Altitudinal variation in the taxonomic composition of ground‐dwelling beetle assemblages in NW Patagonia, Argentina: environmental correlates at regional and local scales

Environmental and spatial heterogeneity affects the distribution of aquatic insects, determining or influencing the variation in local species composition. Dragonflies and damselflies (Odonata) have different strategies for oviposition site selection that depend on environmental conditions. However, Land Use and Land Cover (LULC) can reduce the availability of suitable sites for Odonata oviposition through environmental homogenization. We investigated the relationship between environmental and spatial heterogeneity and variation in species composition of Odonata with different oviposition strategies (endophytic, epiphytic and exophytic) in Amazonian streams in a gradient of LULC. We used the Jaccard and Bray‐Curtis coefficients and the Manhattan distance to estimate a continuum of variation in species composition. Variation in the composition of endophytic and epiphytic species was explained by spatial heterogeneity. Using abundance data and the Manhattan distance, we found a relationship between variation in species composition and environmental heterogeneity. Endophytic species composition was related to perch heterogeneity, while exophytic species composition was related to perch and canopy cover heterogeneity. Exophytic and endophytic species could be used in biomonitoring as they respond to specific environmental predictors and because exophytic species do not have spatial patterns across the landscape. Different dissimilarity coefficients provide complementary information about the responses of multispecies communities to land use, as some will represent strong effects (presence‐absence indexes) while others will represent more subtle effects (abundance‐based indexes). Land use can increase the environmental heterogeneity of some predictors (perches and canopy cover). Physical changes in streams such as hydromorphological alterations can modify specific habitats, affecting oviposition strategies and supporting tolerant species.

Characterizing habitat associations of species is fundamental to understanding the mechanistic basis of community organization. Typically, investigators estimate microhabitat characteristics that account for significant amounts of variation in species composition. Nonetheless, highly resolved microhabitat characteristics may account for no more variation in species composition than coarse macrohabitat distinctions, particularly in heterogeneous environments. We describe micro- and macrohabitat associations of 13 species of nocturnal rodents distributed across 31 communities within the Mojave Desert. Rodent species composition, biomass of 81 perennial plant species, representation of 9 soil and rock classes, and the percent cover of annuals and grasses were quantified. Communities also were assigned to macrohabitats based on qualitative characteristics. Multivariate analysis of variance indicated highly significant community-wide differences among macrohabitats and species-specific analyses of variance substantiated differences for all but 1 species analyzed. Microhabitat characteristics accounted for approximately 55% of the variation in rodent species composition. Moreover, microhabitat characteristics accounted for 17% variation in rodent species composition over and beyond that shared with macrohabitat distinctions. Micro- and macrohabitat perspectives provide complimentary insights into species composition of rodent communities. Edaphic features in particular represented important environmental heterogeneity that likely acts both directly on rodent species composition and indirectly through influencing variation in plant species composition. Indeed, the Mojave Desert is represented by a spatial mosaic of species-rich and compositionally dynamic rodent communities that will provide many insights into the coexistence of species at regional spatial scales.

QuestionWhat are the relative roles of environmental and spatial factors in influencing variation in species composition of tropical woody plants at different spatial scales?LocationTropical evergreen forests, Western Ghats, South India.MethodsUsing a plot‐based species inventory spanning the entire latitudinal extent (1,200 km) of the Western Ghats’ wet evergreen forests, we collected primary data on spatial variation in species composition of woody plants. Each plot was characterized by a set of environmental descriptors consisting of topographic, edaphic and climatic variables, while eigenvector‐based spatial variables and plot coordinates were used as spatial descriptors. We used ordination‐based as well as distance‐based variation partitioning techniques to partition the variation in species composition into components uniquely and jointly explained by environmental and spatial factors.ResultsThe compositional similarity of woody plants largely showed a linear decline with log‐geographic distance. However, this relationship was spatially structured. After controlling for the differences in environment, compositional similarity was found to be strongly associated with geographic distance only at the smallest spatial scale. Variation partitioning analysis revealed that environmental variables explained a much larger proportion of variation in species composition overall compared to spatial variables. Among environmental variables, climatic variables emerged as the most important predictors of variation in species composition at regional and landscape scales.ConclusionsStrong association between compositional similarity and geographic distance at local scales indicates the influence of dispersal limitation, while niche differentiation seems to be a more important driver of variation in species composition at larger spatial scales. Overall, our results provide evidence for scale‐dependent shifts in the relative importance of factors that are responsible for variation in species composition.

Mexico has higher mammalian diversity than expected for its size and geographic position. High environmental hetero geneity throughout Mexico is hypothesized to promote high turnover rates (β‐diversity), thus contributing more to observed species richness and composition than within‐habitat (α) diversity. This is true if species are strongly associated with their environments, such that changes in environmental attributes will result in changes in species composition. Also, greater heterogeneity in an area will result in greater species richness. This hypothesis has been deemed false for bats, as their ability to fly would reduce opportunities for habitat specialization. If so, we would expect no significant relationships between 1) species composition and environmental variables, 2) species richness and environmental heterogeneity, 3) β‐diversity and environmental heterogeneity. We tested these predictions using 31 bat assemblages distributed across Mexico. Using variance partitioning we evaluated the relative contribution of vegetation, climate, elevation, horizontal heterogeneity (a variate including vegetation, climate, and elevational heterogeneity), spatial variation (lat‐long), and vertical hetero geneity (of vegetation strata) to variation in bat species composition and richness. Variation in vegetation explained 92% of the variation in species composition and was correlated with all other variables examined, indicating that bats respond directly to habitat composition and structure. Beta‐diversity and vegetational heterogeneity were significantly correlated. Bat species richness was significantly correlated with vertical, but not horizontal, heterogeneity. Nonetheless, neither horizontal nor vertical heterogeneity were random; both were related to latitude and to elevation. Variation in bat community composition and richness in Mexico were primarily explained by local landscape heterogeneity and environmental factors. Significant relationships between β‐diversity and environmental variation reveal differences in habitat specialization by bats, and explain their high diversity in Mexico. Understanding mechanisms acting along environmental or geographic gradients is as important for understanding spatial variation in community composition as studying mechanisms that operate at local scales.

Niche-based and neutral models of community structure posit distinct mechanisms underlying patterns in community structure; correlation between species’ distributions and habitat factors points to niche assembly while spatial pattern independent of habitat suggests neutral assembly via dispersal limitation. The challenge is to disentangle the relative contributions when both processes are operating, and to determine the scales at which each is important. We sampled shoreline plant communities on an island in Lake Michigan, varying the extent and the grain of sampling, and used both distance-based correlation methods and variance partitioning to quantify the proportion of the variation in plant species composition that was attributable to habitat factors and to spatial configuration independent of habitat. Our results were highly scale dependent. We found no distance decay of plant community similarity at the island scale (1−33 km). All of the explained variation (32%) in species composition among samples at this scale was attributed to habitat factors. However, at a site intensively sampled at a smaller scale (5−1,200 m), similarity of species composition did decay with distance. Using a coarse sampling grain (transects), habitat factors explained 40% of the variation, but the purely spatial component explained a comparable 22%. Analyzing plots within transects revealed variation in species composition that was still jointly determined by habitat and spatial factors (18 and 11% of the variance, respectively). For both grain sizes, most of the habitat component was spatially structured, reflecting an abrupt alongshore transition from sandy dunes to cobble beach. Space per se explained more variation in species composition at a second site where the habitat transition was more gradual; here, habitat acted as a less selective filter, allowing the signal of dispersal limitation to be detected more readily. We conclude that both adaptation to specific habitat factors and habitat-independent spatial position indicative of dispersal limitation determine plant species composition in this system. Our results support the prediction that dispersal limitation—a potentially, but not necessarily, neutral driver—is relatively more important at smaller scales.

Aim: We aimed to evaluate the variation in planktonic ciliate species composition in different strata of the Guaraná Lake, encompassing high and low water periods, at the Upper Paraná River floodplain. Methods Samplings were collected monthly between March 2007 and February 2008, from the epilimnion, metalimnion and hypolimnion. Ciliates samples were filtered using a plankton net of 10µm mesh size and identified in vivo under an optical microscope. Results Among 112 species identified, 13 were found exclusively during the high water periods and 39 during the low water period. Results of nonparametric extrapolation indices evidenced that the observed richness represented between 70% and 90% of the estimated richness. Regarding the variation in species composition, Beta1 index showed that the alteration in composition between strata during the low water period was slightly greater than that registered during high waters. Cluster analysis evidenced a higher dissimilarity in ciliate species composition between periods than among the different strata. The greatest variation in species composition was verified during the distinct hydrological periods, whereas no significant differences were observed for the different strata analysed. Conclusions We found that in the pelagic compartment, ciliate species composition changed significantly between hydrological periods, and a higher similarity in species composition among strata was observed during the high water period. Therefore, alterations in the vertical distribution seem to be related to the homogenizing effect of the floods in the water column stability.

Patterns of variation in vascular plant species richness and composition in SE Norwegian agricultural landscapes

The relationship between bird distribution patterns and environmental factors in an ecotone area of northeast Brazil

Despite extensive paleoecological analyses of spatial and temporal turnover in species composition, the fidelity with which time-averaged death assemblages capture variation in species composition and diversity partitioning of living communities remains unexplored. Do death assemblages vary in composition between sites to a lesser degree than do living assemblages, as would be predicted from time-averaging? And is the higher number of species observed in death relative to living assemblages reduced with increasing spatial scale? We quantify the preservation of spatial and temporal variation in species composition using 11 regional data sets based on samples of living molluscan communities and their co-occurring time-averaged death assemblages. (1) Compositional dissimilarities among living assemblages (LA) within data sets are significantly positively rank-correlated to dissimilarities among counterpart pairs of death assemblages (DA), demonstrating that pairwise dissimilarity within a study area has a good preservation potential in the fossil record. Dissimilarity indices that downplay the abundance of dominant species return the highest live-dead agreement of variation in species composition. (2) The average variation in species composition (average dissimilarity) is consistently smaller in DAs than in LAs (9 of 11 data sets). This damping of variation might arise from DAs generally having a larger sample size, but the reduction by ∼10–20% mostly persists even in size-standardized analyses (4 to 7 of 11 data sets, depending on metric). Beta diversity expressed by the number of compositionally distinct communities is also significantly reduced in death assemblages in size-standardized analyses (by ∼25%). This damping of variation and reduction in beta diversity is in accord with the loss of temporal resolution expected from time-averaging, without invoking taphonomic bias (from differential preservation or postmortem transportation) or sample-size effects. The loss of temporal resolution should directly reduce temporal variation, and assuming time-for-space substitution owing to random walk within one habitat and/or temporal habitat shifting, it also decreases spatial variation in species composition. (3) DAs are more diverse than LAs at the alpha scale, but the difference is reduced at gamma scales because partitioning of alpha and beta components differs significantly between LAs and DAs. This indicates that the effects of time-averaging are reduced with increasing spatial scale. Thus, overall, time-averaged molluscan DAs do capture variation among samples of the living assemblage, but they tend to damp the magnitude of variation, making them a conservative means of inferring change over time or variation among regions in species composition and diversity. Rates of temporal and spatial species turnover documented in the fossil record are thus expected to be depressed relative to the turnover rates that are predicted by models of community dynamics, which assume higher temporal resolution. Finally, the capture by DAs of underlying variation in the LA implies little variation in the net preservation potential of death assemblages across environments, despite the different taphonomic pathways suggested by taphofacies studies.

In riparian wetlands total standing crop often fails to account for a significant part of the observed variation in species richness and species composition within communities. In this study, we used abundance of the dominant species instead of total standing crop as the biotic predictor variable and investigated its relationships with species composition and species richness in communities dominated by Phragmites australis (Cav.) Trin. ex Steudel. This was done by measuring soil organic matter content, litter cover and elevation, Phragmites abundance (standing crop and stem density) and species composition in 78 releves. In addition, we tried to identify the environmental boundaries of Phragmites communities by sampling releves in neighbouring communities. Two gradients were related to a decline in Phragmites abundance: one gradient, perpendicular to the shoreline, was mainly related to increased elevation and the second gradient ran parallel to the shoreline and was related to increased amounts of soil organic matter. Within the releves dominated by Phragmites, stem density of Phragmites and litter cover were the only factors significantly related to species composition in the RDA solution. Litter cover and standing crop of the dominant accounted for 64% of the variation in species richness within the Phragmites-dominated community. These results show that dead and living biomass of the dominant species may account for a substantial part of the variation in species composition and species richness within a single community.

Questions: Which environmental and management factors determine plant species composition in semi‐natural grasslands within a local study area? Are vegetation and explanatory factors scale‐dependent?Location: Semi‐natural grasslands in Lærdal, Sognog Fjordane County, western Norway.Methods: We recorded plant species composition and explanatory variables in six grassland sites using a hierarchically nested sampling design with three levels: plots randomly placed within blocks selected within sites. We evaluated vegetation‐environment relationships at all three levels by means of DCA ordination and split‐plot GLM analyses.Results: The most important complex gradient determining variation in grassland species composition showed a broad‐scale relationship with management. Soil moisture conditions were related to vegetation variation on block scale, whereas element concentrations in the soil were significantly related to variation in species composition on all spatial scales. Our results show that vegetation‐environment relationships are dependent on the scale of observation. We suggest that scale‐related (and therefore methodological) issues may explain the wide range of vegetation‐environment relationships reported in the literature, for semi‐natural grassland in particular but also for other ecosystems.Conclusions: Interpretation of the variation in species composition of semi‐natural grasslands requires consideration of the spatial scales on which important environmental variables vary.

Previous studies point to biogeographic (i.e., evolutionary and demographic) and ecological (i.e., habitat differentiation and disturbance) processes as the most important causes of spatial variation in species richness and species composition (occurrence and abundance). We examined patterns of variation in vascular plant and bryophyte species composition among 150 1-m2 plots distributed semi-randomly over 11 Norwegian boreal swamp-forest localities. Swamp forests are species-rich islands in an otherwise species-poor forest landscape. For each plot, 53 environmental variables were recorded. By using Canonical Correspondence Analysis (CCA), we found that ∼20% of the explainable variation in species composition was due to swamp-forest affiliation, in addition to the ∼35% that was due to environmental differences between swamp-forest localities. The uniqueness of the species composition of each swamp forest was also emphasized by analyses of compositional dissimilarity. Plots were significantly more dissimilar if situated in different swamp forests than if situated in the same swamp forest, after environmental differences had been corrected for. The lack of any significant relationship between compositional dissimilarity and geographical distance or swamp-forest area indicated that this pattern was not mainly due to recent successful dispersal and establishment events. We argue that the distinctness of swamp forests, in particular, those richer in species and soil nutrients, is due to a combination of factors among which randomness in establishment in gaps (“windows of opportunity”) and persistence of established clonal species are important. Furthermore, we argue that the probability for successful recruitment may have been higher in previous time periods than it is today. The unique combination of important determinants of the species composition in boreal swamp forests supports the view that there exists a diversity of explanations for diversity, and that these, to a large extent, are system and/or area specific.

A consistent terminology for species diversity is subject of an ongoing debate. Recently Tuomisto (Oecologia 164:853-860, 2010) stated that a consistent terminology for diversity already exists. The paper comments on recent papers by ourselves (Jurasinski et al. Oecologia 159:15-26, 2009) and by Moreno and Rodriguez (Oecologia 163:279-282, 2010). Both started from Whittaker's diversity concept to discuss the ambiguities of the terminology and propose a new, more consistent terminology that is based on the different approaches to diversity analysis. In contrast, Tuomisto adheres to a strict school of thinking and derives a diversity framework in the sense of Whittaker (alpha, beta, gamma) from the conceptual definition of diversity itself. A third group of papers discusses appropriate methods for the analysis of the variation in species composition. Here, we support the idea that alpha, beta and gamma diversity should be used in a strict sense that is based only on the conceptual definition of diversity. We accordingly extend and modify our terminological concept for species diversity. All approaches to the analysis and quantification of species composition and diversity can be assigned to three abstraction levels (species composition, variation in species composition,and variation in variation in species composition) and two scale levels (sample scale, aggregation scale). All methods that investigate the variation in species composition across scale levels evaluate beta relation with beta diversity being just one form of beta relation, which is calculated by dividing gamma diversity of order q by the appropriate alpha diversity of the same order. In contrast, differentiation refers to a pairwise calculation of resemblance in species composition. It is restricted to sample scale and is therefore most often only an intermediate step of analysis. Many ecological questions can be addressed either by direct analysis of the variation in species composition using raw data approaches or by further analysis of differentiation datasets on aggregation scale with or without respect to an external gradient.

AimIn this study we identified large‐scale variation in tree species composition across tropical African forests and determined the underlying environmental and historical factors.LocationTropical forests from Senegal to Mozambique.MethodsDistribution data were gathered for 1175 tree species in 455 sample sites scattered across tropical Africa, including all types of tropical forests (wet, moist, dry, and lowland to moderate elevation montane forests). The value of elevation and 19 climatic variables extracted from theBIOCLIMdata set were assigned to each sample site. We determined the variation in species composition using correspondence analysis and identified the environmental correlates. We defined floristic clusters according to species composition and identified the characteristic species using indicator analysis.ResultsWe identified a major floristic discontinuity located at the Albertine rift that separated the dry, moist and wet forests of West and Central Africa (the entire Guineo‐Congolian Region) from the upland and coastal forests of East Africa. Except for the Albertine Rift, we found no evidence to support the other proposed floristic discontinuities (Dahomey Gap etc.). We detected two main environmental gradients across tropical African forests. The rainfall gradient was strongly correlated with the variation in tree species composition in West and Central Africa. The elevation/temperature gradient highlighted the major floristic differences within East Africa and between East Africa and the Guineo‐Congolian Region, the latter being most probably due to the geological disruption and associated climatic history of the East African uplift.Main conclusionsWe found floristic evidence for three main biogeographical regions across the tropical African forests, and described six floristic clusters with particular environmental conditions within these regions: Coastal and Upland for East Africa, Dry and Wet‐Moist for West Africa, and Moist and Wet for Central Africa.

Spatial and temporal isolation and environmental variability are important factors explaining variation in plant species composition. The effect of fragmentation and disturbance on woody plant species composition was studied using data from 32 remnant church forest patches in northern Ethiopia. The church forests are remnants of dry Afromontane forest, embedded in a matrix of intensively used crop and grazing lands. We used canonical correspondence analysis and partial canonical correspondence analysis to analyze the effects of fragmented and isolated forest-patch identity, environmental and spatial variables on woody plant species composition in different growth stages. The dominance of late successional species was higher at the adult growth stage than seedlings and saplings growth stages. In the adult stages, late successional species like Olea europaea subsp. cuspidate had high frequency of occurrence. Forest patch identity was more important in explaining woody plant assemblages than environmental and spatial variables. For all growth stages combined, environmental variables explained more of the explained total fraction of variation in species composition than spatial variables. Topographic variables best explained variations in species composition for saplings, adults and all growth stages combined, whereas the management regime was most important for seedlings species composition. Our results show that in a matrix of cultivated and grazing land, fragmented and isolated forest patches differ in woody plant species assemblages. Some species are widely distributed and occurred in many patches while other occurred only in one or a few forest patches. Thus, our results indicate that remnant forest patches are important for preserving rare plant species and therefore management practices should focus on minimizing disturbance to the church forests and if possible increase church forest patch size.