Variation In Functional Composition Research Articles

Variation in functional composition of reef fishes along a tropical‐to‐temperate gradient

AbstractAimsTransformation of species and functional composition on subtropical reefs are ongoing due to poleward range shifts of some tropical species, with largely unknown consequences to ecosystem functioning. Trait‐based approaches are powerful tools to quantify such changes. Here, we evaluated changes in the trait composition of coral‐associated fish assemblages along a tropical‐to‐temperate environmental gradient of ca. 1400 km in southern Japan with abundance‐weighted trait expression to assess how trait composition changes with increasing latitude.LocationRyukyu Islands and southern Pacific coast of Japan.TaxonReef fish.MethodsWe tested for shifts in trait space and functional redundancy, based on five morphological, life history and behavioural traits: maximum length, pelagic larval duration, trophic level, substrate preference and reproductive mode. Our trait database was coded with two approaches, first, by attributing a single value to each trait per species, and second, by fuzzy coding that allows more than one value per trait and hence considers some intraspecific trait variation.ResultsWe found a reduction in specialist habitat traits (coral substrate preference, nesters and herbivores) and an increase in generalist traits (predators) with increasing latitude, along with a contraction in trait space from tropical‐to‐temperate reefs. Functional redundancy declined with increasing latitude. These trends were closely linked with latitudinal gradients in temperature, along with changes in other environmental factors such as turbidity and photosynthetically active radiation.Main ConclusionFunctional turnover and contractions are thus likely due to the marginal conditions for coral‐associated fishes at higher latitudes, favouring generalist species, whereas increased resources at lower latitudes favour high redundancy and niche partitioning. Accounting for intraspecific trait variation indicated the same trends but highlighted increased functional vulnerability across all sites. We show that trait complexity in coral‐associated fish communities decreases from tropical‐to‐temperate reefs, highlighting the reduced functional scope that comes with marginal environmental conditions.

Determinants of bryophyte assemblages in traditionally managed grasslands of the Carpathian Mts

Questions Although bryophytes play an important role in grassland ecosystems, environmental factors that drive bryophyte assemblages were rarely studied, especially in low-intensity traditional grasslands. Therefore, using fine-scale data on bryophyte assemblages in traditionally managed secondary grasslands, we studied the relative importance of several sets of environmental drivers (related to topography, soil properties, landscape, and management) of: (i) taxonomic and functional compositions; and (ii) cover and species richness of bryophyte communities. Location Central and Eastern Europe, Carpathian Mountains, 15 sites with preserved traditional management practices distributed in Romania (six sites), Ukraine (four), Slovakia (two), Austria (one), Hungary (one) and Poland (one). Methods Fine-scale data on soil, topography, and vegetation structure as well as on bryophyte assemblages (taxonomic and functional composition, cover, species richness) were collected in 10-m2 plots. We used stratified random sampling to select six 10-m2 plots of traditionally managed grasslands in each of the 15 sites (n = 90). Climatic and landscape variables were extracted from online databases and available maps. Detailed data on present and historical land use were obtained from parcel owners. To assess the effect of drivers on bryophyte taxonomic and functional composition we applied canonical correspondence analysis (CCA) and redundancy analysis (RDA), respectively; for bryophyte species richness and bryophyte cover we used GLMMs. Forward stepwise variable selection procedure was used to find best set of drivers for each of the analyses. Results Topographic (microrelief and solar radiation) and soil-related factors (cover of stones and rocks, soil depth, moisture), as well as the cover of the herb layer and bare soil were the strongest drivers of bryophyte taxonomic composition. Among the management- and landscape-related variables only mean size of grassland parcels within 1-km2 plot surroundings and grazing by horse were included in the CCA model explaining in total 25.9% of variation in species composition. Bryophyte functional composition was explained by a similar set of variables (RDA explained 27.3% of variation in functional composition) including additionally cover of gravel and burning. Solar radiation (negative effect) and management stability (positive effect) were the strongest drivers of bryophyte cover. Management stability had the strongest effect (positive) on bryophyte species richness, followed by grassland age (negative) and microrelief (positive). Conclusions Taxonomic and functional composition of bryophyte assemblages as well as bryophyte cover in traditional grasslands were determined mainly by variables related to moisture and light availability. Management-related factors seem to be at least as equally important as abiotic factors for bryophyte species richness and cover. Our results suggest that for maintaining bryophyte-rich grasslands one should also consider stability of grassland management, that is, temporal continuity and regularity of management practices applied.

Differential speciation rates, colonization time and niche conservatism affect community assembly across adjacent biogeographical regions

AbstractAimTo test the importance of evolutionary and biogeographical processes in shaping the assembly of local frog communities in two adjacent regions (hereafter, coastal and inland regions) with different historical signatures. We asked two main questions: (1) why does the coastal region harbour more frog species than the inland region? and (2) how do these processes affect the spatial variation in taxonomic, phylogenetic and functional diversities within and across these regions?Locationsoutheastern Brazil.TaxonAnurans.MethodsWe generated time‐calibrated phylogenies to estimate the relative timing of colonization, rates of speciation, extinction and dispersal between regions. We tested the phylogenetic signal in reproductive modes. These traits were also used to examine variation in functional composition across sites. We calculated metrics of phylogenetic community structure that capture the relationships near the root and tips of the tree. Finally, we tested the relationships between the spatial variation of multiple diversity dimensions and topographic complexity, Pleistocene and contemporary climate gradients for three spatial extents: (1) only coastal sites; (2) only inland sites; and (3) the two regions combined.ResultsThe structure of communities was related to the region in which they are located, with regional pool size being two times greater for the coastal than inland region. This pattern seems to reflect both a higher speciation rate and earlier colonization time in the coastal than in the inland region. Reproductive modes within frog genera were less variable than among families, indicating phylogenetic signal. This pattern influenced local community assembly within the inland region due to the absence of species with direct development, tadpoles in bromeliads or eggs and tadpoles in streams in this region.Main conclusionsMacroevolutionary dynamics, such as colonization time, differences in speciation rates and niche conservatism generate the disparity in species richness and assembly patterns of local communities between regions, but not within regions, in which local communities were more similar to each other.

Does soil bioengineering benefits aquatic biodiversity? An empirical study of the relative influence of local and regional drivers on benthic macroinvertebrate assemblages

Riverine ecosystems form a dendritic network in which landscape and catchment-scale properties influence freshwater community structure. Placed in a restoration framework, this suggests that regional drivers can overrule the benefit of measures aiming at improving local habitat quality. Disentangling the relative influence of local and regional drivers on freshwater communities is thus crucial for ecosystem management and restoration. Along riverbanks, soil bioengineering is often used to both control erosion and improve ecological conditions. Soil bioengineering techniques aim at copying naturally functioning riverbank models and can thus be viewed as riparian ecosystem restoration. Nevertheless, these techniques are mostly designed at the local scale and are implemented in a broad range of rivers. This implies large variations in regional drivers, which may greatly influence the response of freshwater communities to restoration efforts. We studied 37 riverbanks, from civil engineering to soil bioengineering, plus natural willow stands, in the foothills of the Alps and Jura Mountains, and assessed the relative influence of local (terrestrial and aquatic habitat conditions) and regional (water quality, hydrological context and land cover composition) drivers on benthic macroinvertebrate assemblages. Using multivariate GLM and structural equation modelling, we investigated variations in the taxonomic and functional composition and in the diversity of native, exotic, shredder and scraper taxa to both set of drivers. Our results showed that soil bioengineering improved local habitat conditions, with an increase in the vegetation density and in the aquatic habitat quality. These changes directly influenced functional composition but indirectly diversity patterns. Instead, we found that native and shredder species richness increased between civil engineered and soil bioengineered structures, suggesting a positive effect of vegetated riverbanks on other local abiotic factors (i.e. shade, water temperature, organic matter supply). Our results also showed that macroinvertebrates were more influenced by regional than by local drivers. Thus, the hydrological context best explained the composition of taxa feeding habits and variation in taxa diversity, with larger abundance and richness of scrapers and shredders in small headwater streams. Land cover ranked second in explaining variation in functional composition. Also, the diversity of natives, scrapers and shredders increased as the proportion of predominantly urban landscapes decreased. Finally, the abundance of scraper and native species increased with water quality, while the richness of exotic species decreased. Overall, these results highlight the hierarchical structure of local and regional drivers on freshwater communities. Along river networks, catchment-scale properties and landscape attributes are major drivers of macroinvertebrate assemblages. Soil bioengineering improves habitat quality and as such appears to be a good compromise solution to control erosion and support freshwater communities, even though this nature-based solution cannot solve anthropogenic pressures at larger scales. To improve the efficiency of restoration efforts, integrated approaches accounting for both local and regional drivers remains a priority.

Forested Riparian Buffers Change the Taxonomic and Functional Composition of Stream Invertebrate Communities in Agricultural Catchments

Riparian zones form the interface between stream and terrestrial ecosystems and play a key role through their vegetation structure in determining stream biodiversity, ecosystem functioning and regulating human impacts, such as warming, nutrient enrichment and sedimentation. We assessed how differing riparian vegetation types influence the structural and functional composition (based on species traits) of stream invertebrate communities in agricultural catchments. We characterized riparian and stream habitat conditions and sampled stream invertebrate communities in 10 independent site pairs, each comprising one “unbuffered” reach lacking woody riparian vegetation and a second downstream reach with a woody riparian buffer. Forested riparian buffers were associated with greater shading, increased gravel content in stream substrates and faster flow velocities. We detected changes in invertebrate taxonomic composition in response to buffer presence, with an increase in sensitive Ephemeroptera, Plecoptera and Trichoptera (EPT) taxa and increases in key invertebrate species traits, including species with preference for gravel substrates and aerial active dispersal as adults. Riparian vegetation independently explained most variation in taxa composition, whereas riparian and instream habitat together explained most variation in functional composition. Our results highlight how changes in stream invertebrate trait distributions may indirectly reflect differences in riparian habitat, with implications for stream health and cross-ecosystem connectivity.

Macrophyte functional composition is stable across a strong environmental gradient of a Neotropical floodplain

Ecological communities are compared by the similarity or distinctness of their species. Taking into account community composition at a determined site, one could expect a similar reasoning to explain differences in both taxonomic and functional composition due to environmental gradients. We aim to evaluate spatial variation in functional composition of aquatic macrophyte assemblages in a Neotropical floodplain. The studied floodplain is characterized by encompassing different ecoregions considering both differences in environmental features and macrophyte taxonomic composition. Therefore, we hypothesized that macrophyte functional composition would differ among ecoregions but instead found limited differences in functional composition. There was only a little evidence that some life forms are more or less observed in certain ecoregions. Thus, the considerable environmental heterogeneity found at the ecoregion scale is reflected only in taxonomic, and not in functional composition. This result can be explained by different species having high functional redundancy: different functional traits could be recorded in all ecoregions. Therefore, we suggest that the functioning of the entire ecosystem is probably insured by species functional redundancy in this Neotropical floodplain. Nonetheless, we cannot rule out the fact that trait choice could affect interpretations, and so trait selection should be better explored, particularly for aquatic macrophytes.

Seasonal variation in functional composition and diversity of cladoceran zooplankton of a lotic eutrophic habitat from India

This study explores the seasonal variation in functional composition, diversity and redundancy of Cladocera from an Indian lotic eutrophic habitat using two-year sampling data. Two seasonal clusters distinguishable by faunal and functional diversity patterns were obtained. Cluster A comprised of four functional groups while the ctenopod filter feeders were absent in cluster B. Cluster A had more number of species, higher functional divergence and lower redundancy than cluster B. Relatively, higher divergence values observed during the cluster A time period could be associated with set of functionally varied species occurring throughout the season. Decline in redundancy values seen within cluster A might be explained by the loss of littoral and benthic species in the peak of summer due to disappearance of submerged macrophytes and an increased nutrient load. Peculiar occurrence of Moina species in the most polluted months needs further investigation as a potential local pollution indicator.

Seasonal variation in the composition of ground-dwelling anuran (Amphibia) assemblages in southern Brazil

Climate seasonality may differently influence habitat quality and heterogeneity depending on habitat type. We examined whether the taxonomic, functional and phylogenetic composition of ground-dwelling anuran assemblages from grassland and forest habitats vary seasonally. We tested the hypothesis that the forest anuran assemblage varies less seasonally than the grassland assemblage. We monitored anurans using pitfall trap arrays in two areas, sampled across four seasons over a two-year period. For the functional composition, we acquired information on species morphology, reproduction, and habitat use to represent the anuran niche. For the phylogenetic composition, we used the most comprehensive anuran phylogeny. We used Principal Coordinate Analysis and Analysis of Variance to evaluate seasonal variations in assemblage composition along the study period. Our data revealed significant seasonal variation in the taxonomic and phylogenetic composition of anuran assemblages. Variation in taxonomic composition was higher in the grassland than in the forest assemblage, while variation in phylogenetic composition was higher in the spring-summer than in the autumn-winter seasons. We did not identify seasonal variation in functional composition. Seasonal variations in taxonomic and phylogenetic composition, but not in functional composition, indicate that the species with a fluctuating seasonal abundance have similar life-history traits, but belong to different lineages. Keywords: anuran traits, Brazilian highland grasslands, habitat variability, temporal beta diversity, temporal turnover.

Elevation predicts the functional composition of alpine plant communities based on vegetative traits, but not based on floral traits

The functional diversity and composition of plant traits within communities are tightly linked to important ecosystem functions and processes. Whereas vegetative traits reflecting adaptations to environmental conditions are commonly assessed in community ecology, floral traits are often neglected despite their importance for the plants’ life cycle. The consideration of floral traits covers important aspects such as sexual plant reproduction and pollinator diversity, which remain unobserved in studies focussing on vegetative traits only. To test whether vegetative and floral traits differ in their responses to elevation, we measured morphological and chemical traits of plant species occurring in pastures at seven elevations in the Austrian Alps. Variation in functional composition was examined using the concept of n-dimensional hypervolumes and vector analysis. Our data show that vegetative and floral traits vary differently with the elevational gradient. Whereas vegetative traits changed in a predictable manner with elevation, floral traits did not specifically respond to elevation. Overall variation in vegetative traits mainly resulted from phenotypical differences between plants in different elevations, whereas total variation in floral traits was a result from a high variation within communities. The assessment of functional changes in vegetative and floral traits along mountain slopes thus reveals different patterns in plant responses to elevation and may help to generate testable hypotheses on functional responses to current climate warming.

Decreased plant productivity resulting from plant group removal experiment constrains soil microbial functional diversity.

Anthropogenic environmental changes are accelerating the rate of biodiversity loss on Earth. Plant diversity loss is predicted to reduce soil microbial diversity primarily due to the decreased variety of carbon/energy resources. However, this intuitive hypothesis is supported by sparse empirical evidence, and most underlying mechanisms remain underexplored or obscure altogether. We constructed four diversity gradients (0-3) in a five-year plant functional group removal experiment in a steppe ecosystem in Inner Mongolia, China, and quantified microbial taxonomic and functional diversity with shotgun metagenome sequencing. The treatments had little effect on microbial taxonomic diversity, but were found to decrease functional gene diversity. However, the observed decrease in functional gene diversity was more attributable to a loss in plant productivity, rather than to the loss of any individual plant functional group per se. Reduced productivity limited fresh plant resources supplied to microorganisms, and thus, intensified the pressure of ecological filtering, favoring genes responsible for energy production/conversion, material transport/metabolism and amino acid recycling, and accordingly disfavored many genes with other functions. Furthermore, microbial respiration was correlated with the variation in functional composition but not taxonomic composition. Overall, the amount of carbon/energy resources driving microbial gene diversity was identified to be the critical linkage between above- and belowground communities, contrary to the traditional framework of linking plant clade/taxonomic diversity to microbial taxonomic diversity.

Variation in stem mortality rates determines patterns of above-ground biomass in Amazonian forests: implications for dynamic global vegetation models.

Understanding the processes that determine above‐ground biomass (AGB) in Amazonian forests is important for predicting the sensitivity of these ecosystems to environmental change and for designing and evaluating dynamic global vegetation models (DGVMs). AGB is determined by inputs from woody productivity [woody net primary productivity (NPP)] and the rate at which carbon is lost through tree mortality. Here, we test whether two direct metrics of tree mortality (the absolute rate of woody biomass loss and the rate of stem mortality) and/or woody NPP, control variation in AGB among 167 plots in intact forest across Amazonia. We then compare these relationships and the observed variation in AGB and woody NPP with the predictions of four DGVMs. The observations show that stem mortality rates, rather than absolute rates of woody biomass loss, are the most important predictor of AGB, which is consistent with the importance of stand size structure for determining spatial variation in AGB. The relationship between stem mortality rates and AGB varies among different regions of Amazonia, indicating that variation in wood density and height/diameter relationships also influences AGB. In contrast to previous findings, we find that woody NPP is not correlated with stem mortality rates and is weakly positively correlated with AGB. Across the four models, basin‐wide average AGB is similar to the mean of the observations. However, the models consistently overestimate woody NPP and poorly represent the spatial patterns of both AGB and woody NPP estimated using plot data. In marked contrast to the observations, DGVMs typically show strong positive relationships between woody NPP and AGB. Resolving these differences will require incorporating forest size structure, mechanistic models of stem mortality and variation in functional composition in DGVMs.

Changing gears during succession: shifting functional strategies in young tropical secondary forests.

Adaptations to resource availability strongly shape patterns of community composition along successional gradients in environmental conditions. In the present study, we examined the extent to which variation in functional composition explains shifts in trait-based functional strategies in young tropical secondary forests during the most dynamic stage of succession (0-20 years). Functional composition of two size classes in 51 secondary forest plots was determined using community-weighted means of seven functional traits, which were intensively measured on 55 woody plant species (n = 875-1,761 individuals). Along the successional gradient in forest structure, there was a significant and consistent shift in functional strategies from resource acquisition to resource conservation. Leaf toughness and adult plant size increased significantly, while net photosynthetic capacity (A(mass)) decreased significantly during succession. Shifts in functional strategies within size classes for A(mass) and wood density also support the hypothesis that changes in functional composition are shaped by environmental conditions along successional gradients. In general, 'hard' functional traits, e.g., A(mass) and leaf toughness, linked to different facets of plant performance exhibited greater sensitivity to successional changes in forest structure than 'soft' traits, such as leaf mass area and leaf dry matter content. Our results also suggested that stochastic processes related to previous land-use history, dispersal limitation, and abiotic factors explained variation in functional composition beyond that attributed to deterministic shifts in functional strategies. Further data on seed dispersal vectors and distance and landscape configuration are needed to improve current mechanistic models of succession in tropical secondary forests.

Functional approaches for assessing plant and invertebrate abundance patterns in arable systems

A functional group approach was developed for plant and invertebrate assemblages from UK arable fields to assess the variation in functional composition of these highly disturbed, managed systems. Data were taken from the Farm-Scale Evaluations (FSE) of genetically modified herbicide-tolerant (GMHT) crops where the impact of management of the GMHT crop has been assessed for winter and spring sown oilseed rape, beet and maize. Twenty plant and 36 invertebrate functional groups were defined according to trophic behaviour and traits that affect resource capture, quality and availability. The functional composition of the plant community was significantly affected by season of sowing, the type of crop sown and, to a lesser extent, herbicide management. The invertebrate community composition was also affected by crop type and sowing season, but not by management. Resource and consumer groups were positively related, and data provide strong evidence for top-down control of herbivore populations. Two main interaction groups were identified within the arable food web: one between omnivores, generalist predators and detritivores, which are positively associated with monocots, and one between omnivores, parasitoids, sap feeders and leaf chewers, which have a stronger association with dicots. Although management has an impact on within-field arable biodiversity, crop type and sowing season have an overriding effect on the functional composition of plant and invertebrate assemblages in arable systems. Für Pflanzen- und Invertebratengesellschaften auf Kulturflächen in Großbritannien wurde ein Ansatz über funktionelle Gruppen entwickelt, um die Variation in der funktionalen Zusammensetzung dieser hochgradig gestörten, bewirtschafteten Systeme zu bestimmen. Die Daten stammen aus der “Farm-Scale-Evaluation” von genetisch modifizierten herbizidtoleranten Feldfrüchten (GMHT), bei der der Einfluss der Bewirtschaftung der GHMT-Feldfrüchte für Winter- und Sommerraps, Rüben und Mais abgeschätzt wurde. Es wurden 20 funktionelle Gruppen von Pflanzen und 36 von Invertebraten unter Berücksichtigung der trophischen Stellung und Eigenschaften definiert, welche die Ressourcennutzung, Qualität und Verfügbarkeit beeinflussen. Die funktionelle Zusammensetzung der Pflanzengemeinschaften wurde signifikant durch die Aussaatsaison, durch den ausgesäten Nutzpflanzentyp und in geringerem Maße durch das Herbizidmanagement beeinflusst. Die Zusammensetzung der Invertebratengemeinschaften wurde ebenfalls durch den Nutzpflanzentyp und die Aussaatsaison beeinflusst, aber nicht durch das Management. Die Ressourcen- und Konsumentengruppen standen in einer positiven Beziehung zueinander und die Daten liefern starke Hinweise auf eine top-down Kontrolle der Herbivorenpopulationen. Es wurden zwei wesentliche Interaktionsgruppen innerhalb des Kulturnahrungsnetzes gefunden: Eine zwischen den Omnivoren, unspezialisierten Prädatoren und Detritivoren, die positiv mit Monokotylen assoziiert sind, und eine zwischen Omnivoren, Parasitoiden, Saftsaugern und Blattfressern, die eine stärkere Assoziation mit Dikotylen zeigen. Obwohl die Bewirtschaftung einen Einfluss auf die Biodiversität innerhalb der Kulturfelder hat, zeigen Kulturpflanzentyp und Aussaatsaison eine überwältigenden Einfluss auf die funktionale Zusammensetzung der Pflanzen- und Invertebratengemeinschaften in Kultursystemen.