Trends In Species Richness Research Articles

High species richness of sheep-grazed sand pastures is driven by disturbance-tolerant and weedy short-lived species.

We selected 15 sheep-grazed sand pastures along a gradient of increasing grazing intensity to study the fine-scale patterns of main biomass fractions (green biomass, litter) and that of plant species and functional groups (life forms and social behaviour types). We classified them into five grazing intensity levels based on stocking density, proximity to drinking and resting places and the number of faeces. We aimed to answer the following questions: (i) How does increasing intensity of sheep grazing affect the amount of green biomass, the species richness and their relationship in sand pastures? (ii) How does increasing intensity of sheep grazing affect the biomass of perennial and short-lived graminoids and forbs? (iii) How does the disturbance value-expressed in the biomass ratio of disturbance-tolerant and ruderal species-change along the gradient of grazing intensity? A unimodal relationship between green biomass and species richness was detected; however, the ordination (canonical correspondence analysis, CCA) showed no clustering of pastures subjected to the same levels of grazing intensity. Along the grazing intensity gradient we found an increasing trend in species richness and significant differences in green biomass (decreasing trend), litter (decreasing trend), graminoids (decreasing trend) and short-lived forbs (increasing trend). We found an increasing amount of disturbance-tolerant and ruderal species with increasing grazing intensity. We suggest that we might need to use multiple scales for sampling and a fine-scale assessment of grazing intensity. Our findings might be instructive for pastures in densely populated regions, which are prone to the encroachment of disturbance-tolerant and ruderal species.

Species richness and dominant functional groups enhance aboveground biomass, with no effect on belowground biomass in Qinghai-Tibet Plateau's grasslands

Understanding the role of plant diversity in maintaining grassland ecosystem functioning is of great importance in ecological research. Despite decades of research, ecologists have struggled to understand the biodiversity-ecosystem functioning relationships and how the dominance of plant functional groups impacts ecosystem function. In attempting to understand (i) the temporal patterns of above- and below-ground biomass (AGB and BGB) and species richness, (ii) whether species richness is consistently associated with AGB and BGB, and (iii) the relative contributions of plant functional groups (forb, grass, legume, and sedge) in stabilizing ecosystem function, we used biomass productivity data of meadow steppe and alpine meadow in the Qinghai-Tibet Plateau (QTP) for the period 2015–2019. Our results show that AGB for both grasslands increased, but BGB stayed steady over 5 years. The rising tendency of AGB was caused by the upward trend of AGB in forbs and grasses, which are the dominant functional groups in QTP, stressing the importance of dominant functional groups to ecosystem functioning. The biodiversity-ecosystem functioning relationships were significantly positive for AGB, stable for BGB, and negative for the BGB:AGB ratio, which highlights the crucial role of higher species richness in ecosystem functioning. Significant differences in mean species richness among sites (9–19 species in meadow steppe and 8–22 species in alpine meadow) highlight the varying levels of species diversity across sites in the QTP. While 42% of the sites showed stable species richness, the reported increasing trends in species richness at 58% of the sites indicate the potential for ecological changes or processes in these areas. AGB in both grasslands increased, while BGB remained stable with increasing precipitation. The top soil layer (0–10 cm) dominated the observed BGB in both grasslands, as abundant nutrients in the top layer provide favorable conditions for root proliferation. In meadow steppe, AGB formed an isometric relationship with BGB, indicating that AGB increased with BGB. This study concludes that species richness influenced ecosystem functioning, and forbs and grasses dominated biomass productivity, of which the topsoil layer contributed three-quarters of BGB. Our study (i) provides empirical evidence of stable to increasing species richness in both grasslands over 5 years, and (ii) highlights the role of greater species richness in enhancing ecosystem functioning. These findings serve as a scientific reference for policymaking regarding ecosystem stability.

Variation in fern species richness, assemblages and morphology along a tropical riparian humidity gradient: an example from Borneo

ABSTRACT Riparian vegetation experiences a little spatial distance humidity gradient, especially in the hyper-humid tropics. In Borneo, with almost no seasons and rather constant local climatic conditions, the riparian plant species show a wide range of morphological and physiological adaptations. This study assesses the adaptation strategies of ferns along a riparian humidity gradient in the submontane forest of Sarawak, Malaysia (Borneo). The species richness and cover, morphological traits, leaf area, leaf perimeter, leaf dissection, leaf elongation ratio, and stomatal density of 63 fern species were surveyed in six study areas along six stream transects. Significant trends in species richness and species cover were identified along the six transects, and changes in morphological traits such as leaf area, leaf perimeter, and leaf dissection were also discovered. With increasing distance from the streams (i.e. decreasing humidity), ferns tended to show longer leaves and a lower stomatal density. We conclude that the morphological traits of fronds change significantly within a short tropical riparian humidity gradient. This reveals variations in the energy investment and adaptation efficiency of ferns within a tropical forest microsite.

Spatially‐nested hierarchical species distribution models to overcome niche truncation in national‐scale studies

Spatial truncation in species distribution models (SDMs) might cause niche truncation and model transferability issues, particularly when extrapolating models to non‐analog environmental conditions. While broad calibration extents reduce truncation issues, they usually overlook local ecological factors driving species distributions at finer resolution. Spatially‐nested hierarchical SDMs (HSDMs) address truncation by merging (a) a global model calibrated with broadly extended, yet typically low‐resolution, basic, and imprecise data; and (b) a regional model calibrated with spatially restricted but more precise and reliable data. This study aimed to examine HSDMs' efficacy to overcome spatial truncation in national‐scale studies. We compared two hierarchical strategies (‘covariate', which uses the global model output as a covariate for the regional model, and ‘multiply', which calculates the geometric mean of the global and regional models) and a non‐hierarchical strategy. The three strategies were compared in terms of niche truncation, environmental extrapolation, model performance, species' predicted distributions and shifts, and trends in species richness. We examined the consistency of the results over two study areas (Spain and Switzerland), 108 tree species, and four future climate scenarios. Only the non‐hierarchical strategy was susceptible to niche truncation, and environmental extrapolation issues. Hierarchical strategies, particularly the ‘covariate' one, presented greater model accuracy than non‐hierarchical strategies. The non‐hierarchical strategy predicted the highest overall values and the lowest decreases over time in species distribution ranges and richness. Differences between strategies were more evident in Switzerland, which was more affected by niche truncation issues. Spain was more negatively affected by climate change and environmental extrapolation. The ‘covariate' strategy exhibited higher model performance than the ‘multiply' one. However, uncertainties regarding model temporal transferability advocate for adopting and further examining multiple hierarchical approaches. This research underscores the importance of adopting spatially‐nested hierarchical SDMs given the compromised reliability of non‐hierarchical approaches due to niche truncation and extrapolation issues.

Plant stoichiometric hierarchical responses to nutrient enrichment can enhance understanding regarding the process of biodiversity loss

In this study, our objective was to determine whether plant stoichiometry following nitrogen (N) and phosphorous (P) enrichments can enhance understanding regarding biodiversity loss processes. Thus, we conducted a field experiment involving N, P, and N + P enrichments in a sub-alpine meadow on the northeast of Qinghai-Tibet Plateau within the 2009–2014 period. Plant stoichiometric patterns were investigated using six exemplar species, four functional group levels, as well as the community level. The hierarchical responses of species richness, dominance, plant height, and plant ecological stoichiometry to nutrient addition were investigated. Further, step-wise regression analysis was performed and a structural equation model (SEM) was constructed to assess the linkages between ecological performances and plant stoichiometric characteristics. The model was also used to quantify the contributions of stoichiometric characteristics as drivers of changes in species richness. Our results indicated that N-only and N + P enrichments significantly reduced species richness at community-level, while enhancing grass richness and dominance. Furthermore, only the responses of the N:P ratio, P-related stoichiometry (P concentration, C:P ratios, and N:P ratio), and plant C:N:P stoichiometry to N, P, and N + P fertilizations, at community level could be mirrored at functional group and species levels. Additionally, the responses of the plant N contents and C:N ratios of different species and functional groups showed 28% similarity following nutrient addition. However, at functional group level, only 10% of these responses were similar to those observed at community level, and only in grasses and at community level did the stoichiometric responses show any convergence. We also observed that the major factors affecting ecological performance at different levels included plant N contents and C:N ratios. The species dominance of Elymus nutans (E.n) and the functional group dominance of grasses increased with increasing plant N concentration, and in terms of species richness, species, functional group, and community level stoichiometric traits could fully explain 43% of the observed species richness trend. Further, the effect of the community C:N ratio on species richness was significantly positive. Those results indicated stoichiometric responses to N and P fertilization did not entirely show scale-independence. Moreover, in a N-limited community, plant differences with respect to nitrogen content flexibility and nitrogen use efficiency can serve as key drivers in explaining ecological performance. Community C:N ratios showed suitability for used in the prediction of species richness trends, and to clarify changes in biodiversity, it is necessary to investigate stoichiometric traits at functional group level.

Climate change-related biodiversity fluctuations and composition changes in an old-growth subtropical forest: A 26-yr study

The detection and attribution of biodiversity change is of great scientific interest and central to policy effects aimed at meeting biodiversity targets. Yet, how such a diverse climate scenarios influence forest biodiversity and composition dynamics remains unclear, particularly in high diversity systems of subtropical forests. Here we used data collected from the permanent sample plot spanning 26 years in an old-growth subtropical forest. Combining various climatic events (extreme drought, subsequent drought, warming, and windstorm), we analyzed long-term dynamics in multiple metrics: richness, turnover, density, abundance, reordering and stability. We did not observe consistent and directional trends in species richness under various climatic scenarios. Still, drought and windstorm events either reduced species gains or increased species loss, ultimately increased species turnover. Tree density increased significantly over time as a result of rapid increase in smaller individuals due to mortality in larger trees. Climate events caused rapid changes in dominant populations due to a handful of species undergoing strong increases or declines in abundance over time simultaneously. Species abundance composition underwent significant changes, particularly in the presence of drought and windstorm events. High variance ratio and species synchrony weaken community stability under various climate stress. Our study demonstrates that all processes underlying forest community composition changes often occur simultaneously and are equally affected by climate events, necessitating a holistic approach to quantifying community changes. By recognizing the interconnected nature of these processes, future research should accelerate comprehensive understanding and predicting of how forest vegetation responds to global climate change.

CicadaNet: Deep learning based automatic cicada chorus filtering for improved long-term bird monitoring

Passive acoustic monitoring has been an effective tool for bird sound analysis. However, bird sounds often include cicada noise, which is an obstacle for investigating bird sounds. For example, cicada noise can result in large deviations of acoustic index, which will lead to the mismonitoring of species richness trends. Therefore, there is a critical need to filter cicada noise for helping bird sound analysis. We develop a novel end-to-end deep learning model, named CicadaNet for filtering cicada chorus from recordings containing bird sound. CicadaNet utilizes a convolutional encoder-decoder network to encode and decode acoustic features and a conformer module for global and local sequence modeling. We build a clean bird sound dataset and collect a large amount of real cicada noise data for model evaluation. We compare CicadaNet with current state-of-the-art deep denoising models and traditional denoising algorithms. Experimental results show that CicadaNet achieves the best denoising performance (SegSNR is improved by 9.59 dB and SI-SNR is improved by 20.08 dB when the noisy SNR = 0 dB). Meanwhile, CicadaNet achieves good performance for the real-time denoising of cicada noise. Furthermore, CicadaNet achieves bird species-independent noise reduction. We evaluate the effectiveness of CicadaNet for bird diversity survey. CicadaNet achieves the best performance, which can effectively eliminate the deviation caused by cicada noise to the acoustic index. CicadaNet can be easily extended to the cancellation of other environmental noise, and we propose it for the acoustic denoising of other vocalizing animals.

Seasonality, diversity, and forest type associations of macro moths (Insecta: Lepidoptera: Heterocera) in the Shiwalik landscape of northern India and its conservation implications

A study was carried out to evaluate the seasonal diversity of macro moths across different forest sub-types occurring in theShiwalik landscape of northern India, mainly Uttarakhand and adjoining states of Himachal Pradesh, Uttar Pradesh, and Haryana. Fortythree field surveys of 59 days were carried out from July 2020 to October 2022 using stratified random sampling in each of the 19 selected study sites. Sampling surveys revealed 321 species of moths belonging to 19 families and 49 sub-families. These new range extensions from central Himalaya and northeastern India indicate the affinity of moths found in the northern Indian Shiwaliks with that of the Oriental region. Seasonal trend of species richness showed two annual peaks, with the first peak occurring in August followed by a smaller peak in October, while the seasonal abundance of moth species was maximum in July followed by a smaller peak in September. One-hundredand-forty species occurred only during the ‘monsoon’ season indicating their seasonality, univoltine habit and short flight periods in these tropical forests. Species richness of moths correlated positively with relative humidity (r2 = 0.100; p = 0.0142; n = 59). The most dominant family was Erebidae (95 species) followed by Geometriidae (61), Crambidae (72), and Noctuidae (28), respectively. Maximum number of moth species were sampled in forest sub-type (i) 3C/C2a Moist Shiwalik Sal Forest, followed by (ii) 5B/C2 Northern Dry Mixed Deciduous Forest, (iii) 3C/C2c Moist Tarai Sal Forest, iv) 5B/C1a Dry Shiwalik Sal Forest, respectively. The study also revealed changing moth communities along with the vegetation structure in the Shiwaliks from east (Nandhaur Willife Sanctaury in Uttarakhand bordering Nepal) to west (Simbalbara National Park in Himachal Pradesh,India) across the landscape. The moth communities of (i) 3C/C2a Moist Shiwalik Sal Forest & (ii) 3C/C2c Moist Tarai Sal Forest being different from that of (iii) 5B/C2 Northern Dry Mixed Deciduous Forest, and (iv) 5B/C1a Dry Shiwalik Sal Forest. Besides, six new range extensions into Shiwaliks of northern India from central Nepal and northeastern India, namely: Chlorozancla falcatus (Butler, 1889) (Geometridae); Cynaeda dichroalis (Hampson, 1903), Dichocrocis pyrrhalis (Walker, 1859) & Glyphodes canthusalis Walker, 1859 (Crambidae); and Acropteris iphiata (Guenée, 1857) (Uranidae) were recorded.

Ecological trends in moth communities (Geometridae, Lepidoptera) along a complete rainforest elevation gradient in Papua New Guinea

Abstract The tropical rainforest elevation gradients, extending from lowlands to treeline, often represent global maxima of biodiversity and are models for community studies. We surveyed geometrid moths along a complete rainforest gradient from 200 to 3700 m asl. in Papua New Guinea. The 16,424 moths collected with light traps represented 1102 species, a high diversity for such system. We demonstrated the importance of molecular data for taxonomy as COI sequences (DNA barcodes) changed the definition of 19% of morphological species. The abundance of geometrids did not change with elevation while their species richness peaked at 1200 m asl. The mid‐elevation diversity peak is a common, but poorly understood, pattern for geometrids. It was best explained by the species richness of the vegetation. At the same time, the community was exposed to opposing trends in abiotic favourability (decreasing temperature) and biotic favourability (decreasing predation by ants, birds and bats) with elevation, potentially contributing to such unimodal trends in species richness. Beta diversity of communities separated by 500 m elevation increased with increasing elevation, reflecting decreasing mean elevational range of species—a pattern opposite to that expected under the Rapoport's rule. The total number of species along the elevation gradient corresponded to 280% of the highest local community diversity. This enrichment of species underscores the key role of long elevational gradients in maintaining high regional diversity and makes them a conservation priority, especially as they also allow for redistribution of species in response to climate change.

Accelerated recovery of lake macroinvertebrates in the third decade since the reversal of acidification

Chemical reversal from acidification has been progressing in European freshwaters since the late 1980s, responding to successful control of atmospheric pollution by acidifying emissions. However, biological recovery is often delayed after improvements in water composition. We studied macroinvertebrate recovery from acidification in eight glacial lakes in the Bohemian Forest (central Europe) between 1999 and 2019. The chemical composition of these lakes reflects a complex of environmental changes, dominated by a very steep decline in acid deposition and, currently, by elevated nutrient leaching following climate-induced tree dieback within their catchments. Temporal trends in species richness, abundance, species traits and community composition were evaluated with regard to water chemistry, littoral habitat properties and fish colonisation. The results showed accelerated recovery of macroinvertebrates following two decades of gradual improvement in water composition and slowly progressing biological rehabilitation. We observed a significant increase in macroinvertebrate species richness and abundance, coupled with distinct changes in community composition, the extent of changes varying between lakes, reflecting different littoral habitat properties (vegetated vs. stony) and water chemistry. Overall, the communities shifted toward more specialised (grazers, filterers, and phytophilous species) and acid-tolerant taxa at the expense of detritivorous, eurytopic and acid-resistant taxa. Where fish reappeared, open-water taxa declined greatly. Compositional changes were likely driven by the combined effects of water chemistry reversal, rehabilitation of habitat conditions and fish colonisation. Despite favourable trends, communities in recovering lakes still lack several biotic elements, particularly less vagile, acid-sensitive taxa and specialised herbivores known from the regional species pool. It is expected that future progress in lake recovery will be further promoted or inhibited by stochastic colonisation or disturbance events.

Pan-Arctic marine biodiversity and species co-occurrence patterns under recent climate

The Arctic region is experiencing drastic climatic changes bringing about potential ecological shifts. Here, we explored marine biodiversity and potential species associations across eight Arctic marine areas between 2000 and 2019. We compiled species occurrences for a subset of 69 marine taxa (i.e., 26 apex predators and 43 mesopredators) and environmental factors to predict taxon-specific distributions using a multi-model ensemble approach. Arctic-wide temporal trends of species richness increased in the last 20 years and highlighted potential emerging areas of species accrual due to climate-driven species redistribution. Further, regional species associations were dominated by positive co-occurrences among species pairs with high frequencies in the Pacific and Atlantic Arctic areas. Comparative analyses of species richness, community composition, and co-occurrence between high and low summer sea ice concentrations revealed contrasting impacts of and detected areas vulnerable to sea ice changes. In particular, low (high) summer sea ice generally resulted in species gains (loss) in the inflow and loss (gains) in the outflow shelves, accompanied by substantial changes in community composition and therefore potential species associations. Overall, the recent changes in biodiversity and species co-occurrences in the Arctic were driven by pervasive poleward range shifts, especially for wide-ranging apex predators. Our findings highlight the varying regional impacts of warming and sea ice loss on Arctic marine communities and provide important insights into the vulnerability of Arctic marine areas to climate change.

The undetectability of global biodiversity trends using local species richness

Although species are being lost at alarming rates, previous research has provided conflicting results on the extent and even direction of global biodiversity change at the local scale. Here, we assessed the ability to detect global biodiversity trends using local species richness and how it is affected by the number of monitoring sites, sampling interval (i.e. time between original survey and re‐survey of the site), measurement error (error of the measurement of the local species richness), spatial grain of monitoring (a proxy for the taxa mobility) and spatial sampling biases (i.e. site‐selection biases). We use PREDICTS model‐based estimates as a proxy for the real‐world distribution of biodiversity and randomly selected monitoring sites to calculate local species richness trends. We found that while a monitoring network with hundreds of sites could detect global change in species richness within a 30‐year period, the number of sites for detecting trends doubled for a decade, increased 10‐fold within three years and yearly trends were undetectable. Measurement errors had a non‐linear effect on statistical power, with a 1% error reducing statistical power by a slight margin and a 5% error drastically reducing the power to reliably detect any trend. The ability to detect global change in local species richness was also related to spatial grain, making it harder to detect trends for sites sampled at smaller plot sizes. Spatial sampling biases not only reduced the ability to detect negative global biodiversity trends but sometimes yielded positive trends. We conclude that detecting accurate global biodiversity trends using local richness may simply be unfeasible with current approaches. We suggest that monitoring a representative network of sites implemented at the national level, combined with models accounting for errors and biases, can help improve our understanding of global biodiversity change.

Steady turnover in a bird community in a periurban landscape in Northern Italy: a look at the change in species richness over time

From November 2017 until February 2022, with a partial interruption during 2020 linked to the COVID 19 pandemic, the bird community was monitored in a 30 hectares periurban plot in north-western Lombardy, in the province of Varese. The study area consists of a mosaic of farmland/ urban habitat (Luino and Germignaga municipalities) with scattered strips of woodland on the east side of Lake Maggiore. The farmland is mainly cultivated ryegrass or maize and permanent grassland. The turnover and phenology of the avifauna was regularly monitored. The year was divided up 4 seasons: winter, spring migration, breeding season and autumn migration. Each season was further divided into 10-day periods, giving a total of 37 ten-day periods over the whole year. For each ten-day period, there was a minimum of 4 surveys, alternating a 500m transect over 30 minutes with a single point count for 30 minutes. A total of 134 species were observed. The trend in species richness follows a sinusoidal curve relating to the migration periods. The area of farmland, while not having any regularly breeding species, supported 65 foraging species, with permanent grassland being more species rich than either maize or ryegrass. The Sorensen Similarity Index, based on incidence matrices, ranged from the lowest value of 0.6480 (during the winter of 2018/19 to spring migration in 2019) to the highest value of 0.8572 (from spring migration 2019 to the breeding period in 2019). Most of the nesting species are synanthropic, occupying the urban areas of this plot, including a colony of northern house martins.

Comparison of destructive and nondestructive DNA extraction methods for the metabarcoding of arthropod bulk samples.

DNA metabarcoding is routinely used for biodiversity assessment, in particular targeting highly diverse groups for which limited taxonomic expertise is available. Various protocols are currently in use, although standardization is key to its application in large-scale monitoring. DNA metabarcoding of arthropod bulk samples can be conducted either destructively from sample tissue, or nondestructively from sample fixative or lysis buffer. Nondestructive methods are highly desirable for the preservation of sample integrity but have yet to be experimentally evaluated in detail. Here, we compare diversity estimates from 14 size-sorted Malaise trap samples processed consecutively with three nondestructive approaches (one using fixative ethanol and two using lysis buffers) and one destructive approach (using homogenized tissue). Extraction from commercial lysis buffer yielded comparable species richness and high overlap in species composition to the ground tissue extracts. A significantly divergent community was detected from preservative ethanol-based DNA extraction. No consistent trend in species richness was found with increasing incubation time in lysis buffer. These results indicate that nondestructive DNA extraction from incubation in lysis buffer could provide a comparable alternative to destructive approaches with the added advantage of preserving the specimens for postmetabarcoding taxonomic work but at a higher cost per sample.

Long-term changes in bryophyte diversity of central European managed forests depending on site environmental features

Cryptogamic diversity is a reliable indicator of the state of forest ecosystems. In this study we analysed the variations in both bryophyte species richness overall and number of hemerophobic bryophyte species in Central European managed forests over a 20-year time span, based on data collected in 132 plots scattered across Poland. We tested differences in species richness among five temporal replicates, as well as among site types grouped based on elevation a.s.l., dominant tree species and stand age. The analyses revealed no significant trend in species richness across years. Meanwhile, species richness significantly increased along with elevation a.s.l., especially in broadleaved forests. No significant difference in species number between spruce and pine dominated stands emerged for mature stands, while there was a strong difference for young stands, with spruce forest hosting a much higher number of species. Species richness exhibited a slight, but not significant, increase over time in broadleaved forests, no significant variations in pine dominated stands and significant fluctuations in spruce dominated stands, yet without a significant trend. Out of the tested drivers, dominant tree species exhibited the strongest impact on species community composition. Number of hemerophobic and strongly hemerophobic species did not undergo significant variations across years either. The lack of bryophyte diversity trends highlighted in this study suggests Central European managed forests are in an equilibrium sate, maintained by the opposing effects of climate changes, on one side and of more sustainable forest management and pollutant deposition decline, from the other.

Contrasting elevational patterns and underlying drivers of stream bacteria and fungi at the regional scale on the Tibetan Plateau.

Elevational gradients are the focus of development and evaluation of general theories on biodiversity. However, elevational studies of microorganisms and the underlying mechanisms remain understudied, especially at regional scales. Here, we examined stream bacterial and fungal communities along an elevational gradient of 990-4600m with a geographic distance up to 500km in the southeastern Tibetan Plateau and further analyzed their elevational patterns and drivers of three biodiversity indicators, including species richness, ecological uniqueness, and community composition. Bacteria and fungi showed distinct elevational trends in species richness and consistently decreasing patterns in their ecological uniqueness. The distance-decay relationships were concordant for the two microbial groups, while fungi showed higher dissimilarity and a lower turnover rate. Interestingly, bacterial and fungal compositions substantially differed between the elevations below and above 3000m. Climate predictors, such as the mean annual temperature and precipitation seasonality, had greater effects than local environment drivers. Notably, fungal diversity was mainly influenced by climate, while bacterial diversity was explained by the shared contributions of climate and local factors. Collectively, these findings revealed the elevational patterns of stream microbial biodiversity across mountains on a large spatial scale and highlight their underlying response mechanisms to environmental predictors.

Impacts of nutrient reduction on temporal β-diversity of rotifers: A 19-year limnology case study on Lake Wuli, China

There have been many studies on the effects of eutrophication on beta diversity (β-diversity) of species assemblages. However, few studies have focused on the effects of nutrient reduction on β-diversity and community structure, and long-time series analyses are particularly scarce. We conducted a 19-year case study on the impacts of management intervention on the temporal β-diversity of aquatic grazers in a lake at the Yangtze River Basin. In our study, we compared the changes in temporal β-diversity as well as its two components, nestedness and turnover, and the synchrony of the rotifer community after management intervention. Our results showed that while the abundance of some sensitive species increased, there was no trend in species richness. Moreover, both the seasonality and interannual stabilities of rotifer assemblages increased. The species synchrony decreased in both spring and summer after management intervention. We also found that management intervention significantly reduced nutrient concentrations but not water clarity and phytoplankton abundance. The total nitrogen (TN): total phosphorous (TP) ratio was reduced after management intervention, causing an increase in the abundance of cyanobacteria that may contribute to the increase of rotifer synchrony in autumn. Our results imply that stable environmental fluctuations after management intervention may increase temporal β-diversity and stability of herbivorous assemblages. However, imbalanced changes in TN and TP after management intervention may weaken the top-down control of zooplankton on phytoplankton and slow down water clarity improvement.

Forest fires have long-term effects on the composition of vascular plants and bryophytes in Scots pine forests of hemiboreal Estonia

Since fire frequency is expected to increase globally due to climate change, it is important to understand its effects on forest ecosystems. We studied the long-term patterns in species diversity, cover and composition of vascular plants and bryophytes after forest fire and the site-related factors behind them. Research was carried out in northwestern Estonia, using a chronosequence of Scots pine ( L.) stands, located on nutrient poor sandy soils, where fires had occurred 12, 23, 38, 69, 80 and 183 years ago. In every stand three 100 m vegetation plots were established to collect floristic and environmental information. The effects on floristic characteristics of time since fire, light, and soil variables were evaluated with linear mixed models, followed by backward variable selection. Compositional variation was analysed with non-metric multidimensional scaling, Multi-response Permutation Procedures, and Indicator Species Analysis. Altogether, 31 vascular plant and 39 bryophyte species were found in vegetation plots. The cover of the vascular plant and bryophyte layers increased with a longer time since fire. Soil and light variables impacted the richness of several vascular plant and bryophyte groups, whereas only the richness of liverworts and dwarf-shrubs correlated with time since fire. Considerable compositional differences were observed in vascular plant and bryophyte assemblages between recently vs. long-time ago burned stands. To conclude, time since fire significantly impacted compositional patterns of vascular plants and bryophytes in pine forests on nutrient poor soils, although time-related trends in species richness were less evident.Pinus sylvestris2

A pan-Himalayan test of predictions on plant species richness based on primary production and water-energy dynamics

Spatial variation in plant species diversity is well-documented but an overarching first-principles theory for diversity variation is lacking. Chemical energy expressed as Net Primary Production (NPP) is related to a monotonic increase in species richness at a macroscale and supports one of the leading energy-productivity hypotheses, the More individuals Hypothesis. Alternatively, water-energy dynamics (WED) hypothesizes enhanced species richness when water is freely available and energy supply is optimal. This theoretical model emphasises the amount and duration of photosynthesis across the year and therefore we include the length of the growing season and its interaction with precipitation. This seasonal-WED model assumes that biotemperature and available water represent the photosynthetically active period for the plants and hence, is directly related to NPP, especially in temperate and alpine regions. This study aims to evaluate the above-mentioned theoretical models using interpolated elevational species richness of woody and herbaceous flowering plants of the entire Himalayan range based on data compiled from databases. Generalized linear models (GLM) and generalized linear mixed models (GLMM) were used to analyse species richness (elevational gamma diversity) in the six geopolitical sectors of the Himalaya. NPP, annual precipitation, potential evapotranspiration (derived by the Holdridge formula), and length of growing season were treated as the explanatory variables and the models were evaluated using the Akaike Information Criterion (AIC) and explained deviance. Both precipitation plus potential evapotranspiration (PET), and NPP explain plant species richness in the Himalaya. The seasonal-WED model explains the species richness trends of both plant life-forms in all sectors of the Himalayan range better than the NPP-model. Despite the linear precipitation term failing to precisely capture the amount of water available to plants, the seasonal-WED model, which is based on the thermodynamical transition between water phases, is reasonably good and can forecast peaks in species richness under different climate and primary production conditions.

Complex community responses underpin biodiversity change following invasion

How do invasive species change native biodiversity? One reason why this long-standing question remains challenging to answer could be because the main focus of the invasion literature has been on shifts in species richness (a measure of α-diversity). As the underlying components of community structure—intraspecific aggregation, interspecific density and the species abundance distribution (SAD)—are potentially impacted in different ways during invasion, trends in species richness provide only limited insight into the mechanisms leading to biodiversity change. In addition, these impacts can be manifested in distinct ways at different spatial scales. Here we take advantage of the new Measurement of Biodiversity (MoB) framework to reanalyse data collected in an invasion front in the Brazilian Cerrado biodiversity hotspot. We show that, by using the MoB multi-scale approach, we are able to link reductions in species richness in invaded sites to restructuring in the SAD. This restructuring takes the form of lower evenness in sites invaded by pines relative to sites without pines. Shifts in aggregation also occur. There is a clear signature of spatial scale in biodiversity change linked to the presence of an invasive species. These results demonstrate how the MoB approach can play an important role in helping invasion ecologists, field biologists and conservation managers move towards a more mechanistic approach to detecting and interpreting changes in ecological systems following invasion.