Gradient In Species Richness Research Articles

Untangling human and environmental effects on geographical gradients of mammal species richness: a global and regional evaluation.

Different hypotheses (geographical, ecological, evolutionary or a combination of them) have been suggested to account for the spatial variation in species richness. However, the relative importance of environment and human impacts in explaining these patterns, either globally or at the biogeographical region level, remains largely unexplored. Here, we jointly evaluate how current environmental conditions and human impacts shape global and regional gradients of species richness in terrestrial mammals. We processed IUCN global distributional data for 3939 mammal species and a set of seven environmental and two human impact variables at a spatial resolution of 96.5 × 96.5 km. We used simple, multiple and partial regression techniques to evaluate environmental and human effects on species richness. Actual evapotranspiration (AET) is the main driver of mammal species richness globally. Together with our results at the biogeographical realm level, this lends strong support for the water-energy hypothesis (i.e. global diversity gradients are best explained by the interaction of water and energy, with a latitudinal shift in the relative importance of ambient energy vs. water availability as we move from the poles to the equator). While human effects on species richness are not easily detected at a global scale due to the large proportion of shared variance with the environment, these effects significantly emerge at the regional level. In the Nearctic, Palearctic and Oriental regions, the independent contribution of human impacts is almost as important as current environmental conditions in explaining richness patterns. The intersection of human impacts with climate drives the geographical variation in mammal species richness in the Palearctic, Nearctic and Oriental regions. Using a human accessibility variable, we show, for the first time, that the zones most accessible to humans are often those where we find lower mammal species richness.

Shifts in trait means and variances in North American tree assemblages: species richness patterns are loosely related to the functional space

One of the key hypothesized drivers of gradients in species richness is environmental filtering, where environmental stress limits which species from a larger species pool gain membership in a local community owing to their traits. Whereas most studies focus on small‐scale variation in functional traits along environmental gradient, the effect of large‐scale environmental filtering is less well understood. Furthermore, it has been rarely tested whether the factors that constrain the niche space limit the total number of coexisting species. We assessed the role of environmental filtering in shaping tree assemblages across North America north of Mexico by testing the hypothesis that colder, drier, or seasonal environments (stressful conditions for most plants) constrain tree trait diversity and thereby limit species richness. We assessed geographic patterns in trait filtering and their relationships to species richness pattern using a comprehensive set of tree range maps. We focused on four key plant functional traits reflecting major life history axes (maximum height, specific leaf area, seed mass, and wood density) and four climatic variables (annual mean and seasonality of temperature and precipitation). We tested for significant spatial shifts in trait means and variances using a null model approach. While we found significant shifts in mean species’ trait values at most grid cells, trait variances at most grid cells did not deviate from the null expectation. Measures of environmental harshness (cold, dry, seasonal climates) and lower species richness were weakly associated with a reduction in variance of seed mass and specific leaf area. The pattern in variance of height and wood density was, however, opposite. These findings do not support the hypothesis that more stressful conditions universally limit species and trait diversity in North America. Environmental filtering does, however, structure assemblage composition, by selecting for certain optimum trait values under a given set of conditions.

Productivity enhances benthic species richness along an oligotrophic Indian Ocean continental margin

AbstractAimsMarine soft sediments cover much of the deep ocean and are one of the largest habitats in the world, yet much of our understanding about their diversity is based on sampling in the North Atlantic. The deep‐sea benthos provides a simplified environment in which to explore the processes which maintain species richness. Here we investigate the influence of energy and habitat complexity on benthic species richness along an oligotrophic continental margin within the Indian Ocean.LocationThe upper continental margin of western Australia (c. 13–35° S, 100–1000 m depth).MethodsWe examined the species richness of selected polychaetes (Annelida) and crustaceans in sediment grab samples. We used generalized linear models and hierarchical partitioning to examine the relationship and relative importance of temperature, productivity (particulate organic carbon flux, net primary productivity and depth) and habitat complexity (sediment particle size diversity and grain size) on species richness at 51 sites.ResultsIn contrast to benthic studies in the North Atlantic, we found that species richness was higher on the shelf than on the slope. Species richness was positively correlated with net primary productivity; this relationship was influenced by high species richness in two areas where oceanic mixing is known to enhance primary productivity. Habitat heterogeneity and temperature were less influential.Main conclusionThis study represents one of the first extensive quantitative studies of deep‐water benthos in the Indo‐West Pacific, and provides further evidence that bathymetric gradients of species richness are variable between regions, probably due to variation in local oceanography and productivity regimes. Our findings provide support for the overriding influence of productivity on species richness, even over relatively small ranges in depth and productivity. As climate change is expected to modify biogeochemical fluxes to the deep seafloor, this is likely to affect the communities of deep‐sea fauna.

Conservation status affects elevational gradient in bird diversity in the Himalaya: A new perspective

Understanding diversity patterns along altitudinal gradients, and their underlying causes are important for conserving biodiversity. Previous studies have focused on climatic, energetic, and geographic variables (e.g., mid-domain effects), with less attention paid to human-induced habitat modifications. We used published data of bird distributions along an elevational gradient (0–4900 m) in the Nepalese Himalaya and interpolated species presence between elevational limits. The relationship between species richness and environmental variables was analyzed using generalized linear models. A low plateau relationship between bird richness and elevation was observed, with a main peak at intermediate elevations (2800 m). Across the total gradient, interpolated bird species richness had a unimodal relationship to maximum monthly precipitation and a linear response to seasonal variation in temperature, proportion of forest cover, and proportion of protected area. In lower elevations (0–2800 m), interpolated species richness had a positive and linear response to the proportion of Ramsar sites and a unimodal response to habitat heterogeneity. At higher elevations (2900–4900 m), interpolated bird richness had a positive linear response to monthly variation in temperature and a negative linear response to proportion forest cover. We conclude that factors related to human management are important drivers of elevational gradients in bird species richness.

Association of host and microbial species diversity across spatial scales in desert rodent communities.

Relationships between host and microbial diversity have important ecological and applied implications. Theory predicts that these relationships will depend on the spatio-temporal scale of the analysis and the niche breadth of the organisms in question, but representative data on host-microbial community assemblage in nature is lacking. We employed a natural gradient of rodent species richness and quantified bacterial communities in rodent blood at several hierarchical spatial scales to test the hypothesis that associations between host and microbial species diversity will be positive in communities dominated by organisms with broad niches sampled at large scales. Following pyrosequencing of rodent blood samples, bacterial communities were found to be comprised primarily of broad niche lineages. These communities exhibited positive correlations between host diversity, microbial diversity and the likelihood for rare pathogens at the regional scale but not at finer scales. These findings demonstrate how microbial diversity is affected by host diversity at different spatial scales and suggest that the relationships between host diversity and overall disease risk are not always negative, as the dilution hypothesis predicts.

Season-specific and guild-specific effects of anthropogenic landscape modification on metacommunity structure of tropical bats.

Fragmentation per se due to human land conversion is a landscape-scale phenomenon. Accordingly, assessment of distributional patterns across a suite of potentially connected communities (i.e. metacommunity structure) is an appropriate approach for understanding the effects of landscape modification and complements the plethora of fragmentation studies that have focused on local community structure. To date, metacommunity structure within human-modified landscapes has been assessed with regard to nestedness along species richness gradients. This is problematic because there is little support that species richness gradients are associated with the factors moulding species distributions. More importantly, many alternative patterns are possible, and different patterns may manifest during different seasons and for different guilds because of variation in resource availability and resource requirements of taxa. We determined the best-fit metacommunity structure of a phyllostomid bat assemblage, frugivore ensemble, and gleaning animalivore ensemble within a human-modified landscape in the Caribbean lowlands of Costa Rica during the dry and wet seasons to elucidate important structuring mechanisms. Furthermore, we identified the landscape characteristics associated with the latent gradient underlying metacommunity structure. We discriminated among multiple metacommunity structures by assessing coherence, range turnover, and boundary clumping of an ordinated site-by-species matrix. We identified the landscape characteristics associated with the latent gradient underlying metacommunity structure via hierarchical partitioning. Metacommunity structure was never nested nor structured along a richness gradient. The phyllostomid assemblage and frugivore ensemble exhibited Gleasonian structure (range turnover along a common gradient) during the dry season and Clementsian structure (range turnover and shared boundaries along a common gradient) during the wet season. Distance between forest patches and forest edge density structured the phyllostomid metacommunity during the dry and wet seasons, respectively. Proportion of pasture and forest patch density structured the frugivore metacommunity during the dry season. Gleaning animalivores exhibited chequerboard structure (mutually exclusive species pairs) during the dry season and random structure during the wet season. Metacommunity structure was likely mediated by differential resource use or interspecific relationships. Furthermore, the interaction between landscape characteristics and seasonal variation in resources resulted in season-specific and guild-specific distributional patterns.

Does species richness affect fine root biomass and production in young forest plantations?

Tree species diversity has been reported to increase forest ecosystem above-ground biomass and productivity, but little is known about below-ground biomass and production in diverse mixed forests compared to single-species forests. For testing whether species richness increases below-ground biomass and production and thus complementarity between forest tree species in young stands, we determined fine root biomass and production of trees and ground vegetation in two experimental plantations representing gradients in tree species richness. Additionally, we measured tree fine root length and determined species composition from fine root biomass samples with the near-infrared reflectance spectroscopy method. We did not observe higher biomass or production in mixed stands compared to monocultures. Neither did we observe any differences in tree root length or fine root turnover. One reason for this could be that these stands were still young, and canopy closure had not always taken place, i.e. a situation where above- or below-ground competition did not yet exist. Another reason could be that the rooting traits of the tree species did not differ sufficiently to support niche differentiation. Our results suggested that functional group identity (i.e. conifers vs. broadleaved species) can be more important for below-ground biomass and production than the species richness itself, as conifers seemed to be more competitive in colonising the soil volume, compared to broadleaved species.

Species sorting determines variation in the community composition of common and rare macrophytes at various spatial extents

Patterns of rarity in the context of species richness gradients have intrigued researchers for decades, but the same patterns have only rarely been considered in the context of community composition. There is thus a need to combine the classical rarity theory with expectations from metacommunity research. We studied the responses of assemblages of common and rare lake macrophytes to ecological gradients across various spatial extents. Based on the ideas of metacommunity research, we first hypothesised that the communities of common species are mainly affected by environmental factors and rare species are mainly controlled by spatial processes. Alternatively, following the classical theory of rarity, we expected that common species are environmental generalists (their assemblages are controlled by the spatial processes) and rare species are environmental specialists (their assemblages are controlled by the environment). We used two criteria to define common and rare species: the inflection point criterion and the 50th quartile criterion. Partial redundancy analysis was employed to decompose variation in the assemblage composition of common and rare macrophytes between environmental and spatial variables at each spatial extent and geographical region. Both criteria defined similar sets of common and rare macrophytes across spatial extents. As found in previous studies, the amount of explained variation in the composition of the macrophyte communities along ecological gradients was low overall. However, most of the explained variation, was related to the responses of common species. Assemblage composition of common and rare species was similarly explained by environmental factors. We did not find clear support for current ecological theories with regard to variation in the assemblage composition of common and rare macrophytes. In contrast, our findings suggested that species sorting is collectively structuring the assemblages of both common and rare macrophytes. Spatial variation in metacommunity structuring, however, hinders our ability to draw general conclusions on how common and rare species respond to specific ecological gradients in different regions and at various spatial extents.

Functional trait space and the latitudinal diversity gradient.

The processes causing the latitudinal gradient in species richness remain elusive. Ecological theories for the origin of biodiversity gradients, such as competitive exclusion, neutral dynamics, and environmental filtering, make predictions for how functional diversity should vary at the alpha (within local assemblages), beta (among assemblages), and gamma (regional pool) scales. We test these predictions by quantifying hypervolumes constructed from functional traits representing major axes of plant strategy variation (specific leaf area, plant height, and seed mass) in tree assemblages spanning the temperate and tropical New World. Alpha-scale trait volume decreases with absolute latitude and is often lower than sampling expectation, consistent with environmental filtering theory. Beta-scale overlap decays with geographic distance fastest in the temperate zone, again consistent with environmental filtering theory. In contrast, gamma-scale trait space shows a hump-shaped relationship with absolute latitude, consistent with no theory. Furthermore, the overall temperate trait hypervolume was larger than the overall tropical hypervolume, indicating that the temperate zone permits a wider range of trait combinations or that niche packing is stronger in the tropical zone. Although there are limitations in the data, our analyses suggest that multiple processes have shaped trait diversity in trees, reflecting no consistent support for any one theory.

Hybridization of Quercus castanea (Fagaceae) across a red oak species gradient in Mexico

Interspecific gene flow between more than two species is a common phenomenon in oaks, which can occur simultaneously among different species, promoting the transfer of genetic material across species boundaries. However, the hybridization dynamics in multispecies hybrid zones remain unknown. In this study, we provide genetic evidence of hybridization and introgression of Quercus castanea across a natural gradient of red oak species richness. We analyzed five populations recognized morphologically as “pure” Q. castanea, one allopatric and four sympatric populations, where the number of red oak species associated with Q. castanea ranged from one to four. Also, one allopatric population of each red oak species that occurs in sympatry with Q. castanea was chosen as reference population (Q. crassipes, Q. laurina, Q. mexicana and Q. crassifolia). In total, six nSSRs were used in 10 and 20 individuals from each allopatric and sympatric populations, respectively. Our results showed that allopatric populations formed completely distinct genetic clusters. In sympatric populations, we found evidence of hybridization and introgression among Q. castanea and three of its associated red oak species. However, the occurrence and frequency of hybrids between Q. castanea and these species varied among stands. Our analyses provide evidence and new insights into hybridization and introgression dynamics within a Mexican red oak species complex, through a focal species, Q. castanea.

Biogeographic distribution patterns and their correlates in the diverse frog fauna of the Atlantic Forest hotspot.

Anurans are a highly diverse group in the Atlantic Forest hotspot (AF), yet distribution patterns and species richness gradients are not randomly distributed throughout the biome. Thus, we explore how anuran species are distributed in this complex and biodiverse hotspot, and hypothesize that this group can be distinguished by different cohesive regions. We used range maps of 497 species to obtain a presence/absence data grid, resolved to 50×50 km grain size, which was submitted to k-means clustering with v-fold cross-validation to determine the biogeographic regions. We also explored the extent to which current environmental variables, topography, and floristic structure of the AF are expected to identify the cluster patterns recognized by the k-means clustering. The biogeographic patterns found for amphibians are broadly congruent with ecoregions identified in the AF, but their edges, and sometimes the whole extent of some clusters, present much less resolved pattern compared to previous classification. We also identified that climate, topography, and vegetation structure of the AF explained a high percentage of variance of the cluster patterns identified, but the magnitude of the regression coefficients shifted regarding their importance in explaining the variance for each cluster. Specifically, we propose that the anuran fauna of the AF can be split into four biogeographic regions: a) less diverse and widely-ranged species that predominantly occur in the inland semideciduous forests; b) northern small-ranged species that presumably evolved within the Pleistocene forest refugia; c) highly diverse and small-ranged species from the southeastern Brazilian mountain chain and its adjacent semideciduous forest; and d) southern species from the Araucaria forest. Finally, the high congruence among the cluster patterns and previous eco-regions identified for the AF suggests that preserving the underlying habitat structure helps to preserve the historical and ecological signals that underlie the geographic distribution of AF anurans.

A framework for evaluating the influence of climate, dispersal limitation, and biotic interactions using fossil pollen associations across the late Quaternary

Environmental conditions, dispersal lags, and interactions among species are major factors structuring communities through time and across space. Ecologists have emphasized the importance of biotic interactions in determining local patterns of species association. In contrast, abiotic limits, dispersal limitation, and historical factors have commonly been invoked to explain community structure patterns at larger spatiotemporal scales, such as the appearance of late Pleistocene no‐analog communities or latitudinal gradients of species richness in both modern and fossil assemblages. Quantifying the relative influence of these processes on species co‐occurrence patterns is not straightforward. We provide a framework for assessing causes of species associations by combining a null‐model analysis of co‐occurrence with additional analyses of climatic differences and spatial pattern for pairs of pollen taxa that are significantly associated across geographic space.We tested this framework with data on associations among 106 fossil pollen taxa and paleoclimate simulations from eastern North America across the late Quaternary. The number and proportion of significantly associated taxon pairs increased over time, but only 449 of 56 194 taxon pairs were significantly different from random. Within this significant subset of pollen taxa, biotic interactions were rarely the exclusive cause of associations. Instead, climatic or spatial differences among sites were most frequently associated with significant patterns of taxon association. Most taxon pairs that exhibited co‐occurrence patterns indicative of biotic interactions at one time did not exhibit significant associations at other times. Evidence for environmental filtering and dispersal limitation was weakest for aggregated pairs between 16 and 11 kyr BP, suggesting enhanced importance of positive species interactions during this interval. The framework can thus be used to identify species associations that may reflect biotic interactions because these associations are not tied to environmental or spatial differences. Furthermore, temporally repeated analyses of spatial associations can reveal whether such associations persist through time.

On the packing and filling of functional space in eastern North American tree assemblages

A fundamental question in ecology is how are species added to the phenotypic or functional trait space when one moves from a species poor to species rich assemblage. Specifically, the functional volume of an assemblage can expand and/or be packed more tightly to accommodate an increasing number of species. Quantifying the packing and filling of trait space therefore provides critical information regarding the generation of species richness gradients, but it is also informative for our understanding of community assembly as the functional volume is expected to be constrained by abiotic factors while the degree of the packing of the volume should be limited by biotic interactions. In this investigation we quantify the packing and filling of trait volumes in tree assemblages in eastern North America. We demonstrate that both the functional volume and the degree of packing both increase with increasing species richness. However, the increase in the functional volume is less than expected suggesting that the overall functional space is constrained. We then show that null models that incorporate a functional volume constraint uncover a greater degree of separation in trait space than expected suggesting the importance of biotic interactions within an abiotically defined functional volume.

Effect of (a)synchronous light fluctuation on diversity, functional and structural stability of a marine phytoplankton metacommunity

Disentangling the mechanisms that maintain the stability of communities and ecosystem properties has become a major research focus in ecology in the face of anthropogenic environmental change. Dispersal plays a pivotal role in maintaining diversity in spatially subdivided communities, but only a few experiments have simultaneously investigated how dispersal and environmental fluctuation affect community dynamics and ecosystem stability. We performed an experimental study using marine phytoplankton species as model organisms to test these mechanisms in a metacommunity context. We established three levels of dispersal and exposed the phytoplankton to fluctuating light levels, where fluctuations were either spatially asynchronous or synchronous across patches of the metacommunity. Dispersal had no effect on diversity and ecosystem function (biomass), while light fluctuations affected both evenness and community biomass. The temporal variability of community biomass was reduced by fluctuating light and temporal beta diversity was influenced interactively by dispersal and fluctuation, whereas spatial variability in community biomass and beta diversity were barely affected by treatments. Along the establishing gradient of species richness and dominance, community biomass increased but temporal variability of biomass decreased, thus highest stability was associated with species-rich but highly uneven communities and less influenced by compensatory dynamics. In conclusion, both specific traits (dominance) and diversity (richness) affected the stability of metacommunities under fluctuating conditions.

Spatial gradients in freshwater fish diversity, abundance and current pattern in the Himalayan region of Upper Ganges Basin, India

Pathak AK, Sarkar UK, Singh SP. 2014. Spatial gradients in freshwater fish diversity, abundance and current pattern in the Himalayan region of Upper Ganges Basin, India. Biodiversitas 15: 186-194.The present study describes the analysis and mapping of the differentmeasurements of freshwater fish biodiversity of the Upper Ganges basin in the Himalayan region using spatial interpolation methods ofGeographical Information System. The diversity, richness and abundance of fishes for each sampling location were determined andKriging interpolation was applied on each fisheries measurement to predict and produce semivariogram. The semivariogarms producedwere cross validated and reclassified. The reclassified maps for richness, abundance and diversity of fishes, occurrence of cold waterthreatened fish and abundance of important genera like Tor, Schizothorax and species were produced. The result of the Krigingproduced good results and overall error in the estimation process was found significant. The cross validation of semovariograms alsoprovided a better result with the observed data sets. Moreover, weighted overlay analysis of the reclassified raster maps of richness andabundance of fishes produced the classified raster map at different evaluation scale (0-10) qualitatively describing the gradient ofspecies richness and abundance compositely. Similarly, the classified raster map at same evaluation scale qualitatively describing thegradient of species abundance and diversity compositely was produced and published. Further, basin wise analysis betweenAlaknanda/Pindar and Ganga1 sub basins showed 0.745 disparities at 0.745 distances in 2 dimensional spaces. The richness, diversityand abundance of threatened fishes among the different sampling locations were not significant (p = 0.9).

Long‐term study of root biomass in a biodiversity experiment reveals shifts in diversity effects over time

Biodiversity experiments generally report a positive effect of plant biodiversity on aboveground biomass (overyielding), which typically increases with time. Various studies also found overyielding for belowground plant biomass, but this has never been measured over time. Also, potential underlying mechanisms have remained unclear. Differentiation in rooting patterns among plant species and plant functional groups has been proposed as a main driver of the observed biodiversity effect on belowground biomass, leading to more efficient belowground resource use with increasing diversity, but so far there is little evidence to support this. We analyzed standing root biomass and its distribution over the soil profile, along a 1–16 species richness gradient over eight years in the Jena Experiment in Germany, and compared belowground to aboveground overyielding.In our long‐term dataset, total root biomass increased with increasing species richness but this effect was only apparent after four years. The increasingly positive relationship between species richness and root biomass, explaining 12% of overall variation and up to 28% in the last year of our study, was mainly due to decreasing root biomass at low diversity over time. Functional group composition strongly affected total standing root biomass, explaining 44% of variation, with grasses and legumes having strong overall positive and negative effects, respectively. Functional group richness or interactions between functional group presences did not strongly contribute to overyielding. We found no support for the hypothesis that vertical root differentiation increases with species richness, with functional group richness or composition. Other explanations, such as stronger negative plant–soil feedbacks in low‐diverse plant communities on standing root biomass and vertical distribution should be considered.

On the measurement of dimensionality of biodiversity

AbstractAimTo characterize relationships among indices of taxonomic, phylogenetic, functional and phenetic diversity (TPFP diversity) for Neotropical bats and examine if dimensionality is different from null model expectations after controlling for sampling effects owing to underlying variation in species richness.LocationNeotropics.MethodsBat distributions were estimated using geographic range maps. By overlaying range maps on a gridded map of the New World, the species composition of each cell was determined. Then, species richness and three indices each of phylogenetic, functional and phenetic diversity were calculated. A principal components analysis (PCA) determined the dimensionality of the entire multivariate data set. This was followed by two additional PCAs that examined the dimensionality of spatial and non‐spatial fractions of the original data. Spearman rank correlations determined pair‐wise association among indices. Correlations and dimensionality were compared with two different null models that account for species richness gradients.ResultsTen measures characterizing TPFP diversity exhibited much spatial structure across the New World. Pair‐wise correlations between indices were typically different from null model expectations. While patterns of multivariate covariation were similar across spatial and non‐spatial data sets, the dimensionality of biodiversity was low and either lower than or no different from null model expectations.Main conclusionsMost measures of biodiversity exhibit at least some level of quantitative redundancy, and this redundancy is often higher than expected given sampling effects owing to species richness gradients. Considerations of uniqueness should be made when examining conceptually different dimensions of biodiversity.

The latitudinal species richness gradient in New World woody angiosperms is consistent with the tropical conservatism hypothesis.

Plant diversity, like that of most other taxonomic groups, peaks in the tropics, where climatic conditions are warm and wet, and it declines toward the temperate and polar zones as conditions become colder and drier, with more seasonally variable temperatures. Climate and evolutionary history are often considered competing explanations for the latitudinal gradient, but they are linked by the evolutionarily conserved environmental adaptations of species and the history of Earth's climate system. The tropical conservatism hypothesis (TCH) invokes niche conservatism, climatic limitations on establishment and survival, and paleoclimatic history to explain the latitudinal diversity gradient. Here, we use latitudinal distributions for over 12,500 woody angiosperm species, a fossil-calibrated supertree, and null modeling to test predictions of the TCH. Regional assemblages in the northern and southern temperate zones are less phylogenetically diverse than expected based on their species richness, because temperate taxa are clustered into relatively few clades. Moreover, lineages with temperate affinities are generally younger and nested within older, more tropical lineages. As predicted by the TCH, the vast majority of temperate lineages have arisen since global cooling began at the Eocene-Oligocene boundary (34 Mya). By linking physiological tolerances of species to evolutionary and biogeographic processes, phylogenetic niche conservatism may provide a theoretical framework for a generalized explanation for Earth's predominant pattern of biodiversity.

Ecoregional Vulnerability Assessment for the Functional Richness of South American Carnivorans (Mammalia: Carnivora)

Mapping geographic trends in biodiversity is a key step in conservation planning, which has been mainly focused on taxonomic criteria or species of particular concern. More recently, higher consideration of ecosystem functioning has been advocated, allocating more attention to traits and functional diversity of species assemblages. Carnivorans (Mammalia: Carnivora) are charismatic, albeit threatened, species that variously affect ecosystem functioning through consumptive processes, and whose functional diversity depends on traits associated with their trophic habits and energetic requirements. Yet, analyses of spatial trends in the diversity and vulnerability of carnivoran assemblages have mostly focused on taxonomic and phylogenetic criteria. Then, the present study assessed the vulnerability of the functional richness of South American carnivoran assemblages, both at continental and regional levels. As a first diagnostic of vulnerability, the form of the association between functional richness and species richness (FRS) was assessed through simulations. The resulting nearly linear association indicated low functional redundancy and high sensitivity to global extinctions. A more realistic FRS accounting for actual extinction threats exacerbated losses of functional richness. Further, a positive correlation between effect and response traits suggests non-compensatory responses to environmental stressors by functionally redundant species and, thus, sensitivity of carnivoran functional richness to ongoing trends in land conversion and habitat degradation. Regionally, functional richness paralleled latitudinal gradients in species richness, but vulnerability did not entirely match these variables in space, nor did it risk estimates that accounted for regions’ conservation status. This suggests regional differentiation in conservation priorities, complementing existing taxonomically oriented prioritization schemes.

Bathymetric patterns of polychaete (Annelida) species richness in the continental shelf of the Gulf of California, Eastern Pacific

The mid-domain effect was tested to evaluate the bathymetric patterns of the polychaete species richness in the Upper and Lower Gulf of California as a possible hypothesis to explain the species richness gradient, exploring the overlapping of species depth ranges towards the middle continental shelf. The bathymetric gradient of the number of species was estimated with the depth ranges of 554 polychaete species, and the mid-domain effect was tested using a Monte Carlo simulation program at bands of 10m depth. The Upper (251 species) and Lower (491 species) Gulf regions showed clear differences in their faunal composition (Jaccard similarity index=0.34); the species richness pattern was characterized by a highly significant presence of polychaetes with short depth ranges (<10m). The richness distribution could be described as a cubic polynomial curve, but the maximum values in both Gulf regions (141 and 317 species, respectively for Upper and Lower Gulf regions) are strongly biased to shallow waters (40m). This is not consistent with the peak of diversity at 60–70m predicted by the model. The observed patterns cannot be reproduced by the mid-domain effect, suggesting the existence of non-random factors affecting the species richness gradients in the Gulf.