Local Environmental Variables Research Articles

Physiology of maerl algae: Comparison of inter- and intraspecies variations.

Free-living red coralline algae play an important role in the carbon and carbonate cycles of coastal environments. In this study, we examined the physiology of free-living coralline algae-forming maerl beds in the Bay of Brest (Brittany, France), where Lithothamnion corallioides is the dominant maerl (i.e., rhodolith) species. Phymatolithon calcareum and Lithophyllum incrustans are also present (in lower abundances) at a specific site in the bay. We aimed to assess how maerl physiology is affected by seasonality and/or local environmental variations at the inter- and intraspecific levels. Physiological measurements (respiration, photosynthetic, and calcification rates) were performed using incubation chambers in winter and summer to compare (1) the dominant maerl species at three sites and (2) three coexisting maerl species at one site. Comparison of the three coexisting maerl species suggests that L.corallioides is the best adapted to the current environmental conditions in the Bay of Brest, because this species is the most robust to dissolution in the dark in winter and has the highest calcification efficiency in the light. Comparisons of L.corallioides metabolic rates between stations showed that morphological variations within this species are the main factor affecting its photosynthetic and calcification rates. Environmental factors such as freshwater inputs also affect its calcification rates in the dark. In addition to interspecies variation in maerl physiology, there were intraspecific variations associated with direct (water physico-chemistry) or indirect (morphology) local environmental conditions. This study demonstrates the plasticity of maerl physiology in response to environmental changes, which is fundamental for maerl persistence.

Tourism informing conservation: The distribution of four dolphin species varies with calf presence and increases their vulnerability to vessel traffic in the four‐island region of Maui, Hawai‘i

Abstract We need reliable information about the spatial and temporal distribution of mobile species to effectively manage anthropogenic impacts to which they are exposed. Yet, we often cannot sustain dedicated annual surveys and data obtained from platforms of opportunity offer an alternative avenue to understand where these species spend time. Four odontocete species that occur in the four‐island region of Maui, Hawai'i, USA, are vulnerable to a range of human activities, but there is a lack of information regarding their distribution. We therefore do not know the extent of the risk these activities present for the conservation of these species (bottlenose dolphins, spinner dolphins, Pantropical spotted dolphins and false killer whales). We used a cross‐validated maximum entropy (MaxEnt) occupancy model to estimate the distribution of these four species in an area extensively observed from platforms of opportunity (PoP). We then determined in a similar fashion whether the calves of those species were more likely to be observed in particular areas and whether distribution changed with season. Maxent models relying on local environmental variables described dolphin observations well (AUC > 0.7). Their distribution differed for all species when calves were present, indicating that different environmental variables describe area use for schools with calves present. The number of sighting events of all species varied significantly with season. Bottlenose dolphins and false killer whales were more prevalent in winter, while spotted and spinner dolphins were more prevalent in summer. We show that an overlap in the distribution of dolphin schools with calves and vessel traffic in the region could result in collision and chronic stress risks. This suggests a need for specific regulations for mitigating anthropogenic influences, such as acoustic disturbance or chronic energetic disturbance from vessel traffic. This elevated risk associated with vessel traffic is likely of conservation concern in this region for the endangered population of false killer whales and for spinner dolphins.

Influences of pesticides, nutrients, and local environmental variables on phytoplankton communities in lentic small water bodies in a German lowland agricultural area.

Agrochemicals such as pesticides and nutrients are concurrent chemical stressors in freshwater aquatic ecosystems surrounded by agricultural areas. Lentic small water bodies (LSWB) are ecologically significant habitats especially for maintaining biodiversity but highly understudied. Phytoplankton are ideal indicator species for stress responses. Functional features of the phytoplankton are important in revealing the processes that determine the structure of the communities. In this study, we investigated the effects of pesticides, nutrients, and local environmental variables on the species composition and functional features of phytoplankton communities in LSWB. We studied pesticide toxicity of ninety-four pesticides, three nutrients (NH4-N, NO3-N and PO4-P) and local environment variables (precipitation, water level change, temperature, dissolved oxygen concentration, electrical conductivity, pH) in five LSWB over twelve weeks during the spring pesticide application period. We explored respective changes in species composition of phytoplankton community and functional features. Redundancy analysis and variance partitioning analysis were applied to correlate phytoplankton community compositions with the pesticide toxicity (as maximum toxicity in toxic units), nutrients and local environment variables. We used multiple linear regression models to identify the main environmental variables driving the functional features of phytoplankton communities. Pesticide toxicity, nutrients and local environmental variables significantly (p < 0.001) contributed to shaping phytoplankton community composition individually. Local environment variables showed the highest pure contribution for driving phytoplankton composition (12%), followed by nutrients (8%) and pesticide toxicity (2%). Functional features (represented by functional diversity and functional redundancy) of the phytoplankton community were significantly affected by pesticide toxicity and nutrients concentrations. The functional richness and functional evenness were negatively affected by PO4-P concentrations. Pesticide toxicity was positively correlated with functional redundancy indices. Our findings emphasized the relative importance of concurrent multiple stressors (e.g., pesticides and nutrients) on phytoplankton community structure, directing potential effects on metacommunity structures in aquatic ecosystems subjected to agricultural runoff.

Can Landsat Thermal Imagery and Environmental Data Accurately Estimate Water Temperatures in Small Streams?

AbstractThe ability to monitor water temperature is important for assessing changes in riverine ecosystems resulting from climate warming. Direct in situ water temperature collection efforts provide point samples but are cost-prohibitive for characterizing stream temperatures across large spatial scales, especially for small, remote streams. In contrast, satellite thermal infrared imagery may provide a spatially extensive means of monitoring riverine water temperatures; however, researchers do not have a good understanding of the accuracy of these remotely sensed temperatures for small streams. Here, we investigated the utility of Landsat 8 thermal infrared imagery and both local and regional environmental variables to estimate subsurface temperatures in high-latitude small streams (2–30 m wetted width) from a test watershed in southcentral Alaska. Our results suggested that Landsat-based surface temperatures were biased high, and the degree of bias varied with hydrological and meteorological factors. However, with limited in-stream validation work, results indicated it is possible to reconstruct average in situ water temperatures for small streams at regional scales using a regression modelling framework coupled with publicly available Landsat or air temperature information. Generalized additive models built from stream stage information from a single gage and air temperatures from a single weather station in the drainage fit to a limited set of in situ temperature recordings could estimate average stream temperatures at the watershed level with reasonable accuracy (root mean square error = 2.4°C). Landsat information did track closely with regional air temperatures and we could also incorporate it into a regression model as a substitute for air temperature to estimate in situ stream temperatures at watershed scales. Importantly, however, while average watershed-scale stream temperatures may be predictable, site-level estimates did not improve with the use of Landsat information or other local covariates, indicating that additional information may be necessary to generate accurate spatially explicit temperature predictions for small order streams.

DNA metabarcoding and morphological methods show complementary patterns in the metacommunity organization of lentic epiphytic diatoms

Diatoms are important organisms in freshwater ecosystems due to their position as primary producers and therefore, analyzing their communities provides relevant information on ecosystem functioning. Diatoms have historically been identified based on morphological traits, which is time-consuming and requires well-trained specialists. Nevertheless, DNA barcoding offers an alternative approach to overcome some limitations of the morphological method. Here, we assess if both approaches are comparable methods to study patterns and mechanisms (including environmental filtering and dispersal limitation) of epiphytic diatom metacommunities using a comprehensive dataset from 22 Mediterranean ponds at different taxonomic resolutions. We used a fragment of rbcL barcode gene combined with High-Throughput Sequencing to infer diatom community composition. The overall degree of correspondence between both approaches was assessed by Procrustean rotation analysis and Procrustean randomization tests, whereas the role of local environmental variables and geographical distances was studied using a comprehensive combination of BIOENV, Mantel tests and distance-based redundancy analysis. Our results showed a relatively poor correspondence in the compositional variation of diatom metacommunity between both approaches. We speculate that the incompleteness of the reference database and the bioinformatics processing are the biases most likely affecting the molecular approach, whereas the limited counting effort and the presence of cryptic species are presumably the major biases related with the morphological method. On the other hand, variation in diatom community composition detected with both approaches was strongly related to the environmental template, which may be related with the narrow ecological niche and the strong preferences for particular substrata of some diatom species. Nevertheless, we found no significant relationship between compositional variation and geographical distances at regional extent. Overall, our work highlights the importance of DNA metabarcoding to address empirical research questions of community ecology in freshwaters, especially once the reference databases include most genotypes of occurring taxa and bioinformatics biases are overcome.

Local environmental variables are key drivers of ant taxonomic and functional beta-diversity in a Mediterranean dryland

The decomposition of beta-diversity (β-diversity) into its replacement (βrepl) and richness (βrich) components in combination with a taxonomic and functional approach, may help to identify processes driving community composition along environmental gradients. We aimed to understand which abiotic and spatial variables influence ant β-diversity and identify which processes may drive ant β-diversity patterns in Mediterranean drylands by measuring the percentage of variation in ant taxonomic and functional β-diversity explained by local environmental, regional climatic and spatial variables. We found that taxonomic and functional replacement (βrepl) primarily drove patterns in overall β-diversity (βtot). Variation partitioning analysis showed that respectively 16.8%, 12.9% and 21.6% of taxonomic βtot, βrepl and βrich variation were mainly explained by local environmental variables. Local environmental variables were also the main determinants of functional β-diversity, explaining 20.4%, 17.9% and 23.2% of βtot, βrepl and βrich variation, respectively. Findings suggest that niche-based processes drive changes in ant β-diversity, as local environmental variables may act as environmental filters on species and trait composition. While we found that local environmental variables were important predictors of ant β-diversity, further analysis should address the contribution of other mechanisms, e.g. competitive exclusion and resource partitioning, on ant β-diversity.

The role of environmental conditions, climatic factors and spatial processes in driving multiple facets of stream macroinvertebrate beta diversity in a climatically heterogeneous mountain region

There is a growing recognition that examining patterns of ecological communities and their underlying determinants is not only feasible based on taxonomic data, but also functional and phylogenetic approaches. This is because these additional facets can enhance the understanding of the relative contribution of multiple processes in shaping biodiversity. However, few studies have focused on multifaceted beta diversities in lotic macroinvertebrates, especially when considering driving factors operating at multiple spatial scales. Here, we examined the spatial patterns of multi-faceted (i.e., taxonomic, functional and phylogenetic) beta diversity and their components (i.e., turnover and nestedness) of macroinvertebrates in 50 sites in 10 streams situated in the north and south slope of the Qinling Mountains, the geographical dividing line of Northern and Southern China. We found that the streams draining the north slope showed significantly lower values of beta diversity based on all three facets than the streams draining the south slope. Such north-to-south increases of beta diversity were caused by the distinct climatic and local environmental conditions between the sides of the mountain range. Moreover, spatial variables generally played the most important role in structuring all facets and components of beta diversity, followed by local environmental and climatic variables, whereas catchment variables were less important. Despite the similar results of relative contribution of explanatory variables on each beta diversity facet, the details of community-environment relationships (e.g., important explanatory variables and explanatory power) were distinct among different diversity facets and their components. In conclusion, measuring functional and phylogenetic beta diversity provides complementary information to traditional taxonomic approach. Therefore, an integrative approach embracing multiple facets of diversity can better reveal the mechanisms shaping biodiversity, which is essential in assessing and valuing aquatic ecosystems for biodiversity management and conservation.

Patterns in macroinvertebrate taxonomic richness and community assembly among urban wetlands in Cape Town, South Africa: implications for wetland management

Urbanization has significantly increased globally during the last century and has far-reaching consequences for biodiversity and their associated habitats, particularly wetland ecosystems. Previous studies have focused primarily on wetlands in non-urban areas, and urban wetland biodiversity patterns are currently not well understood, particularly across Africa. Here, we investigate two highly transformed urban wetlands in Cape Town, South Africa, and determine the relative importance and influence of local environmental variables as drivers of macroinvertebrate richness and community structuring. We also determine the influence of local environmental variables for patterns of species turnover and nestedness within and among these wetlands, and provide management recommendations based on our findings. We found that few macroinvertebrate species were associated with these wetlands, yet community variation was driven by a combination of local environmental variables. Our results also indicate that the turnover component of beta diversity, rather than nestedness, was responsible for most of the variation in the overall macroinvertebrate community. We identified two major problems regarding the current ecological state of the investigated wetlands. Firstly, high nutrient loads originating from the surrounding land uses which reduced wetland biodiversity, and secondly, the transformation of these wetlands from seasonal to perennial water bodies. We recommend local and regional scale approaches to limit urban waste from entering these systems, and management of water levels simulating natural Mediterranean-type climate dynamics more closely are required to ensure that the maximum possible diversity can be supported in these wetlands.

Unraveling the role of environmental factors and dispersal capacity in a metacommunity of Amazonian stream fishes

Separating species in terms of dispersal capacity can be useful to understand how local and regional factors affect the distribution of organisms in metacommunities. In this study, we sought to unravel how the characteristics of local habitats and spatial distances structure fish communities in Amazonian streams. We hypothesized that fishes classified with high dispersal capacity are mainly structured by mass effects and respond to environmental and spatial variables in the same proportion, while fishes classified with low dispersal capacity are mainly structured by species sorting, responding mainly to local environmental variables. We collected fish from 36 well-preserved streams in the Capim river basin in northern Brazil during the dry season. In general, the community composition was structured by characteristics of the local habitat. Spatial variables influenced each group at different intensities, agreeing with the models of species sorting and mass effects and corroborating our hypotheses. Thus, our findings suggest that the dispersal mode affects how metacommunities are structured. The differences in the patterns observed between the groups compared can help in the management and conservation of species, such as those with greater environmental requirements and more susceptible to habitat changes. We emphasize the need to maintain habitat integrity and connectivity in headwater streams to conserve species in their habitats.

Arboreta reveal the invasive potential of several conifer species in the temperate forests of western Europe

Identifying emerging invasive species is a priority to implement early preventive and control actions. In terms of the number of invasive tree species, forestry represents the second largest pathway of introduction, with an invasive debt likely existing for alien conifers in Europe. In the early 1900s, a network of arboreta was established in southern Belgium to assess the wood production potential of prospective conifer and broadleaved species. Here, we use eight arboreta as natural experiments to identify alien conifers presenting invasive behavior. Through systematic sampling, we quantified the natural regeneration of alien conifers and recorded local environmental variables. For each species, regeneration density, dispersal distances, and age structure were analyzed. Generalized mixed effects models were fitted to test the effect of planted area and tree-stand type on regeneration. The environmental space occupied by regenerating alien conifers was evaluated using principal component analysis. Out of 31 planted alien species, 15 (48%) were identified in natural regeneration, of which eight (26%) exhibited important regeneration density and dispersal distances. The most invasive species were Tsuga heterophylla and Abies grandis, confirming earlier field observations. Both large planted areas and areas planted with alien conifer species increased the density of regeneration. Species that had the highest regeneration density tolerated a wide range of environmental conditions, including shaded understory, which could lead to the invasion of mature, undisturbed forests. This study showed that 17% of the studied alien conifers are potentially invasive because they show important regeneration, long-distance dispersal, and, of importance, have already produced offspring that have matured and are capable of creating new satellite populations. In conclusion, our results provide a guideline for future planting operations, recommending extreme caution when planting these species in the temperate forests of Western Europe.

Connecting spatial structure in subtidal benthic communities with temporal variability in bottom temperature and dissolved oxygen along an upwelling coast

While spatial patterns in the structure of intertidal communities have been linked to changes in surface-ocean conditions indicative of coastal advection, nutrient supply, and productivity, less is known as to environmental features that, in addition to substrate type, are most influential in structuring subtidal benthic communities. Here we analyze data from subtidal benthic surveys conducted at six sites spanning ca. 180 km of shoreline along the upwelling coast of central Chile. Using continuous records of temperature and dissolved oxygen in bottom waters from each site, we tested whether among-site differences in community structure can be better explained by considering features of local environmental variability in addition to changes in substrate type. Starting from the NMDS ordination of benthic sites based on the presence and relative abundance of 29 species, we used PERMANOVA to test the explanatory power of substrate type and nine indices of environmental variability derived from in situ records. Three indices, namely the high-frequency variability and 95th percentile of bottom temperatures together with an index for the duration of hypoxia events, explained individually as much of the total variance as substrate type alone (ca. 30%). When combined into a single PERMANOVA analysis, these four factors explained 84% of the total variance in the NMDS-based ordination of benthic communities across the study region. A comparison of the benthic species ordination and environment-based site ordination suggests that soft-bottom species such as the razor clam Ensis macha, the snail Chorus giganteus, and the crab Cancer setosus, might be physiologically more tolerant to more rigorous conditions in terms of more intense warming and longer hypoxia events. Hard bottom species such as the gastropods Concholepas concholepas and Fissurella sp. and the barnacle Austromegabalanus psittacus thrive in environments where the temperature is lower on average but highly variable and where hypoxic conditions are intense but more intermittent. Our findings highlight the structuring role of the variability and the occurrence of extreme conditions, rather than the most frequent levels, in bottom-water properties such as temperature and dissolved oxygen. These two properties are closely intertwined in this and other coastal upwelling regions and are susceptible to change widely under future climate scenarios.

Incorporating Network Connectivity into Stream Classification Frameworks.

Stream classification frameworks are important tools for conserving aquatic resources. Yet despite their utility, most classification frameworks have not incorporated network connectivity. We developed and compared three biologically informed stream classification frameworks considering the effects of variables indexing local habitat and/or connectivity on stream fish communities. The first framework classified streams according to local environmental variables largely following the precedent set by previous stream classifications. The second framework classified streams according solely to network connectivity variables, while the third framework considered both local and connectivity variables. Using fish community data from 291 wadeable streams in South Carolina, USA, we used conditional inference tree analyses to identify either seven or eight discrete types of wadeable streams within each framework. Classifications were evaluated on their ability to describe community composition at a subset of sites not used in model training, and canonical correspondence analysis suggested that each framework performed similarly in describing overall community variation, with about 19% of variation explained. After accounting for the effects of biogeography and land use in our analytical approach, each classification explained a substantially higher amount of community variation with 46% of variation explained by our connectivity-informed classification and 42% explained by our locally informed classification. Classifications differed in their ability to describe elements of community structure; a classification incorporating connectivity predicted species richness better than the one that did not. This study ultimately addresses an important knowledge gap in the classification literature while providing broader implications for the conservation of aquatic organisms and their habitats.

Application of attached algae flow-ways for coupling biomass production with the utilization of dilute non-point source nutrients in the Upper Laguna Madre, TX

The purpose of this study is to determine the potential for an attached algae flow-way system to efficiently produce algal biomass in estuarine surface waters by utilizing dilute non-point source nutrients from local urban, industrial, and agricultural discharges into the Upper Laguna Madre, Corpus Christi, Texas. The study was conducted over the course of two years to establish seasonal base-line biomass productivity and composition for bioproducts applications, and to identify key environmental factors and flow-way cohorts impacting biomass production. For the entire cultivation period, continuous ash-free biomass production at 4 to 10 g/m2/day (corresponding to nutrient recovery at 300 to 500 mg of nitrogen/m2/day and 15 to 30 mg of phosphorus/m2/day) was successfully achieved without system restart. Upon start-up, a latency period was observed which indicates roles for species succession from relatively low productivity, high ash content pioneer periphytic culture composed primarily of benthic diatoms from the source waters to higher productivity, reduced ash content, and more resilient culture mainly composed of filamentous chlorophyta, Ulva lactuca. Principal Component Analysis (PCA) was used to identify environmental factors driving biomass production, and machine learning (ML) models were constructed to assess the predictive capability of the data set for system performance using the local multi-season environmental variations. Environmental datasets were segregated for ML training, validation, and testing using three methods: regression tree, ensemble regression, and Gaussian process regression (GPR). The predicted ash-free biomass productivity using ML models resulted in root-squared-mean-errors (RSME) from 1.78 to 1.86 g/m2/day, and R2 values from 0.67 to 0.75 using different methods. The greatest contributor to net productivity was total solar irradiation, followed by air temperature, salinity, and pH. The results of the study should be useful as a decision-making tool to application of attached algae flow-ways for biomass production while preventing algal blooms in the environment.

Variation in δ13C and δ15N within and among plant species in the alpine tundra

ABSTRACT Ratios of carbon (C) and nitrogen (N) stable isotopes in plants are important indicators of intrinsic water use efficiency and N acquisition strategies. Here, we examined patterns of inter- and intraspecific variations and phylogenetic signal in foliar δ13C and δ15N for 59 alpine tundra plant species, stratifying our sampling across five habitat types. Overall, we found that variation in both δ13C and δ15N mirrored well-known patterns of water and nitrogen limitation among habitat types and that there was significant intraspecific trait variation in both δ13C and δ15N for some species. Lastly, we only found a strong signal of phylogenetic conservatism in δ13C in two habitat types and no phylogenetic signal in δ15N. Our results suggest that although local environmental conditions do play a role in determining variation in δ13C and δ15N among habitat types, there is considerable variation within and among species that is only weakly explained by shared ancestry. Taken together, our results suggest that considering local environmental variation, intraspecific trait variation, and shared ancestry can help with interpreting isotope patterns in nature and with predicting which species may be able to respond to rapidly changing environmental conditions.

Development of artificial intelligence-based air pollution analysis and prediction system using local environmental variables

Development of artificial intelligence-based air pollution analysis and prediction system using local environmental variables

Diferentes distúrbios antrópicos na paisagem podem influenciar padrões florísticos e estruturais da Mata Atlântica?

Este estudo teve por objetivo descrever e comparar as diversidades alfa e beta e estrutura do componente arbóreo em remanescente de Floresta Estacional Semidecidual. A vegetação arbórea foi amostrada em duas bordas em contato com pastagem (BP), cafeicultura (BC), e no interior do fragmento (INT). Foram amostrados no total 2.840 indivíduos, identificados em 56 famílias, 144 gêneros e 271 espécies (94 na BC, 128 BP e 178 INT). Os trechos de borda foram caracterizados por maior densidade e menor área basal que o interior, indicando a influência de distúrbios. As variações na composição florística estrutural das comunidades arbóreas sofreram influência das variações ambientais regionais e locais, além do histórico de uso da área, conforme as Teorias de Nicho e do Distúrbio Intermediário. Different Anthropic Disturbances in the Landscape can influence Floristic and Structural Patterns of the Atlantic Forest? This study aimed to describe and compare the floristic and structural component of the tree component, as well as the alpha and beta diversity, as well as the floristic similarity of a remnant of Semideciduous Forest. The tree vegetation was sampled at two edges in contact with pasture (BP) and coffee growing (BC), and inside the fragment (INT). 2.840 individuals were sampled, identified in 56 families, 144 genera and 271 species (94 BC, 128 BP and 178 INT). The border stretches were characterized by higher density and smaller basal area than the interior, indicating the occurrence of disturbances. The variations in the structural floristic composition of the tree communities wereinfluenced by regional and local environmental variations, as well as the historical use of the area, according to Niche and Intermediate Disturbance Theories.Keywords:Phytosociology, Intermediate Disturbance Theory, Serra do Espinhaço Biosphere Reserve.

Detecting Electromagnetic Geographical Environment Changes Based on the Frequency‐Intensity Curve

Electromagnetic geographic environment is closely related to human life. With continuous popularization of public infrastructures and daily electronic instruments, such as electric power communication systems and household appliances, electromagnetic radiation sources have increased sharply in the geographic environment, which leads to increasingly serious electromagnetic radiation pollution. Thus, it is significant to monitor, evaluate, and analyze the electromagnetic radiation condition and explore its changing law in the environment. However, the traditional monitoring method can only detect anomalies within certain frequencies in the fixed stations. To fill this gap, this research first develops a vehicle‐mounted electromagnetic environment monitoring system to collect both spatial positioning data and electromagnetic data of the whole frequency range. The acquired data are then used to construct the location‐based frequency‐intensity curve to reflect the variation of electromagnetic radiation at different frequency ranges. On this basis, a curve similarity measurement method is introduced to analyze the similarity of different curves, which is effective to diagnose time‐varying sources from both global and local perspectives. This research provides a real‐time mobile monitoring method, which is significant to know the dynamic variation of local electromagnetic environment and promotes subsequent comprehensive geographic analyses.

Hyperiid amphipod vertical distribution and community structure in the upper 100 m of the northwestern Caribbean Sea

The community structure and variability of the hyperiid amphipods of the Northwestern Tropical Atlantic (NWTA) remain largely unknown. We described and analyzed the hyperiid nictemeral, vertical, and horizontal distribution and the influence of environmental variables in the upper 100 m of the northwestern Caribbean Sea. We examined 196 zooplankton samples obtained during both day and nighttime at four depth strata from 49 sampling stations in January 2007. Up to 82 hyperiid species including 14 new regional records were identified and quantified. Both day/night and some interstrata differences were significant, particularly in reference to the uppermost and deepest strata. The local hyperiid community structure appeared to be profiled by the frequency and abundance variations of the two most abundant species, Lestrigonus bengalensis and Brachyscelus crusculum, both being most abundant in the uppermost (0–25 m) stratum. The horizontal distribution of the highest hyperiid abundance and diversity appears to be related to the influence of mesoscale processes like upwelling and cyclonic eddies. The Gulf of Honduras area had relatively low hyperiid abundances. The principal component analysis revealed density and temperature as the main factors explaining the local environmental variability. The canonical analysis of principal coordinates (CAP) showed that salinity and temperature strongly influenced the variability of the local hyperiid community. Overall, the two middle vertical strata (25–75 m) were relatively uniform; the main differences were found only between the uppermost and deepest strata. This study is the first to provide information regarding small-scale vertical distribution of hyperiid amphipods in the NWTA.

吉林蛟河针阔混交林功能性状分布格局及其对地形因素的响应

森林群落的构建过程及其内在机制是生态学研究的热点问题。植物功能性状是指能够代表植物的生活史策略，反映植物对环境变化响应的一系列植物属性。通过植物功能性状的分布格局及其对环境因素的响应有助于推测群落的构建过程及其内在作用机制。以吉林蛟河21.12hm²温带针阔混交林样地为研究对象，采集并测量了样地内34种木本植物的6种不同的功能性状。以20m×20m的样方为研究单元，通过计算平均成对性状距离指数（mean pairwise trait distance；PW）和平均最近邻体性状距离指数（mean nearest neighbor trait distance；NN）来探讨群落中单个性状和综合性状的分布格局。同时结合地形因子采用回归分析探讨功能性状的分布格局对局域生境变化的响应。基于PW的结果显示：单个性状中除叶面积外，其余性状的分布格局均为聚集分布多于离散分布；基于NN的结果显示：除叶面积和最大树高外，其余性状的分布格局为聚集分布多于离散分布。此外，由6种单个性状组成的综合性状的分布格局同样为聚集分布多于离散分布。基于回归分析的结果显示：森林群落中功能性状的分布格局受到海拔、坡度和坡向等因素的显著影响，而凹凸度的影响则不显著。研究结果表明包括环境过滤和生物相互作用的非随机过程能够影响温带针阔混交林的群落构建过程，中性过程对该区域群落构建过程的影响不显著。;Understanding the mechanism and process of community assembly is a key issue in ecological research. Functional traits, which represent plant physiological, morphological, and phenological attributes, have decisive effects on plant growth, survival, reproduction and dispersal. Examining the spatial distribution pattern of plant functional traits and its response to local environmental variation is helpful to speculate the underlying processes and mechanisms that regulate community assembly. In this study, we explored the underlying mechanisms of community assembly using the dataset from a 21.12hm² temperate conifer and broad-leaved mixed forest plot in Jiaohe, Northeast China. Four topographic attributes, including elevation, convexity, slope, and aspect, were measured as local environmental factors. Six functional traits, namely leaf area, specific leaf area, leaf carbon content, leaf nitrogen content, leaf carbon to nitrogen ratio, and maximum tree height, were collected and measured for all 34 woody species that present in this temperate forest plot. Two functional structure indices, including the mean pair-wise trait distance (PW) and the mean nearest neighbor trait distance (NN), were used to explore the spatial distribution pattern of plant traits. Furthermore, regression analyses were used to investigate the response of trait patterns to environmental variation. Based on the results of PW, we found that, except for the leaf area traits, the remaining traits mainly showed the clumped spatial patterns. The results based on NN showed that, except for the leaf area and maximum tree height, the remaining traits presented the clumped spatial patterns. The results of regression analyses showed that the distribution patterns of functional traits were significantly affected by elevation, slope, and aspect. In contrast, convexity had no significant effect on trait distribution in this temperate forest community. Our results indicate that the non-random processes including environmental filtering and biological interactions played important roles in regulating forest community assembly, while the role of neutral process was not significant in this temperate conifer and broad-leaved mixed forest.

Trait coordination and environmental filters shape functional trait distributions of forest understory herbs.

Understanding the drivers of trait selection is critical for resolving community assembly processes. Here, we test the importance of environmental filtering and trait covariance for structuring the functional traits of understory herbaceous communities distributed along a natural environmental resource gradient that varied in soil moisture, temperature, and nitrogen availability, produced by different topographic positions in the southern Appalachian Mountains.To uncover potential differences in community‐level trait responses to the resource gradient, we quantified the averages and variances of both abundance‐weighted and unweighted values for six functional traits (vegetative height, leaf area, specific leaf area, leaf dry matter content, leaf nitrogen, and leaf δ13C) using 15 individuals of each of the 108 species of understory herbs found at two sites in the southern Appalachians of western North Carolina, USA.Environmental variables were better predictors of weighted than unweighted community‐level average trait values for all but height and leaf N, indicating strong environmental filtering of plant abundance. Community‐level variance patterns also showed increased convergence of abundance‐weighted traits as resource limitation became more severe.Functional trait covariance patterns based on weighted averages were uniform across the gradient, whereas coordination based on unweighted averages was inconsistent and varied with environmental context. In line with these results, structural equation modeling revealed that unweighted community‐average traits responded directly to local environmental variation, whereas weighted community‐average traits responded indirectly to local environmental variation through trait coordination.Our finding that trait coordination is more important for explaining the distribution of weighted than unweighted average trait values along the gradient indicates that environmental filtering acts on multiple traits simultaneously, with abundant species possessing more favorable combinations of traits for maximizing fitness in a given environment.