Broad Environmental Tolerance Research Articles

Effect of rhizome exposure to contrasting abiotic conditions on the performance of the invasive macrophyte Hedychium coronarium J. Koenig (Zingiberaceae)

Although invasive species are often better competitors than native species, broad environmental tolerance may also drive invasion success. Tolerance to abiotic heterogeneity in riparian ecosystems tends to favour the establishment of alien clonal species, as well as their dispersion by vegetative fragments. Hedychium coronarium J. Koenig is a rhizomatous emergent macrophyte native to Asia and has invaded Neotropical riparian ecosystems. We assessed the effect of H. coronarium rhizome exposure to distinct abiotic conditions on ramet growth. We exposed rhizomes to different desiccation periods (1–90 days), temperatures (15, 25 and 35 °C), and light regimes (0, 12, 16 h) and then assessed the effect of each of these variables on subsequent clonal growth (aboveground biomass production per plant and per ramet, and number and height of ramets) under ambient conditions. While no rhizome survived desiccation periods longer than 30 days, ramet growth among surviving rhizomes was not affected by the period of desiccation. Biomass production per rhizome, ramet biomass, and ramet height were significantly lower at 35 °C than at 25 °C. Constant darkness increased rhizome survival, but decreased ramet growth. Although rhizome exposure to extremes of each abiotic variable may hinder the invasion success of H. coronarium, the subsequent aboveground biomass production of surviving rhizomes did not decrease strongly in response to any treatment. This resilience may contribute to successful establishment of H. coronarium after dispersal through rhizome fragments and to varying abiotic conditions.

Functional traits explain crayfish invasive success in the Netherlands

Biological invasions by nonindigenous species can have negative effects on economies and ecosystems. To limit this impact, current research on biological invasions uses functional traits to facilitate a mechanistic understanding of theoretical and applied questions. Here we aimed to assess the role of functional traits in the progression of crayfish species through different stages of invasion and determine the traits associated with invasive success. A dataset of thirteen functional traits of 15 species currently occurring or available for sale in the Netherlands was evaluated. Six of these crayfish appeared invasive. Important traits distinguishing successful from unsuccessful invaders were a temperate climate in the native range, a medium to high egg count and producing more than one egg clutch per year. The most successful invaders had different functional trait combinations: Procambarus clarkii has a higher reproductive output, can migrate over longer distances and possesses a higher aggression level; Faxonius limosus is adapted to a colder climate, can reproduce parthenogetically and has broader environmental tolerances. Using a suit of functional traits to analyse invasive potential can help risk management and prevention. For example, based on our data Procambarus virginalis is predicted to become the next successful invasive crayfish in the Netherlands.

Enhanced degradation of different crude oils by defined engineered consortia of Acinetobacter venetianus RAG-1 mutants based on their alkane metabolism

Microbial consortia offer an attractive biodegradation strategy for removing hydrocarbons from oil-contaminated sites. In this study, we explored the degradation properties of Acinetobacter venetianus strain RAG-1 (RAG-1). RAG-1 effectively degrades three crude oils with excellent emulsification activity and cell surface hydrophobicity, while exhibiting broad environmental tolerance. RAG-1 accepts a range of alkane substrates (C10–C38) using three alkane hydroxylases (AlkMa, AlkMb, and AlmA). Bacterial mutant with alkMa or alkMb deletion enhanced degradation of C10–C20 or C22–C32 n-alkanes, respectively. Based on the substrate metabolism of the mutants, adjustable and targeted consortia consisting of ΔalkMa/almA and ΔalkMb were constructed, achieving enhanced degradation (10 days) of light crude oil (73.42% to 88.65%), viscous crude oil (68.40% to 90.05%), and high waxy crude oil (47.46% to 60.52%) compared with the single wild-type strain. The degradation properties of RAG-1 and the engineered consortia strategy may have potential use in microbial biodegradation applications.

Risk of short-term biodiversity loss under more persistent precipitation regimes.

Recent findings indicate that atmospheric warming increases the persistence of weather patterns in the mid-latitudes, resulting in sequences of longer dry and wet periods compared to historic averages. The alternation of progressively longer dry and wet extremes could increasingly select for species with a broad environmental tolerance. As a consequence, biodiversity may decline. Here we explore the relationship between the persistence of summer precipitation regimes and plant diversity by subjecting experimental grassland mesocosms to a gradient of dry-wet alternation frequencies whilst keeping the total precipitation constant. The gradient varied the duration of consecutive wet and dry periods, from 1 up to 60days with or without precipitation, over a total of 120days. An alternation of longer dry and wet spells led to a severe loss of species richness (up to -75% relative to the current rainfall pattern in W-Europe) and functional diversity (enhanced dominance of grasses relative to nitrogen (N)-fixers and non-N-fixing forbs). Loss of N-fixers and non-N-fixing forbs in severe treatments was linked to lower baseline competitive success and higher physiological sensitivity to changes in soil moisture compared to grasses. The extent of diversity losses also strongly depended on the timing of the dry and wet periods. Regimes in which long droughts (≥20days) coincided with above-average temperatures showed significantly more physiological plant stress over the experimental period, greater plant mortality, and impoverished communities by the end of the season. Across all regimes, the duration of the longest period below permanent wilting point was an accurate predictor of mortality across the communities, indicating that increasingly persistent precipitation regimes may reduce opportunities for drought stress alleviation. We conclude that without recruitment, which was precluded in this experiment, summer precipitation regimes with longer dry and wet spells will likely diminish plant diversity, at least in the short term.

Explaining the worldwide distributions of two highly mobile species: Cakile edentula and Cakile maritima

AbstractAimIf we are able to determine the geographic origin of an invasion, as well as its known area of introduction, we can better appreciate the innate environmental tolerance of a species and the strength of selection for adaptation that colonizing populations have undergone. It also enables us to maximize the success of searches for effective biological control agents. We determined the number of successful colonization events that have occurred throughout the world for two Cakile species and compared the climates from which they originated, in which they established and then spread.LocationWorldwide.TaxonSea‐Rockets (Cakile spp.), Brassicaceae.MethodsWe used a high‐throughput sequencing and a genome skimming approach combined with Bayesian Inference phylogenetics to examine variation in entire chloroplast genomes and regions of nuclear ribosomal DNA within native and introduced areas. Databases were used to compare climates between native ranges and introduced regions for multiple clades within each species.ResultsAt least seven clades have invaded different regions of the world. In most cases we were able to identify their source regions and climates. The environmental bottlenecks differed in intensity: while some clades colonized into climates that were similar to climates in their native range, other clades had a very broad innate environmental tolerance such that new invasions succeeded beyond the climate range of native populations. We found clear evidence of hybridization—specifically, chloroplast capture—between two species in Australia.ConclusionsResults here show that these species are sometimes capable of colonizing in climates that are beyond the climate range of native populations. Whether successful colonization beyond native climate niches requires de novo adaptation, or whether it represents an innate broad fundamental niche requires further investigation. Cakile species provide an excellent opportunity to study replicated climate adaptation trajectories.

Spatial variation in invasive silver carp population ecology throughout the upper Mississippi River basin*

AbstractUnderstanding spatial variation in non‐native fish species population ecology is imperative, where environmental, biotic and invasion‐related mechanisms contribute to spatial heterogeneity. Established populations of invasive silver carp Hypophthalmichthys molitrix are currently found throughout a large portion of the upper Mississippi River (UMR) basin. Despite their recent invasion and broad environmental tolerances, silver carp population ecology and linkages to environmental conditions in the UMR remain understudied. There were two objectives for this investigation: (a) to estimate correlations among population characteristics and the influence of latitude and the time since first detection, and (b) to model the influence of river discharge and temperature on growth early in life to age 3. We estimated spatial variability in silver carp population characteristics and dynamics from nine sites across the UMR and assessed if biotic, abiotic or invasion‐related (time since first detection) variables influence spatial patterns. Silver carp body weight, size structure, annual mortality, and growth parameters varied among locations. Silver carp recruitment was less stable for populations with higher relative abundance estimates and where carp were first detected ≥20 years ago whereas maximum carp age decreased with increasing latitude. Although model selection indicated silver carp length at age 3 was associated with mean daily discharge (m3/s) coefficient of variation, mean May‐June temperatures, and ordinal date of maximum discharge, parameter coefficients and effect sizes were small and not biologically meaningful. Our results suggest that silver carp populations are governed by intraspecific mechanisms, but time‐dependent changes in populations may partially underpin heterogeneity across populations. Our study helped further disentangle silver carp population ecology in the UMR by understanding carp ecology as a function of their invasion.

Salinity tolerance and geographical origin predict global alien amphipod invasions

Invasive alien species are driving global biodiversity loss, compromising ecosystem function and service provision, and human, animal and plant health. Habitat characteristics and geographical origin may predict invasion success, and in aquatic environments could be mediated principally by salinity tolerance. Crustacean invaders are causing global problems and we urgently require better predictive power of their invasiveness. Here, we compiled global aquatic gammarid (Crustacea: Amphipoda: Gammaroidea) diversity and examined their salinity tolerances and regions of origin to test whether these factors predict invasion success. Across 918 aquatic species within this superfamily, relatively few gammarids (n = 27, 3%) were reported as aliens, despite extensive invasion opportunities and high numbers of published studies on amphipod invasions. However, reported alien species were disproportionately salt-tolerant (i.e. 32% of brackish-water species), with significantly lower proportions of aliens originating from freshwater and marine environments (both 1%). Alien gammarids also significantly disproportionally originated from the Ponto-Caspian (20% of these taxa) when compared with all ‘other' grouped regions (1%), and principally invaded Eurasian waters, with translocations of salt-tolerant taxa to freshwaters being pervasive. This suggests habitat characteristics, alongside regional contexts, help predict invasibility. In particular, broad environmental tolerances to harsh environments and associated evolutionary history probably promote success of aliens globally.

Environmental tolerance of entomopathogenic nematodes differs among nematodes arising from host cadavers versus aqueous suspension

Environmental factors such as temperature and desiccation impact the survival and efficacy of entomopathogenic nematodes (EPNs). Most studies on environmental tolerance have focused on EPNs applied in aqueous suspension. Another approach for EPN application is via infected host cadavers. Emergence in host cadavers is also more representative of nematodes in natural populations. In prior studies, certain advantages in fitness have been observed with the cadaver application approach relative to aqueous application, yet the impact of environmental stress on these approaches requires investigation. In this study, we compared the effects of various temperatures (heat and cold) and desiccation intervals (48 and 72 hr) on the survival, virulence and reproductive capacity of Heterorhabditis bacteriophora and Steinernema glaseri when applied via cadaver versus aqueous suspension. In the heat tolerance bioassays, following exposure to 30 °C, 35 °C and 37. 5 °C, nematodes (from both species) in the cadaver treatments exhibited higher survival, and reproductive capacity compared with aqueous application. No survival was observed above 37.5 °C regardless of species or application approach. In cold tolerance, no differences were observed between the cadaver and aqueous treatments after a sequence of exposures from 10 °C to −2 °C. In desiccation assays, following exposure to 85% relative humidity for 2 or 3 days, nematodes (from both species) exhibited higher survival and reproduction in the cadaver treatment than in the aqueous treatment, whereas no differences were observed in virulence. This is the first study to find differential stress tolerance among nematodes emerged from infected host cadavers versus those applied in aqueous suspension. Our findings indicate additional advantages when using the cadaver approach for biocontrol applications, and suggest EPNs existing in natural populations may have broader environmental tolerance than those applied via aqueous suspension.

A Middle Pennsylvanian (early Asturian) tropical dry forest, Atokan-Desmoinesian boundary, Illinois Basin, USA

Six late Atokan (early Asturian) floras from seasonally dry environments are described and quantitatively analysed from adpressions and palynomorphs. Collections are from the eastern margin of the Illinois Basin, USA, in an 80 km N-S transect. Plant fossils occur in sedimentary rocks below the underclay (paleosol) of the Minshall-Buffaloville Coal Member (thus, not “roof-shale” assemblages), uppermost Brazil Formation. Growth of floras under season dryness is indicated by outcrop and lithological features that suggest deposition in flashy discharge streams, including intraformational conglomerates, plant fossils that cross bedding planes indicating rapid, episodic burial, and local rhythmically laminated sediments. Common charcoal clasts are consistent with seasonal climate. Cordaitalean foliage dominates the macroflora, accompanied by the dryland elements Lesleya sp., Taeniopteris sp. cf. T. multinervia, and Sphenopteridium sp. Two unusual forms of foliage are presumed to be rare or novel dryland species. Small numbers of wetland/periwetland taxa include calamitaleans, Linopteris neuropteroides, Karinopteris/Eusphenopteris sp., marattialean fern foliage, Senftenbergia plumosa, cf. Zeilleria avoldensis and Sphenopteris sp. The palynoflora is dominated by marattialean tree ferns, wetland plants with broad dispersal capacities and environmental tolerances. Subdominant elements also have strong wetland affinities. Palynoflora-macroflora mismatches may reflect primary ecology, palynomorph reworking, or both. The occurrence of these floras near the Atokan-Desmoinesian (~ Bolsovian-Asturian) boundary coincides with an array of physical and geochemical data that indicate change from weak rainfall seasonality to marked seasonality at all phases of glacial-interglacial cycles, reflected prominently in the stratigraphic record from the localities studied.

Climatic-niche evolution follows similar rules in plants and animals.

Climatic niches are essential in determining where species can occur and how they will respond to climate change. However, it remains unclear if climatic-niche evolution is similar in plants and animals or is intrinsically different. For example, previous authors have proposed that plants have broader environmental tolerances than animals but are more sensitive to climate change. Here, we test ten predictions about climatic-niche evolution in plants and animals, using phylogenetic and climatic data for 19 plant clades and 17 vertebrate clades (2,087 species total). Surprisingly, we find that for all ten predictions, plants and animals show similar patterns. For example, in both groups, climatic niches change at similar mean rates and species have similar mean niche breadths, and niche breadths show similar relationships with latitude across groups. Our results suggest that there are general 'rules' of climatic-niche evolution that span plants and animals, despite the fundamental differences in their biology. These results may help to explain why plants and animals have similar responses to climate change and why they often have shared species richness patterns, biogeographic regions, biomes and biodiversity hotspots.

The effect of local species composition on the distribution of an avian invader

Estimating the potential distribution of invasive species has been primarily achieved by employing species distribution models (SDM). Recently introduced joint species distribution models (JSDM) that include species interactions are expected to improve model output. Here we compare the predictive ability of SDM and JSDM by modelling the distribution of one of the most prolific avian invaders in the world, the common myna (Acridotheres tristis), in a recent introduction in Israel. Our results indicate that including information on the local species composition did not improve model accuracy, possibly because of the unique characteristics of this species that include broad environmental tolerance and behavior flexibility. However, the JSDM provided insights into co-occurrence patterns of common mynas and their local heterospecifics, suggesting that at this time point, there is no evidence of species exclusion by common mynas. Our findings suggest that the invasion potential of common mynas depends greatly on urbanization and less so on the local species composition and reflect the major role of anthropogenic impact in increasing the distribution of avian invaders.

Alien aquatic plants in Slovakia over 130 years: historical overview, current distribution and future perspectives

Alien aquatic plants rank amongst the major threats to aquatic biodiversity and, since ongoing climate change is expected to facilitate their further spread, there is an urgent need for sound knowledge of their distribution and ecology. We collected published and unpublished data spanning the last ~130 years and performed the first comprehensive assessment of alien aquatic vascular plants in Slovakia with the following aims: (i) to prepare a national inventory, (ii) to assess the effects of climate and landscape on species diversity and (iii) to evaluate the habitat preferences of the species. The historical overview showed a strongly increasing trend in the number of alien species related to an increased amount of intensive research of aquatic vegetation over the last 30 years. Altogether, 20 neophyte alien aquatic plant taxa were recorded from 479 sampling sites. However, the species inventory seems to be far from complete and approximately 14 species are expected to remain undetected. Elodeacanadensis and E.nuttallii are the most frequently occurring alien aquatic plants, while eight other species have been found at a single site only. The majority of alien plants were deliberately introduced as aquarium ornamentals or released through pond waste. The fragmented information on local habitat conditions did not allow us to draw firm conclusions about the habitat preferences of alien aquatic plants. However, artificial water bodies are more frequently colonised by alien species than natural habitats (95% of aliens were found in artificial water bodies and 60% of them were recorded exclusively in these habitats) and many species have broad environmental tolerances (ability to colonise both standing and running waters, tolerances to a wide range of temperatures and water chemistry). Our results reaffirm the major role of increased temperatures and landscape modification in the distribution of alien aquatic plants and we can expect enhanced invasiveness and spreading of alien species into new habitats driven by climate change and land use intensification. Filling a main gap in the recognition of alien aquatic plant environmental preferences is a challenge for future research with the ultimate goal of maintaining natural aquatic plant diversity and ecosystem functioning.

Hydraulic conductance, resistance, and resilience: how leaves of a tropical epiphyte respond to drought.

PremiseBecause of its broad range in the neotropical rainforest and within tree canopies, the tank bromeliad Guzmania monostachia was investigated as a model of how varying leaf hydraulic conductance (K leaf) could help plants resist and recover from episodic drought. The two pathways of K leaf, inside and outside the xylem, were also examined to determine the sites and causes of major hydraulic resistances within the leaf.MethodsWe measured leaf hydraulic conductance for plants in the field and laboratory under wet, dry, and rewetted conditions and applied physiological, anatomical, and gene expression analysis with modeling to investigate changes in K leaf.ResultsAfter 7 d with no rain in the field or 14 days with no water in the glasshouse, K leaf decreased by 50% yet increased to hydrated values within 4 d of tank refilling. Staining to detect embolism combined with modeling indicated that changes outside the xylem were of greater importance to K leaf than were changes inside the xylem and were associated with changes in intercellular air spaces (aerenchyma), aquaporin expression and inhibition, and cuticular conductance.ConclusionsLow values for all conductances during drying, particularly in pathways outside the xylem, lead to hydraulic resilience for this species and may also contribute to its broad environmental tolerances.

Broad Environmental Tolerance for a Salicola Host-Phage Pair Isolated from the Cargill Solar Saltworks, Newark, CA, USA.

Phages greatly influence the ecology and evolution of their bacterial hosts; however, compared to hosts, a relatively low number of phages, especially halophilic phages, have been studied. This study describes a comparative investigation of physicochemical tolerance between a strain of the halophilic bacterium, Salicola, isolated from the Cargill Saltworks (Newark, CA, USA) and its associated phage. The host grew in media between pH 6–8.5, had a salinity growth optimum of 20% total salts (ranging from 10%–30%) and an upper temperature growth limit of 48 °C. The host utilized 61 of 190 substrates tested using BIOLOG Phenotype MicroArrays. The CGφ29 phage, one of only four reported Salicola phages, is a DNA virus of the Siphoviridae family. Overall, the phage tolerated a broader range of environmental conditions than its host (salinity 0–30% total salts; pH 3–9; upper thermal limit 80 °C) and is the most thermotolerant halophilic phage ever reported. This study is the most comprehensive investigation to date of a Salicola host–phage pair and provides novel insights into extreme environmental tolerances among bacteriophages.

Whistling invaders: Status and distribution of Johnstone’s Whistling frog (Eleutherodactylus johnstonei Barbour, 1914), 25 years after its introduction to Colombia

Despite increased attention to the problem of alien amphibian invasions, systematic assessments of the actual invasion status and potential, required to estimate possible environmental and economic impacts of introduced species, are often missing. A prime example is Johnstone’s Whistling Frog (Eleutherodactylusjohnstonei), a Caribbean native that now occurs widely throughout the South American mainland, including Colombia. We conducted the first systematic and comprehensive countrywide assessment of the introduction status of the species in Colombia, combining both intensive field surveys, as well as a first population genetic analysis. The species was strictly confined to urban habitats with specific environmental conditions (plant nurseries and private gardens) and did not show any signs of dispersal into the extra-urban matrix. Genetic data support previously hypothesised independent introduction events in the Andes and along the Caribbean Coast and shed light on potential dispersal pathways. The results of this study challenge both the active spread, as well as the broad environmental tolerance hypothesis previously suggested, to explain the observed range extension. A critical reassessment of the categorisation of the species as highly invasive under IUCN-ISSG standards is required.

Morphological variation of a rapidly spreading native macroalga across a range of spatial scales and its tolerance to sedimentation

Understanding how species' traits can shape winners and losers of environmental change can help resolve drivers of current community composition patterns and predict future drivers. Sedimentation is one of the main environmental stressors shaping coastal marine communities and tolerance of high sedimentation rates (e.g. via morphological variation) may allow for competitive dominance. In New South Wales, Australia, the abundance and range of the native green macroalga Caulerpa filiformis have increased over recent decades, apparently associated with sediment disturbance. We used field measurements to test hypotheses about morphological variability in C. filiformis in relation to local- and large-scale environmental variation in water depth, sediment cover and latitude. Using a lab experiment, we tested hypotheses about survival and morphological change under different sedimentation regimes. In the field, C. filiformis fronds were more elongated and less branched when a sediment veneer is present and when water depth increased (i.e. reduced light). At larger spatial scales, frond length and width decreased with increased latitude, but latitude was less important in explaining the variation C. filiformis’ length than were depth or sedimentation. Our lab experiment showed a high tolerance to sedimentation, aided by increased investment in vertical growth. This study shows that rapid morphological plasticity is a likely key attribute of the spreading native macroalga C. filiformis. We argue that having a broad environmental tolerance is key to define a species success under environmental change.

Taxonomic revision of Cypridopsis silvestrii comb. nov. (Ostracoda, Crustacea) from Patagonia, Argentina with morphometric analysis of their intraspecific shape variability and sexual dimorphism.

In this study we redescribe an ostracod species belonging to the subfamily Cypridopsinae Kaufmann, 1900, sampled in seven localities of northern and southern Patagonia, Argentina. A new taxonomical combination is proposed, Cypridopsis silvestrii comb. nov., based on detailed description of females and the first descriptions of males. Cypridopsis silvestrii occurred on a wide geographical distribution range, from 40º to 48º S latitude, as well as broad environmental tolerance ranges. We evaluated morphological variations in two populations of C. silvestrii from northern (El Toro lake) and southern (El Sello lake) Patagonia, with contrasting limnological conditions. El Toro is a small shallow lake with high salinity waters and El Sello is a large deep lake with lower salinity. Based on morphometric analysis, our results showed intraspecific variation in valve shape and size between populations. Sexual dimorphism in El Toro population was identified through morphometric analyses. Additionally, comparison of valve outlines in living and subfossil individuals from El Toro lake allowed specimens previously described as juveniles of Eucypris fontana (Graf, 1931) to be identified as adults of C. silvestrii comb. nov. The present contribution increases knowledge of the taxonomic identity, the ecological requirements and the geographical distribution of C. silvestrii, and shows that morphometric analyses are a feasible and useful tool for exploring intraspecific shape differences and assisting in taxonomic identification. Furthermore, the results presented herein provide tools for C. silvestrii identification in paleolimnological studies, and emphasize the usefulness of studying living representatives for clarification of the taxonomic status of species widely distributed in Quaternary sediments.

Global invasion in progress: modeling the past, current and potential global distribution of the common myna

Determining the distribution and potential ranges of detrimental invasive species has become an essential task in light of their impacts on the environment. However, this effort has been challenging, especially for global invaders. Our goal was to test whether potential ranges of global invaders can be predicted, and examine the factors that shape them by studying the past, current and potential global distribution of a broad-ranging avian invader. We used the common myna (Acridotheres tristis), one of the most broad-ranging avian invaders whose range is currently expanding globally, as a case study. We collected the first detailed global database of global occurrence (n = 7990) of the common myna over the past 150 years, including records from the native and the introduced ranges. We employed MaxEnt to construct species distribution models (SDM) for the global database using climatic, anthropogenic and environmental factors. We provide evidence that invasive species distributions can be predicted from older records, and that model accuracy requires integrating data from the introduced range. This first comprehensive distribution for an avian invader indicates an extensive expansion in the common myna global distribution, with the potential of large areas worldwide being at risk of common myna invasion, thus threatening local biodiversity globally. Range expansion has been facilitated by proximity to urbanized areas and broad environmental tolerance. Our findings reflect the major role of anthropogenic impact in increasing the global distribution of avian invaders and emphasize the value of using SDMs to inform global management practices.

Spatial autocorrelation inflates niche breadth–range size relationships

AbstractAimSpecies with broader environmental tolerances are expected to be more widely distributed than specialist species, implying a positive correlation between niche breadth and geographic range size. When this relationship is evaluated using data derived from broad‐scale geographic distributions of species, spatial autocorrelation of species distribution data and environments may inflate niche breadth–range size relationships, bringing into question the causal relationship between environmental tolerance and range size. Using null models, we quantify the contribution of spatial autocorrelation to the frequently reported relationship between species’ range size and niche breadth.LocationSouth Africa.Time periodCurrent.Major taxa studiedEighty species in the genus Pelargonium.MethodsUsing phylogenetic least squares regression, we examined the extent to which variation in range size of Pelargonium species is related to temperature and precipitation niche breadths. We developed null models that randomized the spatial distribution of the climatic variables, but retained their broad spatial autocorrelation structure. We tested whether observed niche breadth–range size relationships were stronger than expected, given spatial autocorrelation of climatic variables.ResultsWe found the expected positive relationships between measures of niche breadth and range size, but these were no stronger than expected based on our spatial null models. Including spatial structure in simulations reduced expected niche breadths compared to simulations based on fully randomized environmental variables, resulting in steeper slopes for the simulated niche breadth–range size relationships.Main conclusionOur results indicate that spatial autocorrelation may positively bias niche breadth–range size relationships. This bias suggests that previously reported relationships between range size and niche breadth based on broad‐scale distributional data may be, at least in part, artefactual. Future studies need to explicitly account for spatial autocorrelation, and inferences on the role of environmental tolerance in driving patterns of species range size variation should be derived in conjunction with laboratory and field‐based experiments.

Filter‐dispersal assembly of lowland Neotropical rainforests across the Andes

Numerous Neotropical rainforest species are distributed in both Amazonia and Central America, reflecting a rich history of biotic interchange between regions. However, some plant lineages are endemic to one region, due in part to the dispersal barrier posed by the Northern Andean Cordilleras and adjacent savannas. To investigate the role of biogeographic filtering across the northern Andes in regional community assembly, we examined environmental tolerances, functional traits, and biogeographic distributions of >1000 woody plant species (trees, shrubs, lianas) locally co‐occurring in forest plots in lowland Panama (542 species) and Amazonian Ecuador (667 species). High regional abundance was strongly predictive of the probability of being geographically widespread (i.e. present on both sides of the Andes). However, we also found that species with broad environmental tolerances (those that are able to inhabit high elevations and areas of low mean annual precipitation) were more likely to have a cross‐Andean distribution even after accounting for regional abundance, suggesting that biogeographic filtering for these traits has mediated cross‐Andean dispersal. Regional abundance and environmental tolerances were additionally associated with a suite of life‐history traits related to high dispersal–colonization ability, but most traits reflecting dispersal–colonization ability were not predictive of biogeographic distribution. Our results highlight how the process of biogeographic filtering, based primarily on environmental tolerances, has mediated regional‐scale floristic assembly of Neotropical rainforests. The impacts of this process, which we term filter‐dispersal assembly, are likely to be especially important to forests in Central America, where biotic interchange with Amazonia has heavily influenced regional community composition.