Β-diversity Components Research Articles

Metropolitan pressures: Significant biodiversity declines and strong filtering of functional traits in fish assemblages

Accelerating global urbanization is leading to drastic losses and restructuring of biodiversity. Although it is crucial to understand urban impacts on biodiversity to develop mitigation strategies, there is a dearth of knowledge on the functional structure of fish assemblages spanning the entire city-scale spectrum of urbanization intensity. Here, using environmental DNA sampled from 109 water sites in Beijing, we investigated the taxonomic and functional diversity patterns of fish assemblages across the city and uncovered community-, trait-, and species-level responses to various environmental stressors. By ranking sampling sites into three disturbance levels according to water physiochemical and landcover conditions, we found that both native and non-native fish taxonomic and functional α-diversity decreased significantly with elevating disturbance, as strong disturbance led to the disappearance of many species. However, the quantitative taxonomic and functional β-diversity components of native and non-native fish showed distinct patterns; assemblage turnover dominated native fish β-diversity and decreased with increasing disturbance, whereas species/trait richness differences dominated non-native fish β-diversity and increased with disturbance intensity particularly in lotic waters. RLQ and fourth-corner analyses revealed that fish size, fecundity, diet, and reproductive behaviors were significantly correlated with water quality, with pollution-tolerant, larger-sized native and omnivorous non-native fishes being urban winners, which indicates strong trait-dependent environmental filtering. Potential ecological indicator species were identified based on the sensitivity of fish responses to pollution loads; these were mostly small native species, and many have bivalve-dependent reproduction. Our results demonstrate that, along with native fish assemblage simplification and homogenization, urban stressors exert profound impacts on community trait composition, highlighting the need to consider both biodiversity loss and functional reorganization in combating disturbance of aquatic ecosystems under global urbanization. Furthermore, correlations between cropland cover and water nutrient level suggested that the management of agricultural runoff might be critically important for safeguarding urban water quality.

Plant beta-turnover rather than nestedness shapes overall taxonomic and phylogenetic beta-diversity triggered by favorable spatial-environmental conditions in large-scale Chinese grasslands.

Although it is widely acknowledged that biodiversity maintains plant community assembly processes, exploring the patterns and drivers of beta-diversity (β-diversity; species variation among local plant communities) has received much less attention compared to alpha-diversity (α-diversity; species variation within a local plant community). Here, we aim to examine the patterns and spatial-environmental drivers of taxonomic and phylogenetic β-diversity, and their components such as species turnover and nestedness, in large-scale Leymus chinensis grassland communities. We collected plant community data from 166 sites across widely distributed L. chinensis communities in northern China, and then calculated the taxonomic and phylogenetic β-diversity indices (overall, turnover and nestedness) using a pairwise dissimilarity approach. To assess the effects and to explain the variation in the patterns of β-diversity, we collected data on geospatial, climate and soil conditions. We applied descriptive statistics, Mental correlations, and multiple linear regression models to assess the patterns and spatial-environmental drivers of β-diversity. The β-turnover, as compared to β-nestedness, exhibited a predominant influence, constituting 92.6% of the taxonomic β-diversity and 80.4% of the phylogenetic β-diversity. Most of the spatial-environmental variables were significantly positively correlated with the overall taxonomic and phylogenetic β-diversity and β-turnover, but not with β-nestedness. Climatic factors such as MAP and MAT were the strongest predictors of both taxonomic and phylogenetic β-diversity and β-turnover. The variance partitioning analysis showed that the combined effects of spatial and environmental factors accounted for 19% and 16% of the variation in the taxonomic and phylogenetic β-diversity (overall), 17% and 12% of the variation in the β-turnover, and 7% and 1% of the variation in the β-nestedness, respectively, which were higher than independent effects of either spatial or environmental factors. At larger spatial scales, the turnover component of β-diversity may be associated with the species complementarity effect, but dominant or functionally important species can vary among communities due to the species selection effect. By incorporating β-diversity into grassland management strategies, we can enhance the provision of vital ecosystem services that bolster human welfare, serving as a resilient barrier against the adverse effects of climate change at regional and global scales.

Homogenization of soil seed bank communities by fire and invasive species in the Mojave Desert

Soil seed banks help maintain species diversity through temporal storage effects and function as germination pools that can optimize fitness across varying environmental conditions. These characteristics promote the persistence of native plant communities, yet disturbances such as fire and associated invasions by non-native species can disrupt these reserves, fundamentally altering successional trajectories. This may be particularly true in deserts, where native plant communities are less adapted to fire. While studies of fire effects on desert plant communities are not uncommon, information regarding the short- and long-term effects of fire on seed banks is less available. To better understand the influence of fire and invasive species on desert seed banks, we investigated soil seed bank biodiversity from 30 wildfires that burned between 1972 and 2010 across the Mojave Desert ecoregion of North America. We assessed how characteristics of fire regimes (frequency, time since fire, and burn severity) interacted with climate and invasive plants on measures of α-, β-, and γ-diversities. Because β-diversity is a direct measure of community variability and reveals important information about biodiversity loss, we further examined the nestedness and turnover components of β-diversity. Mean α- and γ-diversities were generally higher for burned locations than in unburned reference sites, however individual fire variables had little influence on patterns of seed bank diversity. Burned area seed banks tended to be dominated by non-native invasive species, primarily two grasses, (Bromus rubens, Bromus tectorum), as well as an invasive forb (Erodium cicutarium). The most striking pattern we observed was a collective sharp decline in α-, β-, and γ-diversities with increased invasive species dominance, indicating the homogenization of seed bank communities with the colonization of invasive species after fire. Evidence of homogenization was further supported by reduced turnover and increased nestedness in burn areas compared to reference areas indicating potential biodiversity loss. Our findings highlight how biological processes such as plant invasions can combine with disturbance from fire to alter patterns of seed bank composition and diversity in desert ecosystems.

Taxonomic and functional β-diversity patterns reveal stochastic assembly rules in microbial communities of seagrass beds.

Microorganisms are important members of seagrass bed ecosystems and play a crucial role in maintaining the health of seagrasses and the ecological functions of the ecosystem. In this study, we systematically quantified the assembly processes of microbial communities in fragmented seagrass beds and examined their correlation with environmental factors. Concurrently, we explored the relative contributions of species replacement and richness differences to the taxonomic and functional β-diversity of microbial communities, investigated the potential interrelation between these components, and assessed the explanatory power of environmental factors. The results suggest that stochastic processes dominate community assembly. Taxonomic β-diversity differences are governed by species replacement, while for functional β-diversity, the contribution of richness differences slightly outweighs that of replacement processes. A weak but significant correlation (p < 0.05) exists between the two components of β-diversity in taxonomy and functionality, with almost no observed significant correlation with environmental factors. This implies significant differences in taxonomy, but functional convergence and redundancy within microbial communities. Environmental factors are insufficient to explain the β-diversity differences. In conclusion, the assembly of microbial communities in fragmented seagrass beds is governed by stochastic processes. The patterns of taxonomic and functional β-diversity provide new insights and evidence for a better understanding of these stochastic assembly rules. This has important implications for the conservation and management of fragmented seagrass beds.

Impact of age on pneumococcal colonization of the nasopharynx and oral cavity: an ecological perspective.

Pneumococcal carriage studies have suggested that pneumococcal colonization in adults is largely limited to the oral cavity and oropharynx. In this study, we used total abundance-based β-diversity (dissimilarity) and β-diversity components to characterize age-related differences in pneumococcal serotype composition of respiratory samples. quantitative PCR (qPCR) was applied to detect pneumococcal serotypes in nasopharyngeal samples collected from 946 toddlers and 602 adults, saliva samples collected from a subset of 653 toddlers, and saliva and oropharyngeal samples collected from a subset of 318 adults. Bacterial culture rates from nasopharyngeal samples were used to characterize age-related differences in rates of colonizing bacteria. Dissimilarity in pneumococcal serotype composition was low among saliva and nasopharyngeal samples from children. In contrast, respiratory samples from adults exhibited high serotype dissimilarity, which predominantly consisted of abundance gradients and was associated with reduced nasopharyngeal colonization. Age-related serotype dissimilarity was high among nasopharyngeal samples and relatively low for saliva samples. Reduced nasopharyngeal colonization by pneumococcal serotypes coincided with significantly reduced Moraxella catarrhalis and Haemophilus influenzae and increased Staphylococcus aureus nasopharyngeal colonization rates among adults. Findings from this study suggest that within-host environmental conditions, utilized in the upper airways by pneumococcus and other bacteria, undergo age-related changes. It may result in a host-driven ecological succession of bacterial species colonizing the nasopharynx and lead to competitive exclusion of pneumococcus from the nasopharynx but not from the oral habitat. This explains the poor performance of nasopharyngeal samples for pneumococcal carriage among adults and indicates that in adults saliva more accurately represents the epidemiology of pneumococcal carriage than nasopharyngeal samples.

Differential response of fire on the community dynamics of five insect taxa in a tropical mountaintop forest archipelago.

The Earth's most diverse group of organisms is facing an imminent crisis, as recent investigations suggest a remarkable decline in insect diversity. Within this context, altimontane forest islands might emerge as important refuges holding an invaluable diversity of species that would be doomed to disappear. Here, we aimed to examine the impact of fire on the temporal variation of ant, bee, butterfly, dung beetle, and wasp communities in natural and highly threatened altimontane forest islands. We predicted that fire incidence would increase the natural variation in the structure of these insects' communities over time. Furthermore, we predicted that each taxon would respond accordingly to their ability to move between forest islands (i.e., vagility). We sampled these five bioindicator taxa in the rainy seasons of 2014, 2015, 2018, and 2020 within 14 forest islands in southeast Brazil. We assessed the incidence (presence/absence) of fire occurrence on each forest island toward the end of the dry season in each sampling year. We found an influence of fire incidence on the species composition changes over time (temporal β-diversity) in the less vagile insect groups: ants, and dung beetles. Nevertheless, we found no influence of fire incidence on shifts in species composition of highly vagile insects: bees, butterflies, and wasps. Importantly, species turnover was the primary component of temporal β-diversity driving the interannual variation of all insect taxa examined in this study. Our results highlight the distinct responses of more-or-less vagile insect groups to fire in forested ecosystems and shed light on the drivers of vulnerability and resilience of these groups to this critical anthropogenic pressure. By understanding and elucidating the intricate responses of distinct insect communities to global stressors, we can strengthen our capacity to predict future trends in biodiversity decline and provide valuable insights for conservation efforts and environmental management strategies.

Aerial insectivorous bat responses to 30 years of forest insularization in a dam-created Amazonian archipelagic landscape

Mega dams result in habitat loss and fragmentation in lowland tropical forests, compromising the diversity and ecosystem functioning in remnant habitat islands. We investigated the structure of aerial insectivorous bat assemblages within insular forest patches created by a vast ∼30-year-old hydropower reservoir and adjacent mainland continuous forests in Central Amazonia. Bats were surveyed using passive bat recorders across 34 sites. We assessed bat assemblage responses to landscape insularization and estimated the contribution of assemblage-wide components of β-diversity. Additionally, we assessed the effects of local vegetation, and both patch and landscape variables on bat species diversity. Continuous forest sites in the mainland retained higher species richness and bat activity compared to islands, leading to divergent species composition between forest sites. Larger islands (>100 ha) and continuous forests tended to share a similar assemblage composition manly drive by species richness differences with a minor contribution of species replacements. Moreover, local vegetation structure, island size, and landscape edge area exerted significant effects on species richness, bat activity, and species composition, with small degraded islands and landscapes dominated by forest edges exhibiting pervasive species loss. Our study highlights the detrimental impacts of forest fragmentation induced by large dams on aerial insectivorous bat assemblages. If new dam projects are inevitable, we recommend the creation of extensive protected areas in land-bridge island systems and their adjacent continuous forests. Those protected sites can minimize the negative impacts of small islands, safeguarding forest quality for forest-dependent bats, which ensures the continuity of their ecosystem services.

Effects of seining effort on estimates of fish diversity in a sand-bed river

Changes in species diversity can be an indicator of ecosystem disturbance, impairment, or recovery. Estimating sampling effort needed to adequately represent stream fish assemblages is necessary for informing conservation actions. Increased sampling intensity can increase species detection, affecting the accuracy and precision of biodiversity indices. Seining is commonly used in fish surveys in sand-bottomed streams of the western USA. Here, we sampled 20, 200-m long stream sites each with 40 consecutive seine hauls to determine how increased within-site effort affected measures of species diversity. An average of 10 seine hauls were required to collect 75% of species present at sites in 40 seine hauls, while 18 seine hauls were required to collect 100% of species observed at a site sampled with 40 hauls. Simpson’s diversity index was highly variable when fewer than 7 seine hauls were performed at each site but stabilized when effort was > 15 seine hauls per site. Total dissimilarity and β-diversity components were variable under low sampling effort and also stabilized when effort reached 15 seine hauls per site. However, sampling with more than 18–20 seine hauls per site yielded few additional species. In shallow, sand-bed streams, we suggest sampling with < 5 seine hauls per 200 m of stream can result in unreliable estimates of α-diversity and variation in β-diversity. Increased effort of 15–20 seine hauls per 200 m of stream captured nearly all species present in 40 hauls per 200 m and stabilized species evenness and β-diversity indices.

Eutrophication as a homogenizer process of phytoplankton β-diversity in lowland streams

Phytoplankton diversity was assessed in subtropical lowland streams in two regions (Espinal and Islas) with different land uses to determine if eutrophication homogenized diversity. We sampled phytoplankton and took relevant information on several environmental variables across twelve streams in two sampling periods (April and November). We partitioned the β-diversity into its components (richness difference and turnover) to describe the diversity variation. Furthermore, we performed redundancy analyses and regression models to approach the relevance of environmental and spatial variables (geographical distance) on such variation. We identified low β-diversity values, and turnover was the dominant component of β-diversity for both regions. In the most eutrophic region (Espinal), eutrophication (inferred from total phosphorus concentration) appeared as a homogenizing process of total β-diversity while in the less eutrophic (Islas), variations in soluble reactive phosphorus among sites appeared as the main driver. The turnover component at both regions was regulated by other processes (e.g., biological oxygen demand and temperature). We conclude that eutrophication acts as a homogenizing process of phytoplankton β-diversity in lowland streams linked to agriculture (Espinal). Still, it is not the same on Islas, where other factors not revealed in this study could determine low β-diversity values.

Seasonal flooding decreases fruit-feeding butterfly species dominance and increases spatial turnover in floodplain forests of central Amazonia.

The seasonal flood pulse in Amazonia can be considered a primary driver of community structure in floodplain environments. Although this natural periodic disturbance is part of the landscape dynamics, the seasonal inundation presents a considerable challenge to organisms that inhabit floodplain forests. The present study investigated the effect of seasonal flooding on fruit-feeding butterfly assemblages in different forest types and strata in central Amazonia. We sampled fruit-feeding butterflies in the canopy and the understory using baited traps in adjacent upland (unflooded forests-terra firme), white and blackwater floodplain forests (várzea and igapó, respectively) during the low- and high-water seasons. Butterfly abundance decreased in the high-water season, especially of dominant species in várzea, but the number of species was similar between seasons in the three forest types. Species composition differed between strata in all forest types. However, the flood pulse only affected butterfly assemblages in várzea forest. The β-diversity components also differed only in várzea. Species replacement (turnover) dominated the spatial β-diversity in igapó and terra firme in both seasons and várzea in the high-water season. Nonetheless, nestedness was relatively higher in várzea forests during the low-water season, mainly due to the effect of dominant species. These results emphasize the importance of seasonal flooding to structure butterfly assemblages in floodplain forests and reveal the idiosyncrasy of butterfly community responses to flooding in different forest types. Our results also suggest that any major and rapid changes to the hydrological regime could severely affect floodplain communities adapted to this natural seasonal hydrological cycle, threatening the existence of these unique environments.

Spatial Factors Outperform Local Environmental and Geo-Climatic Variables in Structuring Multiple Facets of Stream Macroinvertebrates' β-Diversity.

Simple SummaryOne of the key targets of community ecology and biogeography concerns revealing the variability and underlying drivers of biodiversity. Most current studies understand biodiversity based on taxonomic information alone. Our study was based on macroinvertebrates from 179 stream sampling sites in the Hun-Tai River Basin in Northeastern China. The correlation of different facets of β-diversity was compared while revealing the relative contribution of multiple abiotic factors (i.e., local environmental, geo-climatic, and spatial factors) to shaping β-diversity based on taxonomic, functional, and phylogenetic information. The results showed that functional β-diversity provides important complementary information to taxonomic and phylogenetic β-diversity. Moreover, spatial factors outperform local environmental and geo-climatic variables in structuring multiple facets of stream macroinvertebrates’ β-diversity. Our study provides guidance for future conservation studies of watershed biodiversity, as well as implications for future studies of β-diversity.One of the key targets of community ecology and biogeography concerns revealing the variability and underlying drivers of biodiversity. Most current studies understand biodiversity based on taxonomic information alone, but few studies have shown the relative contributions of multiple abiotic factors in shaping biodiversity based on taxonomic, functional, and phylogenetic information. We collected 179 samples of macroinvertebrates in the Hun-Tai River Basin. We validated the complementarity between the three facets and components of β-diversity using the Mantel test. Distance-based redundancy analysis and variance partitioning were applied to explore the comparative importance of local environmental, geo-climatic, and spatial factors on each facet and component of β-diversity. Our study found that taxonomic and phylogenetic total β-diversity was mainly forced by turnover, while functional total β-diversity was largely contributed by nestedness. There is a strong correlation between taxonomic and phylogenetic β-diversity. However, the correlations of functional with both taxonomic and phylogenetic β-diversity were relatively weak. The findings of variation partitioning suggested that distinct facets and components of macroinvertebrates’ β-diversity were impacted by abiotic factors to varying degrees. The contribution of spatial factors was greater than that of the local environment and geo-climatic factors for taxonomic, functional, and phylogenetic β-diversity. Thus, studying different facets and components of β-diversity allows a clearer comprehension of the influence of abiotic factors on diversity patterns. Therefore, future research should investigate patterns and mechanisms of β-diversity from taxonomic, functional, and phylogenetic perspectives.

Discriminating ecological processes affecting different dimensions of α- and β-diversity in desert plant communities.

Understanding the spatial distribution of plant diversity and its drivers are major challenges in biogeography and conservation biology. Integrating multiple facets of biodiversity (e.g., taxonomic, phylogenetic, and functional biodiversity) may advance our understanding on how community assembly processes drive the distribution of biodiversity. In this study, plant communities in 60 sampling plots in desert ecosystems were investigated. The effects of local environment and spatial factors on the species, functional, and phylogenetic α‐ and β‐diversity (including turnover and nestedness components) of desert plant communities were investigated. The results showed that functional and phylogenetic α‐diversity were negatively correlated with species richness, and were significantly positively correlated with each other. Environmental filtering mainly influenced species richness and Rao quadratic entropy; phylogenetic α‐diversity was mainly influenced by dispersal limitation. Species and phylogenetic β‐diversity were mainly consisted of turnover component. The functional β‐diversity and its turnover component were mainly influenced by environmental factors, while dispersal limitation dominantly effected species and phylogenetic β‐diversity and their turnover component of species and phylogenetic β‐diversity. Soil organic carbon and soil pH significantly influenced different dimensions of α‐diversity, and soil moisture, salinity, organic carbon, and total nitrogen significantly influenced different dimensions of α‐ and β‐diversity and their components. Overall, it appeared that the relative influence of environmental and spatial factors on taxonomic, functional, and phylogenetic diversity differed at the α and β scales. Quantifying α‐ and β‐diversity at different biodiversity dimensions can help researchers to more accurately assess patterns of diversity and community assembly.

Functionally explicit partitioning of plant β-diversity reveal soil fungal assembly in the subarctic tundra.

Metabarcoding technologies for soil fungal DNA pools have enabled to capture the diversity of fungal community and the agreement of their β-diversity with plant β-diversity. However, processes underlying the synchrony of the aboveground-belowground biodiversity is still unclear. By using partitioning methods for plant β-diversity, this study explored the process driving synchrony in tundra ecosystems, in which drastic vegetation shifts are observed with climate warming. Our methods based on Baselga's partitioning enabled the division of plant β-diversity into two phenomena and three functional components. Correlation of fungal β-diversity with the components of plant β-diversity showed that the spatial replacement of fungi was promoted by plant species turnover, in particular, plant species turnover with functional exchange. In addition, spatial variety of graminoid or forbs species, rather than shrubs, enhanced fungal β-diversity. These results suggest the importance of small-scale factors such as plant-fungal interactions or local environments modified by plants for the fungal community assemblage. The process-based understanding of community dynamics of plants and fungi allows us to predict the ongoing shrub encroachment in the Arctic region, which could weaken the aboveground-belowground synchrony.

The different facets of native bird diversity (taxonomic, functional and phylogenetic) as predictors of alien birds increasing richness and expanding range in Great Britain

Native-alien species relationship is one of the potential mechanisms to explain alien species' success. Most approaches have so far focused on species richness, but species-centric approaches alone are of limited explanatory ability. We utilized the breeding bird atlases of Great Britain at three time points, to examine the temporal patterns of alien bird species assemblages' richness and composition and analyze the spatio-temporal relationship between them and native species functional and phylogenetic diversity. Alien birds were successful in increasing their average local richness and range from the 1970s to the 2010s, without high values of the replacement component of β-diversity in most assemblages and with increasing richness in the majority of atlas cells. Communities with higher native diversity were positively associated with higher alien species richness and overall, our results showed that native biodiversity metrics can act as reliable predictors of alien species richness patterns. Native phylogenetic diversity emerged as an important predictor of alien species richness, whereas functional diversity was not as successful. Phylogenetic diversity may have captured native species' functional differences more effectively and/or the added layer of phylogenetic information increased phylogenetic diversity's ability to predict alien species richness patterns and may be indicative of evolutionary processes reflecting the mechanisms shaping native-alien species' relationship. If we were to predict where these alien birds may spread within the next 20 years, our results point to phylogenetically rich communities. This is likely a reflection of habitat heterogeneity and/or resource availability in these communities. In any case, a multifaceted approach is preferable, as different measures highlight different mechanisms driving communities' invasibility.

Determinants of zooplankton functional dissimilarity during years of El Niño and La Niña in floodplain shallow lakes

In floodplain lakes, precipitation events shape the environmental heterogeneity and the occurrence of species and functional traits. However, the importance of each biotic and abiotic factor on structuring communities might depend on the local environmental conditions and the identity of such communities. We investigated through Permutational analyses of variance and functional β-diversity components, the effects of neutral and extreme events of precipitation on environmental heterogeneity and distribution of zooplankton functional traits in floodplain lakes. We also examined through distance-based redundancy analysis and fourth-corner analysis, how different variables (physical–chemical, food availability, predation, and temporal dynamics) structure the distribution of zooplankton functional traits and which traits were related to these variables. We used data from six lakes of the Upper Parana River floodplain over 19 years. Environmental heterogeneity and β-diversity were higher during El Nino and lower during La Nina (extreme rainy and extremely dry season, respectively). Physical–chemical were the variables that most explained zooplankton β-diversity during all seasons and predation during both extreme seasons (La Nina and El Nino). We observed a set of multiple biotic and abiotic factors causing complex effects on zooplankton functional diversity. The homogenization of traits—observed during extreme dry seasons—can lead to losses in ecosystem functions and services if these events continue to be more frequent and intense. We reaffirm the importance of natural flood caused by the rainy seasons to maintain high biotic and abiotic heterogeneity and ecosystem processes.

Spatial patterns and ecological drivers of soil nematode β-diversity in natural grasslands vary among vegetation types and trophic position.

Understanding biogeographic patterns of community assemblages is a core objective in ecology, but for soil communities these patterns are poorly understood. To understand the spatial patterns and underlying mechanisms of β-diversity in soil communities, we investigated the β-diversity of soil nematode communities along a 3,200-km transect across semi-arid and arid grasslands. Spatial turnover and nested-resultant are the two fundamental components of β-diversity, which have been attributed to various processes of community assembly. We calculated the spatial turnover and nested-resultant components of soil nematode β-diversity based on the β-partitioning framework. Distance matrices for the dissimilarity of soil nematode communities were computed using the 'Sørensen' method. We fitted negative exponential models to compare the distance decay patterns in nematode community similarity with geographic distance and plant community distance in three vegetation types (desert, desert steppe and typical steppe) and along the whole transect. Variation partitioning was used to distinguish the contribution of geographic distance and environmental variables to β-diversity and the partitioned components. Geographic distance and environmental filtering jointly drove the β-diversity patterns of nematode community, but environmental filtering explained more of the variation in β-diversity in the desert and typical steppe, whereas geographic distance was important in the desert steppe. Nematode community assembly was explained more by the spatial turnover component than by the nested-resultant component. For nematode feeding groups, the β-diversity in different vegetation types increased with geographic distance and plant community distance, but the nested-resultant component of bacterial feeders in the desert ecosystem decreased with geographic distance and plant community distance. Our findings show that spatial variation in soil nematode communities is regulated by environmental processes at the vegetation type scale, while spatial processes mainly work on the regional scale, and emphasize that the spatial patterns and drivers of nematode β-diversity differ among trophic levels. Our study provides insight into the ecological processes that maintain soil biodiversity and biogeographic patterns of soil community assemblage at large spatial scales.

High Temporal Beta Diversity in an Ant Metacommunity, With Increasing Temporal Functional Replacement Along the Elevational Gradient

Ecological communities vary considerably in space and time and understanding such changes has fundamental relevance for ecology and conservation sciences. Mountains provide an excellent scenario for studies addressing spatial and temporal variation, as they vary in conditions and resources in a small geographic region. Here, we aimed to understand the patterns of variation in ant metacommunity composition across time and along an elevational gradient in a tropical mountain, focusing both on the taxonomic and functional facets of diversity. We used a β-diversity metric and broke it into nestedness and turnover to estimate short-term temporal changes in ant metacommunity composition. We tested the following hypotheses: i. taxonomic and functional temporal β-diversity increase along the elevational gradient and ii. turnover is the main component driving taxonomic temporal β-diversity and nestedness for functional temporal β-diversity. Rejecting our first hypothesis, we found that both taxonomic and functional temporal β-diversity did not increase with elevation. Yet, the values were always high, indicating that both species and functional traits are highly variable over time. In accordance with our second hypothesis, we found that turnover was the main component of taxonomic β-diversity. Yet adding complexity to our hypothesis, the contribution of nestedness to functional β-diversity decreased with increasing elevation. These results suggest that at low elevations, the turnover in species composition may then cause changes in trait composition because of the loss of some traits, yet preserving the most common functions (nested functional communities), while at high elevations functional capabilities may change over time (turnover of traits). In the context of global warming, where tropical mountain insects are expected to change their distributional range upwards, it is extremely important to consider the importance of the turnover on the temporal variation in functional traits and functions of ant metacommunity at higher elevations.

Spatiotemporal patterns of β-diversity of flower chafer beetles in urban park and natural reserve sites in Brazilian Cerrado

Understanding the drivers underlying spatial and temporal changes of species distribution is a major and urgent challenge, given the scenario of increased climate and land use changes. The creation and maintenance of urban parks is an efficient conservation strategy in urbanized landscapes. In this study, we explore how spatiotemporal β-diversity components of turnover and nestedness of flower chafer beetles are influenced by climate conditions in urban park and natural reserve sites in Brazilian Cerrado, one of the largest, richest and possibly the most threatened tropical savannah on the Planet. We sampled flower chafer beetles using aerial fruit-baited traps, every 2 weeks from January to December 2014, in six ‘natural reserve’ sites (outside the urban matrix) and four ‘urban park’ sites (within the urban matrix) in Brazilian Cerrado. Our results highlighted four main findings: (i) spatially, ‘natural reserve’ and ‘urban park’ sites presented similar values of dissimilarity and substitution of flower chafer beetles but ‘urban park’ sites had higher nestedness values than ‘natural reserve’ sites; (ii) temporally, ‘natural reserve’ and ‘urban park’ sites presented similar values of dissimilarity, turnover, and nestedness; (iii) average β-diversity, turnover and nestedness values did not differ between dry and rainy seasons in both ‘natural reserve’ and ‘urban park’ sites; and (iv) none of the climatic variables influenced the temporal variation in β-diversity and its components of flower chafer beetles. Therefore, most of spatiotemporal changes in β-diversity patterns of flower chafer beetles are not related to urbanization effects or changes in climatic variables in Brazilian Cerrado. This group of insects seems to respond more to environmental and climatic filters with changes in richness, abundance, and species composition than changes in β-diversity patterns.

Plant community composition and structure under short-term grazing exclusion in steppic arid rangelands

Grazing exclusion has been proved to be an effective approach for naturally restoring degraded rangelands. Still, the effect of this management practice on plant community composition and structure is ambiguous, especially under prolonged and repeated drought events. Here, we investigated the responses of community composition (i.e. incidence-based) and structure (i.e. abundance-based) to short-term sheep grazing exclusion under severe drought episode in the arid steppes of Alfa-grass (Stipa tenacissima L.) with a long evolutionary history of grazing. Individual species responses were tested based on species occurrence and abundance in either grazed or grazing-excluded steppes. Besides, indicator species analysis was used to identify species indicative of grazing-excluded steppes. Likewise, incidence-based and abundance-based α-diversity, β-diversity and functional groups’ diversities were quantified using Hill Numbers and compared between the two steppe managements types. Under severe drought conditions, sheep grazing exclusion allowed the apparition of a large number of increasers, colonizers, and native indicator plant species. It also improved the size of regional species pool and increased overall incidence-based and abundance-based α-diversity. Moreover, grazing exclusion decreased the abundance-based β-diversity at local scale but increased it at landscape scale. The incidence-based β-diversity significantly decreased at the landscape scale. Grazing exclusion enabled a significant spatial structuration of abundance-based β-diversity components by maintaining high balanced variation in species abundance at large spatial scale and greater abundance-gradient at fine-scale. Our results suggest that the implementation of short-term grazing exclusion in arid steppes would be the appropriate management practice for vegetation and habitat during prolonged droughts since it permits the recovery of native plant species and affects positively the size of the regional species pool, the overall incidence- and abundance-based α-diversity as well as the abundance-based β-diversity (chiefly at landscape scale).

Partitioning β-diversity reveals that invasions and extinctions promote the biotic homogenization of Chilean freshwater fish fauna.

AimExotic species’ introductions together with extinction of native species represent the main mechanisms driving biotic homogenization of freshwater fish assemblages around the world. While generally ichtyofaunistic realms transit towards biotic homogenization, for conservation purposes it is essential to understand what specific mechanisms are promoting it on particular areas or regions. Here, we report the occurrence of biotic homogenization in 29 Chilean watersheds, analyzing its β-diversity (including turnover and nestedness) and predicting future trends.LocationContinental Chile (18o–56o S).MethodsWe determined fish composition per basin for historical and current assemblages; extant native, exotic, and extinct species were recorded as 1 (presence) or 0 (absence) in two matrices basins × species. For each matrix, we calculated the turnover (βsim), nestedness (βnes), and β-diversity (βsor); then, we obtained Δβsim, Δβnes, and Δβsor, as the arithmetical difference between basin pairs over time. In addition, we search for explanatory variables correlating Δβsim, Δβnes, and Δβsor with geographical and land use variables. Finally, simulating events of species introduction (i.e., invasion) and extinction, we generated 15 hypothetical assemblages, looking to establish future trends towards biotic change in Chilean basins.ResultsSpecies turnover and β-diversity significantly decreased from historical to current assemblages (Δβsim = -0.084; Δβsor = -0.061, respectively), while the species nestedness did not show significant changes (Δβnes = 0.08). Biotic changes have been driven mainly by the introduction of 28 exotic species, with a minor role of extinctions (one species) and translocations (0 species) of native species. Changes in β-diversity were negatively correlated with area, elevation, and geographical distance between basins but not with land-use nor human population. Finally, the analysis of 15 future assemblages predicts a significant decrease of β-diversity and turnover, and an increase for species nestedness, this time promoted by an increase in the extinction of native species.Main conclusionChilean basins show a significant decrease of the distributional β-diversity and species turnover of the freshwater fish fauna, evidencing a trend towards biotic homogenization. This trend is shared with other Neotropical basins; however, specific mechanisms driving it show different magnitude. Changes in the β-diversity components do not show correlation with variables associated to land use, thus suggesting that casual introductions of freshwater fishes in Chile follow an opportunistic mode related to commercial use. According to future scenarios simulated, biotic homogenization should increase further, mainly as consequence of increased native extinctions.