

Dynamic vegetation models are important tools in ecological research, but not all processes of vegetation dynamics are captured adequately. Tree mortality is often modeled as a function of growth efficiency and maximum age. However, empirical studies have shown for different species that slow-growing trees may become older than fast-growing trees, implying a correlation of mortality with growth rate and size rather than age. We used the ecosystem model LPJ-GUESS to compare the standard age-dependent mortality with two size-dependent mortality approaches. We found that all mortality approaches, when calibrated, yield a realistic pattern of growing stock and Plant Functional Type (PFT) distribution at five study sites in Switzerland. However, only the size-dependent approaches match a third pattern, i.e. the observed negative relationship between growth rate and longevity. As a consequence, trees are simulated to get older at higher than at lower altitudes/latitudes. In contrast, maximum tree ages do not change along these climatic gradients when the standard age-dependent mortality is used. As tree age and size determine forest structure, our more realistic mortality assumptions improved forest biomass estimation, but indicate a potential decline of carbon storage under climate change. We conclude that tree mortality should be modeled as a function of size rather than age. [Copyright &y& Elsevier]

Ectomycorrhizal (EM) networks are hypothesized to facilitate regeneration under abiotic stress. We tested the role of networks in interactions between P. menziesii var. glauca trees and conspecific seedlings along a climatic moisture gradient to: (1) determine the effects of climatic factors on network facilitation of Pseudotsuga menziesii (Mirb.) Franco var. glauca (Mayr) seedling establishment, (2) infer the changing importance of P. menziesii var. glauca parent trees in conspecific regeneration with climate, and (3) parse the competitive from facilitative effects of P. menziesii var. glauca trees on seedlings. When drought conditions were greatest, seedling growth increased when seedlings could form a network with trees in the absence of root competition, but was reduced when unable to form a network. Survival was maximized when seedlings were able to form a network in the absence of root competition. Seedling stem natural abundance δC increased with drought due to increasing water use efficiency, but was unaffected by distance from tree or network potential. We conclude that P. menziesii seedlings may benefit from the presence of established P. menziesii trees when growing under climatic drought, but that this benefit is contingent upon the establishment of an EM network prior to the onset of summer drought. These results suggest that networks are an important mechanism for EM plants establishing in a pattern consistent with the stress-gradient hypothesis, and therefore the importance of EM networks to facilitation in regeneration of EM trees is expected to increase with drought. [ABSTRACT FROM AUTHOR]

The frequency of clonal plants in different vegetation types is known to be influenced by environmental and land-use factors. However, the underlying behavior of individual clonal traits or clonal trait diversity has received little attention. Here, we assess for species- and trait-diverse grasslands of the Swiss Alps the relative importance of temperature, soil moisture, land use and species richness on the diversity and frequency of individual compared with all clonal traits. We further analyzed how cover-weighted data alters the relationships found with commonly used presence-absence data. We combined species compositional, land-use and environmental data from 236 28-m grassland plots with clonal trait information for 527 species following the Clonal Growth Organ (CGO) classification. Test results are based on linear models, ANOVAs and ANCOVAs. The grassland sites were 84% dominated by clonal species. Drought-prone grasslands harbored the least clonal species. No increase in clonality was detected with decreasing temperature (= altitude). Mown or pastured grasslands had more clonal species than fallows. Certain sets of traits were correlated. Rhizomatous species especially reacted strongly to climatic and land-use gradients and had highest frequencies in cold, moist and disturbed sites. Clonal diversity was strongly dependent on species richness. Cover-weighted and presence-absence based estimates were largely similar. Overall, our data outlined that common clonal traits react differently to natural and land-use gradients as well as differently to the sum of clonal traits. Also, soil moisture was more decisive than temperature (= altitude) for the presence of clonal species. Lastly, the strong correlation between species-richness and clonal trait diversity needs to be accounted for when interpreting the functional role of clonal traits. [ABSTRACT FROM AUTHOR]

Aim To identify the reasons behind differing geographical species richness patterns of range-restricted and widespread species. Location The Western Hemisphere. Methods We used regression to determine the strongest environmental predictors of richness for widespread and range-restricted mammal species in 10,000 km2 quadrats in the continental Americas. We then used range-placement models to predict the expected correlation between range-restricted and widespread species richness were they to be determined by identical, random, or contrasting environmental factors. Finally, to determine the reasons underlying deviations from these predictions, we divided the Americas into 5% quantiles based on temperature and topographic heterogeneity and correlated richness of these two assemblages across quantiles – an approach that avoids constraints on statistical testing imposed by low potential for range overlap among range-restricted species. Results Minimum annual temperature was the strongest predictor of widespread species richness while topographic heterogeneity was the best, although weak, predictor of range-restricted species richness in conventional regression analysis. Our models revealed that the observed correlation between range-restricted and widespread species richness was similar to what would be observed if both range-restricted and widespread species richness were determined by temperature. Patterns of range-restricted and widespread species richness were highly correlated across temperature quantiles, but range-restricted species uniquely showed an increasing pattern across heterogeneity quantiles. Main conclusions Species richness gradients among range-restricted species differ from those of widespread species, but not as extensively or for the reasons reported previously. Instead, these assemblages appear to share some but not all underlying environmental determinants of species richness. Our new approach to examining species richness patterns reveals that range-restricted and widespread species richnesses share a common response to temperature that conventional analyses have not previously revealed. However, topographic heterogeneity has assemblage-specific effects on range-restricted species. [ABSTRACT FROM AUTHOR]

We tested whether local abundance of rain forest trees in the medium elevation wet forests of the southern Western Ghats (WG) was related to environmental tolerance, life form, and geographical range. We selected trees in medium elevation wet forests (750–1700 m asl) of the southern WG, using two data bases: a small plot (30 × 30 m) data base of 288 species of trees (≥ 3 cm dbh) in 33 plots totaling 2.97 ha, and a data base of 135 species of tree (≥ 10 cm dbh) in larger plots of 1 ha each, totaling 4.84 ha. The species density per hectare and number of records in the plot network was used in a factor analysis to give a measure of the local abundance of each species. The altitude and seasonality ranges of these species in the WG was assessed from independent data bases and used to generate an environmental tolerance score. Results indicated that as a species became locally more abundant, it occurred across a wider range of environmental gradients, but regional distribution was not related to geographical distribution. Understory species tended to be rarer with smaller range sizes and lower environmental tolerances than overstory species. Climate change is predicted to have drastic effects on restricted range species with limited environmental tolerances. [ABSTRACT FROM AUTHOR]

Aim To describe the geographical pattern of mean body size of the non-volant mammals of the Nearctic and Neotropics and evaluate the influence of five environmental variables that are likely to affect body size gradients. Location The Western Hemisphere. Methods We calculated mean body size (average log mass) values in 110 × 110 km cells covering the continental Nearctic and Neotropics. We also generated cell averages for mean annual temperature, range in elevation, their interaction, actual evapotranspiration, and the global vegetation index and its coefficient of variation. Associations between mean body size and environmental variables were tested with simple correlations and ordinary least squares multiple regression, complemented with spatial autocorrelation analyses and split-line regression. We evaluated the relative support for each multiple-regression model using AIC. Results Mean body size increases to the north in the Nearctic and is negatively correlated with temperature. In contrast, across the Neotropics mammals are largest in the tropical and subtropical lowlands and smaller in the Andes, generating a positive correlation with temperature. Finally, body size and temperature are nonlinearly related in both regions, and split-line linear regression found temperature thresholds marking clear shifts in these relationships (Nearctic 10.9 °C; Neotropics 12.6 °C). The increase in body sizes with decreasing temperature is strongest in the northern Nearctic, whereas a decrease in body size in mountains dominates the body size gradients in the warmer parts of both regions. Main conclusions We confirm previous work finding strong broad-scale Bergmann trends in cold macroclimates but not in warmer areas. For the latter regions (i.e. the southern Nearctic and the Neotropics), our analyses also suggest that both local and broad-scale patterns of mammal body size variation are influenced in part by the strong mesoscale climatic gradients existing in mountainous areas. A likely explanation is that reduced habitat sizes in mountains limit the presence of larger-sized mammals. [ABSTRACT FROM AUTHOR]