Trait Distribution Patterns Research Articles

Multi-environment phenotyping of linseed (Linum usitatissimum L.) germplasm for morphological and seed quality traits to assemble a core collection

Linseed or flax (Linum usitatissimum L.) is one of the most ancient industrial crops domesticated for oilseed and natural fiber. India is one of the two proposed centers of origin of linseed and harbours high genetic diversity. The Indian Council of Agricultural Research-National Bureau of Plant Genetic Resources (ICAR-NBPGR) conserves one of the largest base collections of Linum with around 2800 germplasm accessions at National Genebank, of which 2576 are the unique accessions of cultivated linseed and were characterized for 10 qualitative and 26 quantitative traits and the resultant multi-environment data along with passport information was used to develop a multipurpose core collection. Initially, five different core sets were derived using the core collection assembler tool ‘Core Hunter 3’ by optimization of average genetic distances between each accession and nearest entry in the core (A-NE) and the average distance between each entry and nearest neighbouring entry (E-NE). These five core sets were subjected to different quality evaluation indices to select one set that best represents the maximum genetic diversity and representativeness present in the entire tested collection. The Core collection-4, developed with weightage of E-NE and A-NE in the ratio of 0.7–0.3 was chosen as the best core collection as it exhibited desirable genetic distance, variance difference percentage (VD; 85%), coincidence rate of range (CR; 91.66%) and variable rate of coefficient of variance (VR; 117.76%), which were more than threshold value of VD (80%), CR (80%), and VR (100%) required for an optimally good core collection. Several summary statistics, Kullback-Leibler distance and Shannon Weaver diversity index indicated similar trait distribution patterns among the chosen core set and the entire collection. Correlogram and principal component analysis revealed that trait associations and their magnitude were conserved for most of the traits in the chosen best core collection. The development of this multipurpose core collection is expected to cater to the needs of linseed breeders and germplasm curators to pave the way for expedited access to genetically diverse and agronomically important material for trait introgression.

Phenotypic Characterization, Genetic Diversity Assessment in 6,778 Accessions of Barley (Hordeum vulgare L. ssp. vulgare) Germplasm Conserved in National Genebank of India and Development of a Core Set.

The entire collection of cultivated barley germplasm accessions conserved in the Indian National Genebank (INGB) was characterized for nine qualitative and 8 quantitative traits to assess the nature and magnitude of prevailing genetic variability and to develop a core set. A wide range of variability was observed for days to spike emergence (51–139 days), days to physiological maturity (100–152 days), plant height (45.96–171.32 cm), spike length (3.44–13.73 cm), grain number/spike (10.48–82.35), and 100-grain weight (1.20–6.86 g). Initially, seven independent core sets were derived using 3 core construction tools– MSTRAT, PowerCore, and Core Hunter 3 by employing the maximization method, heuristic sampling, and optimisation of average genetic distances, respectively. The core set-3 generated by Core Hunter 3 by simultaneous optimisation of diversity and representativeness, captured maximum genetic diversity of the whole collection as evident from the desirable genetic distance, variance difference percentage (VD; 87.5%), coincidence rate of range (CR; 94.27%) and variable rate of coefficient of variance (VR; 113.8%), which were more than threshold value of VD (80%), CR (80%), and VR (100%) required for good core collection. The coefficient of variation and Shannon–Weaver diversity indices were increased in the core set as compared with the whole collection. The low value of Kullback-Leibler distance (0.024–0.071) for all traits and quantile-quantile plots revealed a negligible difference between trait distribution patterns among the core set and entire assembly. Correlogram revealed that trait associations and their magnitude were conserved for most of the traits after sampling of the core set. The extraction of the INGB barley core set and identification of promising accessions for agronomically important traits in different genetic backgrounds will pave the way for expedited access to genetically diverse and agronomically important germplasm for barley breeding.

Exploring Macroinvertebrates Ecological Preferences and Trait-Based Indicators of Suspended Fine Sediment Effects in the Tsitsa River and Its Tributaries, Eastern Cape, South Africa

The taxonomy-based response pattern of macroinvertebrates to sediment stress is well established, with tolerant taxa increasing in impacted conditions, while sensitive taxa decrease along a deteriorating water quality gradient. However, the distribution patterns of traits in response to environmental stress gradient, including suspended sediments, remain unclear, particularly in Africa, where trait-based studies are under-explored. We examined the distribution patterns of macroinvertebrate traits along a suspended sediment stress gradient and identified tolerant and sensitive traits for suspended sediment stress. We sampled macroinvertebrates and environmental variables seasonally in winter, spring, summer and autumn of 2016 to 2018 in eight selected sites in the Tsitsa River and its tributaries. We selected 12 traits and ecological preferences, resolved them into 47 trait attributes, and analysed them using the RLQ and fourth-corner analyses. Our results revealed that macroinvertebrate traits and ecological preferences were differentially influenced by fine suspended sediments in the Tsitsa River and its tributaries. Traits such as a preference for CPOM, collector-filtering, and a high sensitivity to oxygen depletion, were deemed sensitive to suspended sediments stress, exhibiting positive associations with the control sites, and negatively associated with any of the environmental parameters (sediment grain sizes, turbidity, TSS and EC). Tolerant indicator traits included a high tolerance of oxygen depletion, skating and a preference for FPOM. The fourth-corner analysis results indicated that suspended fine sediment grain sizes, (including coarse sand, fine silt and clay) were the most important variables influencing macroinvertebrate trait distribution patterns during the dry season, while gravel, mud and medium sand were more important during the wet season. Overall, our study provided critical insights towards trait-based responses of macroinvertebrates communities to suspended sediment stress, key information that could stimulate the development of macroinvertebrate trait-based biomonitoring tools for the assessment of suspended sediment stress in the Afrotropical region.

Integrating floral trait and flowering time distribution patterns help reveal a more dynamic nature of co‐flowering community assembly processes

Abstract Species' floral traits and flowering times are known to be the major drivers of pollinator‐mediated plant–plant interactions in diverse co‐flowering communities. However, their simultaneous role in mediating plant community assembly and plant–pollinator interactions is still poorly understood. Since not all species flower at the same time, inference of facilitative and competitive interactions based on floral trait distribution patterns should account for fine phenological structure (intensity of flowering overlap) within co‐flowering communities. Such an approach may also help reveal the simultaneous action of competitive and facilitative interactions in structuring co‐flowering communities. Here we used modularity within a co‐flowering network context, as a novel approach to detect convergent and/or over‐dispersed patterns in floral trait distribution and pollinator sharing. Specifically, we evaluate differences in floral trait and pollinator distribution patterns within (high temporal flowering overlap) and among co‐flowering modules (low temporal flowering overlap). We further evaluate the consistency of observed floral trait and pollinator sharing distribution patterns across space (three geographical regions) and time (dry and rainy seasons). We found that floral trait similarity was significantly higher in plant species within co‐flowering modules than in species among them. This suggests pollinator facilitation may lead to floral trait convergence, but only within co‐flowering modules. However, our results also revealed seasonal and spatial shifts in the underlying interactions (facilitation or competition) driving co‐flowering assembly, suggesting that the prevalent dominant interactions are not static. Synthesis. Overall, we provide strong evidence showing that the use of flowering time and floral trait distribution alone may be insufficient to fully uncover the role of pollinator‐mediated interactions in community assembly. Integrating this information along with patterns of pollinator sharing will greatly help reveal the simultaneous action of facilitative and competitive pollinator‐mediated interactions in co‐flowering communities. The spatial and temporal variation in flowering and trait distribution patterns observed further emphasize the importance of adopting a more dynamic view of community assembly processes.

Biogeography of intraspecific trait variability in matgrass (Nardus stricta): High phenotypic variation at the local scale exceeds large scale variability patterns

Intraspecific trait variability (ITV) is an important component of functional ecology studies. While functional biogeography requires us to understand broad-scale patterns of trait distribution, ITV remains inadequately studied. Due to isolation of ranges, habitat fragmentation and sharp topoclimatic gradients over short distances, temperate mountains offer opportunities to study the ITV in widespread species. In this study, we explored ITV in geographically separated populations of matgrass (Nardus stricta), a clonal dominant plant species of mountain pastures. We measured plant height and leaf traits in 55 populations distributed across six European mountain ranges (from the Pyrenees to the Carpathians) to examine the structure of ITV. We hypothesised that the leaf economics spectrum (LES) and plant size exhibit a strong convergence across a prevailing gradient of growing season length (GSL). We then partitioned the ITV into between ranges, between populations nested in ranges and between individuals nested in populations, and examined the role of climate and local variables on the spatial variation and covariation of traits. Traits showed large ITV and higher between- than within-population variability. Leaf traits displayed a high dependency on height reflecting the growing phase climate and other local factors, while range identity alone (differentiation between ranges) explained a low to moderate amount of the variability in the traits. The strength of coordination between several of the LES traits was higher under shorter GSL due to late snowmelt, suggesting higher phenotypic integration. In the context of functional biogeography of mountain ecosystems, allometric effects and growing phase climate are both key to understanding ITV. We discuss the implications of these findings as they relate to future comparative studies of ITV in seasonal environments.

Plant species richness and community assembly along gradients of elevation and soil nitrogen availability.

Environmental filters affect community assembly through the functional traits of species. However, the process of community assembly remains unclear because of the complex interactions among the many biotic and abiotic factors. This study aimed to examine the community assembly process of vascular plants along gradients of elevation (45‒2500 m a.s.l.) and soil nitrogen availability. This study examined the trait distribution patterns of four functional traits (plant height, leaf area, specific leaf area and leaf nitrogen concentration) of vascular plants (trees, herbs and ferns) in central Japan, using null model testing. The number of species decreased and increased at high elevations for tree species and herb and fern species, respectively. The numbers of both tree species and herb and fern species were positively correlated with soil nitrogen availability. Community-weighted means (CWMs) of the four traits decreased with elevation. CWMs and ranges of the three leaf traits were positively correlated with soil nitrogen availability. The community-weighted variance of plant height was higher at higher elevations, indicating that niche differentiation of vertical stratum in habitats with a low canopy was important for community assembly. This study suggests that severe climatic conditions reduce the number of tree species and the canopy height at high elevations, leading to increases in the number of herb and fern species due to increased light intensity at the forest floor. The elevational change of leaf traits also indicates the change of adaptive leaf traits. It further suggests that lower nitrogen availability decreases the number of tree, herb and fern species by excluding those species with leaf traits unsuited to lower nitrogen availability. Therefore, community structure is most likely regulated by both elevation and soil nitrogen availability.

Exploring the relationships between aquatic macrophyte functional traits and anthropogenic pressures in freshwater lakes

Modern water resource management requires biomonitoring of the structure and functioning of freshwater ecosystems, which may be better illuminated by functional trait distribution patterns and responses across human-induced pressure gradients. In this study, we applied the RLQ, the fourth-corner and their novel combination methods, in order to assess the relationship between the distribution of 30 aquatic macrophyte functional traits and 14 indicators of anthropogenic pressures across 16 freshwater lakes. Our findings showed that there is a statistically significant relationship between the distribution of specific functional traits and anthropogenic pressures. Eutrophication was the dominant pressure and the shift from a submerged-macrophyte dominated vegetation community to an emergent one was the most important functional response. Aerial reproduction and dispersal traits were found to replace water-related ones under higher nutrient concentrations. Trophic and light preferences of macrophytic species increased, while their leaf morphology was found to change from tubular/capillary leaf types with low leaf area values to entire leaf types with greater leaf area. These results provide hints on the changes in ecosystem functioning occurring as a response to human-induced drivers. Therefore, this assessment approach could provide important support to the tasks of biomonitoring, conservation and management planning in freshwater ecosystems.

The importance of nonrandom and random trait patterns in phytoplankton communities: a case study from Lake Müggelsee, Germany

A fundamental challenge in ecology is to identify the processes which explain how species come to occupy diverse communities. There is uncertainty about whether community composition arises through deterministic processes, whereby trait differences between species make them more or less adapted to certain environmental conditions. We tested the capacity for deterministic processes to explain the long-term dynamics of phytoplankton community structure in Lake Muggelsee—a shallow and eutrophic lake in Berlin, Germany using a trait-based approach. We developed a null model representing random processes alone by generating a time series of random trait distributions derived from the observed long-term data. We determined the extent to which deterministic processes lead to nonrandom patterns in phytoplankton communities by comparing the resulting null-trait distributions with the observed trait distributions in the long-term data. We found that phytoplankton communities fell along a gradient from random to nonrandom trait distributions, suggesting that deterministic processes alone do not fully describe the community structure. Nonrandom patterns were observed in communities with high species richness and during late spring as well as early winter. But neither species richness nor seasonality explained nonrandom patterns consistently for different metrics and traits given the high relevance of random trait distribution patterns. Thus, deterministic and stochastic processes may be needed to fully explain the structure of phytoplankton communities under changing environmental conditions.

Generalizing clusters of similar species as a signature of coexistence under competition.

Patterns of trait distribution among competing species can potentially reveal the processes that allow them to coexist. It has been recently proposed that competition may drive the spontaneous emergence of niches comprising clusters of similar species, in contrast with the dominant paradigm of greater-than-chance species differences. However, current clustering theory relies largely on heuristic rather than mechanistic models. Furthermore, studies of models incorporating demographic stochasticity and immigration, two key players in community assembly, did not observe clusters. Here we demonstrate clustering under partitioning of resources, partitioning of environmental gradients, and a competition-colonization tradeoff. We show that clusters are robust to demographic stochasticity, and can persist under immigration. While immigration may sustain clusters that are otherwise transient, too much dilutes the pattern. In order to detect and quantify clusters in nature, we introduce and validate metrics which have no free parameters nor require arbitrary trait binning, and weigh species by their abundances rather than relying on a presence-absence count. By generalizing beyond the circumstances where clusters have been observed, our study contributes to establishing them as an update to classical trait patterning theory.

Ecological functioning of mudflats: global analysis reveals both regional differences and widespread conservation of functioning

Mudflats—unvegetated, soft-sediment, intertidal habitats—support macrofaunal assemblages that contribute to a number of important ecosystem functions (e.g. food for fish and birds, nutrient and Ccycling). These habitats are widespread but are threatened by increasing pressure from anthropogenic activities. Greater knowledge of the consequences of biodiversity loss for the functioning of ecosystems can aid management, by identifying potential threats. Systematic searches of the Web of Science and SCOPUS identified 163 published datasets of essentially ‘pristine’ mudflat macrofaunal assemblages, comprising data on 448 taxa from 4 climatic zones and 10 biogeographic regions. Broad-scale patterns of trait distribution confirmed established patterns showing that taxa at low latitudes have smaller body sizes, shorter life spans and more taxa have exoskeletons, and that direct developmental modes are more prevalent at high latitudes. Greater occurrences of burrow dwellers in the temperate zone may support greater rates of sediment turnover, organic matter decomposition and nutrient cycling, whereas in the tropics, tube dwellers provide more biogenic habitat. Despite these trait differences, the overall similarity in trait composition relative to taxonomic composition indicated that globally, mudflats are functionally similar. The functional redundancy observed across regional and climatic boundaries suggests that ecosystem functioning and service delivery will show some resilience in the face of perturbation. However, the growing anthropogenic pressures on coastal mudflats means the risk of system collapse, beyond resilience thresholds, is high. This study illustrates how an extensive body of published literature can provide a foundation for developing a global understanding of ecological functioning in mudflats to inform management responses.

Phylogenetic patterns of rarity in a regional species pool of tropical woody plants

AbstractAimRarity, which is believed to influence extinction risk, can be defined in terms of local abundance, geographical range size and habitat breadth. Phylogenetic patterns in these attributes provide insight into the extent to which rarity and extinction risk are conserved during evolution and the potential for species‐level heritability. We evaluated phylogenetic signal (i.e., related species resembling each other more than species drawn at random) and evolutionary conservatism (similarity among related species exceeding that expected from a Brownian model of evolution) in three axes of rarity (local abundance, geographical range size and habitat breadth) among species in a regional pool of tropical woody plants.LocationThe Madidi region in Bolivia.Time period2001–2010.Major taxa studiedLignophyta clade.MethodsWe used a network of 48 1‐ha forest plots and 442 0.1‐ha forest plots to measure local abundance and habitat breadth of 1,700+ woody plant species (from 100+ plant families). We estimated geographical range size from occurrence records of individual species across the Neotropics. We characterized overall phylogenetic patterns of rarity using Blomberg'sKand applied variance partitioning among taxonomic levels, as well as disparity analysis, to describe patterns of trait distribution at different depths in the phylogeny.ResultsWe found phylogenetic signal, but not evolutionary conservatism, in the three axes of rarity. The variance in rarity among supra‐specific taxa, particularly families and genera, exceeded that calculated from random draws of species from the Madidi region. Phylogenetic signal, estimated by the proportion of variance among supra‐specific taxonomic levels, varied between 23 and 36% for local abundance and geographical range size, and between 9 and 10% for habitat breadth.Main conclusionsThe regional pool of woody plant species in Madidi exhibits phylogenetic signal in rarity that is consistent with biologically significant species‐level heritability.

Seasonal changes in the assembly mechanisms structuring tropical fish communities.

Despite growing interest in trait-based approaches to community assembly, little attention has been given to seasonal variation in trait distribution patterns. Mobile animals can rapidly mediate influences of environmental factors and species interactions through dispersal, suggesting that the relative importance of different assembly mechanisms can vary over short time scales. This study analyzes seasonal changes in functional trait distributions of tropical fishes in the Xingu River, a major tributary of the Amazon with large predictable temporal variation in hydrologic conditions and species density. Comparison of observed functional diversity revealed that species within wet-season assemblages were more functionally similar than those in dry-season assemblages. Further, species within wet-season assemblages were more similar than random expectations based on null model predictions. Higher functional richness within dry season communities is consistent with increased niche complementarity during the period when fish densities are highest and biotic interactions should be stronger; however, null model tests suggest that stochastic factors or a combination of assembly mechanisms influence dry-season assemblages. These results demonstrate that the relative influence of community assembly mechanisms can vary seasonally in response to changing abiotic conditions, and suggest that studies attempting to infer a single dominant mechanism from functional patterns may overlook important aspects of the assembly process. During the prolonged flood pulse of the wet season, expanded habitat and lower densities of aquatic organisms likely reduce the influence of competition and predation. This temporal shift in the influence of different assembly mechanisms, rather than any single mechanism, may play a large role in maintaining the structure and diversity of tropical rivers and perhaps other dynamic and biodiverse systems.

Relative importance of habitat filtering and limiting similarity on species assemblages of alpine and subalpine plant communities.

This study examined how habitat filtering and limiting similarity affect species assemblages of alpine and subalpine plant communities along a slope gradient on Mt. Norikura in central Japan. Plant traits (plant height, individual leaf area, specific leaf area (SLA), leaf linearity, leaf nitrogen and chlorophyll concentrations) and abiotic environmental factors (elevation, slope inclination, ground surface texture, soil water, soil pH, soil nutrient concentrations of NH4-N and NO3-N) were examined. The metrics of variance, range, kurtosis and the standard deviation of neighbor distance divided by the range of traits present (SDNDr) were calculated for each plant trait to measure trait distribution patterns. Limiting similarity was detected only for chlorophyll concentration. By contrast, habitat filtering was detected for individual leaf area, SLA, leaf linearity, chlorophyll concentration. Abiotic environmental factors were summarized by the principal component analysis (PCA). The first PCA axis positively correlated with elevation and soil pH, and negatively correlated with sand cover, soil water, NH4-N and NO3-N concentrations. High values of the first PCA axis represent the wind-exposed upper slope with lower soil moisture and nutrient availabilities. Plant traits changed along the first PCA axis. Leaf area, SLA and chlorophyll concentration decreased, and leaf linearity increased with the first PCA axis. This study showed that the species assemblage of alpine and subalpine plants was determined mainly by habitat filtering, indicating that abiotic environmental factors are more important for species assemblage than interspecific competition. Therefore, only species adapting to abiotic environments can distribute to these environments.

Biotic Regulation of CO2 Uptake–Climate Responses: Links to Vegetation Properties

Identifying the plant traits and patterns of trait distribution in communities that are responsible for biotic regulation of CO2 uptake–climate responses remains a priority for modeling terrestrial C dynamics. We used remotely sensed estimates of gross primary productivity (GPP) from plots planted to different combinations of perennial grassland species in order to determine links between traits and GPP–climate relationships. Climatic variables explained about 50% of the variance in temporal trends in GPP despite large variation in CO2 uptake among seasons, years, and plots of differing composition. GPP was highly correlated with contemporary changes in net radiation (Rn) and precipitation deficit (potential evapotranspiration minus precipitation) but was negatively correlated with precipitation summed over 210 days prior to flux measurements. Plots differed in GPP–Rn and GPP–water (deficit, precipitation) relationships. Accounting for differences in GPP–climate relationships explained an additional 11% of variance in GPP. Plot differences in GPP–Rn and GPP–precipitation slopes were linked to differences in community-level light-use efficiency (GEE*). Plot differences in GPP–deficit slopes were linked to differences in a species abundance-weighted index of specific leaf area (SLA). GEE* and weighted SLA represent vegetation properties that may regulate how CO2 uptake responds to climatic variation in grasslands.

A new modeling approach estimates the relative importance of different community assembly processes

The relative importance of niche‐based (e.g., competitive or stress‐based) and stochastic (e.g., random dispersal) processes in structuring ecological communities is frequently analyzed by studying trait distributions of co‐occurring species. While filtering processes, such as the exclusion of stress‐intolerant species from particular habitats, increase the trait similarity between co‐occurring species, other processes, such as resource competition, can limit the similarity of co‐occurring species. Comparing the observed trait distribution patterns in communities to null expectations from randomized communities (e.g., a draw of the same observed richness from the regional pool) therefore gives a first indication of the dominant process driving community assembly.However, such comparisons do not inform us about the relative contribution of these different processes in shaping community compositions in case of their joint operation (a likely scenario). Using an Approximate Bayesian Computation approach, we develop a new method that allows inference of the relative importance of dispersal, filtering, and limiting similarity processes for the assembly of observed communities with known species and trait composition. We applied this approach to a tree community data set, collected across 20 plots along strong rainfall and fire gradients in a South African savanna.Based on comparisons with simulations, we find that our new approach is powerful in identifying which community assembly scenario has the highest probability to generate the observed trait distribution patterns, while traditional null model comparisons perform poorly in detecting signs of limiting similarity. For the studied savanna tree communities, our analysis yields that dispersal processes are most important in shaping the functional trait distribution patterns. Furthermore, our models indicate that filtering processes were relatively most important in areas with high fire frequencies, while limiting similarity processes were relatively most important in areas with low fire frequency and high rainfall. We conclude that our new method is a promising improvement on current approaches to estimate the relative importance of community assembly processes across different species groups, ecosystems, and biomes. Future model modifications (e.g., the inclusion of individual‐based processes) could provide further steps in uncovering the underlying assembly processes behind observed community patterns.

Trait distribution patterns in savanna and forest plant assemblages and their relationship with soil features

Community ecologists seek to understand the processes acting on community assembly and the importance of species ecological differences to the co-existence of organisms. Here we investigated trait distribution patterns in two contrasting vegetation types, how the inclusion of intraspecific variability improves our ability to understand trait-based assembly, and if soil features predict the occurrence of non-random trait distribution patterns. We conducted our study at Emas National Park, Goias, Brazil. We used a null model approach to investigate trait distribution patterns and a model selection approach to quantify soil features important in structuring assemblages. In savanna, we detected trait convergence at individual and species level (evidence of environmental filters) favoring plants with resource conservation strategies. In forests, however, trait dispersion at individual level equal to a random expectation corroborated a premise of neutral theory (individuals ecological equivalence). Nevertheless, at species level, we found convergence (seed mass) and divergence (height), reflecting distinct strategies related to light capture and resource use. Therefore, including intraspecific trait variability did not improve the detection of non-random trait distribution patterns. Furthermore, the influence of soil features on trait patterns was different between savanna and forest. There was a tendency for niche differentiation toward more fertile and clayey soils, but the relative importance of soil factors in assembling communities could not be generalized for savannas and dry forests.

Robustness of trait distribution metrics for community assembly studies under the uncertainties of assembly processes

Numerous studies have revealed the existence of nonrandom trait distribution patterns as a sign of environmental filtering and/or biotic interactions in a community assembly process. A number of metrics with various algorithms have been used to detect these patterns without any clear guidelines. Although some studies have compared their statistical powers, the differences in performance among the metrics under the conditions close to actual studies are not clear. Therefore, the performances of five metrics of convergence and 16 metrics of divergence under alternative conditions were comparatively analyzed using a suite of simulated communities. We focused particularly on the robustness of the performances to conditions that are often uncertain and uncontrollable in actual studies; e.g., atypical trait distribution patterns stemming from the operation of multiple assembly mechanisms, a scaling of trait-function relationships, and a sufficiency of analyzed traits. Most tested metrics, for either convergence or divergence, had sufficient statistical power to distinguish nonrandom trait distribution patterns without uncertainty. However, the performances of the metrics were considerably influenced by both atypical trait distribution patterns and other uncertainties. Influences from these uncertainties varied among the metrics of different algorithms and their performances were often complementary. Therefore, under the uncertainties of an assembly process, the selection of appropriate metrics and the combined use of complementary metrics are critically important to reliably distinguish nonrandom patterns in a trait distribution. We provide a tentative list of recommended metrics for future studies.

Reproductive strategies of Amazonian stream fishes and their fine‐scale use of habitat are ordered along a hydrological gradient

Summary Macroecological comparisons have shown that habitat characteristics have a major influence on the evolution of life‐history strategies of fishes in large river systems. Specifically, habitat variability and predictability seem to forge the reproductive strategies of fishes into a trilateral continuum with three main types: seasonal, opportunistic and equilibrium. Despite the usefulness of such a broad categorisation, large‐scale patterns of trait distribution should ultimately be influenced by selection at smaller (i.e. individual) spatial scales. However, the scarcity of studies developed at the organismal scale leaves gaps in our understanding of how habitat characteristics affect life history and behavioural tactics of stream fishes. We examined the fine‐scale spatial distribution of fishes in pristine Amazonian headwater streams over a full seasonal cycle to test whether segregation into main channel and associated temporary pond habitats was predictably related to hydrological variation and species’ life‐history traits. Most species could not be unambiguously assigned to one of the three end points of the trilateral continuum, but seemingly occupied instead the intermediate multivariate space between the end points. However, species were clearly ordered along a gradient of relative habitat use, ranging from strict channel dwellers throughout the hydrological cycle to pond specialists, with some species occupying the ponds at high water levels. Hydrological effects on habitat use were significantly related to species’ reproductive strategies, with the strongest responses found in species with large eggs and seasonally concentrated reproduction, which were most abundant in ponds at high water levels. We suggest that trophic limitations and hydrological characteristics of Amazonian headwater forest streams may severely limit the seasonal strategy, one of the end points of the trilateral model. The species‐specific habitat segregation reported here adds to the list of mechanisms, such as miniaturisation and isolation by distance, previously postulated to contribute to high diversity of stream fish faunas in the Amazon basin.

Hydrologic Connectivity Affects Fish Assemblage Structure, Diversity, and Ecological Traits in the Unregulated Gambia River, West Africa

AbstractThe Gambia River of West Africa is a large unobstructed river, characterized by a natural flow regime and lateral connectivity across its floodplain. Construction of a major dam, however, is planned. We compared patterns of fish diversity, habitat use, assemblage structure, and the distribution of trophic position and body morphology in riverine and floodplain habitats in Niokolo Koba National Park, located downstream of the planned dam site. A total of 49 fish species were captured, revealing a lognormal distribution as expected for species‐rich assemblages. Fish species exhibited a range of habitat use patterns, from generalist to highly habitat‐specific, and appeared to migrate laterally among habitats between seasons. Species richness was homogenous among habitats in the wet season yet appeared to increase with isolation from the main river in the dry season. Fish assemblage structure was best explained by the interaction between habitat type and season, underlining the importance of the natural flow regime and lateral connectivity among floodplain habitats. The abundance of fishes having elongate bodies increased with isolation from the main channel in the wet season only. The distribution of fishes having compressed cross‐sectional morphology decreased with isolation from the main channel in the dry season only. These patterns of trait distribution support the conclusion that variation in hydrologic connectivity structures the fish assemblage. Our results suggest that altered flow regimes and loss of floodplain habitats after damming could lead to both decreased taxonomic and functional diversity of the fish assemblage.

COMMUNITY AND PHYLOGENETIC STRUCTURE OF REPRODUCTIVE TRAITS OF WOODY SPECIES IN WET TROPICAL FORESTS

We compare the distribution of reproductive traits in woody vegetation of 10 wet tropical forests in northeastern Costa Rica. Based on quantitative sampling of seedlings, saplings, and trees, we assess whether particular sexual systems, pollination syndromes, or seed-dispersal modes are associated with successional stage, prior selective logging, woody growth forms, or patterns of abundance or rarity. We further examine the phylogenetic structure of these traits in the regional woody flora, testing explicit hypotheses regarding phylogenetic clustering of reproductive traits and habitat distributions. Animal dispersal and insect pollination predominate across all forest types and size classes. In second-growth trees, relative abundance of species with explosive dispersal, hermaphroditic flowers, and insect pollination is higher, and relative abundance of species with animal dispersal and mammal pollination is lower, compared to old-growth and logged forests. Overall, dioecy and wind dispersal are more frequent than expected in canopy trees, and hermaphroditic flowers are more frequent than expected in shrubs. Reproductive traits, growth-form traits, and relative abundance patterns show significant clustering within the supertree phylogeny. Patterns of trait distribution across forest types are closely linked with patterns of floristic composition at the genus and family level. Species-level associations among reproductive traits and woody growth form can be explained by phylogenetic cor- relations. Wind dispersal and hummingbird pollination are significantly concentrated in clades with hermaphroditic flowers, whereas wind pollination is concentrated in clades with unisexual flowers. Legacies of both phylogenetic history and forest disturbance structure the distribution of reproductive traits within and among tropical wet forest communities.