Abiotic Filters Research Articles

How does spatial micro‐environmental heterogeneity influence seedling recruitment in ironstone outcrops?

AbstractQuestionsEnvironmental filters limit the set of potentially coexisting species in plant communities. Paradoxically, some of the world's most biodiverse communities are subjected to strong abiotic filters. We explored how environmental heterogeneity provides conditions for niche segregation in a harsh megadiverse ecosystem, focusing on fine‐scale factors that drive seedling recruitment. Due to the environmental stress (mainly nutrient and water scarcity), we expected the prevalence of positive plant interactions over negative ones to contribute to species coexistence.LocationIronstone outcrop (canga) at Serra da Calçada, southeast Brazil.MethodsWe characterised microhabitats with one or neither of two dominant shrubs Mimosa calodendron (Fabaceae) and Lychnophora pinaster (Asteraceae), and assessed which micro‐environmental attributes affect seedling survival, growth, and abundance, as well as adult richness in the ecosystem.ResultsSpatial heterogeneity in the community was mostly driven by differences in substrate properties, and plots with Mimosa calodendron and Lychnophora pinaster exhibited different biotic and abiotic conditions from those lacking these species. Microhabitats under both shrubs had greater adult richness, and those occupied by Mimosa calodendron had greater seedling abundance, suggesting positive effects of environmental conditions associated with these plants. Nevertheless, we identified two potential negative plant–plant interactions: larger crown area of the two dominant shrubs was associated with lower species richness, and greater understorey plant cover with lower seedling abundance. Over one year, 63% of the recorded seedlings survived, but measured attributes failed to predict survival. Seedling relative growth rates were species‐specific and lower in microsites where the rocky substrate is fragmented. The most abundant seedling taxa occurred in association with specific microhabitats.ConclusionsOur study suggested that fine‐scale spatial heterogeneity determines the outcome of plant–plant interactions in a stressful ecosystem. Micro‐environmental heterogeneity allows for the spatial segregation of species recruitment, thereby broadening the range of viable strategies within a harsh megadiverse ecosystem.

Soil chemistry drives below ground traits in an alternate successional pathway from forest to heath.

To understand impacts of post-disturbance assembly mechanisms on the functional diversity (FD) of plant communities, it is necessary to determine how the environment drives their functional trait composition. In the boreal forest, post-fire abiotic filters may control community assembly by selecting plants with specific traits. Ericaceous heaths are characterized by low FD and are thought to be subject to such filters. We hypothesized that soil parameters select for a specific suite of traits and act as a secondary abiotic filter in post-fire ericaceous heath and contribute to the observed reduction of FD. We measured six soil parameters, five functional traits, and plant species abundances in eight post-fire heath and four regenerating forest sites in Eastern Canada. We conducted a combined analysis of RLQ (R-table Linked to Q-table) and fourth-corner methods to examine the links between plant traits and plot-level soil parameters, mediated by species abundances. Only below ground traits were significantly linked to soil variables. Specific root length and ericoid mycorrhizal associations were negatively linked to total soil nitrogen, available ammonium, and pH. Post-fire heath soils favour a specific suite of species traits. Only a portion of the regional species pool possesses the above-mentioned traits, and when they are favoured by habitat conditions, they assemble into a community with low FD. The novelty of our study is here we show how the relationship between traits and soil chemistry can act as a secondary filter and exert community-level trait changes responsible for the low functional diversity observed in heaths.

Ecological drivers of avian community assembly along a tropical elevation gradient

Community assembly theory hypothesizes that two main niche‐based processes act to shape composition and organization of biological assemblages: abiotic filtering and biological interactions. Here, we conducted repeated surveys of bird abundance along an undisturbed elevational gradient in the tropical Andes to investigate 1) signals of deterministic processes driving community assembly and 2) potential mechanisms by which these forces operate (temperature, habitat complexity, fruit and insect availability), while correcting for imperfect detection and modeling species abundances with N‐mixture models. We observed strong signals of abiotic filtering driving functionally and phylogenetically clustered assemblages towards higher elevations, and a weaker signal of limiting similarity resulting in few overdispersed assemblages at lower elevations. Whereas the decay in species richness with increasing elevation was explained by temperature, trait and phylogenetic dispersion were explained by both temperature and vegetation structure, implying that an interplay of abiotic and biotic mechanisms determines abundance‐based community structure in our montane assemblages. Interestingly, trait and phylogenetic dispersion consistently decreased until ~3000 m but increased above this elevation, highlighting a potential role of competition in resource‐scarce habitats. Combined, our findings suggest abiotic filters are still the main process shaping montane biotas across elevations, whereas resource availability might act locally upon assemblages further modifying them. Our study challenges recent studies in tropical mountains that suggest that biotic filters are a stronger force than abiotic filters in shaping tropical montane assemblages, and exemplifies how accounting for imperfect detection might overcome potential biases in detecting environmental filtering signals in community assembly studies.

Can transplanting seedlings with protection against herbivory be a cost-effective restoration strategy for seasonally flooded environments?

Transplantation of naturally regenerating seedlings (hereafter wildlings) has great potential as a restoration tool as it involves the use of acclimatized individuals and preservation of local and endemic genotypes. When successfully used, this technique has the added benefits of increasing structural and compositional diversity, preserving local and endemic genotypes, and reducing ecological restoration costs. In wetland ecosystems, flooding is an abiotic filter that may hinder success of restoration efforts. We hypothesized that transplanting “ecologically toughened” wildlings from low-lying, flooded areas into restoration areas of higher relief and lower frequency of flooding, would be a successful strategy. In this study, we transplanted wildlings from periodically flooded areas upslope to test the effect of topographic position (where they were collected and outplanted), and protection against herbivory on seedling survival and growth. The experimental design included two collection times and planting areas (high and low topography), two seedling height, use of protection against mammalian herbivory, and four species that represent different functional types. We also evaluated the costs involved. The best experimental outcome for the four study species (most abundance floodplain species) was found with small seedlings (10–39 cm) collected at low relief and outplanted to higher elevations, with protection against herbivory. Even under unusually extreme flood events (high flooding over 7 months) the tree legume Inga vera has emerged with the highest survival rate. The costs of transplantation are lower (USD 739 ha−1) than those found in previous studies and the use of protection against herbivory was also considerably low (USD 2484 ha−1). That said, these estimated costs are on an experimental scale and do not represent large-scale operations, which could reduce and improve cost-benefits significantly. In remote places such as the Pantanal, the lack of nursery infrastructure, high associated costs of seedling production and vulnerability to herbivory are the main challenges for restoration. Hence, wildling collection can be a useful strategy to overcome such obstacles.

Best served deep: The seedbank from salvaged topsoil underscores the role of the dispersal filter in restoration practice

AbstractQuestionsGlobally, ecological restoration is required to restore degraded landscapes and to contribute to biodiversity conservation. Ecological theory suggests that manipulating dispersal, abiotic and biotic filters limiting plant re‐establishment will improve restoration outcomes. Here, we manipulated spread depth of soil containing a salvaged soil seedbank (dispersal filter), soil compaction (abiotic filter) and herbivore grazing (biotic filter) in a topsoil transfer experiment to test their effects on restoration success.LocationBanksiawoodland of the Swan Coastal Plain, Western Australia.MethodsTopsoil (upper ~7 cm) with its seedbank was removed from a donor site (20 ha) of recently cleared native vegetation and transferred to six recipient restoration sites (16 ha). Deep (10 cm thick) and shallow (5 cm thick) layers of topsoil were applied in a fully factorial experiment, with and without soil ripping and fencing, respectively. We analysed emergence, survival and functional types (alien/native, life form, fire response) of all vascular plant species for two consecutive years after topsoil transfer.ResultsThe most successful restoration treatment was deep topsoil with a mean density of 14.3 m−2native perennial germinants in year one and 7.3 m−2in year two. Application of deep topsoil increased native seedling emergence by 34% and decreased weed density by 21% compared with shallow topsoil. Overall seedling survival across the two‐year period was unaffected by filter treatments (range 0.6%–5%). After two years, the resulting plant community was 6%–38% weed species and of native perennial species, 12%–48% were capable of resprouting.ConclusionsManipulation of the dispersal filter alone, that is deep topsoil application, can lead to near‐equivalent native species number emerging on restoration sites as compared to pre‐cleared woodland. However, more research is required to test additional restoration tools to improve survival of biodiverse plant communities. For example, targeted herbicide application coupled with soil ripping to improve weed management and native seedling establishment.

Legacy Effects Overshadow Tree Diversity Effects on Soil Fungal Communities in Oil Palm-Enrichment Plantations.

Financially profitable large-scale cultivation of oil palm monocultures in previously diverse tropical rain forest areas constitutes a major ecological crisis today. Not only is a large proportion of the aboveground diversity lost, but the belowground soil microbiome, which is important for the sustainability of soil function, is massively altered. Intermixing oil palms with native tree species promotes vegetation biodiversity and stand structural complexity in plantations, but the impact on soil fungi remains unknown. Here, we analyzed the diversity and community composition of soil fungi three years after tree diversity enrichment in an oil palm plantation in Sumatra (Indonesia). We tested the effects of tree diversity, stand structural complexity indices, and soil abiotic conditions on the diversity and community composition of soil fungi. We hypothesized that the enrichment experiment alters the taxonomic and functional community composition, promoting soil fungal diversity. Fungal community composition was affected by soil abiotic conditions (pH, N, and P), but not by tree diversity and stand structural complexity indices. These results suggest that intensive land use and abiotic filters are a legacy to fungal communities, overshadowing the structuring effects of the vegetation, at least in the initial years after enrichment plantings.

A dimmer shade of pale: revealing the faint signature of local assembly processes on the structure of strongly filtered plant communities

Trait‐based ecology suggests that abiotic filtering is the main mechanism structuring the regional species pool in different subsets of habitat‐specific species. At more local spatial scales, other ecological processes may add on giving rise to complex patterns of functional diversity (FD). Understanding how assembly processes operating on the habitat‐specific species pools produce the locally observed plant assemblages is an ongoing challenge. Here, we evaluated the importance of different processes to community assembly in an alpine fellfield, assessing its effects on local plant trait FD. Using classical randomization tests and linear mixed models, we compared the observed FD with expectations from three null models that hierarchically incorporate additional assembly constraints: stochastic null models (random assembly), independence null models (each species responding individual and independently to abiotic environment), and co‐occurrence null models (species responding to environmental variation and to the presence of other species). We sampled species composition in 115 quadrats across 24 locations in the central Pyrenees (Spain) that differed in soil conditions, solar radiation and elevation. Overall, the classical randomization tests were unable to find differences between the observed and expected functional patterns, suggesting that the strong abiotic filters that sort out the flora of extreme regional environments blur any signal of other local processes. However, our approach based on linear mixed models revealed the signature of different ecological processes. In the case of seed mass and leaf thickness, observed FD significantly deviated from the expectations of the stochastic model, suggesting that fine‐scale abiotic filtering and facilitation can be behind these patterns. Our study highlights how the hierarchical incorporation of ecological additional constraints may shed light on the dim signal left by local assembly processes in alpine environments.

Trait-environment relationships differ between mixed-species flocking and nonflocking bird assemblages.

Hypotheses about the mechanisms of community assembly suggest that biotic and abiotic filters constrain species establishment through selection on their functional traits. It is unclear how differences in traits influence the niche dimensions of closely related bird species when they coexist in spatiotemporally heterogeneous environments. Further, it is necessary to take into account their participation in mixed-species flocks, social systems that can include both competition and facilitation. For 6 yr, we conducted counts of forest bird species and took measurements of environmental variables along an elevational gradient in the Nanling Mountains, China. To disentangle different deterministic and historical/stochastic processes between flocking and nonflocking bird assemblages, we first compared phylogenetic and functional structure, and community-weighted mean trait values (CWM). We further assessed elevational variations in trait-environment relationships. We found that the flocking and nonflocking bird assemblages were structured by environmental gradients in contrasting ways. The nonflocking assemblage showed a strong change from over-dispersed to clustered community structure with increasing elevations, consistent with the strong selective pressures of a harsh environment (i.e., environmental filtering). The nonflocking assemblage also displayed significant trait-environment relationships in bivariate correlations and multivariate ordination space, including specific morphological and foraging traits that are linked to vegetation characteristics (e.g., short trees at high elevations). By contrast, flocking birds were more resilient to habitat change with elevation, with relatively consistent community membership, and showed fewer trait-environment associations. CWM of traits that are known to be associated with species' propensity to join mixed-species flocks, including small body size and broad habitat specificity, were linked to the flocking assemblage consistently across the elevational gradient. Collectively, our trait-based analyses provide strong evidence that trait-environment relationships differ between flocking and nonflocking bird assemblages. Besides serving as bellwethers of changing environments, emergent properties of flock systems may increase the resilience of animal communities undergoing environmental change. Mixed-species flocks present an ideal model with which to explore cooccurrence of closely related species, because habitat filtering may be buffered, and the patterns observed are therefore the outcomes of species interactions including both competition and facilitation.

Divergent role of abiotic factors in shaping microbial community assembly of paocai brine during aging process

Microbial communities in fermented food are shaped by a myriad of abiotic factors. The respective roles of abiotic factors in shaping the dynamic bacterial community of paocai during aging remain unclear. In the present study, 100 paocai samples (pH: 2.95–5.23; NaCl content: 0.13–15.41%; total acid: 6.61–18.33 mg/mL; total sugars: 7.96–487.90 μg/mL; total viable count: 3.55–8.99 LogCFU/mL; aging time: 5 day–15 year) were analyzed through high-throughput sequencing and the results revealed five dominant bacterial genera across different samples, including Lactobacillus, Pediococcus, Leuconostoc, Lactococcus and unclassified genera. Both NaCl and total acid (TA) were the major factors regulating bacterial community divergence in paocai. Based on these results, the microbial communities were reconstructed by manipulating the TA and NaCl contents in vitro to validate the effectiveness of these factors in shaping microbial communities during paocai fermentation. Results showed that roles of abiotic factors differentiated during fermentation. At the early stage, salt was the first abiotic filter, mainly working through promoting the abundance of Lactococcus and Leuconostoc. As the TA content increased, the selective role of salt weakened while acid became the dominant at the later stage, as evidenced by the increased abundance of Lactobacillus and Pediococcus following the increase of TA content.

The effects of land degradation on plant community assembly: Implications for the restoration of the Tibetan Plateau

AbstractUnderstanding how biotic and abiotic filters drive plant distributions is critical for informing restoration efforts of degraded lands. However, it remains unclear whether or not it is possible to develop efficient restoration strategies that are based on field investigations? Here, we conducted a field‐based investigation along a land degradation gradient on the Tibetan Plateau. Along this gradient, we compared species composition, Pianka's niche overlap, and total aboveground biomass among grasses, sedges, legumes, and forbs. We also used Faith's (1992) phylogenetic diversity index (PD) and the net relatedness index (NRI) to measure community phylogenetic patterns. To understand the effects of abiotic filtering, we measured soil pH, moisture, electrical conductivity, total soil organic carbon, microbial biomass carbon, and microbial biomass nitrogen. Our results show that grasses replaced sedges and mesoxerophytes replaced mesohydrophytes with increasing land degradation. We also found that niche overlap declined with increasing degradation intensity. Furthermore, grass biomass increased, while sedges and legumes decreased, and forb biomass showed a hump‐shaped relationship with degradation intensity. In addition, the communities transitioned from a clustered to a more random phylogenetic pattern. Soil conditions changed from acidic to alkaline and from fertile to harsh (p < .05). High niche overlap indicates a high biotic filtering at lightly degraded land where abiotic filtering is less stressful. However, when degradation is intense, abiotic filtering is apparent, as indicated by low levels of niche overlap. Overall, we suggest that distantly related, arid tolerant and hardy plants, and soil reclamation should be considered in degraded alpine lands restoration.

Experimental assessment of biotic and abiotic filters driving community composition.

Species occurrence in a site can be limited by both the abiotic environment and biotic interactions. These two factors operate in concert, but their relative importance is often unclear. By experimentally introducing seeds or plants into competition‐free gaps or into the intact vegetation, we can disentangle the biotic and abiotic effects on plant establishment.We established a seed‐sowing/transplant experiment in three different meadows. Species were introduced, as seeds and pregrown transplants, into competition‐free gaps and the intact vegetation. They included 12 resident plants from the locality and 18 species typical for different habitats. Last two years, gaps were overgrown with vegetation from surrounding plants and we observed the competitive exclusion of our focal plants. We compared plant survival with the expected occurrence in target locality (Beals index).Many of the species with habitat preferences different from our localities were able to successfully establish from seeds and grow in the focal habitat if competition was removed. They included species typical for much drier conditions. These species were thus not limited by the abiotic conditions, but by competition. Pregrown transplants were less sensitive to competition, when compared to seedlings germinated from seeds. Beals index significantly predicted both species success in gaps and the ability to withstand competition. Survival in a community is dependent on the adaptation to both the abiotic environment and biotic interactions. Statistically significant correlation coefficients of the ratio of seedling survival in vegetation and gaps with Beals index suggest the importance of biotic interactions as a determinant of plant community composition.To disentangle the importance of abiotic and biotic effect on plant establishment, it is important to distinguish between species pool as a set of species typically found in given community type (determined by Beals index) and a set of species for which the abiotic conditions are suitable.

How Climate Shapes the Functioning of Tropical Montane Cloud Forests

Tropical Montane Cloud Forest (TMCF) is a highly vulnerable ecosystem, which occurs at higher elevations in tropical mountains. Many aspects of TMCF vegetation functioning are poorly understood, making it difficult to quantify and project TMCF vulnerability to global change. We compile functional traits data to provide an overview of TMCF functional ecology. We use numerical models to understand the consequences of TMCF functional composition with respect to its responses to climate and link the traits of TMCF to its environmental conditions. TMCF leaves are small and have low SLA but high Rubisco content per leaf area. This implies that TMCF maximum net leaf carbon assimilation (An) is high but often limited by low temperature and leaf wetting. Cloud immersion provides important water and potentially nutrient inputs to TMCF plants. TMCF species possess low sapwood specific conductivity, which is compensated with a lower tree height and higher sapwood to leaf area ratio. These traits associated with a more conservative stomatal regulation results in a higher hydraulic safety margin than nearby forests not affected by clouds. The architecture of TMCF trees including its proportionally thicker trunks and large root systems increases tree mechanical stability. The TMCF functional traits can be conceptually linked to its colder and cloudy environment limiting An, growth, water transport and nutrient availability. A hotter climate would drastically affect the abiotic filters shaping TMCF communities and potentially facilitate the invasion of TMCF by more productive lowland species.

Soil Water Contents Control the Responses of Dissolved Nitrogen Pools and Bacterial Communities to Freeze-Thaw in Temperate Soils.

Background Freeze-thaw influences soil-dissolved nitrogen (N) pools due to variations in bacterial communities in temperate regions. The availability of soil water is important to soil biogeochemical cycles under frozen conditions. However, it is unclear how soil water content (SWC) mediates the effects of freeze-thaw on soil-dissolved N pools and bacterial communities. Method In this study, freeze-thaw microcosms were incubated at three levels of SWC, including 10% (air-dried soils), 15% (natural SWC), and 30% (wet soils). In addition to measuring soil-dissolved N pools, variations in bacterial communities were examined using high-throughput sequencing. Results and Conclusions. Total dissolved N (TDN), NO3−-N, NH4+-N, microbial biomass N (MBN), and net N mineralization rate (NNMR) were significantly influenced by SWC, freeze-thaw, and their interaction (NH4+-N excluded). N immobilization was inhibited under both low and high SWC, which was accompanied by varied bacterial community composition. However, only higher SWC substantially modified the freeze-thaw effects on the soil-dissolved N pools, characterized by a decrease in N mineralization (especially for the content of NO3−-N and NNMR) and an increase in N immobilization (MBN). These scenarios could be significantly correlated to variations in bacterial community composition based on redundancy analysis, especially by species belonging to Bacteroidetes, Nitrospirae, Alphaproteobacteria, Gemmatimonadetes, and Verrucomicrobia (Spearman's correlations). In conclusion, bacterial species passed through biotic (bacterial species) and abiotic filters (soil N pools) in response to freeze-thaw under varied SWC.Bacteroidetes, Nitrospirae, Alphaproteobacteria, Gemmatimonadetes, and Verrucomicrobia (Spearman's correlations). In conclusion, bacterial species passed through biotic (bacterial species) and abiotic filters (soil N pools) in response to freeze-thaw under varied SWC.Nitrospirae, Alphaproteobacteria, Gemmatimonadetes, and Verrucomicrobia (Spearman's correlations). In conclusion, bacterial species passed through biotic (bacterial species) and abiotic filters (soil N pools) in response to freeze-thaw under varied SWC.Alphaproteobacteria, Gemmatimonadetes, and Verrucomicrobia (Spearman's correlations). In conclusion, bacterial species passed through biotic (bacterial species) and abiotic filters (soil N pools) in response to freeze-thaw under varied SWC.Gemmatimonadetes, and Verrucomicrobia (Spearman's correlations). In conclusion, bacterial species passed through biotic (bacterial species) and abiotic filters (soil N pools) in response to freeze-thaw under varied SWC.Verrucomicrobia (Spearman's correlations). In conclusion, bacterial species passed through biotic (bacterial species) and abiotic filters (soil N pools) in response to freeze-thaw under varied SWC.

Tropical pitcher plants (Nepenthes) act as ecological filters by altering properties of their fluid microenvironments

Characteristics of host species can alter how other, interacting species assemble into communities by acting as ecological filters. Pitchers of tropical pitcher plants (Nepenthes) host diverse communities of aquatic arthropods and microbes in nature. This plant genus exhibits considerable interspecific diversity in morphology and physiology; for example, different species can actively control the pH of their pitcher fluids and some species produce viscoelastic fluids. Our study investigated the extent to which Nepenthes species differentially regulate pitcher fluid traits under common garden conditions, and the effects that these trait differences had on their associated communities. Sixteen species of Nepenthes were reared together in the controlled environment of a glasshouse using commonly-sourced pH 6.5 water. We analyzed their bacterial and eukaryotic communities using metabarcoding techniques, and found that different plant species differentially altered fluid pH, viscosity, and color, and these had strong effects on the community structure of their microbiota. Nepenthes species can therefore act as ecological filters, cultivating distinctive microbial communities despite similar external conditions, and blurring the conceptual line between biotic and abiotic filters.

Assessing vegetation recovery in reclaimed opencast mines of the Teruel coalfield (Spain) using Landsat time series and boosted regression trees

Opencast mining is an activity that caters to many economic sectors; however, it has a large impact on society and the environment. After mining, the major concern is to restore the previous land cover, which was generally a natural vegetation cover. Establishing permanent vegetation cover can restore landscape connectivity and previous ecosystem functions, enhance aesthetic values and prevent off-side effects associated with post-mining landscapes. Opencast mining reclamation deals with these issues with several strategies that aim to develop a vegetation cover after mining activity has stopped. However, not all reclamation actions are effective, and assessing their efficiency by monitoring vegetation development at reclaimed sites is a time-consuming task because it usually involves extensive field work. In this study, we present a semi-automatic approach based on analysing satellite data (Landsat) time series and using a machine learning technique to identify suitable conditions for vegetation development at reclaimed opencast mines. We analysed the Teruel coalfield (Aragón, central-eastern Spain). This area is a representative Mediterranean-Continental region that is of particular interest due the diversity of reclamation actions that have been applied and the increase in drier conditions during the last decades. Conditions were described with topography derived variables, technical reclamation features and drought-occurrence variables as potential explanatory factors. The implemented approach allowed us to identify the main abiotic filters for vegetation of this geographic region: the water availability and soil retention (both controlled by the topographic slope), and the proximity to seed sources. The analysis evidenced the negative influence of drought occurrence on vegetation development, and different responses were found depending on the timescale at which drought is calculated. Our results indicate that the reclamation landform model is the main key factor influencing vegetation development. A model such as the smooth berm-slope increases water availability and controls soil erosion, and hence, improves vegetation development. In addition, we found that further than 500-600 m from the mine, the effect of seed source declines dramatically. Therefore, all these issues should be considered in future reclamation designs in a Mediterranean-Continental environment. Our methodology could be adapted to other geographic regions where spatial environmental data are available.

Phylogenetic trajectories during secondary succession in a Neotropical dry forest: Assembly processes, ENSO effects and the role of legumes

Phylogenetic analysis of plant communities is useful for inferring ecological mechanisms driving forest succession. However, such analysis has scarcely been undertaken in tropical dry environments, especially for the dynamics of demographic components (i.e., recruited, surviving and dead plants) affecting the successional process. Here, we combine chronosequence and dynamic data to study the role of habitat filtering and limiting similarity in the old-field succession of a seasonal tropical dry forest subjected to strong climatic events (e.g., the El Niño Southern Oscillation (ENSO) and heavy rains). We documented successional changes in the phylogenetic structure and phylodiversity of regenerative communities (shrubs and trees ≤ 1 m in height), assessed phylogenetic changes in demographic components during succession, and explored the effects of interannual rainfall variation on such changes. Over five years, we monitored the dynamics of regenerative plant communities in a chronosequence of nine abandoned pastures (fallow age of 0–12 years) and three old-growth sites. For each year and site, we quantified changes in the standardized mean phylogenetic distance (MPD.OBS.Z) and phylodiversity (PD) of entire regenerative communities and recruited, surviving and dead plants. For each phylogenetic metric and demographic component, we assessed the effect of successional age, time (years), and interannual rainfall variation. Large variation in MPD.OBS.Z and PD was observed among sites and years, especially in the recently abandoned pastures. Overall, the phylogenetic community structure was clustered early in succession and became more random as succession advanced. Species from the order Fabales made especially strong contributions to the phylogenetic clustering, especially during the first years of succession. In dead plants, the MPD.OBS.Z and PD increased in the drier year due to the high mortality of plants from several clades (orders). The high prevalence of clustered and random phylogenetic structure suggests that abiotic filtering and stochastic processes are major structuring mechanisms in this successional system. Due the strong contribution of Fabales in the phylogenetic structure of regenerative communities of tropical dry forest, the effects of strong climatic events (e.g., ENSO) on Fabales could influence the old-field succession of tropical dry forests.

Disentangling the Effects of Disturbance from Those of Dominant Tall Grass Features in Driving the Functional Variation of Restored Grassland in a Sub-Mediterranean Context

Land abandonment in sub-Mediterranean grasslands causes the spread of tall-grasses, affecting biodiversity and ecosystem functioning. Mowing allows the recovery of the coenological composition after invasion, but the mechanisms acting at the fine-scale are poorly investigated. Since 2010 in the Central Apennines, we fenced a grassland invaded by Brachypodium rupestre, divided it into two areas, half of each was mowed biyearly and half remained unmown. In 2017 we selected ten 20 × 20 cm experimental units per half-area, collecting data on species occurrences, plant traits, B. rupestre height and phytomass. We used generalized linear mixed-effect modelling to disentangle the role of mowing from the impact of B. rupestre features in driving the community functional variations. Mowing was the main driver in the recovery process, acting as an abiotic filter (enhancement of tolerance-avoidance strategies). Furthermore, the reduction of weaker competitor exclusion processes fostered the increase of functional variation between coexisting species. Both drivers acted on different plant traits (e.g., mowing on life span, vegetative propagation types and plant height, mowing and B. rupestre features on space occupation types, seed mass and leaf anatomy), generally enhancing the extent of functional strategies related to resource acquisition and storage, reproduction, space occupation and temporal niche exploitation.

When the company does not matter: High‐quality ant seed‐disperser does not drive the spatial distribution of large‐seeded myrmecochorous plants

AbstractMutualisms are one of the main forces shaping species spatial patterns at all geographic scales. In generalised mutualisms, however, the dependence among partners is highly variable in time and space, and therefore, the effect of diffuse mutualisms on species geographic distributions is unclear. Myrmecochorous seeds in Brazilian semi‐arid vegetation are dispersed by several ant species. However, large‐seeded species are especially dependent on dispersal by the giant ant Dinoponera quadriceps, which is the main disperser of such diaspores and the species that provide the longest dispersal distance among ant species in this system. Hence, we hypothesise that the presence of D. quadriceps shapes the distribution of large‐seeded, but not the distribution of small‐seeded myrmecochorous plant species. To evaluate this hypothesis, we modelled the potential distribution of two large‐seeded (which are predominantly dispersed by D. quadriceps) and two small‐seeded (which are barely dispersed by D. quadriceps) Euphorbiaceae species and the potential distribution of D. quadriceps. We analysed the relationship between the occurrence suitability of D. quadriceps and the occurrence suitability of plant species. We found that the potential distribution of both large‐seeded and small‐seeded myrmecochorous plants was unrelated to D. quadriceps occurrence suitability. It means that the disproportional benefits provided by high‐quality disperser at local scales may not emerge at broader geographical scales. In Caatinga vegetation, diaspores are submitted to strong abiotic filters that constraint seed germination and establishment after the dispersal phase. Such abiotic filters may dilute the initial benefit provided by long‐distance dispersers. Therefore, we suggest that in dry environments like the Caatinga, the benefits of long‐distance removals should be outweighed by the risk of reach new habitats with unfavourable conditions for germination and establishment.

Estimation of Fungal Diversity and Identification of Major Abiotic Drivers Influencing Fungal Richness and Communities in Northern Temperate and Boreal Quebec Forests

Fungi play important roles in forest ecosystems and understanding fungal diversity is crucial to address essential questions about species conservation and ecosystems management. Changes in fungal diversity can have severe impacts on ecosystem functionality. Unfortunately, little is known about fungal diversity in northern temperate and boreal forests, and we have yet to understand how abiotic variables shape fungal richness and composition. Our objectives were to make an overview of the fungal richness and the community composition in the region and identify their major abiotic drivers. We sampled 262 stands across the northern temperate and boreal Quebec forest located in the region of Abitibi-Témiscamingue, Mauricie, and Haute-Mauricie. At each site, we characterized fungal composition using Illumina sequencing, as well as several potential abiotic drivers (e.g., humus thickness, soil pH, vegetation cover, etc.). We tested effects of abiotic drivers on species richness using generalized linear models, while difference in fungal composition between stands was analyzed with permutational multivariate analysis of variance and beta-diversity partitioning analyses. Fungi from the order Agaricales, Helotiales, and Russulales were the most frequent and sites from the north of Abitibi-Témiscamingue showed the highest OTUs (Operational Taxonomic Unit) richness. Stand age and moss cover were the best predictors of fungal richness. On the other hand, the strongest drivers of fungal community structure were soil pH, average cumulative precipitation, and stand age, although much of community variance was left unexplained in our models. Overall, our regional metacommunity was characterized by high turnover rate, even when rare OTUs were removed. This may indicate strong environmental filtering by several unmeasured abiotic filters, or stronger than expected dispersal limitations in soil fungal communities. Our results show how difficult it can be to predict fungal community assembly even with high replication and efforts to include several biologically relevant explanatory variables.

Biotic interactions are the dominant drivers of phylogenetic and functional structure in bird communities along a tropical elevational gradient

AbstractUnderstanding how biotic and abiotic interactions influence community assembly and composition is a fundamental goal in community ecology. Addressing this issue is particularly tractable along elevational gradients in tropical mountains that feature substantial abiotic gradients and rates of species turnover. We examined elevational patterns of avian community structure on 2 mountains in Malaysian Borneo to assess changes in the relative strength of biotic interactions and abiotic constraints. In particular, we used metrics based on (1) phylogenetic relatedness and (2) functional traits associated with both resource acquisition and tolerance of abiotic challenges to identify patterns and causes of elevational differences in community structure. High elevation communities were composed of more phylogenetically and functionally similar species than would be expected by chance. Resource acquisition traits, in particular, were clustered at high elevations, suggesting low resource and habitat diversity were important drivers of those communities. Traits typically associated with tolerance of cold temperatures and low atmospheric pressure showed no elevational patterns. All traits were neutral or overdispersed at low elevations suggesting an absence of strong abiotic filters or an increased influence of interspecific competition. However, relative bill size, which is important for thermoregulation, was larger in low elevation communities, suggesting abiotic factors were also influential there. Regardless of metric, clustered and neutral communities were more frequent than overdispersed communities overall, implying that interspecific competition among close relatives may not be a pervasive driver of elevational distribution and community structure of tropical birds. Overall, our analyses reveal that a diverse set of predominantly biotic factors underlie elevational variation in community structure on tropical mountains.