Strong Environmental Filtering Research Articles

A Renaissance of Atoll Ecology

The approximately 320 atolls of the world, scattered across the tropical oceanic basins, constitute a unique type of ecosystem in that they are each an integrated unit consisting of island, coral reef, and lagoon components. Atolls have a complex geology, ecology, and biogeography, which can be fully appreciated only by transcending the classic boundary thinking of marine and terrestrial realms. The atolls we observe today were shaped by Quaternary sea-level fluctuations, which imposed strong environmental filters on their communities. As entirely biogenic, reef-borne structures, the islands of atolls depend upon marine productivity, which catalyzes island community assembly. Island species communities exist in complex dynamic equilibria with the surrounding oceanographic conditions. Energy fluxes and element cycles of the atoll system readily cross habitat boundaries and create a productive, diverse, and biomass-rich ecosystem on land and underwater. Past human disturbances and future global change put atolls at the forefront of conservation and ecological restoration.

Macroinvertebrate, algal and diatom assemblages respond differently to both drying and wetting transitions in non‐perennial streams

Abstract Biological assemblages in streams are influenced by hydrological dynamics, particularly in non‐perennial systems. Although there has been increasing attention on how drying impacts stream organisms, few studies have investigated how specific characteristics of drying and subsequent wetting transitions influence biotic responses via resistance and resilience traits. Here, we characterized how hydrologic metrics, including those quantifying drying and wetting transitions as well as dry and wet phases, alter diversity and composition of three aquatic assemblages in non‐perennial streams in southern California: benthic macroinvertebrates, soft‐bodied algae and diatoms. We found that flow duration prior to sampling was correlated with variation in macroinvertebrate and soft‐bodied algal assemblage composition. The composition and richness of diatom assemblages, however, were predominantly influenced by the drying start date prior to sampling. Contrary to other studies, the duration of the dry phase prior to sampling did not influence the composition or richness of any assemblage. Although our study was conducted within a region in which each assemblage experienced comparable environmental conditions, we found no single hydrologic metric that influenced all assemblages in the same way. The hot‐summer Mediterranean climate of southern California likely acts as a strong environmental filter, with taxa in this region relying on resistance and resilience adaptations to survive and recolonize non‐perennial streams following wetting. The different responses of algal and diatom assemblages to hydrologic metrics suggest greater resilience to drying and wetting events, particularly for primary producers. As drying and wetting patterns continue to change, understanding biodiversity responses to hydrologic metrics could inform management actions that enhance the ecological resilience of communities in non‐perennial streams. In particular, the creation and enhancement of flow regimes in which natural timing and duration of dry and wet phases sustain refuges that support community persistence in a changing environment.

Unraveling local and regional determinants of high plant diversity at marine rocky outcrops in Uruguay

AbstractQuestionsMarine rocky outcrops are model systems of community assembly under harsh conditions. The prevailing environmental conditions that determine a coast–inland gradient of stress and disturbance impose a strong environmental filter on community assembly. However, the Atlantic rocky outcrops of Uruguay challenge this assumption as they exhibit high plant diversity at small spatial scales. We investigated this study system to answer: (1) which environmental factors determine diversity at the local scale; (2) and how does the regional pool influence species composition along the coast–inland gradient?MethodsWe analyzed the local and regional determinants of plant community assembly in four rocky sites along the Uruguayan coast. Through a random sampling approach stratified by distance to the coast, we recorded species occurrences and microenvironmental conditions. Observed taxa were assigned into different species assemblages according to their typical vegetation type. Generalized Linear Model (GLM)–Poisson regression, quantile regressions and hierarchical cluster analyses were used to identify the factors underlying local richness and the spatial vegetation structure.ResultsNine different vegetation types generate a mass effect that enhances local diversity. Unexpectedly, 56% of the species are from non‐marine environments — e.g. grasslands or hydrophilous herblands. Species assemblages were spatially clustered, with a turnover of these clusters along the coast–inland gradient. Elevation, distance to the coast and vegetation cover promoted richness, likely due to an attenuation of marine filters. Meanwhile, substrate availability reduced richness, likely due to competitive exclusion as a result of more resources and homogeneous microenvironmental conditions.ConclusionsThe high local diversity along the marine rocky outcrops of Uruguay is best explained by a functionally diverse regional species pool, which interacts with local heterogeneity, and by conditions that enhance or attenuate the effect of marine stress. Effective conservation and management strategies are key to minimize the detrimental effects of urbanization, fragmentation, and non‐native plant invasions on these diverse habitats.

The community background alters the evolution of thermal performance.

Microbes are key drivers of global biogeochemical cycles, and their functional roles arey dependent on temperature. Large population sizes and rapid turnover rates mean that the predominant response of microbes to environmental warming is likely to be evolutionary, yet our understanding of evolutionary responses to temperature change in microbial systems is rudimentary. Natural microbial communities are diverse assemblages of interacting taxa. However, most studies investigating the evolutionary response of bacteria to temperature change are focused on monocultures. Here, we utilize high-throughput experimental evolution of bacteria in both monoculture and community contexts along a thermal gradient to determine how interspecific interactions influence the thermal adaptation of community members. We found that community-evolved isolates tended toward higher maximum growth rates across the temperature gradient compared to their monoculture-evolved counterparts. We also saw little evidence of systematic evolutionary change in the shapes of bacterial thermal tolerance curves along the thermal gradient. However, the effect of community background and selection temperature on the evolution of thermal tolerance curves was variable and highly taxon-specific,with some taxa exhibiting pronounced changes in thermal tolerance while others were less impacted. We also found that temperature acted as a strong environmental filter, resulting in the local extinction of taxa along the thermal gradient, implying that temperature-driven ecological change was a key factor shaping the community background upon which evolutionary selection can operate. These findings offer novel insight into how community background impacts thermal adaptation.

Multidimensional trait variability in a widespread, Paleoarctic macrophyte: functional, spectral and genetic drivers

Understanding how environmental conditions and plant functional variation are mutually related is critical to improving our comprehension of plant adaptations. In this context, our knowledge of the interlinks between plant functional, spectral and genetic traits and environmental filters is still very limited, especially for wetland species. To gain new insights on this topic, a multidimensional dataset, centred on the widespread macrophyte species Nuphar lutea, was assembled by collecting data on functional traits (including spectral traits), genetic metrics and environmental determinants from 28 plots spanning north‐central Italy. A strong environmental filter acts on all traits (morphological, biochemical, spectral and the genetic diversity metrics) resulting in significant local control over trait patterns, exemplified by the discrimination value of water electrical conductivity. This is further reinforced by the key contribution of sediment variables in explaining traits variation. Site‐specific environmental conditions were reflected in different patterns of genetic diversity, suggesting a long‐term effect of environmental filters on genotypes as well. High water conductivity – in our study sites indicative of long‐term hydrogeological settings – is linked to more acquisitive behaviour in N. lutea and a progressive reduction in its genetic diversity, while high nutrients availability in sediments promotes higher leaf traits performance. This study better explores how high variability in leaf traits reinforces current genetic and mechanistic knowledge about competitive strategies in the key aquatic plant N. lutea, by testing the effectiveness of a novel integrative approach to assess multiple sources of plant functional variation.

Taxonomic and functional structure of understorey bird assemblages on Amazonian seasonally flooded river islands

Abstract The seasonal inundation of the floodplains of the Amazonian rivers is a natural and strong environmental filter for biota. Its effects on the taxonomic and functional attributes of assemblages, however, remain poorly understood. We investigated the taxonomic and trait diversity of understorey bird assemblages on fluvial islands subject to dramatic seasonal flooding in the Amazon. Birds were captured using mist-nets on ten fluvial islands and at 17 sites in unflooded terra firme forests. We captured 1552 individuals of 116 bird species in 4144 net-hours. Average capture rates were similar between the forest types, but species diversity was higher in terra firme forests. The bird assemblages of the islands showed higher species dominance, with only three species accounting for 47% of the individuals captured. Functional space was occupied similarly in both bird assemblages, as indicated by functional dispersion indices (Fdis). In contrast, functional evenness (Feve) was lower in the river island assemblages indicating that the dominant species share similar traits. Functional divergence indices (Fdiv) showed substantial niche differentiation between the bird assemblages of the two forest types. Low inter-annual variability in avian taxonomic and trait diversity was observed in river islands, probably associated with the predictability of the flooding regime.

Tolerance to aerial exposure influences distributional patterns in multi-species intertidal seagrass meadows

Multi-specific seagrass meadow assemblages dominate most tropical intertidal regions but the relative role of environmental stress in determining distribution patterns is still uncertain. Here we combine observational and experimental approaches to examine aerial exposure as a factor driving species occurrence patterns in intertidal meadows of the Andaman archipelago, where up to 6 seagrass species co-occur. In the studied meadow, patterns of exposure did not map onto distance from the coast, instead creating a patchy matrix of exposure, based on fine-scale bathymetric differences. Distributional surveys showed that seagrass species were similarly patchy, often tracking the degree of aerial exposure during low tide. While some species (Halophila ovalis, Halophila minor, and Thalassia hemprichii) frequently occurred in submerged or subtidal areas and were rarely found in completely exposed areas, other species (Cymodocea rotundata, Halophila beccarii, and Halodule uninervis) also occupied areas that were subject to partial or complete aerial exposure during low tide. To confirm this pattern, we used field-based transplant experiments, employing a natural gradient of tidal exposure to subject six seagrass species to different desiccation exposure times. After a month, H. beccarii and H. uninervis transplants survived in areas that sustained more than 3 h of aerial tidal exposure without significant mortality, compared with other species (H. ovalis, H. minor, T. hemprichii, C. rotundata) that showed dramatic shoot mortality at the same exposure regimes. For all species, 4 h represented the upper limit of exposure, in both experimental and distributional studies. However, despite their wider tolerance of exposure to air, H. beccarii and H. uninervis did not dominate the entire meadow. This could be a result either of their poor tolerance to other environmental factors or their lower competitive abilities among other mechanisms. This suggests that in tropical multi-specific meadows, strong environmental filters could override clear intertidal zonation to create patchy matrices based on species tolerances.

Towards a trait‐based framework for marine macroalgae: Using categorical data to explore the nature of emergent functional groups

Abstract While trait‐based approaches have been effectively leveraged by plant ecologists to advance our understanding of community responses to major global challenges, such as climate change and invasive species, the study of marine macroalgae is still mired in a functional group (FG) framework developed in the 1980s. In this paper, we used predominantly categorical data for 18 macroalgal traits that were accessible in public databases and/or the literature to explore their usefulness in a trait‐based framework for marine macroalgae. Species were clustered into emergent, data‐driven groups using a Gower dissimilarity matrix, then a k‐medoid clustering approach called partitioning around the medoids. We identified 14 emergent groups (EGs) that captured a spectrum of strategies used by different macroalgal species. However, significant ‘gaps’ in trait space may identify evolutionary constraints to algal adaptive strategies. Multivariate analysis showed how the 18 traits created trait space and drove the clustering. A spectrum of strategies and the influence of multiple traits imply that algal strategies are likely governed by complex multivariate, not bivariate, trade‐offs. Finally, we found that our EGs appeared to reflect multivariate trade‐offs and diverse ecological strategies more than the traditional FG model for macroalgae. We tested the usefulness of our EGs by comparing real‐world spatial distributions of species across habitats with known strong environmental filters to their area occupied in trait space. We found significant separation in trait space and divergent occupancy patterns across global distributions, attachment substrates and elevational zones. These results support the use of categorical data accessible in the literature as a useful step towards developing trait‐based ecology for marine macroalgae. Synthesis. Our findings indicate that readily accessible categorical traits produce emergent FGs that reflect environmental filtering and therefore demonstrate the power of trait‐based approaches over the current FG framework. Furthermore, we posit that categorical traits are a valuable and potentially complementary addition to a newly developing database of continuous traits because they encompass a broader, more globally accessible set of traits.

Large‐scale restoration of species‐rich dry grasslands on arable land: Environmental filtering drives successful species establishment over a period of 10 years

Abstract Sowing of regionally specific seed mixtures on former arable land is increasingly used to restore species‐rich grasslands but it often faces important obstacles in environmental conditions and colonisation from preserved surrounding grasslands. Long‐term landscape scale studies, which explore the processes governing plant establishment from seed mixtures and later colonisation from the surrounding landscape are scarce. We studied the species and functional trait composition of 32 grasslands restored 1–11 years before the first sampling by sowing regional seed mixtures in the White Carpathian Mts (SE Czech Republic). We compared them with 23 well‐preserved permanent grasslands in their surroundings. In each grassland, we estimated plant species cover in three plots of 25 m2, in restored grasslands in 2009, 2014 and 2019, in permanent grasslands in 2009. The species composition of the restored grasslands converged towards the permanent grasslands due to expansion of dry grassland species and retreat of mesic grassland and weed species. The majority (60%–71%) of the vegetation cover of restored grasslands was formed by sown species, while the species number was mainly determined by colonising unsown species (61%–63%). The species number of restored grasslands remained lower than that in permanent grasslands. Functional trait composition (community weighted mean) of the sown seed mixtures, permanent grasslands and restored grasslands overlapped in all three samplings. With increasing grassland age, species with resource‐retaining traits of low specific leaf area and high leaf dry matter content, lower stature, higher seed mass and lower capacity for clonal reproduction expanded. Functional trait diversity of the plots was mostly lower than expected by null model randomisations of community, which indicates strong environmental filtering. Comparison of newly colonising species and extinct species indicated that mainly species with traits similar to the rest of the community are able to colonise the grasslands successfully. Synthesis and applications: Sowing of regionally specific seed mixtures was successful and demonstrated to be a fast way of grassland restoration, particularly in terms of functional trait composition. The resulting species diversity depended on the colonisation processes, which are controlled by the functional composition of the local communities.

Chance and necessity in the assembly of plant communities: Stochasticity increases with size, isolation and diversity of temporary ponds

Abstract Biodiversity emerges from niche mechanisms, in which the combination of traits determines species performance, and populations drift because of the inherent stochasticity of community assembly processes. Population biology dictates that small and isolated communities are more prone to show stochastic assemblages. However, a reduced mass effect in isolated communities may promote trait selection. In addition, large and connected communities have a larger species pool, higher functional redundancy, lower population sizes and more random recruitment, which also fosters stochasticity in community assembly. These contradictory expectations demand empirical analyses. Plant metacommunities in temporary ponds are assembled by the action of strong environmental filters and cover wide ranges of local community sizes and connectivity, representing ideal systems for identifying determinants of trait‐selection processes. Using a deviance partition method introduced by the theory of community assembly by trait selection, we evaluated the role of plant traits in local community assemblies along 60 communities from a 14‐year plant survey of temporary ponds. Variation in pond size, hydroperiod, connectitivity and heterogeneity determined a selection gradien in traits related to drought resistance, life history and disperal strategies; and also in the strength of trait‐mediated community assembly. The taxonomic and functional diversity of a pond and its physical heterogeneity fostered stochasticity in the assembly of the community, which also presented a hump‐shaped association with connectivity. The pond area increased taxonomic richness but decreased functional diversity, determining negative and positive indirect effects on stochasticity. Synthesis. Diversity provides the raw material for trait selection putatively reducing stochasticity, but here diversity was positively related to stochasticity. Having enough functional diversity, larger redundancy and lower population sizes in diverse communities is probably fostering stochastic assemblages. The hump‐shaped association between stochasticity and connectivity supports a larger role of trait selection in isolated systems due to a weak mass effect, but also on connected communities in which a set of more optimal traits for the selection scenario could be available. In the ongoing state of ecosystem fragmentation, these empirical trends contribute to the mechanistic understanding of the connection between landscape structure and biodiversity assembly.

Hyd1d and hydflood - R packages to compute water levels and annual flood durations along the rivers Rhine and Elbe, Germany

Floodplains are environments characterized by fluctuating water levels. Spatial and temporal heterogeneity of habitat conditions driven by hydrology are the key factor for their high biodiversity because strong environmental filtering either creates favorable conditions for specialized organisms or eliminates competing generalists.hyd1d and hydflood are two R packages for simplified hydrological modelling in two large central European floodplains – along the rivers Rhine and Elbe in Germany – that enable users to simulate the dynamics of water level changes, flood extents and durations with high spatial and temporal resolution over long time periods and vast areas. They are simplified in the sense of not being based on physical equations, but they implement fast computing interpolation of 1d hydraulic data and GIS extrapolation algorithms. Annual and long-term products provide the possibility to predict the distribution of floodplain habitats.All input datasets are highly integrated into the packages and automatically updated. Computationally expensive products such as annual flood durations between 1960 and 2022 are provided as open data. The software itself is provided as open source software through CRAN and in public code repositories. With minimal efforts users can apply the software within the given conditions or integrate other river systems through data and source code contributions.

Aliens in caves: the global dimension of biological invasions in subterranean ecosystems.

Alien species are a significant threat to natural ecosystems and human economies. Despite global efforts to address this challenge, the documented number of alien species is rapidly increasing worldwide. However, the magnitude of the impact of alien species may vary significantly across habitats. For example, some habitats are naturally less prone to biological invasions due to stringent abiotic and biotic characteristics, selecting for a limited number of introduced species possessing traits closely related to the native organisms. Subterranean ecosystems are quintessential examples of habitats with strong environmental filters (e.g. lack of light and scarcity of food), driving convergent adaptations in species that have successfully adapted to life in darkness. Despite these stringent environmental constraints, the number of records of alien species in subterranean ecosystems has increased in recent decades, but the relevant literature remains largely fragmented and mostly anecdotal. Therefore, even though caves are generally considered very fragile ecosystems, their susceptibility to impacts by alien species remains untested other than for some very specific cases. We provide the first systematic literature survey to synthesise available knowledge on alien species in subterranean ecosystems globally. This review is supported by a database summarising the available literature, aiming to identify gaps in the distribution and spread of alien invertebrate species in subterranean habitats, and laying the foundations for future management practices and interventions. First, we quantitatively assessed the current knowledge of alien species in subterranean ecosystems to shed light on broader questions about taxonomic biases, geographical patterns, modes of dispersal, pathways for introductions and potential impacts. Secondly, we collected species-specific traits for each recorded alien species and tested whether subterranean habitats act as ecological filters for their establishment, favouring organisms with pre-adaptive traits suitable for subterranean life. We found information on the presence of 246 subterranean alien species belonging to 18 different classes. The dominant alien species were invertebrates, especially insects and arachnids. Most species were reported in terrestrial subterranean habitats from all continents except Antarctica. Palaearctic and Nearctic biogeographic regions represented the main source of alien species. The main routes of introductions into the recipient country are linked to commercial activities (84.3% of cases for which there was information available). Negative impacts have been documented for a small number of case studies (22.7%), mostly related to increased competition with native species. For a limited number of case studies (6.1%), management strategies were reported but the effectiveness of these interventions has rarely been quantified. Accordingly, information on costs is very limited. Approximately half of the species in our database can be considered established in subterranean habitats. According to our results, the presence of suitable traits grants access to the stringent environmental filter posed by subterranean environments, facilitating establishment in the new habitat. We recommend that future studies deepen the understanding of invasiveness into subterranean habitats, raising public and scientific community awareness of preserving these fragile ecosystems.

Class 1 integron and related antimicrobial resistance gene dynamics along a complex freshwater system affected by different anthropogenic pressures

The risk for human health posed by polluted aquatic environments, and especially those carrying antibiotic resistance genes (ARGs) of clinical interest, is still debated. This is because of our limited knowledge of the dynamics of antimicrobial resistance in the environment, the selection mechanisms underlying the spread of ARGs, and the ecological factors potentially favoring their return to humans. The Class 1 integron is one of the most effective platforms for the dissemination of ARGs. In this study we investigated a freshwater system consisting of a lake-river-lake continuum, determining the abundance of class 1 integrons and their associated ARGs by a modulated metagenomic approach. Bacterial abundance and community composition were used to identify the potential carriers of class 1 integrons and their associated ARGs over a period of six months. Class 1 integrons and their ARG cargoes were significantly more abundant in riverine sampling sites receiving treated wastewater. Further, class 1 integrons carried ARGs ranked at the highest risk for human health (e.g., catB genes), in particular, genes encoding resistance to aminoglycosides. Genera of potential pathogens, such as Pseudomonas and Escherichia-Shigella, were correlated with class 1 integrons. The lake-river-lake system demonstrated a clear relationship between the integrase gene of class 1 integrons (intI1) and anthropogenic impact, but also a strong environmental filtering that favored the elimination of intI1 once the human derived stressors were reduced. Overall, the results of this study underline the role class 1 integrons as proxy of anthropogenic pollution and suggest this genetic platform as an important driver of aminoglycoside resistance genes, including high risk ARGs, of potential concern for human health.

Evolutionary history constrains heat tolerance of native and exotic tropical Zingiberales

AbstractTropical wet forest plants experience relatively stable temperatures throughout the year. However, tropical forests represent a mosaic of habitats characterized by different temperatures. Heat tolerances are expected to be adapted to temperatures specific to their habitats. Although heat tolerance of species sharing similar environments is expected to be similar, it is also possible that heat tolerance is constrained by evolutionary history because closely related species usually display similar physiologies. When exotic species are introduced to novel communities, colonization may be facilitated by their previous adaptation to high temperatures and other physiological, genetic and demographic traits, which may grant them some competitive advantage. Increasing temperatures may represent a strong environmental filter affecting community assembly, and higher heat tolerances could facilitate the persistence of exotic species in novel environments.Using a community of 32 native and 7 exotic Zingiberales species from different tropical habitats in Costa Rica, Central America, we aim to answer the following questions: (a) does evolutionary history constrain heat tolerance? (b) do plants in the same habitat display similar heat tolerances? (c) do the heat tolerances of exotic species differ from those of native species?We measured temperature‐dependent changes in photosynthetic fluorescence to determine the temperature at which the first sign of damage to photosystem II is observed (T15), and the temperature at which the fluorescence of photosystem II is reduced by 50% (T50). Using a community phylogeny, we tested for phylogenetic signal inT15andT50. In addition, we tested for differences in heat tolerance among Zingiberales from old growth, secondary forests and open areas, as well as between native and exotic species.Our results support (a) a significant phylogenetic signal (Pagel'sλ) for bothT15andT50, (b) communities from open areas displayed similar photosynthetic heat tolerance compared to species from old growth and secondary forests, and (c) exotic Zingiberales are marginally tolerant to high temperatures than native species, but only forT15. Our results suggest that evolutionary history constraints heat responses of native and exotic Zingiberales in a warming world.Read the freePlain Language Summaryfor this article on the Journal blog.

Environment shapes tree community traits in China's forests

AbstractQuestionEnvironmental filtering plays an important role in plant community assembly. To what extent does the broad‐scale environment influence the functional composition of woody plants in China's forests? Is there stronger trait convergence under harsher environmental conditions?LocationChina.MethodsWe characterized community traits and their relationships to climate and soil, using a data set with 1312 plots of tree communities composed of 1591 tree species and 10 functional traits across China. Using quadratic models, we explored how community traits change with different environmental factors.ResultsTrait spectra at the species level and the community level were significantly correlated, and the first two principal components captured 74.5% of the variation in community‐weighted mean traits. The trait spectra showed a clear elevational pattern and varied along climate and soil gradients. Compared with random expectations, the multi‐trait functional diversity showed a divergence pattern on poor soils at the plot scale.ConclusionsTwo well‐known dimensions, the leaf economics spectrum and size‐related spectrum, could be extended from the species level to the community level. Environment, especially climate conditions, drives the trait spectra and their elevational patterns at the broad scale, indicating environmental filtering might shape the trait composition of tree communities in China. However, stronger environmental filtering does not occur under harsher environmental conditions.

Hiking and livestock favor non-native plants in the high Andes

Hikers and livestock using mountain trails damage native vegetation and act as seed vectors, thus favouring the spread of non-native plants. We evaluated the effect of trails and livestock abundance on the success of non-native plants in the arid central Andes of Argentina. We surveyed six trails, covering elevations between 2400 and 3570 m a.s.l. and recorded non-native and native vegetation using transects distributed along the elevational gradient and spanning distances up to 22 m from the trail. We assessed how non-native occurrence, richness and cover varied with distance from the trail, intensity of use by livestock, native plant community composition and elevation. We found that trails favoured non-native occurrence, but did not influence richness and cover, while livestock favoured non-native occurrence, richness and cover. Non-native richness and cover decreased with elevation and varied with native community composition. In addition, non-native richness was positively correlated with native shrub cover suggesting possible facilitative interactions. Our results show that despite strong environmental filtering that leads to decreasing non-native abundance with increasing elevation, non-natives occur up to the upper limits of vegetation, and that trails and livestock favour non-native spread in these mountains.Second Abstract in native language.

Elevational trends of tree fine root traits in species‐rich tropical Andean forests

With increasing elevation, trees in tropical montane forests have to invest larger fractions of their resources into their fine roots in order to compensate for increasingly unfavorable soil conditions. It is unclear how elevation and related edaphic changes influence the variability in tree fine root traits and belowground functional diversity. We measured six fine root traits related to resource acquisition on absorptive fine roots of 288 trees from 145 species along an elevational gradient from 1000 m to 3000 m a.s.l. in tropical montane forests of the Ecuadorian Andes. We analyzed trait relationships with elevation and soil nutrient availability, and tested whether root functional diversity varied along these gradients. Fine roots at higher elevations and at more nutrient‐poor sites were thicker, had higher tissue densities, and lower specific root length and nutrient concentrations than at lower elevations. These trends were diluted by the coexistence of tree species with a broad range of different root traits within communities particularly towards lower elevations, where root functional diversity was significantly higher. We conclude that nutrient limitation and potentially further adverse conditions at higher elevations are strong environmental filters that lead to trait convergence towards a conservative resource use strategy, whereas different trait syndromes are equally successful at lower elevations.

Elevational diversity patterns of rodents differ between wet and arid mountains

AbstractAimPatterns of species richness along elevation gradients vary with geographic and environmental factors but evidence for similar variation in functional and phylogenetic diversity remains scarce. Here, we provide the most comprehensive evaluation to date of elevational gradients in taxonomic, functional, and phylogenetic diversity of rodents – one of the most ecologically diverse groups of mammals – and test the effects of latitude and aridity on their variation for the first time.LocationForty‐nine mountains on five continents.Time periodContemporary.Major taxa studiedRodents (Rodentia).MethodsWe compiled elevational distributions of 374 rodent species across 49 elevational gradients. For each gradient, we quantified – in 100‐m elevational bins – rodent species richness and functional and phylogenetic richness, evenness, and dispersion, and their species richness‐corrected equivalents. To assess how rodent diversity varies with elevation, we fitted a series of models that included elevation, average latitude, and aridity of each mountain system while accounting for variation in study design and sampling effort.ResultsA common mid‐elevational peak in species richness among mountains contrasts with functional and phylogenetic diversity pattern variation (model shape and slope) explained by the aridity at a mountain's base. Specifically, we find that functional and phylogenetic richness and dispersion decline with elevation in wet mountain systems but increase with elevation in arid mountains.Main conclusionsIn this first comparative analysis of mammal functional and phylogenetic elevational gradients, we find that the decoupling of each from species richness is particularly pronounced in arid regions. Wet‐mountain lowlands and arid‐mountain highlands harbour the most functionally and phylogenetically diverse rodent communities, indicating that water availability is a strong environmental filter in structuring diversity of small mammals on mountain gradients. High regularity of species distances within assemblages supports a constant role for competition across all elevations and niche expansion in elevations with greater species richness.

Few plants and one dominant fly shape a unique pollination network in a Neotropical mangrove

Mangroves are unique ecosystems supported by very small plant assemblages. Those few plants tend to be insect-pollinated and make generalized interactions, which leads to competition for pollinators. Mangroves are poorly studied in terms of pollination ecology, and we still do not know how those interactions scale up to form networks. We described the pollination network of a Neotropical mangrove to understand how plant species share pollinators and to gain insight into network assembly in a species-poor ecosystem. We assessed year-round pollination interactions in a mangrove in north-eastern Brazil comprising three entomophilous plant species and described the topology of the resulting network in terms of nestedness, specialization, and modularity. We also assessed the relative importance and niche breadth of different pollinator groups using centrality metrics. The network had highly imbalanced node classes, comprising three zoophilous plant species and 29 insect species from the orders Diptera, Hymenoptera, and Lepidoptera. Pollinator species were mostly peripheral and rarely interacted with all plants, while plant species formed a generalized core. A single dominant fly species, Palpada albifrons, visited all plants and made most interactions, softening the separation between modules. The network was nonetheless moderately specialized due to several exclusive interactions with a taxonomic signal. These taxon-specific interaction patterns point to idiosyncrasies in mangrove pollination systems instead of the expected generalized interactions with non-selective insects. However, the mangrove’s reproductive dynamics seems to be dominated by a single pollinator species, and its network topology is heavily influenced by the low plant richness resultant from strong environmental filters.

Is elevation a strong environmental filter? Combining taxonomy, functional traits and phylogeny of butterflies in a tropical mountain

AbstractEnvironmental filters select species that tolerate and respond to habitat conditions similarly. By combining taxonomy, functional traits and phylogeny, we aimed to understand the spatial distribution of a tropical butterfly community, evaluating whether elevation acts as an environmental filter strong enough to select flight‐related traits.Frugivorous and nectarivorous butterflies were sampled with nets at seven altitudinal bands (800–1400 m) in four sampling periods. We tested seven flight‐related traits (wing length, width, and area; thorax volume; wing:thorax ratio [WTR]length, WTRwidthand WTRarea) and incorporated the effects of phylogeny in the relationships among these traits and with elevation.Butterfly diversity decreased with increased elevation, and four traits exhibited larger values at higher elevations: wing length, width, area and WTRarea.This suggests that butterflies tended to have smaller wings and robust bodies at lower elevations, and larger wings with slender bodies at higher elevations, possibly related to flight speed or wind conditions. Although the phylogenetic relatedness did not exert significant weight in the traits and elevation, we found indication of phylogenetic conservatism of wing area and WTR.Butterflies in mountains experience a strong selection by several environmental filters related to flight performance, and our study demonstrated a robust relationship between elevation, flight‐related traits and species distribution. These relationships occurred regardless of phylogenetic relatedness, but most traits are conserved and exhibit resemblance in the phylogenetic lineages of these species. These findings suggest an influence of a widespread filter promoted by the elevational gradient with convergent trait evolution.