Abiotic Filters Research Articles

Beta diversity of herbivorous insects is coupled to high species and phylogenetic turnover of plant communities across short spatial scales in the Cape Floristic Region

AbstractAimInsect distribution patterns can result from historical contingency (biogeography and dispersal limitation), abiotic filtering and biotic factors (ecological interactions and evolutionary associations). Here, we analyse turnover of plant and insect herbivore community composition at multiple spatial scales to tease apart these influences. While positive associations between plant and insect turnover across broad spatial scales could arise through any of these influences, strong association at very local scales is only likely if insect distributions are determined primarily by biotic factors (i.e. host specificity).LocationThe Cape Floristic Region (CFR), South Africa.MethodsTo characterize the relationship between spatial turnover in plant and insect composition in the CFR, communities of Restionaceae, a dominant family in the florally diverse CFR, and their associated herbivores were sampled using a spatially nested sampling design on three spatially separated mountain blocks with similar climates, thus controlling for broad abiotic influences. This allowed us to quantify insect and plant turnover, and their association, at multiple independent spatial scales. Redundancy analysis was used to determine the effects of plant on insect composition, controlling for geographical distance.ResultsInsect species turnover was significantly related to plant species and phylogenetic turnover at local, as well as broad, spatial scales, suggesting that insect distribution patterns are mainly structured by host specificity. Plant communities show near complete turnover at small spatial scales (i.e. communities situated 0.1–3 km apart), with insects mirroring this pattern. Further, insect turnover increased significantly with increasing geographical separation (e.g. between mountains), suggesting an additional influence of biogeographical factors on insect distributions in the CFR. Measured environmental and plant structural components had no influence on insect composition.Main conclusionsHigh insect beta diversity positively associated with plant turnover at local scales suggests insect herbivore diversity patterns in the CFR are primarily structured by plant distribution patterns.

Plant traits of propagule banks and standing vegetation reveal flooding alleviates impacts of agriculture on wetland restoration

Summary Restoration of degraded plant communities requires understanding of community assembly processes. Human land use can influence plant community assembly by altering environmental conditions and species’ dispersal patterns. Flooding, including from environmental flows, may counteract land use effects on wetland vegetation. We examined the influence of land use history and flood frequency on the functional composition of wetland plant communities along a regulated river. We applied fourth corner modelling to determine species’ trait‐based responses to flooding and land use by combining data on (i) the occupancy and abundance of species in propagule banks and standing vegetation, (ii) species traits, and (iii) environmental conditions of 22 standing vegetation and 108 soil propagule bank study sites. We used analysis of deviance to test how well each dataset characterised trait–environment interactions, and generalised linear models to identify traits related to species’ responses. The occupancy and abundance of native species in the propagule bank and standing vegetation increased with flood frequency and decreased with duration of agricultural land use. Species in standing vegetation with water‐borne propagule dispersal (hydrochory) showed similar trends. In contrast, species with higher specific leaf area were associated with longer land use duration. Identifying trait‐based differences in the propagule bank and standing vegetation can help disentangle effects of dispersal and environmental filters. The occupancy and abundance of hydrochorous species in standing vegetation were negatively related to land use duration, but hydrochorous species were positively related to land use duration based on their abundance in the propagule bank. This suggests that land use does not limit plant dispersal, but acts as an in situ abiotic filter, limiting species present in standing vegetation. Synthesis and applications. Land use duration and flood frequency have opposite effects on plant community traits in floodplain wetlands of the Macquarie Marshes, Australia. Legacies of agriculture can impede restoration of plant communities. Environmental flows that increase flooding may alleviate these impacts, especially in areas that have been used for agriculture for over 20 years, by providing dispersal and environmental filters that favour native wetland species. More flooding will likely be required to restore floodplains with longer histories of agricultural land use compared to floodplains less impacted by agriculture.

A Multidimensional Functional Trait Approach Reveals the Imprint of Environmental Stress in Mediterranean Woody Communities

Water availability is one of the most important factors determining species distribution, plant community structure and ecosystem functioning. We explore how the functional structure of Mediterranean woody plant communities varies along a regional gradient of aridity in the Andalusian region (south Spain). We question whether communities located in more arid sites show more similarity in their functional structure when compared with communities located in wetter sites or whether, instead, there is divergence in their functional spaces. We selected five aridity zones (three sampling sites per zone) and measured 13 traits of different functional dimensions (including leaf, stem and root traits) in 74 woody plant species. We quantified functional space differences using the n-dimensional niche space approach (hypervolume). We found a larger functional space for the wetter communities compared with the more arid communities, which showed greater overlap of the trait space occupation. Our results indicate that aridity acts as a key abiotic filter affecting various metrics of the community trait structure, in accordance with the plant economics spectrum. We have also documented consistent variation in the functional space, supporting lower functional diversity under more harsh climatic conditions. The trend of functional space variation along the aridity gradient was different when considering traits from only one plant organ. Thus, the filtering process driving the functional structure of the communities studied here largely depends on the trait axis considered; for example, the root dimension showed considerable variation in wet environments, whereas the leaf dimension exhibited a larger functional space in the drier habitats.

Contrasting processes drive alpha and beta taxonomic, functional and phylogenetic diversity of orthopteran communities in grasslands

Taxonomic, functional and phylogenetic diversities can respond differently to biotic and abiotic filters. However, biodiversity management tends to focus on a single index, generally taxonomic diversity, assuming a strong positive correlation among biodiversity components across scales. This can result in a mismanagement of functional and phylogenetic diversities with negative consequences for ecosystem functioning and long-term maintenance of services. Understanding the relationships among biodiversity components, how they change across scales and which their main drivers are can lead to more sustainable management of biodiversity and its associated ecosystem services and functions.We used an integrative approach of biodiversity where we investigated alpha and beta taxonomic (TD), functional (FD) and phylogenetic (PD) diversity of orthopteran communities as well as species and functional traits composition and their associated drivers at the local and landscape scales in permanent mesic grasslands of the French Jura Mountains. We assessed whether orthopteran TD, FD and PD were positively correlated. We also determined the drivers of TD, FD and PD and their changes across scales and among indices using data related to soil, agricultural practices, elevation, and biotic interactions with plants.Our results showed that (i) elevation was a strong driver of orthopteran community trait composition, (ii) orthopteran alpha TD, FD and PD were correlated among themselves and increased with plant species richness, and (iii) local beta diversity was not correlated with alpha diversity. Beta diversity had different drivers at local and landscape scale: it was influenced by soil chemistry and texture at the local scale and increased with the difference in elevation among plots at the landscape scale.This study evidences distinct processes driving alpha and beta diversity of orthopteran communities at both the local and landscape scales. It supports the hypothesis that less intensive agricultural practices enhance orthopteran diversity and highlights the importance to consider beta diversity at both local and landscape scale when designing and assessing the management regimes of grassland ecosystems. Prioritizing the importance of the different biodiversity components and spatial scales constitutes an important challenge for sustainable grassland management.

Trait‐mediated community assembly: distinguishing the signatures of biotic and abiotic filters

Conflicting hypotheses predict how traits mediate species establishment and community assembly. Traits of newly establishing individuals are predicted to converge, or be more similar to the resident, preexisting community, when the biotic or abiotic environment favors a single best phenotype, but are predicted to diverge when trait differences reduce competitive interactions. We tested these competing hypotheses using transplant seedlings in an old‐field environment, and assessed the contribution of inter‐ and intra‐specific transplant trait variation to community‐level patterns. Using a soil moisture gradient and resident plant removals, we determined when traits of newly‐establishing plants converge or diverge from the resident community by calculating community weighted mean traits for transplant and resident communities. We saw evidence of environmentally‐ and competitively‐driven trait shifts that resulted in both trait convergence and divergence from the resident community, whose traits reflect the combined effects of both drivers. Leaf dry matter content (LDMC) of transplants diverged in the presence of competition, whereas plant height and stem‐specific density (SSD) showed the opposite pattern, converging with the resident community in their presence. Specific leaf area (SLA) shifted with competition but did not reflect resident community SLA. All transplant traits were influenced by soil moisture, often in an interaction with competition, indicating that the strength of convergence or divergence is contingent on the abiotic environment. Intraspecific differences in transplant traits among treatments were evident in three of four traits; intraspecific height and SLA trends mirrored transplant community‐level trends, whereas intraspecific shifts in SSD were distinct from community‐level trends. Our study shows competition between plant species may cause traits of newly establishing plants to converge with the resident community, as frequently as it selects for trait divergence. These opposing effects of competition suggest that it plays a pervasive role in both intraspecific and species‐level trait differences among communities.

Time lags in functional response to management regimes - evidence from a 26-year field experiment in wet meadows

Questions (i) How does functional composition and diversity respond to different timings and frequencies of mowing or fallow treatment? (ii) To which species assembly and related ecosystem processes do these developments correspond? (iii) What is the time course of these developments, and do they reach a stable state? Location North-western Germany Methods In 1987, a field experiment in nine wet meadow sites formerly exploited as fertilized meadows or pastures was established with four management treatments: (i) mowing twice a year in June/July and in September, (ii) mowing once a year in June/July, (iii) mowing once a year in September, and (iv) leaving fallow except shrub removal. Vegetation was recorded at least every second year and the functional composition (community weighted means) and diversity (Rao's quadratic entropy) were analysed in the course of the experiment. We selected eight plant functional traits (Canopy height, SLA, LDMC, Seed mass, Shoot cyclicity, Clonal Index, Onset of flowering, Leaf distribution) capturing the main plant life strategies. Results Temporal changes, fluctuations and divergences between treatments could be observed in both functional composition and diversity. In particular, the vegetation of the fallow treatment showed strong competition for light and a higher investment into internal nutrient cycling. Over time, all treatments respond towards more stressful conditions due to generally less intensive management compared with the former management and respective nutrient depletion, leading to a more nutrient retentive and patch holding strategy and little investment into competitive seedlings. High competition and loose abiotic filters in the fallow treatment led to a niche separation in foliar traits. Mowing on the other hand enforced a divergence of reproduction mechanisms. Conclusion We detected long-term fluctuations and ongoing changes in functional composition and diversity even after 26 years. Especially early succession was characterized by a transient loss of functional diversity, caused by strong time lags in immigration and extinction of species. Our findings stress the importance of long-term experimental studies to avoid precarious misinterpretations. This article is protected by copyright. All rights reserved.

Recovery of Forest and Phylogenetic Structure in Abandoned Cocoa Agroforestry in the Atlantic Forest of Brazil

Cocoa agroforests like the cabrucas of Brazil's Atlantic forest are among the agro-ecosystems with greatest potential for biodiversity conservation. Despite a global trend for their intensification, cocoa agroforests are also being abandoned for socioeconomic reasons especially on marginal sites, because they are incorporated in public or private protected areas, or are part of mandatory set-asides under Brazilian environmental legislation. However, little is known about phylogenetic structure, the processes of forest regeneration after abandonment and the conservation value of former cabruca sites. Here we compare the vegetation structure and composition of a former cabruca 30-40 years after abandonment with a managed cabruca and mature forest in the Atlantic forest region of Espirito Santo, Brazil. The forest in the abandoned cabruca had recovered a substantial part of its original structure. Abandoned cabruca have a higher density (mean ± CI95 %: 525.0 ± 40.3 stems per ha), basal area (34.0 ± 6.5 m2 per ha) and species richness (148 ± 11.5 species) than managed cabruca (96.0 ± 17.7; 24.15 ± 3.9 and 114.5 ± 16.0, respectively) but no significant differences to mature forest in density (581.0 ± 42.2), basal area (29.9.0 ± 3.3) and species richness (162.6 ± 15.5 species). Thinning (understory removal) changes phylogenetic structure from evenness in mature forest to clustering in managed cabruca, but after 30-40 years abandoned cabruca had a random phylogenetic structure, probably due to a balance between biotic and abiotic filters at this age. We conclude that abandoned cocoa agroforests present highly favorable conditions for the regeneration of Atlantic forest and could contribute to the formation of an interconnected network of forest habitat in this biodiversity hotspot.

What processes shape early-successional vegetation in fly ash and mine tailings?

Local abiotic filters and regional processes (i.e., regional pools of species that are dispersal-limited to varying degrees) interactively structure the development of vegetation in human-disturbed habitats, yet their relative contributions to this process are still to be determined. In this study conducted in the Czech Republic, we related plant species diversity and composition of 10 fly ash and 7 mine tailings to local edaphic conditions, and to vegetation from a 100-m perimeter (regional species pool). We found that the species richness and composition on the tailings were significantly associated with diversity and composition of vegetation in the surroundings, but not with the local edaphic conditions. Species from adjacent vegetation that were more abundant and those producing lighter seeds were more likely to establish on the tailings. The same characteristics also enhanced species abundance on the tailings, but the two predictors explained less than 10% in variation of establishment success or of species abundance. A non-significant relationship between species number and tailings size, but a significant association between diversity and time of vegetation development indicate that the study systems are still far from equilibrium. Our study provides evidence for a strong effect of regional processes, with a limited influence of measured edaphic conditions on plant communities developing de novo. It also highlights the necessity to consider the broader spatial context in the analysis of vegetation succession in human-disturbed habitats.

Evolutionary conservatism explains increasing relatedness of plant communities along a flooding gradient.

Abiotic filters have been found either to increase or reduce evolutionary relatedness in plant communities, making it difficult to generalize responses of this major feature of biodiversity to future environmental change. Here, we hypothesized that the responses of phylogenetic structure to environmental change ultimately depend on how species have evolved traits for tolerating the resulting abiotic changes. Working within ephemeral wetlands, we tested whether species were increasingly related as flooding duration intensified. We also identified the mechanisms underlying increased relatedness by measuring root aerenchyma volume (RAV), a trait which promotes waterlogging tolerance. We found that species-specific responses to flooding explained most of the variation in occurrence for 63 vascular plant species across 5170 plots. For a subset of 22 species, we attributed these responses to variation in RAV. Large RAV specifically increased occurrence when flooding lasted for longer time periods, because large RAV reduced above-ground biomass loss. As large RAV was evolutionarily conserved within obligate wetland species, communities were more phylogenetically related as flooding increased. Our study shows how reconstructing the evolutionary history of traits that influence the responses of species to environmental change can help to predict future patterns in phylogenetic structure.

Shifts and linkages of functional diversity between above‐ and below‐ground compartments along a flooding gradient

Summary Trait‐based approaches have the potential to reveal general and predictive relationships between organisms and ecosystem functioning. However, the mechanisms underlying the functional structure of communities are still unclear. Within terrestrial ecosystems, several studies have shown that many ecological processes are controlled by the interacting above‐ and below‐ground compartments. However, few studies have used traits to reveal the functional relationships between plants and soil fauna. Mostly, research combining plants and soil fauna solely used the traits of one assemblage in predictive studies. Above‐ground (plants) and below‐ground (Collembola) compartments were sampled over a flooding gradient in northern France along the Seine River. First, we measured the effect of flooding on functional and taxonomic assembly within both communities. We then considered the linkages between plant and Collembolan species richness, community traits and assessed whether traits of both compartments converged at high flooding intensity (abiotic filtering) and diverged when this constraint is released (biotic filtering). Species richness of both taxa followed the same bell‐shaped pattern along the gradient, while a similar significant pattern of functional richness was only observed for plants. Further analyses revealed a progressive shift from trait convergence to divergence for plants, but not for Collembola, as constraints intensity decreased. Instead, our results highlighted that Collembola traits were mainly linked to the variations in plant traits. This leads, within Collembola assemblages, to convergence of a subset of perception and habitat‐related traits for which the relationship with plant traits was assessed. Synthesis. Using a trait‐based approach, our study highlighted that functional relationships occur between above‐ and below‐ground compartments. We underlined that functional composition of plant communities plays a key role in structuring Collembola assemblages in addition to the role of abiotic variables. Our study clearly shows that functional diversity provides a new approach to link the above‐ and below‐ground compartments and might, therefore, be further considered when studying ecological processes at the interface between both compartments.

Herbivory and nutrient limitation protect warming tundra from lowland species' invasion and diversity loss.

Herbivory and nutrient limitation can increase the resistance of temperature-limited systems to invasions under climate warming. We imported seeds of lowland species to tundra under factorial treatments of warming, fertilization, herbivore exclusion and biomass removal. We show that warming alone had little impact on lowland species, while exclusion of native herbivores and relaxation of nutrient limitation greatly benefitted them. In contrast, warming alone benefitted resident tundra species and increased species richness; however, these were canceled by negative effects of herbivore exclusion and fertilization. Dominance of lowland species was associated with low cover of tundra species and resulted in decreased species richness. Our results highlight the critical role of biotic and abiotic filters unrelated to temperature in protecting tundra under warmer climate. While scarcity of soil nutrients and native herbivores act as important agents of resistance to invasions by lowland species, they concurrently promote overall species coexistence. However, when these biotic and abiotic resistances are relaxed, invasion of lowland species can lead to decreased abundance of resident tundra species and diminished diversity.

Predicting plant trait similarity along environmental gradients

Plant traits affect the success or failure of plants to establish, grow, and reproduce. Although we have an increased understanding of certain individual plant traits and their relative effects on performance and fitness, it is a challenge to predict relative similarity of traits between neighbouring plants. Assembly rules suggest that abiotic filters will restrict the range of viable strategies, thus creating a community of plants that share a similar suite of traits. In contrast, limiting similarity predicts that segregation of species’ resource use will lead to character displacement. What is the relative strength of these two processes and do they differ depending on site condition? We know that trait similarity of plants can vary with site productivity and disturbance. In this study, we investigate the interaction of these two ecological factors and how they affect plant trait similarity. We find support for the hypothesis that trait convergence occurs at low productivity/high disturbance and high productivity/low disturbance, and trait dispersion is most likely at intermediate levels of disturbance and productivity. The relationships among evolution, plant traits, and ecology are multivariate, hierarchical, and complex making plant traits at the ecosystem level an exciting and challenging agenda for the future.

Regeneration: an overlooked aspect of trait‐based plant community assembly models

Summary Despite the disproportionate influence that propagule production, dispersal, seed‐to‐seedling recruitment and vegetative reproduction can have on plant population and community dynamics, progress has been slow in the directed collection of regeneration traits to inform community assembly outcomes. While seed mass is globally available and linked to growth and reproductive output, there are limits to its explanatory ability. In this essay, we call for expanded efforts to integrate a more diverse set of regeneration traits into community assembly models. First, we extend an existing community assembly framework to conceptualize regeneration as a series of transitional processes whose outcomes are influenced by abiotic filters, biotic interactions and species traits. We then briefly review the literature, highlighting filters and traits of demonstrated or theorized importance for each transition. Finally, we place regeneration in the context of existing and emerging modelling approaches in trait‐based community assembly, summarizing key areas of progress needed to integrate regeneration traits into these efforts. Synthesis. By incorporating influential regeneration traits into empirical studies and global data bases, we can begin to disentangle regenerative mechanisms underlying community assembly outcomes and enhance rapidly developing models of species’ abundances, distributions and responses to environmental change.

Fertilization triggers 11 yr of changes in community assembly in Mediterranean grassland

AbstractQuestionFertilization, i.e. nutrient addition, and changes in grazing intensity are important factors associated with global change that threaten grasslands worldwide. How does the plant community assembly in Mediterranean grasslands respond after 11 yr to a single fertilization event?LocationSpecies‐rich Mediterranean grassland, Navarra, northern Spain.MethodsIn 2003, 11 permanent plots were established in a Mediterranean grassland: six plots were fertilized and five were used as controls. Fertilization consisted in the addition of sewage sludge on the soil surface. Grazing was excluded during the course of the experiment. Changes in vegetation abundance were monitored from 2004 to 2014. In 2012, key plant functional traits (height, leaf area, SLA, LDMC) of the most frequent species were collected. We measured taxonomic and functional species composition and diversity. Niche overlap compared to null models was used to assess the mechanisms influencing community assembly.ResultsSpecies composition changed markedly in the fertilized plots. These changes were accompanied by a reduction in taxonomic diversity. One yr after starting the experiment there were no differences in functional composition (i.e. CWM trait values) between fertilized and control plots (excluding SLA), but 11 yr later fertilized plots were composed of taller plants with larger SLA and lower LDMC. We found a major reduction in niche overlap in plant height and SLA after fertilizing associated with a replacement in several species that could be indicative of competitive exclusion (principle of limiting similarity). Conversely, we found an increase in niche overlap in leaf area indicating that competition increases similarity among species (weaker competitor exclusion or abiotic filtering). At the end of the experiment, we found large differences in SLA and LDMC between fertilized and control plots.ConclusionsA single fertilization event that occurred 11 yr ago triggered a wave of changes in grassland community assembly that are still on‐going. Fertilization enhanced the establishment of taller species with larger leaf areas, which displaced, by competitive exclusion, the species that had previously been present. Community assembly patterns in Mediterranean grassland are highly sensitive to abrupt changes in resource availability.

Which abiotic filters shape earthworm distribution patterns at the catchment scale?

SummaryEarthworms affect various soil ecosystem processes in their role as ecosystem engineers. The spatial distribution of earthworms determines the spatial distribution of their functional effects. In particular, earthworm‐induced macropore networks may act as preferential flow pathways. In this research we aimed to determine earthworm distributions at the catchment scale with species distribution models (SDMs). We used land‐use types, temporally invariant topography‐related variables and plot‐scale soil characteristics such as pH and organic matter content. We used data from spring 2013 to estimate probability distributions of the occurrence of ten earthworm species. To assess the robustness of these models, we tested temporal transferability by evaluating the accuracy of predictions from the models derived for the spring data with the predictions from data of two other field surveys in autumn 2012 and 2013. In addition, we compared the performance of SDMs based (i) on temporally varying plot‐scale predictor variables with (ii) those based on temporally invariant catchment‐scale predictors. Models based on catchment‐scale predictors, especially land use and slope, experience a small loss of predictive performance only compared with plot‐scale SDMs but have greater temporal transferability. Earthworm distribution maps derived from this kind of SDM are a prerequisite for understanding the spatial distribution patterns of functional effects related to earthworms.Highlights Do plot‐scale variables explain earthworm distributions better than landscape‐scale variables? We modelled ten earthworm species and give comprehensive model evaluations. Landscape‐scale variables are almost as useful as proximate plot‐scale variables. Landscape‐scale variables allow temporally robust mapping, but are limited to the study area.

The enhancement of invasion ability of an annual grass by its fungal endophyte depends on recipient community structure

Most terrestrial plants establish symbiotic associations with microorganisms that enable them to overcome abiotic or biotic filters in ecosystems. Here we investigated how aerial mutualisms involving invasive species may affect the recipient community’s structure. We hypothesized that the endophyte Epichloe occultans enhances the ability of Lolium multiflorum to establish and colonize, but that success would depend on the structure and invasion resistance of the recipient grassland community. Seeds of L. multiflorum with high (E+) and low (E−) endophyte incidence were sown in plots located in grasslands with or without recent grazing history. Relative cover of L. multiflorum and floristic groups was determined during the growing season. Whereas we did not detect any endophyte effect in sites with grazing history, L. multiflorum cover was 63 % in E+ and 27 % in E− plots in sites without grazing history. As cover of L. multiflorum increased in these sites, the cover of warm- and cool-season grasses decreased in spring, with that of warm-season grasses continuing to decrease in summer. These decreases corresponded to 1.9, 3.7 and 1.6 %, for every % increase of L. multiflorum cover. Path analysis and posterior modelling predicted a greater impact of the endophyte on L. multiflorum cover than of seed addition when resident L. multiflorum cover was ≤20 %. This effect decreased asymptotically as L. multiflorum cover increased beyond 20 %. Our results suggest that the endophyte may boost the invasion ability of L. multiflorum particularly in natural grassland without grazing history with potential longer-term consequences for community structure and dynamics.

The application of a filter‐based assembly model to develop best practices for Pannonian sand grassland restoration

Summary The application of a filter‐based assembly model is a promising concept to support ecological restoration. The filters illustrate dispersal, abiotic and biotic constraints that narrow down the species pool and determine the realized species composition. The aim of restoration interventions is the manipulation of filters to achieve a restoration target. We tested the applicability of a filter‐based assembly model in the restoration of endemic Pannonian sandy grassland on old‐fields. We report the results of a six‐year experiment to identify key filters and find possible interactions. Treatments included the following: (i) seeding (dispersal filter), (ii) carbon amendment to lower nitrogen availability (abiotic filter) and (iii) mowing (biotic filter). Treatments were carried out in 1 m2 plots following the same Latin square design in three old‐fields. Seeding was the most important treatment increasing species richness, vascular cover and enhancing target species composition. Mowing played a secondary role, acting primarily in interaction with the other treatments. Carbon amendment significantly reduced soil mineral nitrogen, but played a subordinate role in determining vegetation composition. Significant interactions were found between the biotic and dispersal and the biotic and abiotic filters determining primarily the structural characteristics of the vegetation in terms of vascular cover, moss cover, litter and bare ground. Regarding species composition, synergistic links between the dispersal and biotic filters for seeded species and long‐lived forbs, and antagonistic interaction between the dispersal and abiotic filters for seeded species were found. Synthesis and applications. Based on the impact and interactions of filters uncovered in this experiment, we propose a scheme for Pannonian grassland restoration, which can be validated and also used for other oligotrophic systems. In the proposed conceptual model, the dispersal filter plays a key role in determining the outcome of restoration measures followed by the biotic filter if manipulated by mowing, while the abiotic filter altered by nitrogen immobilization proved to have a weak effect. Based on our results, targeting several filters in parallel would improve restoration outcome. We propose that filter interactions should form an integral part of filter‐based assembly models and should be taken into account in restoration decisions.

The relative influences of fine and landscape scale factors on the structure of lentic plant assemblages

ABSTRACTJune-Wells M, Gallagher F, Hart B, Malik V, Bugbee G. 2016. The relative influences of fine and landscape scale factors on the structure of lentic plant assemblages. Lake Reserv Manage. 32:116–131.The process of plant community assembly has long been a topic of debate among ecologists. Aquatic plant assemblages and their structure may be the result of a series of abiotic and biotic filters that include transport (i.e., physical movement of species), water chemistry, sediment chemistry, basin structure, and competitive interactions. The influences of transport and water chemistry have been well investigated, but many questions persist about the interrelationships among water and sediment variables, including their combined influences on the structure of the aquatic plant assemblage. To understand how these abiotic conditions interact, we sampled 750 points in 30 lakes. Using these data, a split canonical correspondence design was used to evaluate the relative influences of regional and fine-scale conditions in structuring the plant assemblage. Additionally, multiple logistic regressions were employed to determine the individual species’ abiotic preferences. The results suggest that the plant assemblage structure is principally determined by the lake-sediment characteristics. Sediment variables explained 28% of the total species-data variance and water chemistry accounted for 9% (total variance explained = 46%; 9% due to intercorrelation of water/sediment characteristics). There were also strong species–environmental relationships; nonnative species showed distinct correlations with sediment pH and lake water conductivity, which may be useful in lake management initiatives such as risk assessment and nonnative species monitoring. Finally, and as expected, the Shannon diversity index was strongly related to depth and light.

Summer Freezing Resistance: A Critical Filter for Plant Community Assemblies in Mediterranean High Mountains.

Assessing freezing community response and whether freezing resistance is related to other functional traits is essential for understanding alpine community assemblages, particularly in Mediterranean environments where plants are exposed to freezing temperatures and summer droughts. Thus, we characterized the leaf freezing resistance of 42 plant species in 38 plots at Sierra de Guadarrama (Spain) by measuring their ice nucleation temperature, freezing point (FP), and low-temperature damage (LT50), as well as determining their freezing resistance mechanisms (i.e., tolerance or avoidance). The community response to freezing was estimated for each plot as community weighted means (CWMs) and functional diversity (FD), and we assessed their relative importance with altitude. We established the relationships between freezing resistance, growth forms, and four key plant functional traits (i.e., plant height, specific leaf area, leaf dry matter content (LDMC), and seed mass). There was a wide range of freezing resistance responses and more than in other alpine habitats. At the community level, the CWMs of FP and LT50 responded negatively to altitude, whereas the FD of both traits increased with altitude. The proportion of freezing-tolerant species also increased with altitude. The ranges of FP and LT50 varied among growth forms, and only leaf dry matter content was negatively correlated with freezing-resistance traits. Summer freezing events represent important abiotic filters for assemblies of Mediterranean high mountain communities, as suggested by the CWMs. However, a concomitant summer drought constraint may also explain the high freezing resistance of species that thrive in these areas and the lower FD of freezing resistance traits at lower altitudes. Leaves with high dry matter contents may maintain turgor at lower water potential and enhance drought tolerance in parallel to freezing resistance. This adaptation to drought seems to be a general prerequisite for plants found in xeric mountains.

Re‐growing a tropical dry forest: functional plant trait composition and community assembly during succession

SummaryA longstanding goal of ecology and conservation biology is to understand the environmental and biological controls of forest succession. However, the patterns and mechanisms that guide successional trajectories, especially within tropical forests, remain unclear.We collected leaf functional trait and abiotic data across a 110‐year chronosequence within a tropical dry forest in Costa Rica. Focusing on six key leaf functional traits related to resource acquisition and competition, along with measures of forest stand structure, we propose a mechanistic framework to link species composition, community trait distributions and forest structure. We quantified the community‐weighted trait distributions for specific leaf area, leaf dry matter concentration, leaf phosphorus concentration, leaf carbon to nitrogen ratio and leaf stable isotopic carbon and nitrogen. We assessed several prominent hypotheses for how these functional measures shift in response to changing environmental variables (soil water content, bulk density andpH) across the chronosequence.Increasingly, older forests differed significantly from younger forests in species composition, above‐ground biomass and shifted trait distributions. Early stages of succession were uniformly characterized by lower values of community‐weighted mean specific leaf area, leaf stable nitrogen isotope and leaf phosphorus concentration. Leaf dry matter concentration and leaf carbon to nitrogen ratio were lower during earlier stages of succession, and each trait reached an optimum during intermediate stages of succession. The leaf carbon isotope ratio was the only trait to decrease linearly with increasing stand age indicating reduced water use efficiency in older forests. However, in contrast with expectations, community‐weighted trait variances did not generally change through succession, and when compared to null expectations were lower than expected.The observed directional shift in community‐weighted mean trait values is consistent with the ‘productivity filtering’ hypothesis where a directional shift in water and light availability shifts physiological strategies from ‘slow’ to ‘fast’. In contrast with expectations arising from niche based ecology, none of the community trait distributions were over‐dispersed. Instead, patterns of trait dispersion are consistent with the abiotic filtering and/or competitive hierarchy hypotheses.