Dissimilarity In Species Composition Research Articles

Livestock‐exclusion duration required for restoring grassland in semiarid, loess region in China: Estimate based on species composition measured from small‐scale vegetation patterns

AbstractTo restore the degraded grassland in the Yunwushan Natural Reserve of Ningxia semiarid loess region, Ningxia Autonomous Region, China, managers have established grasslands with excluding livestock from one large area every 5 years since 1982. The annual precipitation at the site is around 400 mm, and heavy grazing by sheep/goats has been conducted in the past. In July 2009 in which vegetation surveys were conducted, seven grasslands with different exclusion durations such as 0, 2, 7, 12, 17, 22 or 27 years had already been established. The objectives of survey were to clarify the vegetation changes with exclusion duration, and to estimate the number of years required for recovering the vegetation. In each of these grasslands, 100 50 × 50 cm2 quadrats, each of which was further divided into four 25 × 25 cm2 sub‐quadrats, were set, and then each of the species occurring within each sub‐quadrat was recorded. Aboveground biomass and soil hardness within each quadrat were also measured as auxiliary variables. We used eco‐statistical survey and analysis methods of small‐scale spatial patterns of vegetation. The followings are results obtained: after 12–17 years of exclusion, (a) the soil had softened; (b) the aboveground biomass had increased to amounts >200 dw g m–2; (c) the spatial uniformity in biomass increased to a stationary state; and (d) the dissimilarity of species composition between two successive exclusion durations decreased to a stationary state. We conclude from these observations that the degraded grassland required 12–17 years of exclusion to restore vegetation and productivity. We also proposed candidates of plant species to be seeded or planted for recovering degraded grassland in this area.

Quantitative evaluation of species composition dissimilarity within a community and among communities

AbstractIt is often necessary to perform quantitative comparisons and assessments of species composition among plant communities under various land use conditions and landscapes, as well as among plant communities at different stages of restoration or degradation in arid grasslands. In landscapes composed of a number of plant communities, in which many quadrats for a survey are set in each community, the species composition in each quadrat is measured using community variables, such as the presence/absence data (i.e., binary variable), biomass, cover, the number of individuals, or the frequency of occurrences (i.e., quantitative variables) of each species per quadrat. In this study, we defined two types of species composition dissimilarity in vegetation surveys: between different communities and within each community which were calculated based on the species composition of each quadrat, using the Bray–Curtis index. The second type dissimilarity occurs incidentally among quadrats (or micro‐sites) even in a community with a relatively uniform structure. Both dissimilarity measures take values from 0 to 1, where larger values indicate larger dissimilarities, and the quadrat‐to‐quadrat variation in dissimilarity also indicates the degree of heterogeneity in the spatial pattern of species composition. Quantifying dissimilarity between and within communities remains a challenge in ecological applications. We proposed a new model to quantify community dissimilarity and applied this model to a grassland vegetation survey dataset. Quantitative variables resulted in more precise measures of community structure than binary variable. The advantages of our model relative to other broadly used community structure metrics based on the Jaccard and Sørensen indices were discussed.

Native plant turnover and limited exotic spread explain swamp biotic differentiation with urbanization

AbstractQuestionsDoes urbanization promote biotic differentiation or homogenization of swamp plant communities? What is the contribution of natives and exotics to swamp response to urbanization?LocationQuebec City, Canada.MethodsPlant communities of 34 swamps located in low, moderately or highly urbanized landscapes were sampled, and species classified into three exclusive groups: native wetland, native upland and exotic plants. Urbanization’s influence on the richness of each plant group was assessed using mixed models. Between‐site compositional similarities were calculated to identify variations in beta diversity with urbanization level using tests for homogeneity in multivariate dispersion. Beta diversity was further partitioned into species replacement and richness difference for each plant group. Finally, the relationships of ten environmental variables representing soil water saturation and microtopography with plant assemblages were determined by redundancy analysis.ResultsAlthough the richness of exotics increased with urbanization intensity, revealing increasing propagule pressure, it remained six to 27 times lower compared to the richness of natives, which remained stable with urbanization. On the other hand, beta diversity increased with urbanization, with higher dissimilarities in species composition between highly urbanized swamps than between low‐urbanized ones. This pattern resulted from high species replacement among natives, while richness difference mainly contributed to exotic beta diversity. Changes in plant assemblages were mostly associated with bryophyte cover and soil drainage and red mottle size, suggesting that hydrological conditions likely acted as a strong driver of swamp plant community response to urbanization.ConclusionsSwamp plant communities experienced biotic differentiation with increasing urbanization. This differentiation pattern likely was linked to the unpredictable effect of urbanization on hydrological regimes, which promoted high native turnover while limiting exotic spread. Long‐term monitoring is recommended to ensure that exotics do not outcompete natives through time. Designing sustainable cities requires a greater understanding of the multifaceted effect of urbanization on biodiversity.

Environmental drivers of ant dominance in a tropical rainforest canopy at different spatial scales

Tropical trees accommodate a high co‐occurrence of ant species, mainly due to the high diversity of microhabitats available. However, a few ant species are highly abundant, dominating resources and defending territories in tree canopies. Although arboreal ants have been studied extensively, little is known about the structural drivers of ant spatial dominance in tropical rainforest canopies. This study investigated whether canopy tree microhabitats and micro‐environmental factors (given by branch characteristics and spatial position of sampling points within tree crowns) are determinants of ant presence and species composition in a Mexican tropical rainforest. It also analysed whether whole tree characteristics, that is, the tree canopy, given by tree size and epiphyte/climbing plant richness and abundance, could determine ant spatial dominance of food resources. This study found a higher probability of ant presence on baits lower in the canopy, probably a result of ants foraging in the zones between the treetops and the ground layer. No microhabitat or micro‐environmental variables were related to ant species composition. It also observed less dissimilarity of species composition between baits and between trees than between plots, revealing that each plot presents a unique set of species. Moreover, increased tree height and epiphyte/climbing plant abundance (i.e., structural heterogeneity and greater foraging area) and lower epiphyte/climbing plant richness led to decreasing ant dominance. This study's findings reveal that, while micro‐environmental factors have almost no influence on the foraging of dominant ant species within canopy trees, the size and heterogeneity of trees shape ants' spatial dominance.

Regional Pelagic Rotifer Biodiversity in a Tropical Karst Lake District

The species richness, composition, abundance, and biomass of pelagic rotifers were determined in 17 karst lakes of the “Lagunas de Montebello” National Park, Chiapas, Mexico. The species richness of the region (21 species) and single lakes (1–12 species) was smaller than that of other Mexican, tropical, and temperate lakes. It is worth noting the high dissimilarity in species composition—about half (52%) of the species were observed in only 1–3 lakes. A total of eight rotifer families, all from the Monogononta subclass, were recorded. Keratella americana was the species with the highest occurrence (13 lakes), followed by Ptygura sp. (8 lakes). The abundance (0 to 536 ind L−1) and biomass (0 to 21 µg L−1) of rotifers were low. The highest values of species richness, abundance, and biomass were found in eutrophic lakes, and the lowest in oligotrophic lakes. The low values of rotifer biodiversity, abundance, and biomass in the Montebello lakes are probably the product of the interaction of different factors—such as environmental homogeneity (all water bodies are karst lakes), the low availability of “good-quality” food, and predation by cyclopoid copepods in the eutrophic lakes, and the low availability of food, and competitive interference by calanoid copepods and cladocerans in the oligotrophic lakes.

Patterns of Rotifer Diversity in the Chihuahuan Desert

Desert aquatic systems are widely separated, lack hydrologic connections, and are subject to drought. However, they provide unique settings to investigate distributional patterns of micrometazoans, including rotifers. Thus, to understand rotifer biodiversity we sampled 236 sites across an array of habitats including rock pools, springs, tanks, flowing waters, playas, lakes, and reservoirs in the Chihuahuan Desert of the USA (n = 202) and Mexico (n = 34) over a period of >20 years. This allowed us to calculate diversity indices and examine geographic patterns in rotifer community composition. Of ~1850 recognized rotifer species, we recorded 246 taxa (~13%), with greatest diversity in springs (n = 175), lakes (n = 112), and rock pools (n = 72). Sampling effort was positively related to observed richness in springs, lakes, rivers, and tanks. Nestedness analyses indicated that rotifers in these sites, and most subsets thereof, were highly nested (support from 4 null models). Distance was positively correlated with species composition dissimilarity on small spatial scales. We predicted species richness for unsampled locations using empirical Bayesian kriging. These findings provide a better understanding of regional rotifer diversity in aridlands and provide information on potential biodiversity hotspots for aquatic scientists and resource managers.

Experimental Evidence for the Importance of Light on Understory Grass Communities in a Subtropical Forest.

Light is one of the most important environmental filters for forest understory grass communities. It is predicted that light can select species with the same light requirements, resulting in a decrease in species compositional dissimilarity among grass communities experiencing the same light intensity, and an increase in community dissimilarity under variable light intensities. However, these predictions have been questioned recently in light of modern coexistence theories, and evidence for them in natural communities is often indistinguishable from patterns created by dispersal limitation and biotic interactions. To help fill this gap, we sampled 48 understory grass communities that had regenerated from the same soil seed bank in Southern China. Plots were established under a light intensity gradient. Changes in species composition and neighborhood densities were monitored over a growing season. Our experimental setup controls for bias from dispersal limitation and is useful for detecting the effects of biotic interactions at different intensities of light. As expected, (1) compositional dissimilarity of grass communities increased between communities with different light intensities. The extent to which communities became more dissimilar was positively correlated with the difference in the light intensity. (2) No significant change in compositional dissimilarity was observed among communities experiencing the same light intensity. (3) Finally, relative neighborhood density significantly decreased in communities with moderate to high shading treatments. Our results clearly show that light can drive compositional divergence among communities under different light densities. However, the light may not lead to convergence among communities experiencing the same low light intensity, because intense competition induced by low light might enlarge species compositional differences, as shown with the neighborhood density analysis. Therefore, our study provides more convincing evidence for the importance of light on understory grass communities in subtropical forests and highlights the need to jointly consider biotic interactions when testing for evidence for environmental filtering.

Urban tree species composition and diversity in Zomba city, Malawi: Does land use type matter?

Urban landscapes do harbour trees despite being predominantly built-up areas. These trees are increasingly becoming a depository of tree species diversity. Even so, little is known about such potential in developing countries. This study therefore sought to establish tree species composition and diversity, and their variations across six land use types of Zomba city, Malawi. The study results revealed that Zomba city harbours 168 tree species, belonging to 47 families. Of these species, 63.6% were indigenous. Mangifera indica, an exotic fruit tree, is found among the top three most abundant tree species in three land use types: Roads, residential areas, and institutional land. Shannon diversity index values were different across six land use types, with high values observed in institutional areas (H’=4.08). Species evenness was high in graveyards (EQ=0.31) and low in residential areas (EQ=0.15). Bray-Curtis index revealed high dissimilarity of species composition in all pairs except a pair of institutional land and residential areas (0.67). The pattern was also confirmed using detrended correspondence analysis. The discrepancies in species composition between land use types was associated with difference in their levels of anthropogenic activities. Overall, the study results confirm that urban landscapes in Africa are important depository of tree species composition and diversity that differ with land use type. The influence of other factors to species heterogeneity and importance of such diversity in providing ecosystem services to the urban landscapes needs further investigation.

The effect of species composition dissimilarity on plant–herbivore network structure is not consistent over time

AbstractThe structural organization of several antagonistic networks has been demonstrated to be largely conserved through time and space even when species beta‐diversity is high. This might occur either because species are replaced by others that fulfill similar network roles or because interaction probabilities are given by species relative abundances rather than by their functional traits. Alternatively, if species‐specific traits are important drivers of realized interactions, any change in species composition should promote a certain degree of network structural dissimilarity. Here, we used a spatial‐temporal system comprising asteraceous plants and flower head herbivores from remnants of Brazilian Cerrado to investigate whether the relationship between spatial beta‐diversity of species and network structural dissimilarity changes over time. We measured species beta‐diversity using Sørensen's dissimilarity index (βsor) and its components of species replacement (β‐3) and richness differences (βrich). Network structural dissimilarity was estimated using three different metrics: connectance, modularity, and web asymmetry. We show that, in general, the effect of species beta‐diversity on network structure was time‐dependent: While some periods presented a positive relationship between spatial beta‐diversity and network structural dissimilarity, others presented no significant relationship. This indicates that functionally similar species may present different turnover rates at distinct periods, and different non‐exclusive processes affect plant–herbivore network organization across time.Abstract in Portuguese is available with online material.

Turnover and change in plant species composition in a shielded salt marsh following variation in precipitation and temperature

AbstractQuestionsTemperature and precipitation variation between years may affect plant species composition directly or indirectly. We wish to investigate whether salt marsh edaphic conditions and plant species composition change as a result of climatic variation. Further, whether areas with the largest edaphic variations also experience the largest change in species composition and turnover. Finally, do temperature and precipitation variations change the way the plant community is able to respond to natural edaphic gradients?LocationBygholmengen, a shielded salt marsh in Vejlerne, Denmark, Northern Europe.MethodsBotanical surveys were conducted and soil samples collected from 40 plots during a wet and dry summer to register changes in vegetation cover, species richness composition and edaphic factors (moisture, nutrients, salinity). These data were used to calculate dissimilarities in species composition, temporal turnover and environmental dissimilarity between years. A linear mixed‐effects model was used to link species richness with the measured edaphic factors.ResultsWe found that the precipitation and temperature variations altered the edaphic conditions; furthermore, the vegetation cover and species richness decreased when conditions were dry whereas the number of salt marsh species increased. Further, species composition changed significantly between years, and sampling plots that experienced the least edaphic change also retained more species between years. Species richness responded more to changes in nutrient availability during wet than dry conditions.ConclusionOur results pointed toward the climatic variations, and subsequent change in edaphic conditions, being responsible for the significant change in species composition as areas with the least change in edaphic factors retained most species between years. Dry conditions favored salt marsh‐adapted species and the extent to which increased nutrient levels led to a higher species richness decreased in dry compared to wet conditions.

Avian Beta Diversity in a Neotropical Wetland: the Effects of Flooding and Vegetation Structure

Habitat heterogeneity in the Pantanal results from flood dynamics and vegetation characteristics. Considering that these impacts affect landbird nesting conditions and food resource availability, species turnover and richness should respond to them. We conducted this study in the northeastern Pantanal, in two dominant habitats, savanna and forest, covering two annual cycles. The objectives were: (1) evaluation of trophic structure, (2) analyses of species dissimilarity patterns, and (3) investigation of whether seasonal changes in the flood regime and/or vegetation characteristics drive these patterns. We used mist nests to acquire data on bird species composition, abundance, and guilds. Insectivore and omnivore species were the predominant guilds. The bird community showed very high overall dissimilarity, with a Jaccard Index of 0.86, with 86% attributed to species replacement and 14% to species nestednesss. This high dissimilarity reflects the reduced number of shared species, mainly between some savannas and forests (12%). Our analyses also showed that habitat characteristics, specifically the differences in vegetation structure and composition, mostly explained the species turnover. Flood seasonality was also an important driver of bird community spatial variability, in which dissimilarities in species composition increased from the terrestrial to the aquatic phases, with the wettest phase being the most dissimilar.

Relative Efficiency of Pitfall Trapping vs. Nocturnal Hand Collecting in Assessing Soil-Dwelling Spider Diversity along A Structural Gradient of Neotropical Habitats

Assessing spider diversity remains a great challenge, especially in tropical habitats where dozens of species can locally co-occur. Pitfall trapping is one of the most widely used techniques to collect spiders, but it suffers from several biases, and its accuracy likely varies with habitat complexity. In this study, we compared the efficiency of passive pitfall trapping versus active nocturnal hand collecting (NHC) to capture low understory-dwelling spider taxonomical (morpho-species) and functional (hunting guilds) diversity along a structural gradient of habitats in French Guiana. We focused on four habitats describing a structural gradient: garden to the orchard to the forest edge to the undisturbed forest. Overall, estimated morpho-species richness and composition did not vary consistently between habitats, but abundances of ground-hunting spiders decreased significantly with increasing habitat complexity. We found habitat-dependence differences in taxonomic diversity between sampling strategies: NHC revealed higher diversity in the orchard, whereas pitfalls resulted in higher diversity in the forest. Species turnover resulted in high dissimilarity in species composition between habitats using either method. This study shows how pitfall trapping is influenced by habitat structure, rendering this sampling method incomplete for complex, tropical environments. However, pitfall traps remain a valuable component of inventories because they sample distinct assemblage of spiders.

Assessment of Sediment and Benthic Macrofauna Distribution at Dar es Salaam Harbour Channel

Sediment and macrobenthic fauna distribution at Dar es Salaam harbour channel were investigated to attest the influence of sediment grain size distribution and total organic carbon contents on benthic macrofauna dominance and diversity. Sampling campaign was conducted from January to April, 2019 in 25 sampling stations along the channel. Sediment grain sizes ranged between 0.7405 and 0.00273 mm with an average of 0.0804 mm classified as medium silt. Sediment distribution showed an onshore-offshore pattern consisting of fine dark clay-silt sediments in the southern part of the harbour close to Mwalimu Nyerere Bridge, medium (sandy) at the harbour and coarse sandy offshore. Five classes of macrofauna were identified with sedentary Polychaetes (Diopatra cuprea) found in tubes and free forms being dominant in most of the sediment types, however more abundant in clay-silt. High species diversity index values were encountered in sediments with medium total organic carbon (TOC) and sediment grain sizes (sand-silt). Apparently, low species similarity indices were observed in all sediment type indicating significant dissimilarities in species composition among sediment grain sizes. Thus, the distribution of benthic macrofauna species along Dar es Salaam harbour channel is strongly influenced by the sediment grain sizes and organic carbon contents in sediments.

Community responses to fine-scale environmental conditions: Ferns alpha and beta diversity along Brazilian Atlantic forest remnants

Understanding how local environmental factors affect communities and compositional patterns are crucial to biodiversity conservation, especially in environments that were severally affected by anthropic actions. We analyzed the effects of fine-scale local environmental conditions on alpha and beta diversity of fern communities in three Atlantic forest areas and investigated the mechanisms underlying fern community responses. We sampled ferns and collected local environmental variables in 22 plots in three Atlantic forest areas and used multi-model inferences to identify the relationship between community diversity and composition and local environmental factors. We also applied multivariate analyses to verify whether community composition is constrained by local environmental factors. Finally, we analyzed beta-diversity (dissimilarity in species composition) patterns between and within forest areas and identified the contribution of turnover and nestedness to observed beta-diversity patterns. At the local scale, fern diversity was positively and strongly affected by fine-scale variations in nutrient availability and negatively influenced by soil acidity. Meanwhile, changes in community composition were also related to fine-scale variations in nutrient availability and soil rock coverage. Beta-diversity within forest areas (local scale) was as high as between forest areas (regional scale), a pattern that was virtually driven by species turnover at both scales of analysis. Our results highlight a prominent role of environmental filtering in regulating fine-scale local fern community diversity and composition, to such an extent that fine-scale local variation in species composition is as high as between spatially and climatically distant forest areas.

Influence of Environmental Heterogeneity on the Species Composition, Species Richness and Species Abundances Unevenness in Reef-associated Conus Communities (Neogastropoda) from Papua New-Guinea

To what extent differences in species composition, species richness and species abundance unevenness between marine communities are attributable to heterogeneities of the surrounding environment and/or to inter-community distance is a fundamental issue to be addressed, in order to more deeply understand the functioning of marine ecosystems. A comparison between six reef-associated Conus communities, differing more or less in both their surrounding environment and their mutual geographical distance, offers a relevant opportunity to address these questions.
 As expected, environmental heterogeneities prove having a significant influence on the dissimilarity in species composition, whereas distance-decay in similarity reveals comparatively negligible, at least within the investigated range of distances, up to 60 km. Less expectedly, more homogeneous surrounding environments between communities tend, here, to increase the dissimilarity in species richness. At last, here, difference in species abundance unevenness between communities seems unrelated to either environmental heterogeneity or inter-community distance.
 From a methodological point of view, these results could not have been reliably established without the prior implementation of a least-biased procedure of numerical extrapolation applied to the available incomplete samplings. Also, the relevant assessment of dissimilarity in species composition required using a modified Jaccard index, rendered insensitive to bias-induced differences in communities species richness.

Large‐scale α‐diversity patterns in plants and ground beetles (Coleoptera: Carabidae) indicate a high biodiversity conservation value of China's restored temperate forest landscapes

AbstractAimFollowing the near‐complete destruction of China's forest ecosystems during the 20th century, recent reforestation programmes have created large‐scale mosaics of protected secondary and plantation forests. These restored forests are often assumed to have limited biodiversity conservation value, but large‐scale evaluations of their diversity are lacking. In our study, we compared α‐diversity and species dissimilarity patterns of vascular plants and ground beetles (Coleoptera: Carabidae) in restored secondary and plantation forests to remnant mature forests across north‐eastern temperate China. We also assessed functional traits of beetles and cross‐taxon diversity links to evaluate differences in ecosystem functioning among forest types.Location. Northeast China.MethodsVascular plant and ground beetle assemblages were recorded in 159 temperate forest plots. The α‐diversity and species compositional dissimilarity of these taxa and the functional traits of beetles were compared between plantation, secondary and mature forest ecosystems.ResultsHerbaceous plant species richness peaked in mature forests, while carabid and woody plant diversity did not differ between forest types. Species dissimilarity of carabids was lowest in mature forests and highest in plantation forests. Mature forest contained the highest proportion of carnivorous beetles and secondary forests of large‐bodied carabids. Carabid diversity and woody plant species richness were positively correlated in mature forests, but not in secondary or plantation forests.Main conclusionsWhile China's mature forests show a great conservation value in harbouring highly diverse herbaceous plant assemblages and an abundance of distinct invertebrate trait groups such as small predatory carabids, China's restored temperate forests also support a high diversity of woody plants and carabids. Overall, our findings offer an encouraging conservation message for biodiversity conservation in China and demonstrate the importance of policy measures that ensure effective long‐term protection of both, China's remnant mature forests, but also its new forest ecosystems.

Biotic heterogeneity among scarab beetle communities in an anthropized landscape in the Central Valleys of Oaxaca, Mexico

In the tropics, changes in land use are a major concern given that the transformation of natural ecosystems to degraded environments for human use occurs rapidly and is associated with deforestation, fragmentation, isolation, among other impacts. Scarab beetles are well represented in tropical and warm temperate ecosystems due to their high diversity, numerous ecological functions, sensitivity to habitat disturbances, and responses to anthropized areas, so they are considered as a model group to study the consequences of environmental disturbance in tropical regions. We present an analysis of the scarab beetle diversity in an anthropized landscape with five different land uses in the Central Valleys of the state of Oaxaca, Mexico, with an emphasis on the dissimilarity in species composition. The organisms were collected with dung-, carrion- and fruit-baited traps during five sampling periods. We identified 2766 individuals belonging to 40 species, the majority being coprophagous or copro-necrophagous. The most abundant species was Phanaeus nimrod, with 624 individuals, although the most abundant species changed according to land uses. Beta diversity was high (80% on average), and between four sites dissimilarity was 100%. Species replacement was more important than differences in richness for the total beta diversity calculated with incidence data; and balanced variation in abundance was more important than the abundance gradient in the case of analyses with abundances. The landscape presented high scarab beetle diversity, mainly due to a high species replacement and the balanced variation in abundance, indicating that a high biotic heterogeneity has been maintained, or even enhanced following landscape modification.

Variations in Total Species Richness and the Unevenness of Species Abundance Distribution between Two Distant Conus Communities (Neogastropoda): A Case Study in Mannar Gulf (India)

The genus Conus forms a conspicuous and rather homogeneous group within marine Gastropods. This makes it all the more interesting to focus on the sub-communities formed by Conus species and to analyze the potential specificities in the internal organization of species in these communities, in particular species richness, species abundance distribution and the effect of geographical distance between communities on differences in their respective species composition. Accordingly, two Conus communities along the coast in Mannar Gulf (India), separated by 80 km, are considered. Reliable analysis requires, first, to treat exhaustive data from complete samplings or, else – as here – to implement an appropriate extrapolation procedure to complete numerically the partial samplings. After numerical completion, substantial differences were highlighted between the two communities, not only in terms of true (total) species richness but, even more, as regards the profile and the average unevenness of the distributions of species abundance. Also, significant dissimilarity in species composition was found between the two communities, that may be tentatively attributed to either deterministic distance decay in similarity of species composition or, alternatively, to the persistence in the stochastic process of species recruitment from the regional stock of Conus planktonic larvae. This preliminary study yet requests to be complemented by other similar case studies, before drawing any safer interpretative conclusions.

Comparison of automated extraction and amplification platforms on quantification of plasma HDV RNA: A multicenter study

Understanding how local environmental factors affect communities and compositional patterns are crucial to biodiversity conservation, especially in environments that were severally affected by anthropic actions. We analyzed the effects of fine-scale local environmental conditions on alpha and beta diversity of fern communities in three Atlantic forest areas and investigated the mechanisms underlying fern community responses. We sampled ferns and collected local environmental variables in 22 plots in three Atlantic forest areas and used multi-model inferences to identify the relationship between community diversity and composition and local environmental factors. We also applied multivariate analyses to verify whether community composition is constrained by local environmental factors. Finally, we analyzed beta-diversity (dissimilarity in species composition) patterns between and within forest areas and identified the contribution of turnover and nestedness to observed beta-diversity patterns. At the local scale, fern diversity was positively and strongly affected by fine-scale variations in nutrient availability and negatively influenced by soil acidity. Meanwhile, changes in community composition were also related to fine-scale variations in nutrient availability and soil rock coverage. Beta-diversity within forest areas (local scale) was as high as between forest areas (regional scale), a pattern that was virtually driven by species turnover at both scales of analysis. Our results highlight a prominent role of environmental filtering in regulating fine-scale local fern community diversity and composition, to such an extent that fine-scale local variation in species composition is as high as between spatially and climatically distant forest areas.

Environmental heterogeneity and dispersal limitation explain different aspects of β‐diversity in Neotropical fish assemblages

Abstract From a metacommunity perspective, patterns of β‐diversity emerge from the interplay between spatial and environmental processes. For obligate aquatic dispersers, river network constraints can be reflected in diversity patterns. Here, we aimed to determine the effects of environmental heterogeneity and spatial connectivity on β‐diversity components. We sampled fish assemblages in 21 sites across a longitudinal gradient. Beta‐diversity for taxonomic and functional composition among sites was decomposed into its turnover and nestedness components. We investigated whether environment was more important to functional β‐diversity and spatial factors had a higher contribution to dissimilarity in species composition. Further, we tested whether environmentally homogeneous sites with higher spatial connectivity showed lower compositional changes. We found that spatial factors were more important for taxonomic β‐diversity, whereas environment explained functional dissimilarity among habitats. Although environment and spatial factors contribute to total β‐diversity, they explained different components: while environment explained a higher portion of turnover, spatial factors were related to nestedness. The effects of mere spatial isolation and directional connectivity differed for species and functional β‐diversity and for the components of β‐diversity. Including directionality in spatial connectivity enabled the explanation of a higher proportion of variation of total species β‐diversity and its turnover. Our results suggest that niche and spatial processes may influence differently taxonomic and functional β‐diversity components. Thus, habitat filtering was the primary mechanism affecting functional diversity and species turnover, whereas spatial connectivity drove species nestedness.