Richness Difference Components Research Articles

Effects of plant taxonomic position on soil nematode communities in Antarctica.

Antarctica terrestrial ecosystems are facing the most threats from global climate change, which is altering plant composition greatly. These transformations may cause major reshuffling of soil community composition, including functional traits and diversity, and therefore affect ecosystem processes in Antarctica. We used high-throughput sequencing analysis to investigate soil nematodes under 3 dominant plant functional groups (lichens, mosses, and vascular plants) and bare ground in the Antarctic region. We calculated functional diversity of nematodes based on their diet, life histories, and body mass with kernel density n-dimensional hypervolumes. We also calculated taxonomic and functional beta diversity of the nematode communities based on Jaccard dissimilarity. The presence of plants had no significant effect on the taxonomic richness of nematodes but significantly increased nematode functional richness. The presence of plants also significantly decreased taxonomic beta diversity (homogenization). Only mosses and vascular plants decreased nematode functional beta diversity, which was mostly due to a decreased effect of the richness difference component. The presence of plants also increased the effect of deterministic processes potentially because environmental filtering created conditions favorable to nematodes at low trophic levels with short life histories and small body size. Increasing plant cover in the Antarctic due to climate change may lead to increased diversity of nematode species that can use the scarce resources and nematode taxonomic and functional homogenization. In a future under climate change, community restructuring in the region is possible.

Eutrophication modifies the relationships between multiple facets of macroinvertebrate beta diversity and geographic distance in freshwater lakes

AbstractAimUnderstanding the distance–decay relationship (DDR) has been considered important because it reflects a combination of several ecological processes such as dispersal limitation and environmental sorting. However, effects of human disturbances on DDR are poorly known, especially in freshwater lakes. This study is aimed to examine how anthropogenic eutrophication modified the relationships between three facets (taxonomic, functional and phylogenetic) of macroinvertebrate beta diversity and geographic and environmental distances across 30 freshwater lakes.LocationThe Yangtze River floodplain, China.MethodsWe used Mantel tests to examine the relationships between multiple facets of assemblage dissimilarities (overall beta diversity, replacement and richness difference components) and geographic and environmental distances. Distance‐based redundancy analysis (dbRDA) and associated variation partitioning procedures were applied to explore the relative contributions of environmental and spatial factors on the three facets of beta diversity.ResultsWe found that none of the three beta diversity facets was related to geographic distance, but all were significantly related to environmental distance, mainly mirroring eutrophication‐related variables. Based on the variation partitioning approach, the macroinvertebrate assemblages examined were almost exclusively structured by environmental factors associated with eutrophication, while spatial variables had a negligible effect. Nevertheless, the different facets of beta diversity did not decrease (i.e., no homogenization trend) in lake groups showing the highest eutrophication levels, implying complex influences of anthropogenic disturbances in driving homogenization or differentiation in assemblage compositional dissimilarity.Main ConclusionsOur findings suggested that the high degrees of eutrophication acted as an environmental filter to significantly modify the spatial distance–decay relationships, possibly via decreasing the importance of dispersal limitation in shaping macroinvertebrate assemblages in the studied lakes. Given the sensitivity of beta diversity patterns to eutrophication we found in this study, we recommend that the role of anthropogenic disturbances should be incorporated into research on general ecological patterns like the DDR.

The effects of longitudinal fragmentation on riverine beta diversity are modulated by fragmentation intensity

The loss of longitudinal connectivity affects river systems globally, being one of the leading causes of the freshwater biodiversity crisis. Barriers alter the dispersal of aquatic organisms and limit the exchange of species between local communities, disrupting metacommunity dynamics. However, the interplay between connectivity losses due to dams and other drivers of metacommunity structure, such as the configuration of the river network, needs to be explored. In this paper, we analyzed the response of fish communities to the network position and the fragmentation induced by dams while controlling for human pressures and environmental gradients. We studied three large European catchments covering a fragmentation gradient: Upper Danube (Austrian section), Ebro (Spain), and Odra/Oder (Poland). We quantified fragmentation through reach-scaled connectivity indices that account for the position of barriers along the dendritic network and the dispersal capacity of the organisms. We used generalized linear models to explain species richness and Local Contributions to Beta Diversity (LCBD) and multilinear regressions on the distance matrix to describe Beta Diversity and its Replacement and Richness Difference components. Results show that species richness was not affected by fragmentation. Network centrality metrics were relevant drivers of beta diversity for catchments with lower fragmentation (Ebro, Odra), and fragmentation indices were strong beta diversity predictors for the catchment with higher fragmentation (Danube). We conclude that in highly fragmented catchments, the effects of network centrality/isolation on biodiversity could be masked by the effects of dam fragmentation. In such catchments, metapopulation and metacommunity dynamics can be strongly altered by barriers, and the restoration of longitudinal connectivity (i.e. the natural centrality/isolation gradient) is urgent to prevent local extinctions.

Temporal changes of taxonomic and functional diversity in dung beetles inhabiting forest fragments and pastures in Los Tuxtlas Biosphere Reserve, Mexico

We evaluated short- (among months within-years) and long-term (between 1999-2000 and 2016-2017) temporal patterns of taxonomic and functional β- diversity (and its components of substitution and gain/loss) of dung beetle assemblages in forest fragments and pastures in the Los Tuxtlas Biosphere Reserve (LTBR). Habitat type affected the taxonomic dissimilarity and the richness difference component, with average values being respectively 1.42 and 1.56 times higher in pastures than in forest fragments. Only habitat type was important for functional richness, being 1.93 and 1.69 higher in forest fragments than pastures in 1999-2000 and 2016-2017, respectively. Pastures were taxonomically and functionally poorer but were also more temporally dynamic than forest fragments both within-year and between-years. Habitat type is a determining factor for temporal dynamics, with forest fragments presenting more stable dung beetle assemblages than cattle pastures.

Replacement drives native β‐diversity of British avifauna, while richness differences shape alien β‐diversity

AbstractAimWe explored the range shifts of alien and native birds, the responses of alien and native β‐diversity to abiotic factors, and the effect of native diversity on alien β‐diversity in two time periods.LocationGreat Britain.Time period1968–1972, 2007–2011.Taxa studiedBreeding birds.MethodsWe estimated range shifts of alien and native species between the periods 1968–1972 and 2007–2011. Following, β‐diversity of alien and native communities was estimated by Jaccard pairwise index (βtot) and partitioned into richness difference and replacement component for each period. We built abiotic generalized dissimilarity models including abiotic factors for alien and native βtot and their components and a biotic model for aliens including native taxonomic and functional diversity as predictors.ResultsMost alien and half native species expanded into new regions during the 40‐year period. The native species range shifts did not exhibit a clear pattern along the longitudinal or latitudinal gradient, while alien species tended to move north‐westwards. The richness difference was the dominant component of alien β‐diversity, and the replacement component contributed mostly to native β‐diversity. Alien β‐diversity responded similarly but less strongly than native β‐diversity, to the abiotic gradients. Temperature‐related variables, distance and precipitation were the most important abiotic drivers of native and alien β‐diversity. The biotic model of alien β‐diversity explained more deviance than the abiotic model.Main conclusionsAlien species expanded into new regions over the 40 years, with alien β‐diversity driven mostly by species gains. The effect of environmental filtering on alien communities was weaker compared with native communities but was slightly reinforced in the second period compared with the first period, highlighting the role of environmental change in shaping diversity patterns. Native diversity played a key role in driving alien β‐diversity, through biotic interactions or/and by reflecting climatic suitability or niche availability for aliens.

Different responses of incidence-weighted and abundance-weighted multiple facets of macroinvertebrate beta diversity to urbanization in a subtropical river system

• Beta diversity weighted by incidence vs abundance data varied differently along urbanization gradient. • Richness difference contributed more to beta diversity weighted by abundance than incidence data. • Stochasticity was more dominant in shaping beta diversity weighted by abundance than incidence data. • Homogenization studies should consider the roles of rare and abundant taxa. Urbanization is one of the major drivers of biotic homogenization (i.e., decrease in beta diversity) in freshwater systems. However, only a few studies have simultaneously examined how urbanization affects multiple facets (i.e., taxonomic, functional and phylogenetic) of beta diversity and its underlying ecological drivers in urban river macroinvertebrates. Here, we distinguished the patterns and ecological mechanisms of multiple facets of macroinvertebrate beta diversity weighted by incidence and abundance data in a subtropical river system with a distinct urbanization gradient. We also investigated how total beta diversity patterns stem from replacement versus richness difference among sites. Our results showed that taxonomic and phylogenetic beta diversities weighted by incidence data were primarily driven by replacement of taxa, whereas the richness difference contributed more to multiple facets of beta diversity based on abundance data. Furthermore, multiple facets of beta diversity decreased with urbanization for both incidence-weighted and abundance-weighted data, but the former showed more substantial decreases. Both replacement and richness difference components contributed roughly equally to the decline of incidence-weighted beta diversity. In contrast, the losses of abundance-weighted beta diversity were mainly associated with replacement of taxa. Variation partitioning results revealed that all beta diversity measures based on incidence data were governed primarily by local and land-use variables, whereas spatial variables were more relevant in driving beta diversity weighted by abundance data. Overall, by comparing different facets and components of beta diversity weighted by incidence versus abundance data, we suggest that incidence-weighted data may be more sensitive in portraying the impacts of urbanization on macroinvertebrate diversity. This likely resulted from the fact that incidence-weighted data shows the importance of rare taxa in shaping homogenization induced by urbanization.

The value of novel ecosystems: Disclosing the ecological quality of quarry lakes

Intense sand and gravel mining has created numerous man-made lakes around the world in the past century. These small quarry lakes (1–50 ha) are usually hydrologically isolated, often deep (6–40 m) and stratify during summer and in cold winters. Due to their small size, these deep man-made lakes are usually not included in the regular monitoring campaigns, e.g. as required for the European Water Framework Directive (WFD). Therefore, not much is known about the ecological functioning of these novel ecosystems. During two summers, we determined the macrophyte diversity and measured a range of physico-chemical and biological parameters in 51 quarry lakes in the catchment area of the rivers Meuse and Rhine. We compared the results of this campaign to the chemical and macrophyte sampling as performed for the WFD in the immediate surrounding shallow standing waters. Alpha (local) and beta diversity (regional), and local contribution to beta diversity were calculated for the whole region of which beta diversity was further partitioned into a true species replacement and richness difference component. Quarry lakes contain higher water quality reflected by lower nutrient and chlorophyll-a concentration compared with shallow water bodies. Additionally, quarry lakes contribute significantly to the regional macrophyte diversity pool by harboring distinctly different macrophyte communities (beta diversity — replacement). Specifically quarry lakes with a total phosphorus concentration in the water column below 35 μg P/l contribute most to beta diversity among quarry lakes.Novel ecosystems such as deep quarry lakes are often perceived as less valuable ecosystems, with strong implications regarding their management. Our results show that quarry lakes are in general of better chemical and biological quality compared with shallow standing waters. We therefore call for a more integrated assessment of the quality of quarry lakes and corresponding management strategy of these waters by water managers.

Phylogenetic beta diversity of Odonata assemblages in the extreme condition of Central Iran

Freshwater ecosystems are of the most diverse ecosystems in the world, but anthropogenic disturbance and climate change are threatening the biodiversity of these habitats, particularly in the highly vulnerable arid regions. Understanding the compositional patterns in aquatic biota and discovering factors responsible for these patterns enable researchers to predict the impacts of environmental changes and reduce their destructive effects. As a first step for evaluating the conservation value of freshwater ecosystems in the arid areas of Central Iran, we investigated the phylogenetic beta diversity of Odonata assemblages and their response to climate, landscape, and local predictors. A total of 41 water bodies were surveyed and 42 species of Odonata were recorded. The distance matrices related to the total phylogenetic beta diversity of Odonata and the replacement and richness difference components were computed. Each of the three dissimilarity matrices were modelled by generalized dissimilarity modelling (GDM). The average phylogenetic beta diversity was high, and the replacement component had a higher contribution rather than the richness difference component. GDMs results showed that total phylogenetic beta diversity was strongly associated with climate and local predictors. The most influential variables observed were climate variables. Our findings indicated that even in extreme conditions, the freshwater ecosystems could support species with various phylogenetic histories. We emphasize the importance of man-made water bodies in supporting freshwater biodiversity in arid areas. Given the growing threat of habitat degradation and climate change, with no conservation plan, many vulnerable species may be in danger of localized extinction within the region.

Ecological drivers of Odonata beta diversity in arid and semi‐arid regions of the Central Plateau of Iran

Abstract Freshwater habitats are among the most threatened and least studied habitats in arid regions of Iran. Discovering factors responsible for the spatial variation of biodiversity are one of the main considerations in conservation biology. As a first step towards developing conservation strategies, we aimed to investigate the beta diversity and response of Odonata assemblages to climate and landscape variables in arid and semi‐arid regions of Iran. A total of 120 water bodies were surveyed. The beta diversity distance matrices were calculated for Odonata, Anisoptera, and Zygoptera, using the Jaccard dissimilarity coefficient. Also, the replacement and richness difference components of Odonata beta diversity were computed. Each of the five dissimilarity matrices was modelled by generalised dissimilarity modelling (GDM). We recorded 58 species of Odonata that represent 58% of the Odonata species in Iran. The average total beta diversity was high (0.873). GDMs results showed that the most influential variables varied between the replacement and richness difference components of Odonata beta diversity as well as between the two Odonata suborders. Anisoptera were most strongly affected by the temperature annual range, while the most important variable for Zygoptera was the average wind speed in April. Our results suggest that the studies of the drivers of biodiversity patterns benefit from beta diversity partitioning also from comparing species groups with different ecological preferences. The high biodiversity of the studied water bodies as well as the anthropogenic and climate threats that they are faced with, make these ecosystems a conservation priority.

Distance decay of benthic macroinvertebrate communities in a mountain river network: Do dispersal routes and dispersal ability matter?

Environmental heterogeneity and dispersal limitation are important drivers of beta diversity; however, their relative influence on the two fundamental components of beta diversity (i.e., species replacement and richness difference) has not been fully examined in montane streams. Here, we examined the relative importance of local environmental gradients and three physical distance matrices (i.e., overland, watercourse and cost distances) on beta diversity and its two components for a macroinvertebrate metacommunity in a stream network. To provide additional insights into community assembly, we also analysed variation in two deconstructed sub-communities based on dispersal ability (i.e., weak and strong dispersers). Both environmental filters and physical distances (dispersal limitation) drove patterns of overall beta diversity, with the former generally prevailing over the latter. Species replacement components showed stronger correlations with environmental gradients than physical distances, while the opposite is true for the richness difference components. Overland distances were generally more important than cost and watercourse distances for community dissimilarity of stream macroinvertebrates, implying that lateral dispersal out of stream corridors through flight was the major dispersal route in the studied steam network. As expected, community dissimilarity of strong dispersers was primarily shaped by environmental filtering, while community dissimilarity of weak dispersers was associated with the joint effects of environmental filtering and dispersal limitation. Our findings demonstrate that partitioning overall dissimilarity into species replacement and richness difference provides more insights into the processes driving spatial variability in biological communities compared with the utilization of total beta diversity alone. Our results support the notion that maintaining environmental heterogeneity and natural connectivity of stream networks should be effective measures to conserve regional biodiversity.

Spatial scale drives diversity patterns of benthic macroinvertebrate communities in tropical estuaries

AbstractIdentifying the hierarchical spatial levels that show the greatest dissimilarities between communities and how these patterns are generated is essential to provide insights into the monitoring and protection of biodiversity. In this study, we additively partitioned diversity of macroinvertebrates into alpha, beta, and gamma diversity across multiple scales in typical and semi‐arid tropical estuaries. We also determined which components of the total beta diversity, in terms of species replacement or richness difference (presence‐absence data) and abundance difference (relative abundance data), had the greatest relative importance in structuring the composition of benthic macrofauna. In typical and semi‐arid tropical estuaries, a non‐random spatial pattern was observed in additive partitioning of diversity, with higher values of beta diversity obtained at the largest scales analyzed. When considering the presence‐absence data, in general there was no clear trend which components of beta diversity had greater relative importance in typical estuaries. In the semi‐arid tropical estuaries, the richness difference component showed greater relative importance in the rainy season, whereas the species replacement presented greater proportions in the dry season. When considering abundance data, in general the abundance difference component showed greater relative importance in typical and semi‐arid tropical estuaries in the two seasonal periods. Therefore, approaches based on the presence/absence and on the relative abundance of species provided complementary answers about the distribution patterns of benthic macroinvertebrate communities. We demonstrated that environmental filtering and dispersal limitation may affect the patterns of distribution of benthic macrofauna in estuaries located in regions with different climatic conditions.

Historical legacies and contemporary processes shape beta diversity in Neotropical montane streams

AbstractAimContemporary dispersal constraints and environmental conditions are broadly recognized as significant drivers of beta diversity patterns. However, beta diversity patterns may also reflect the legacy of past climatic and geological events. In this study, we investigated the relative importance of historical and contemporary factors as drivers of taxonomic, functional and phylogenetic beta diversity in Neotropical stream communities.LocationThe Colombian Orinoco basin.TaxonDiatoms and insects.MethodsWe estimated taxonomic, phylogenetic and functional beta diversity using Baselga's (BAS) and Podani's (POD) frameworks. Following both frameworks, we further partitioned every biodiversity facet into turnover and nestedness or richness difference components. Then, we used generalized linear models (GLM) to relate each biodiversity facet with environmental, spatial and historical factors.ResultsWe found that both historical and contemporary factors affected current patterns of beta diversity. Historical factors and water pH and temperature had the strongest effect on beta diversity patterns, particularly for taxonomic and phylogenetic facets. GLM models performed better for insects than for diatoms in all three facets. Within communities, our analysis also revealed a partial congruence between BAS‐ and POD‐based results.Main conclusionsDue to their past geological history and contemporary environmental gradients, tropical montane streams are natural laboratories for disentangling the joint effects of ecological and biogeographical factors on biodiversity patterns. Our study reveals that present‐day distribution patterns cannot be fully explained without accounting for the effects of past geological and climatic events on mountain landscapes. In the Neotropics, montane geology sets the stage for speciation and landscape formation, with which ecological (e.g., dispersal limitation) and environmental factors interact to generate spatial variation in species turnover.

Damming affects riverine macroinvertebrate metacommunity dynamics: Insights from taxonomic and functional beta diversity

Understanding ecological processes that drive metacommunity dynamics is essential for elucidating the mechanisms of community assembly and for guiding biodiversity conservation. This is especially important in dammed rivers. Here, we examined the taxonomic and functional beta diversity of macroinvertebrates and their underlying drivers in a dammed tropical river and compared the patterns with those in an adjacent undammed river. We found that both taxonomic and functional beta diversities were higher in the dammed river than in the undammed river across wet and dry seasons. The replacement component contributed most to the overall beta diversity for both taxonomic and functional facets, and this component was higher in the dammed river than in the undammed river. In addition, the taxonomic richness difference component was significantly higher in the dammed river in the dry season, but the functional richness difference component showed no difference between the two rivers and between the two seasons. Environmental filtering was the primary driver of total beta diversity and its replacement component, whereas the richness difference component was mainly explained by spatial factors, but these drivers varied in the dammed river in different seasons. Overall, our results indicated that damming induced changes in physiochemical variables (e.g., temperature, conductivity, and nutrients), accompanied by alterations in flow regime and longitudinal connectivity, increased replacement and loss of taxa or traits. These changes have consequently led to alteration of macroinvertebrate taxonomic and functional community dissimilarity and affected the relative effects of environmental and spatial factors on beta diversity and its components. Our study helps understand the ecological processes associated with dam impacts on macroinvertebrate biodiversity and the conservation potential of undammed rivers. In addition, our results showed that taxonomic and functional beta diversities can provide complementary information about dam impacts on riverine biodiversity.

Ecological correlates of riverine diatom and macroinvertebrate alpha and beta diversity across Arctic Fennoscandia

Abstract Arctic freshwaters support biota adapted to the harsh conditions at these latitudes, but the climate is changing rapidly and so are the underlying environmental filters. Currently, we have limited understanding of broad‐scale patterns of Arctic riverine biodiversity and the correlates of α‐ and β‐diversity. Using information from a database set up within the scope of the Arctic Council's Conservation of Arctic Flora and Fauna Circumpolar Biodiversity Monitoring Plan, we analysed patterns and correlates of α‐ and β‐diversity in benthic diatom and macroinvertebrate communities across northern Norway, Sweden, and Finland. We analysed variation in total β‐diversity and its replacement and richness difference components in relation to location of the river reach and its drainage basin (Baltic Sea in the south, the Barents Sea in the east and the north, and the Norwegian Sea in the west), in addition to climate and environmental variables. In both macroinvertebrates and diatoms, the replacement and richness difference components showed wide variation. For macroinvertebrates, the richness difference component was the more important, whereas for diatoms, the replacement component was the more important in contributing to variation in β‐diversity. There was no significant difference in β‐diversity between the three main drainage basins, but species composition differed among the drainage basins. Based on the richness difference component of β‐diversity, climate variables were most strongly associated with community variation in macroinvertebrates. In diatoms, both environmental and climate variables were strongly correlated with community compositional variation. In both groups, there were also significant differences in α‐diversity among the three main drainage basins, and several taxa were significant indicators of one of these drainage basins. Alpha diversity was greater in areas with a continental climate, while the oceanic areas in the west harboured greatly reduced flora and fauna. The correlates of biodiversity were relatively similar in macroinvertebrates and diatoms. Climate variables, in particular temperature, were the most strongly associated with biodiversity patterns in the Arctic rivers of Fennoscandia. Sedimentary geology may be associated with increased productivity and, to a lesser extent, with sensitivity to acidification. There was considerable variation in community composition across Arctic Fennoscandia, indicating the necessity of protecting several stream reaches or even whole catchments within each region to conserve total riverine biodiversity. Furthermore, it is likely that the predicted changes in temperature in Arctic areas will influence riverine diversity patterns across Fennoscandia.

Macroinvertebrate communities along the main stem and tributaries of a pre-Alpine river: composition responds to altitude, richness does not

We collected quantitative macroinvertebrate samples and measured environmental and geographical parameters at 13 sites: six along the main stem and seven in tributaries close to the main channel over a 700 m gradient in altitude and 22 km longitudinal distance along the River Kokra in the Slovenian Alps. Our objectives were 1) to compare longitudinal patterns in richness and community composition between main stem and tributary sites, and 2) to determine the relative importance of the replacement and richness difference component for overall beta diversity and of environmental versus spatial distance on beta diversity among main stem and tributary sites.In total 138 taxa were identified. There were no differences between main stem and tributary sites in mean abundance or taxon richness (67 and 58, respectively). A nMDS and ANOSIM based on Bray-Curtis similarities found no separation of main stem and tributary sites, but that upper (≥880 m a.s.l) and lower sites (≤680 m a.s.l.) formed two different groups. In both main stem and tributaries taxon richness increased only slightly going downstream while the community composition (DCA1) was much better explained by altitude and distance from source.Overall, beta diversity (Sørensen and Bray-Curtis dissimilarity) was similar for the two groups, and total Sørensen dissimilarity was driven mainly by replacement in main stem (78 %) and tributary sites (77 %). Mantel tests showed that main stem dissimilarities were significantly correlated to environmental PCA distance, watercourse distance, overland distance and altitudinal differences. Tributary dissimilarities were not correlated to any of these four factors. GLMs showed that dissimilarity among main stem sites was explained only by altitude difference, while no factors were significant among tributary sites, even though nearly so for environmental PCA distance.The study illustrates the importance of measuring beta diversity along ecological gradients, such as river continua and/or altitudinal gradients, where alpha diversity may fail to detect relatively minor changes in assemblage composition. Such changes are likely to occur due to present and future climate warming.

INTER-ANNUAL VARIATION OF OSTRACOD (CRUSTACEA) COMMUNITIES IN THE UPPER PARANÁ RIVER FLOODPLAIN, BRAZIL

Riverine floodplains have a large environmental heterogeneity, with lentic and lotic environments and a variety of aquatic macrophytes, providing habitat for various aquatic and terrestrial organisms. Here, we evaluate species composition and beta diversity of ostracod communities over a period of 14 years in two permanently connected lakes (Patos and Guarana) and two rivers (Ivinhema and Baia) of the Upper Parana River floodplain. We predict that the ostracod species composition differs in both types of environments amongst the years, and that beta diversity changes over time. Thirty-eight ostracod species were recorded, including new taxa that remain to be described. The change in ostracod species composition over time may be a result of natural or anthropogenic events occurring in the floodplain, in addition to the influence of local abiotic factors. The sequence of floods and droughts might also explain the difference in the contribution of replacement (turnover) and richness difference (loss or gain) components over time. These results show the importance of long-term research to understand the temporal dynamics of the communities, mainly in dam-regulated floodplains.

Contrasting responses of beta diversity components to environmental and host‐associated factors in insect ectoparasites

1. The present study investigated whether different components (species replacement and species gains/losses) of compositional and phylogenetic beta diversity of insect ectoparasites responded similarly to environmental and host‐associated gradients using a large dataset on distribution of fleas and their rodent hosts in Mongolia.2. Generalised dissimilarity modelling was applied to investigate whether environmental variables or host dissimilarity was the best predictor of species/lineage replacement and species/lineage gains/losses (= richness difference) components of compositional and phylogenetic flea beta diversity.3. The total compositional beta diversity of fleas was influenced mainly by the gradient in air temperature and, to a lesser degree, by total host beta diversity, with the former effect being associated with the richness difference component and the latter effect being associated with species replacement component. The total phylogenetic beta diversity of fleas was best explained by the total phylogenetic beta diversity of hosts, with this effect being mainly associated with the lineage replacement component, whereas the lineage richness difference component responded mainly to the temperature gradient.4. The results of the present indicate that not only multiple beta diversity facets are driven by different factors, but also different components of the same beta diversity facet respond to different environmental (for parasites, including host‐associated) gradients. These patterns were masked when only total beta diversity was analysed.5. This emphasizes the importance of considering the components of insect beta diversity separately. Ignoring the separate components of beta diversity can lead to potentially erroneous inferences about the relative contribution of abiotic and biotic effects on beta diversity.

Taxonomic divergence and functional convergence in Iberian spider forest communities: Insights from beta diversity partitioning

AbstractAimThe main aims were to determine: (a) the relative contribution of species replacement and richness difference from components to overall taxonomic (TDβ) and functional (FDβ) beta diversity of spider communities; (b) the degree to which TDβ and FDβ components can be explained by the environmental or geographic predictors; (c) whether FDβ components were lower than expected given the underlying TDβ variation.LocationThis study was carried out in 22 oak forest sites across the Iberian Peninsula. The area comprises two biogeographic regions, Eurosiberian (North) and Mediterranean (Centre and South).MethodsSpiders were sampled using a standardized protocol. A species x traits matrix was constructed. Total taxonomic (TDβtotal) and total functional (FDβtotal) beta diversity were calculated, by pairwise comparisons, and partitioned into their replacement (βrepl) and richness difference (βrich) components. Mantel tests were used to relate taxonomic and functional dissimilarity with environmental and geographic distances. A spatial eigenfunction model was constructed and the variation in TDβ and FDβ explained by environment and geographic predictors was quantified. Null models were used to test if FDβ was higher or lower than expected given TDβ.Resultsβrepl was the dominant component contributing to 84.2% and 72.8% for TDβtotal and FDβtotal, respectively. TDβtotal and FDβtotal (and their replacement components) were higher between‐ than within‐biogeographic regions. TDβtotal and TDβrepl were positively correlated with environmental and geographic distances, even when controlling for a biogeographic effect, but their functional counterparts were only correlated with environmental distance. Variation partitioning showed that pure environmental and spatially structured environmental effects had a small contribution to beta diversity, except for TDβrich. The observed slopes of the regressions of FDβtotal and FDβrepl in relation to environmental distance were slower than the null model expectations.Main ConclusionsSpider assemblage variation was mainly determined by the replacement, and not the net loss, of species and traits. TDβ was influenced by niche filtering and dispersal limitation, whereas FDβ was mainly generated by niche filtering. A high level of functional convergence among spider communities, despite the high taxonomic divergence, revealed the signal of replacement of species performing similar functions across sites.

Differently dispersing organism groups show contrasting beta diversity patterns in a dammed subtropical river basin.

Although it is widely known that dams can have large impacts on the environmental and biological characteristics of downstream rivers, there is a substantial lack of studies focusing on which ecological processes cause longitudinal changes in biological communities downstream of reservoirs. We investigated longitudinal patterns in the total beta diversity and its replacement and richness difference components for actively (fish) and passively (phytoplankton) dispersing biological groups. Our results, obtained from a 230 km sampling stretch, demonstrated the key role played by tributaries in the downstream direction from main river impoundment, which influenced local environmental conditions and beta diversity patterns of each biological group. Both replacement and richness difference contributed to high values of total beta diversity for fish (average = 0.77) and phytoplankton (average = 0.79), but their relative importance was more associated with the replacement component for both biological groups (average = 0.45 and 0.52, respectively). Moreover, we observed clear differences between fish and phytoplankton in beta diversity patterns operating at small and broad scales, as well as in the mechanisms driving each beta diversity component. Directional dispersal-related processes and environmental filtering played a major role in shaping total beta diversity and its components for fish, while temporal factors explained considerable parts of phytoplankton beta diversity. Our findings contributed to understanding of tributary-induced heterogeneity and highlight the importance of dam-free stretches of rivers for preserving the integrity of dammed river basins.

The effects of environment, hosts and space on compositional, phylogenetic and functional beta-diversity in two taxa of arthropod ectoparasites.

We studied the effects of variation in environmental, host-associated and spatial factors on variation in compositional, phylogenetic/taxonomic and functional facets of beta-diversity in fleas and gamasid mites parasitic on small mammals and asked whether (a) the importance of these factors as drivers of beta-diversity differs among its multiple facets and (b) the effects of variation in environment, hosts and space on beta-diversity variation differ between the two ectoparasite taxa. To understand the relative effects of each group of predictors, we used a distance-based redundancy analysis and variation partitioning. The greatest portions of variation in the compositional beta-diversity of fleas were equally explained by host-associated and spatial predictors, whereas variation in host species composition contributed the most to variation in the compositional beta-diversity of mites. Variation in the phylogenetic (i.e. based on phylogenetic tree) beta-diversity of fleas was mainly due to variation in the phylogenetic composition of host communities, while the taxonomic (i.e. based on Linnean taxonomy) beta-diversity of mites was influenced by environmental variation. Unique contributions of spatial and environmental variation explained most of the variation in functional beta-diversity and its species replacement (= turnover) component (i.e. beta-diversity explained by replacement of species alone) in fleas and mites, respectively. Variation in the richness difference component (i.e. beta-diversity explained by species loss/gain alone) of functional beta-diversity was mainly affected by either variation in the functional composition of host assemblages (fleas) or its joint action with environmental variables (mites). We conclude that the pattern of the relative effects of environmental, host-associated and spatial factors on beta-diversity is context-dependent and may differ among different facets of beta-diversity, among different beta-diversity components and also among taxa dependent on biological affinities.