Global Patterns Of Species Richness Research Articles

Expert‐based range maps cannot be replicated using data‐driven methods but macroecological conclusions arising from them can

AbstractAimAnswering many fundamental and applied scientific questions relies on accurate geographic range maps for species, such as those compiled by experts working with the International Union for Conservation of Nature (IUCN). However, these maps are resource demanding to produce and only available for a limited number of organisms. Here, we test to what extent standardized, data‐driven methods based on publicly available occurrences can reproduce expert‐based IUCN range maps and the macroecological conclusions drawn from them.LocationGlobal.Time PeriodPresent.TaxaBirds.Materials and MethodsWe estimated the geographic ranges for 7385 non‐marine bird species which either were non‐migratory or had spatially connected breeding and wintering ranges from publicly available, georeferenced point occurrences. We then quantified the spatial overlap between these range estimates and the IUCN expert‐derived range estimates. Finally, we compared global species richness patterns and the environmental correlates that emerge from both approaches.ResultsWe find that range estimates based on point occurrence records overlap on average 52% with expert range estimates for the same species. The global species richness patterns estimated under both approaches are overall similar but show local and regional differences, for example, in the tropical Andes of northern South America and the Central Arc region of Africa. The estimated global drivers of richness are similar.Main ConclusionsExpert‐derived estimates of species distributions are not reproducible by data‐driven approaches relying on currently available public records, even for well‐documented taxa such as birds. However, these discrepancies do not substantially change our macroecological understanding of global drivers of bird diversity.

Evolutionary causes of global patterns of species richness in regional fern floras across the world

AbstractAimGlobally, biodiversity is unevenly distributed, as a result of varying environmental conditions and regionally different historical processes. The influence of the latter on current diversity patterns is poorly understood. We explore geographic patterns of matches and mismatches between phylogenetic relatedness metrics measuring different depths of evolutionary history and investigate the effects of evolutionary legacy at different evolutionary depths on species density of ferns.MethodsWe divided the globe into 392 geographic regions on land, and collated species lists of ferns for each geographic region. We related species richness to phylogenetic metrics reflecting different depths of evolutionary history (standardized effect sizes of mean nearest taxon distance and mean pairwise distance, MNTDses and MPDses, respectively) for ferns in regional floras across the world.LocationGlobal.Time PeriodCurrent.TaxonFerns.ResultsWe show that different centers of fern diversity have strikingly different phylogenetic composition. We find that overall fern species diversity is negatively correlated with both MNTDses and MPDses, so that regions with high species diversity tend to have clustered species assemblages, whereas species‐poor regions tend to have overdispersed species assemblages. At the global extent, MNTDses and MPDses together explained 62.2%, 19.3%, and 65.7% of the variation in species diversity for all ferns as a whole, non‐polypod ferns, and polypods, respectively.Main ConclusionsOur study suggests that current geographic patterns of fern species richness are driven, at least in part, by evolutionary history of ferns, which varies among biogeographic regions.

Same process, different patterns: pervasive effect of evolutionary time on species richness in freshwater fishes.

Tropical lands harbour the highest number of species, resulting in the ubiquitous latitudinal diversity gradient (LDG). However, exceptions to this pattern have been observed in some taxa, explained by the interaction between the evolutionary histories and environmental factors that constrain species' physiological and ecological requirements. Here, we applied a deconstruction approach to map the detailed species richness patterns of Actinopterygian freshwater fishes at the class and order levels and to disentangle their drivers using geographical ranges and a phylogeny, comprising 77% (12 557) of all described species. We jointly evaluated seven evolutionary and ecological hypotheses posited to explain the LDG: diversification rate, time for speciation, species-area relationship, environmental heterogeneity, energy, temperature seasonality and past temperature stability. We found distinct diversity gradients across orders, including expected, bimodal and inverse LDGs. Despite these differences, the positive effect of evolutionary time explained patterns for all orders, where species-rich regions are inhabited by older species compared to species-poor regions. Overall, the LDG of each order has been shaped by a unique combination of factors, highlighting the importance of performing a joint evaluation of evolutionary, historical and ecological factors at different taxonomic levels to reach a comprehensive understanding on the causes driving global species richness patterns.

Patterns of species richness and turnover in endemic amphibians of the Guineo‐Congolian rain forest

AbstractAimThe African Guineo‐Congolian (GC) region is a global biodiversity hotspot with high species endemism, bioclimatic heterogeneity, complex landscape features, and multiple biogeographic barriers. Bioclimatic and geographic variables influence global patterns of species richness and endemism, but their relative importance varies across taxa and regions and is poorly understood for many faunas. Here, we test the hypothesis that turnover in endemic amphibians of the GC biodiversity hotspot is influenced mainly by the geographic distance between grid cells and secondarily by rainfall‐ and temperature‐related variables.LocationWest and Central Africa.Major Taxa StudiedAmphibians.MethodsWe compiled species‐occurrence records via field sampling, online databases, and taxonomic literature. Our study used 1205 unique georeferenced records of 222 amphibian species endemic to the GC region. Patterns of species richness were mapped onto a grid with a spatial resolution of 0.5° × 0.5°. We estimated weighted endemism and tested whether endemism was higher than the expected species richness (randomization test). We quantified species turnover using generalized dissimilarity modelling to evaluate the processes underlying observed patterns of species richness in GC endemic amphibians. We explored bioregionalization using agglomerative hierarchical clustering based on the unweighted pair group method with arithmetic averages.ResultsWe identified seven areas within the lower GC region – forests in Cameroon, Gabon, Southern Nigeria, Equatorial Guinea, Republic of Congo, Democratic Republic of Congo, and Cote d'Ivoire – as having high species richness of endemic amphibians. The randomization test returned four major areas of significant weighted endemism: Nigeria‐Cameroon mountains, forest regions of the Democratic Republic of Congo, Cote d'Ivoire, and Ghana. Our analysis revealed five bioregions for amphibian endemism, four of which were located within the lower Guineo‐Congolian forest. Species turnover was strongly related to the geographic distance between grid cells; contributing bioclimatic variables included precipitation of the warmest quarter, mean temperature of the wettest quarter, and mean diurnal temperature range.Main ConclusionsOur results indicate that geographic distance between grid cells is the primary determinant of turnover in GC endemic amphibians, with secondary but significant effects of rainfall‐ and temperature‐related variables. Our study identifies key areas of endemic amphibian richness that could be prioritized for conservation actions.

Co-limitation towards lower latitudes shapes global forest diversity gradients.

The latitudinal diversity gradient (LDG) is one of the most recognized global patterns of species richness exhibited across a wide range of taxa. Numerous hypotheses have been proposed in the past two centuries to explain LDG, but rigorous tests of the drivers of LDGs have been limited by a lack of high-quality global species richness data. Here we produce a high-resolution (0.025° × 0.025°) map of local tree species richness using a global forest inventory database with individual tree information and local biophysical characteristics from ~1.3 million sample plots. We then quantify drivers of local tree species richness patterns across latitudes. Generally, annual mean temperature was a dominant predictor of tree species richness, which is most consistent with the metabolic theory of biodiversity (MTB). However, MTB underestimated LDG in the tropics, where high species richness was also moderated by topographic, soil and anthropogenic factors operating at local scales. Given that local landscape variables operate synergistically with bioclimatic factors in shaping the global LDG pattern, we suggest that MTB be extended to account for co-limitation by subordinate drivers.

Global variation in diversification rate and species richness are unlinked in plants

Species richness varies immensely around the world. Variation in the rate of diversification (speciation minus extinction) is often hypothesized to explain this pattern, while alternative explanations invoke time or ecological carrying capacities as drivers. Focusing on seed plants, the world's most important engineers of terrestrial ecosystems, we investigated the role of diversification rate as a link between the environment and global species richness patterns. Applying structural equation modeling to a comprehensive distribution dataset and phylogenetic tree covering all circa 332,000 seed plant species and 99.9% of the world's terrestrial surface (excluding Antarctica), we test five broad hypotheses postulating that diversification serves as a mechanistic link between species richness and climate, climatic stability, seasonality, environmental heterogeneity, or the distribution of biomes. Our results show that the global patterns of species richness and diversification rate are entirely independent. Diversification rates were not highest in warm and wet climates, running counter to the Metabolic Theory of Ecology, one of the dominant explanations for global gradients in species richness. Instead, diversification rates were highest in edaphically diverse, dry areas that have experienced climate change during the Neogene. Meanwhile, we confirmed climate and environmental heterogeneity as the main drivers of species richness, but these effects did not involve diversification rates as a mechanistic link, calling for alternative explanations. We conclude that high species richness is likely driven by the antiquity of wet tropical areas (supporting the "tropical conservatism hypothesis") or the high ecological carrying capacity of warm, wet, and/or environmentally heterogeneous environments.

Spatiotemporal Evolution of the Global Species Diversity of Rhododendron.

Evolutionary radiation is a widely recognized mode of species diversification, but its underlying mechanisms have not been unambiguously resolved for species-rich cosmopolitan plant genera. In particular, it remains largely unknown how biological and environmental factors have jointly driven its occurrence in specific regions. Here, we use Rhododendron, the largest genus of woody plants in the Northern Hemisphere, to investigate how geographic and climatic factors, as well as functional traits, worked together to trigger plant evolutionary radiations and shape the global patterns of species richness based on a solid species phylogeny. Using 3,437 orthologous nuclear genes, we reconstructed the first highly supported and dated backbone phylogeny of Rhododendron comprising 200 species that represent all subgenera, sections, and nearly all multispecies subsections, and found that most extant species originated by evolutionary radiations when the genus migrated southward from circumboreal areas to tropical/subtropical mountains, showing rapid increases of both net diversification rate and evolutionary rate of environmental factors in the Miocene. We also found that the geographically uneven diversification of Rhododendron led to a much higher diversity in Asia than in other continents, which was mainly driven by two environmental variables, that is, elevation range and annual precipitation, and were further strengthened by the adaptation of leaf functional traits. Our study provides a good example of integrating phylogenomic and ecological analyses in deciphering the mechanisms of plant evolutionary radiations, and sheds new light on how the intensification of the Asian monsoon has driven evolutionary radiations in large plant genera of the Himalaya-Hengduan Mountains.

Environmental heterogeneity predicts global species richness patterns better than area

AbstractAimIt is widely accepted that biodiversity is influenced by both niche‐related and spatial processes from local to global scales. Their relative importance, however, is still disputed, and empirical tests are surprisingly scarce at the global scale. Here, we compare the importance of area (as a proxy for pure spatial processes) and environmental heterogeneity (as a proxy for niche‐related processes) for predicting native mammal species richness world‐wide and within biogeographical regions.LocationGlobal.Time periodWe analyse a spatial snapshot of richness data collated by the International Union for Conservation of Nature.Major taxa studiedAll terrestrial mammal species, including possibly extinct species and species with uncertain presence.MethodsWe applied a spreading dye algorithm to analyse how native mammal species richness changes with area and environmental heterogeneity. As measures for environmental heterogeneity, we used elevation ranges and precipitation ranges, which are well‐known correlates of species richness.ResultsWe found that environmental heterogeneity explained species richness relationships better than did area, suggesting that niche‐related processes are more prevalent than pure area effects at broad scales.Main conclusionsOur results imply that niche‐related processes are essential to understand broad‐scale species–area relationships and that habitat diversity is more important than area alone for the protection of global biodiversity.

Persistent Quaternary climate refugia are hospices for biodiversity in the Anthropocene

Climate stability leads to high levels of speciation and reduced extinction rates, shaping species richness patterns1–3. Hotspots of species diversity often overlap with regions that experienced stable temperatures and, perhaps, variable rates of precipitation during the late Quaternary4,5. These hotspots potentially harbour many species with low vagility and small geographical ranges6, making them more vulnerable to future ecoclimatic change4,7,8. By comparing global and regional patterns of climate stability during short periods of unusually large and widespread climate changes since the Last Glacial Maximum with twenty-first-century patterns, we show that human-driven climate change will disproportionally affect biodiversity in late Quaternary climate refugia, ultimately affecting the species, communities and ecosystems that are most vulnerable to climate change. Moreover, future changes in absolute temperature will probably erode the mechanisms that are theorized to sustain biodiversity hotspots across time. These impending shifts from stable to unstable temperatures—projected for the majority of the world’s biodiversity regions—threaten to reduce the size and extent of important climatic safe havens for diversity. Where climate refugia are forecast to persist until the end of this century, temperatures in these refuges are likely to exceed the acclimation capacity of many species, making them short-term hospices for biodiversity at best7–9. The stability of climatic conditions since the Last Glacial Maximum has contributed to current global patterns of species richness. Changes in patterns of climate stability this century reveal areas where climate change could reduce biodiversity, with largest losses in past climatic safe havens.

Global Patterns of Species Richness in Coastal Cephalopods

Within the context of global climate change and overfishing of fish stocks, there is some evidence that cephalopod populations are benefiting from this changing setting. These invertebrates show enhanced phenotypic flexibility and are found from polar regions to the tropics. Yet, the global patterns of species richness in coastal cephalopods are not known. Here, among the 370 identified-species, 164 are octopuses, 96 are cuttlefishes, 54 are bobtails and bottletails, 48 are inshore squids and 8 are pygmy squids. The most diverse ocean is the Pacific (with 213 cephalopod species), followed by the Indian (146 species) and Atlantic (95 species). The least diverse are the Southern (15 species) and the Arctic (12 species) Oceans. Endemism is higher in the Southern Ocean (87%) and lower in the Arctic (25%), which reflects the younger age and the “Atlantification” of the latter. The former is associated with an old lineage of octopuses that diverged around 33 Ma. Within the 232 ecoregions considered, the highest values of octopus and cuttlefish richness are observed in the Central Kuroshio Current ecoregion (with a total of 64 species), followed by the East China Sea (59 species). This pattern suggests dispersal in the Central Indo-Pacific (CIP) associated with the highly productive Oyashio/Kuroshio current system. In contrast, inshore squid hotspots are found within the CIP, namely in the Sunda Shelf province, which may be linked to the occurrence of an ancient intermittent biogeographic barrier: a land bridge formed during the Pleistocene which severely restricted water flow between the Pacific and Indian Oceans, thereby facilitating squid fauna differentiation. Another marked pattern is a longitudinal richness cline from the Central (CIP) towards the Eastern Indo-Pacific (EIP) realm, with central Pacific archipelagos as evolutionary dead ends. In the Atlantic Ocean, closure of the Atrato Seaway (at the Isthmus of Panama) and Straits of Gibraltar (Mediterranean Sea) are historical processes that may explain the contemporary Caribbean octopus richness and Mediterranean sepiolid endemism, respectively. Last, we discuss how the life cycles and strategies of cephalopods may allow them to adapt quickly to future climate change and extend the borealization of their distribution.

A consistent species richness–climate relationship for oaks across the Northern Hemisphere

AbstractAimAlthough the effects of climate on species richness are known, regional processes may lead to different species richness–climate relationships across continents resulting in species richness anomalies, especially for tropical groups. Phylogenetic niche conservatism may also influence species richness–climate relationships of different lineages. Here, we tested whether regional effects also exist for temperate lineages using the genus Quercus.LocationNorthern Hemisphere.Time periodPresent day.Major taxa studiedQuercus (Fagaceae).MethodsWe used a dated phylogeny and distribution data for Quercus to evaluate its global species richness patterns and phylogenetic niche conservatism. To evaluate the consistency in species richness–climate relationships across continents of the genus Quercus as a whole and the temperate subgenus Quercus, we conducted analyses of covariance with continent as the categorical variable and climate variables as the covariate. We calibrated four widely used models using the global data or data from each continent separately and evaluated the predictive power of each model for different continents using the root mean squared error.ResultsThe relationships between species richness and climate were not significantly different among continents for both the genus Quercus as a whole and the subgenus Quercus. Unlike the models based on European data, those based on North American and eastern Asian data predicted both the global species richness and the richness in other continents. The species richness of a subtropical subgenus Cyclobalanopsis was most influenced by water availability, while that of a temperate subgenus Quercus was most influenced by environmental temperature.Main conclusionsIn contrast to the subtropical subgenus Cyclobalanopsis, our results showed a consistent richness–climate relationship and absence of regional effects on species richness across continents for the temperate subgenus Quercus, likely suggesting that the species richness of temperate lineages, for example subgenus Quercus, may have reached equilibrium with the contemporary climate in the Northern Hemisphere.

Vertical stratification influences global patterns of biodiversity

Species distributions in terrestrial ecosystems are three‐dimensional, spanning both the horizontal landscape and the vertical space provided by the physical environment. Classical hypotheses suggest that communities become more vertically stratified with increasing species richness, owing to reduced competition or finer niche subdivision. However, this assertion remains untested in the context of the broader realm of biogeography. Here, integrating traits and distribution data for amphibians globally, we show how vertical strategies interact with the physical and climatic environments to govern global patterns of species richness and community composition. Our results reveal a marked latitudinal shift in strategies of vertical habitat use, from highly arboreal assemblages in the tropics to highly fossorial assemblages in sub‐tropical and temperate regions. Arboreality is strongly associated with precipitation, vegetation structure and climatic stability, whereas fossoriality is more common in dry environments with high diurnal temperature range and low vegetation structure. These analyses shed light on the importance of vertical stratification for species coexistence in species‐rich regions. As certain tropical habitats become drier from climate change, the rich biological diversity that is emblematic of the tropics may transition from vertically stratified to ‘flattened’, with future communities living mostly on or beneath the ground.

Bimodal latitudinal species richness and high endemicity of razor clams (Mollusca)

AbstractAimTo examine the global distribution, endemicity, and latitudinal gradients of species richness of razor clams, family Solenidae.LocationGlobal.MethodsA total of 3105 distribution records for 77 Solen and Solena species were used. Species richness was plotted in 5° latitude–longitude cells and related to environmental variables.ResultsThe north‐west Pacific and the Indo‐West Pacific have the highest species richness (about 85% of all species)–mostly in the Sea of Japan, China Sea, the Gulf of Thailand and the Andaman Sea. Cluster analysis of similarity patterns of species composition (i.e., presence of Solenidae species) for 5° latitudinal–longitudinal grid cells showed 16 significant biogeographical regions that concur with existing marine biogeographical hypotheses. More than half of the species were endemic to specific biogeographical regions. The geographical distribution of species in 5° latitudinal bands showed a significant bimodal pattern. Global patterns of species richness increased from the poles to intermediate latitudes and dipped near the equator. A non‐linear relationship between species richness and mean sea‐surface temperature (SST) values was compatible with this bimodal pattern. Two inflection points of species richness with correlation of SST at 12 °C (low species richness) and 28 °C (high species richness) were coincident with the bimodal latitudinal species richness pattern. Species richness was highly positively correlated with mean SST over all latitudes, and within the Northern and Southern Hemispheres. Species richness decreased with SST range over all latitudes and in the Northern Hemisphere. Species richness also decreased with chlorophyll‐a concentration and primary productivity, but increased with ocean area in the Northern Hemisphere (only).Main conclusionsThe latitudinal distribution in species richness of Solenidae peaked at 10° N and 25° S rather than at the equator, exhibiting a strongly bimodal pattern that is likely to be temperature driven.

Elucidating the global elapid (Squamata) richness pattern under metabolic theory of ecology

Environmental determinants of global patterns in species richness are still uncertain. The Metabolic Theory of Ecology (MTE) proposes that species richness patterns can be explained by environmental temperature acting on the metabolism of ectothermic organisms. However, the generality of this theory has been questioned due to its low fit to the geographic variation in species richness of different taxonomic groups. Here, we investigated whether the MTE drives elapid richness, testing the non-stationarity of the relationship between the natural logarithm of species richness (ln S) and the inverse function of temperature (1/kT) using a geographically weighted regression (GWR). The relationship between ln S and 1/kT varied systematically over space and showed non-stationarity. Few tropical locations were consistent with MTE predictions, whereas other regions fitted differently. Although the slope of the GWR model ranged from low to high, the temperature did not predict species richness strongly on average and did not limit the upper values of richness. The response of richness to temperature in some areas might reflect a recent history of colonization and diversification of species across tropical and subtropical regions. In regions not affected by temperature, species richness should be structured by other biotic and abiotic interactions. This scenario reveals that the non-stationarity of the relationship would be linked to idiosyncrasies in the sample sites, which can drift the magnitude or change the relationship between species richness and temperature throughout space.

Global Priorities for Marine Biodiversity Conservation

In recent decades, many marine populations have experienced major declines in abundance, but we still know little about where management interventions may help protect the highest levels of marine biodiversity. We used modeled spatial distribution data for nearly 12,500 species to quantify global patterns of species richness and two measures of endemism. By combining these data with spatial information on cumulative human impacts, we identified priority areas where marine biodiversity is most and least impacted by human activities, both within Exclusive Economic Zones (EEZs) and Areas Beyond National Jurisdiction (ABNJ). Our analyses highlighted places that are both accepted priorities for marine conservation like the Coral Triangle, as well as less well-known locations in the southwest Indian Ocean, western Pacific Ocean, Arctic and Antarctic Oceans, and within semi-enclosed seas like the Mediterranean and Baltic Seas. Within highly impacted priority areas, climate and fishing were the biggest stressors. Although new priorities may arise as we continue to improve marine species range datasets, results from this work are an essential first step in guiding limited resources to regions where investment could best sustain marine biodiversity.

Accounting for geographical variation in species–area relationships improves the prediction of plant species richness at the global scale

AbstractAimThe species–area relationship (SAR) is a prominent concept for predicting species richness and biodiversity loss. A key step in defining SARs is to accurately estimate the slope of the relationship, but researchers typically apply only one global (canonical) slope. We hypothesized that this approach is overly simplistic and investigated how geographically varying determinants of SARs affect species richness estimates of vascular plants at the global scale.LocationGlobal.MethodsWe used global species richness data for vascular plants from 1032 geographical units varying in size and shape. As possible determinants of geographical variation in SARs we chose floristic kingdoms and biomes as biogeographical provinces, and land cover as a surrogate for habitat diversity. Using simultaneous autoregressive models we fitted SARs to each set of determinants, compared their ability to predict the observed data and large‐scale species richness patterns, and determined the extent to which varying SARs differed from the global relationship.ResultsIncorporating variation into SARs improved predictions of global species richness patterns. The best model, which accounts for variation due to biomes, explained 46.1% of the species richness variation. Moreover, fitting SARs to biomes produced better results than fitting them to floristic kingdoms, supporting the hypothesis that energy availability complements evolutionary history in generating species richness patterns. Land cover proved to be less important than biomes, explaining only 36.4% of the variation, possibly owing to the high uncertainty in the data set. The incorporation of second‐order interactions of area, land cover and biomes did not improve the predictive ability of the models.Main conclusionsOur study contributes to a deeper understanding of SARs and improves the applicability of SARs through regionalization. Future models should explicitly consider geographically varying determinants of SARs in order to improve our assessment of the impact of global change scenarios on species richness patterns.

Past climate and species ecology drive nested species richness patterns along an east‐west axis in the Himalaya

AbstractAimAlthough global species richness patterns appear consistent across taxa and continents, patterns are elusive at smaller spatial scales. At regional/subcontinental scales, climatic, environmental and taxon‐specific contingencies are likely to interact to modify general richness patterns. We develop a biogeographical paradigm for the Himalayan range as representative of regions at similar spatial scales, and where historical climate fluctuations might interact with species ecology to drive species richness patterns.LocationHimalayan range, AsiaMethodsWe obtained a cell × species presence–absence matrix for babblers and murid rodents in 1° latitude × 1° longitude cells in the Himalayan range. We investigated nestedness in species richness patterns in these taxa along a distance gradient from the species‐rich eastern towards the relatively depauperate west. We also investigated the relationship between species autecology and westward extent along the Himalaya. Climate data were obtained from published sources.ResultsHimalayan babbler and murid assemblages are nested along an east–west axis, with assemblages in westward cells tending to be subsets of assemblages immediately to the east. Distance westward from the eastern Himalaya was related positively to altitudinal mobility of babbler assemblages, while body size increased with distance westward for murid assemblages.Main conclusionsThe eastern Himalaya, which was not glaciated over during glacial maxima, was a potential refugium for babbler and murid species. Following glacial retreat, species could have recolonized the Himalaya westwards to different extents based on ecological traits (size, altitudinal migration) determining ability to deal with the more seasonal west. This produces both (1) a nested species richness pattern, and (2) correlations between ‘filtering’ autecological traits and distance. Such patterns should be replicated in other regions with historical climatic refugia; investigating nestedness along distance gradients from refugia would be a powerful tool in mapping biogeographical history, especially in separating historical effects from currently proposed energy‐productivity relationships.

Phylogenetic beta diversity of angiosperms in North America

AbstractAimEcologists have generally agreed that beta diversity is a key component of global patterns of species richness. Incorporating phylogenetic information into the study of beta diversity allows researchers to identify the degree to which the shared evolutionary histories of species explain ecological patterns observed today. For example, phylogenetic analyses can determine whether closely related species tend to occupy similar positions along broad climatic gradients and whether this explains the compositional turnover along these gradients. Despite the promise of phylogenetic beta diversity analyses, few continental‐scale investigations exist. Here, we quantify the phylogenetic beta diversity and taxonomic beta diversity of the angiosperm flora across North America. We relate these metrics to one another and to geographical and environmental distances to uncover the phylogenetic signal underlying species compositional turnover.LocationNorth America.MethodSeventy‐one regional floras were used and assigned into five latitudinal zones and two longitudinal bands. The Sørensen index and PhyloSor index were used to quantify taxonomic similarity and phylogenetic similarity, respectively, between floras, and were related to geographical and environmental distances.ResultsPhylogenetic similarity between floras is strongly correlated with taxonomic similarity, is higher in eastern North America than in western North America, and increases strikingly with latitude. Geographical and environmental distances together explained on average about 76% of the variation in phylogenetic beta diversity with environmental distance explaining more variation in phylogenetic similarity in three of the four latitudinal bands examined.Main conclusionsThe results show that phylogenetic beta diversity is consistently lower than taxonomic beta diversity, which suggests that the spatial turnover of species in the study system is predominantly the spatial turnover of closely related species and not distantly related species. Thus, the turnover of angiosperm floras in North America is best explained by small divergences along environmental axes for closely related species and a gradual turnover of lineages through space.

Global patterns in sandy beach macrofauna: Species richness, abundance, biomass and body size

Global patterns in species richness in sandy beach ecosystems have been poorly understood until comparatively recently, because of the difficulty of compiling high-resolution databases at continental scales. We analyze information from more than 200 sandy beaches around the world, which harbor hundreds of macrofauna species, and explore latitudinal trends in species richness, abundance and biomass. Species richness increases from temperate to tropical sites. Abundance follows contrasting trends depending on the slope of the beach: in gentle slope beaches, it is higher at temperate sites, whereas in steep-slope beaches it is higher at the tropics. Biomass follows identical negative trends for both climatic regions at the whole range of beach slopes, suggesting decreasing rates in carrying capacity of the environment towards reflective beaches. Various morphodynamic variables determine global trends in beach macrofauna. Species richness, abundance and biomass are higher at dissipative than at reflective beaches, whereas a body size follows the reverse pattern. A generalized linear model showed that large tidal range (which determines the vertical dimension of the intertidal habitat), small size of sand particles and flat beach slope (a product of the interaction among wave energy, tidal range and grain size) are correlated with high species richness, suggesting that these parameters represent the most parsimonious variables for modelling patterns in sandy beach macrofauna. Large-scale patterns indicate a scaling of abundance to a body size, suggesting that dissipative beaches harbor communities with highest abundance and species with the smallest body sizes. Additional information for tropical and northern hemisphere sandy beaches (underrepresented in our compilation) is required to decipher more conclusive trends, particularly in abundance, biomass and body size. Further research should integrate meaningful oceanographic variables, such as temperature and primary production, in deciphering latitudinal trends.

Drivers of β-diversity along latitudinal gradients revisited

Aim Ecologists have generally agreed that β-diversity is driven at least in part by ecological processes and mechanisms of community assembly and is a key determinant of global patterns of species richness. This idea has been challenged by a recent study based on an individual-based null model approach, which aims to account for the species pool. The goal of the present study is twofold: (1) to analyse data sets from different parts of the world to determine whether there are significant latitude–β-diversity gradients after accounting for the species pool, and (2) to evaluate the validity of the null model. Location Global. Methods A total of 257 forest plots, each being 0.1 ha in size and having 10 0.01-ha subplots, were used. We conducted four sets of analyses. A modified version of Whittaker's β-diversity index was used to quantify β-diversity for each forest plot. A randomization procedure was used to determine expected β-diversity. Results The number of individuals per species, which characterizes species abundance distribution, alone explains 56.8–84.2% of the variation in observed β-diversity. Species pool (γ-diversity) explained only an additional 2.6–15.2% of the variation in observed β-diversity. Latitude explains 18.6% of the variation in raw β deviation in Gentry's global data set, and explains 11.0–11.6% of the variation in standardized β deviation in the global and three regional analyses. Latitude explains 33.2–46.2% of the variation in the number of individuals per species. Main conclusions Species abundance distribution, rather than species pool size, plays a key role in driving latitude–β-diversity gradients for β-diversity in local forest communities. The individual-based null model is not a valid null model for investigating β-diversity gradients driven by mechanisms of local community assembly because the null model incorporates species abundance distributions, which are driven by mechanisms of local community assembly and in turn generate β-diversity gradients.