Latitudinal gradients of species richness: a test of the geographic area hypothesis at two ecological scales

The geographic area hypothesis advances area as the primary cause of latitudinal gradients in diversity. The greater area of tropical zones, it suggests, stimulates speciation, inhibits extinction, and leads to increased species richness compared to the situation in smaller temperate and boreal zones. Because bats exhibit exceptionally strong latitudinal gradients of richness at multiple spatial scales in the New World, they are an appropriate system with which to test the geographic area hypothesis. We used range maps for 250 species of New World bats to estimate species richness in biogeographic zones at two hierarchical spatial scales: biome types and provinces. We then conducted a series of regression analyses to evaluate the ability of area to account for latitudinal gradients in species richness. However, spillover (zonal bleeding) of tropical species into extra-tropical zones may mask the species-area relationship and alter perceptions of the latitudinal gradient. To address this issue, we conducted additional analyses excluding tropical species, using a series of increasingly inclusive definitions of tropical ranges. Ecogeographic zones of the New World are not larger at tropical versus extra-tropical latitudes. Moreover, spillover of tropical species into ecogeographic zones within extra-tropical regions generally does not diminish the association between richness and area. Nonetheless, the latitudinal gradient of species richness is strong and significant at both ecogeographic scales. Clearly, area does not drive the latitudinal gradient of bat species richness in the New World. In fact, area represents a source of noise rather than a dominant signal at the focal scale of biome types and provinces in the Western Hemisphere.     

Comparative biogeography of mammals on islands

Insular faunas of terrestrial mammals and bats are examined on a worldwide basis to test the adequacy of equilibrium and historical legacy models as explanations for species-area relationships. Species numbers of bats on islands conform to predictions from equilibrium theory, whereby recurrent immigrations and extinctions influence species richness. By contrast, species numbers of terrestrial mammals on islands result from a historical legacy of very low immigration rates on oceanic islands (the faunas are colonization-limited) and by the fragmentation of once contiguous continental faunas to form relictual populations, which subsequently undergo extinctions, on landbridge islands (the faunas are extinction-limited). This explanation is supported by several lines of evidence: (1) z values (slopes of species-area curves) are lower for non-volant mammals on oceanic islands than for those on landbridge islands, but are the opposite for bats; (2) z values for non-volant mammals are lower than those for bats on oceanic islands, but are higher than those for bats on landbridge islands; and (3) landbridge island faunas are attenuated mainland faunas, whereas those on oceanic islands are ecologically incomplete. No support is found for alternative hypotheses to explain low species-area slopes for terrestrial mammals on oceanic islands.     

Latitudinal patterns of mammalian species richness in the New World: the effects of sampling method and faunal group

Abstract. Although the latitudinal gradient of species richness for mammals in North America is well documented, few investigators have quantified the relationship in South America. We examined the pattern in North and South America, at two spatial scales (2.5° and 5°) for each of two sampling methods (quadrats and latitudinal bands). A scale effect was evident for quadrats but not for bands. Significant linear relationships between species richness and latitude were found for three faunal groups: all mammals, nonvolant species, and bats. Effects of area confound the latitudinal relationship. By statistically removing such effects, we found that the latitudinal gradient is not an artifact of the species-area relationship, and that the latitudinal gradients for North and South America were statistically indistinguishable. Our data suggest that both faunal subgroups, nonvolant species and bats, contributed substantially to the overall mammalian pattern. Further, multiple regression analyses showed that only latitude is a necessary variable to explain bat richness; for nonvolant species, in addition to latitude, area and longitude may be important.     

Local-regional relationships and the geographical distribution of species

Aim Local‐regional (LR) species diversity plots were conceived to assess the contribution of regional and local processes in shaping the patterns of biological diversity, but have been used also to explore the scaling of diversity in terms of its alpha, beta, and gamma components. Here we explore the idea that patterns in the geographical ranges of species over a continent can determine the shape of small region to large region (SRLR) plots, which are equivalent to LR plots when comparing the diversity of sites at two regional scales. Location To test that idea, we analysed the diversity patterns at two regional scales for the mammals of North America, defined as the mainland from Alaska and Canada to Panama. Method We developed a theoretical model relating average range size of species over a large‐scale region with its average regional point species diversity (RPD). Then, we generated a null model of expected SRLR plots based on theoretical predictions. Species diversities at two scales were modelled using linear and saturation functions for Type I and Type II SRLR relationships, respectively. We applied the models to the case of North American mammals by examining the regional diversity and the RPD for 21 large‐scale quadrats (with area equal to 160,000 km²), arranged along a latitudinal gradient. Results Our model showed that continental and large‐scale regional patterns of distribution of species can generate both types of SRLR relationship, and that these patterns can be reflected in LR plots without invoking any kind of local processes. We found that North American nonvolant mammals follow a Type I SRLR relationship, whereas bats follow a Type II pattern. This difference was linked to patterns in which species of the two mammalian groups distribute in geographical space. Conclusion Traditional LR plots and the new SRLR plots are useful tools in exploring the scaling of species diversity and in showing the relationship between distribution and diversity. Their usefulness in comparing the relative role of local and regional processes is, however, very limited.     

A paradox of latitudinal leaf defense strategies in deciduous and evergreen broadleaved trees

The classical “low latitude–high defense” hypothesis is seldom supported by empirical evidence. In this context, we tested latitudinal patterns in the leaf defense traits of deciduous broadleaved (DB) and evergreen broadleaved (EGB) tree species, which are expected to affect herbivore diversity. We examined the co-occurrence of leaf defense traits (tannin and phenol content, leaf mechanical strength, leaf dry matter content, leaf mass per area, and leaf thickness) in 741 broadleaved tree species and their correlations with species geographical range in East Asian island flora. We discovered contrasting latitudinal defense strategy gradients in DB and EGB tree species. DB species employed chemical defenses (increasing tannin and phenol content) at higher latitudes and physical defenses (softer and thinner leaves) at lower latitudes, whereas EGB tree species exhibited opposite latitudinal defense patterns. The “low latitude high defense” hypothesis included a paradoxical aspect in chemical and physical defense traits across broadleaved tree species. To reconcile paradoxical defense strategies along the latitudinal gradient, we conclude that interactive correlations among leaf traits are controlled by leaf longevity, which differs between DB and EGB tree species.     

Global patterns of stream detritivore distribution: implications for biodiversity loss in changing climates

Aim We tested the hypothesis that shredder detritivores, a key trophic guild in stream ecosystems, are more diverse at higher latitudes, which has important ecological implications in the face of potential biodiversity losses that are expected as a result of climate change. We also explored the dependence of local shredder diversity on the regional species pool across latitudes, and examined the influence of environmental factors on shredder diversity. Location World‐wide (156 sites from 17 regions located in all inhabited continents at latitudes ranging from 67° N to 41° S). Methods We used linear regression to examine the latitudinal variation in shredder diversity at different spatial scales: alpha (α), gamma (γ) and beta (β) diversity. We also explored the effect of γ‐diversity on α‐diversity across latitudes with regression analysis, and the possible influence of local environmental factors on shredder diversity with simple correlations. Results Alpha diversity increased with latitude, while γ‐ and β‐diversity showed no clear latitudinal pattern. Temperate sites showed a linear relationship between γ‐ and α‐diversity; in contrast, tropical sites showed evidence of local species saturation, which may explain why the latitudinal gradient in α‐diversity is not accompanied by a gradient in γ‐diversity. Alpha diversity was related to several local habitat characteristics, but γ‐ and β‐diversity were not related to any of the environmental factors measured. Main conclusions Our results indicate that global patterns of shredder diversity are complex and depend on spatial scale. However, we can draw several conclusions that have important ecological implications. Alpha diversity is limited at tropical sites by local factors, implying a higher risk of loss of key species or the whole shredder guild (the latter implying the loss of trophic diversity). Even if regional species pools are not particularly species poor in the tropics, colonization from adjacent sites may be limited. Moreover, many shredder species belong to cool‐adapted taxa that may be close to their thermal maxima in the tropics, which makes them more vulnerable to climate warming. Our results suggest that tropical streams require specific scientific attention and conservation efforts to prevent loss of shredder biodiversity and serious alteration of ecosystem processes.     

美洲森林群落beta多样性的纬度梯度性

Beta多样性度量不同时空尺度物种组成的变化,是生物多样性的重要组成部分;理解其地理格局和形成机制已成为当前生物多样性研究的热点问题。基于Alwyn H. Gentry在美洲收集的131个森林样方数据,采用倍性和加性分配方法度量群落beta多样性,检验beta多样性随纬度的变化趋势,并分析其形成机制。研究表明:(1) 美洲森林群落beta多样性随纬度增加显著下降,热带和亚热带地区beta多样性高于温带地区;此格局可由物种分布范围的纬度梯度性和不同粒度(grain)下物种丰富度与纬度回归斜率的差异推论得出;(2) 加性分配方法表明beta多样性对各个温度带森林群落gamma多样性的相对贡献率平均为78.2%,并且随纬度升高而降低;(3) 美洲南半球森林群落beta多样性高于其北半球,这可能反映了区域间物种进化和环境变迁历史的差异。此外,还探讨了不同beta多样性计算方法的适用情景,首次证实了森林生态系统群落水平beta多样性的纬度梯度性,这对研究生物多样性的形成机制和生物多样性保护都具有重要的意义。     

Climate, history and neutrality as drivers of mammal beta diversity in Europe: insights from multiscale deconstruction

1.?Environmental sorting, historical factors and neutral dynamics may all drive beta diversity (change in species composition across space), but their relative importance remains unresolved. In the case of European mammals, key potential drivers of large-scale beta diversity include current climate, neutral dynamics and two historical factors: Pleistocene glaciations and peninsular dynamics (immigration from extra-regional eastern faunal source areas and inter-linked relictual survival and evolutionary differentiation in isolated areas). 2.?We assessed the relative importance of these drivers using a novel analytical framework to deconstruct beta diversity of non-volant mammals in Europe (138 species) into its turnover (change in species composition because of species replacements) and nestedness components (change in species composition because of species richness differences) at continental and regional (250,000 km(2) ) scales. 3.?We found continental-scale mammal beta diversity to be mainly caused by spatial turnover (99·9%), with only a small contribution (0·1%) from nestedness. 4.?Current climate emerged as an important driver of beta diversity, given the strong continental-scale turnover, particularly in north-south direction, i.e., in line with the latitudinal climate gradient, and, more directly, the strong correlation of climate with spatial turnover at both continental and regional scales. 5.?However, there was also evidence for the importance of non-climatic drivers. Notably, the compositional variation purely accounted for by space was greater than that purely accounted for by environment for both the turnover and the nestedness component of beta diversity. Furthermore, the strong longitudinal turnover within Southern Europe is in accordance with the region's long-term climatic stability having allowed multiple refugia and local evolutionary diversification. As expected from peninsular dynamics, there was increasing dissimilarity with geographic distance in an east-west direction because of nestedness, but only in Central and Northern Europe. 6.?In conclusion, European mammal beta diversity mainly reflects spatial turnover and only to a limited extent nestedness and is driven by current climate in combination with historical - and perhaps, neutral - dynamics. These findings suggest that a key challenge for climate-change predictive studies will be taking the influence of non-climatic factors into account.     

The latitudinal gradient of species diversity among North American grasshoppers (Acrididae) within a single habitat: a test of the spatial heterogeneity hypothesis

Abstract. The spatial heterogeneity hypothesis predicts a positive relationship between habitat complexity and species diversity: the greater the heterogeneity of a habitat, the greater the number of species in that habitat. On a regional scale, this hypothesis has been proposed to explain the increases in species diversity from the poles to the tropics: the tropics are more diverse because they contain more habitats. On the local scale, the spatial heterogeneity hypothesis suggests that the tropics are more diverse because they contain more microhabitats. The positive relationship between habitat heterogeneity and species diversity, on the local scale, is well documented. In this paper, we test whether habitat heterogeneity on the local scale can explain the latitudinal gradient of species diversity on the regional scale. We determined the latitudinal gradient of species diversity of 305 species of North American grasshoppers using published distribution maps. We compared the slope of this multihabitat (regional-scale) gradient with the slope of a within-habitat (local-scale) gradient in the prairie grasslands. Our results show no significant difference between the slopes at the two scales. We tested the generality of our results by comparing multi- and within-habitat latitudinal gradients of species diversity for ants, scorpions and mammals using data from the literature. These results are in accordance with those from grasshoppers. We can therefore reject the local-scale spatial heterogeneity hypothesis as a mechanism explaining the regional-scale latitudinal gradient of species diversity. We discuss alternative mechanisms that produce this gradient.     

Genetic diversity within vertebrate species is greater at lower latitudes

The latitudinal gradient of species diversity is one of the oldest recognized patterns in biology. While the cause of the pattern remains debated, the global signal of greater diversity toward the tropics is widely established. Whether the pattern holds for genetic diversity within species, however, has received much less attention. We examine latitudinal variation of intraspecific genetic diversity by contrasting nucleotide distance within low- and high-latitude animal groups. Using mitochondrial DNA markers across 72 vertebrate species that together span six continents, two oceans, and 129 degrees of latitude, we found significantly greater genetic diversity at low latitudes within mammalian species, and trends consistent with this pattern in reptiles, amphibians, fish, and birds. The signal held even after removing species whose current geographic ranges include areas recently covered by glaciers during the late Pleistocene and which presumably have experienced colonization bottlenecks in high latitudes. Higher genetic diversity within species was found at low latitudes also for genera that do not possess higher species richness toward the tropics. Moreover, examination of a subset of species with sufficient sampling across a broad geographic range revealed that genetic variation demonstrates a typical gradient, with mid-latitude populations intermediate in genetic diversity between high and low latitude ones. These results broaden the pattern of the global latitudinal diversity gradient, to now include variation within species. These results are also concordant with other studies indicating that low latitude populations and species are on different evolutionary trajectories than high latitude ones, and we speculate that higher rates of evolution toward the equator are driving the pattern for genetic diversity within species.     

The latitudinal gradient of beta diversity in relation to climate and topography for mammals in North America

Aim Spatial turnover of species, or beta diversity, varies in relation to geographical distance and environmental conditions, as well as spatial scale. We evaluated the explanatory power of distance, climate and topography on beta diversity of mammalian faunas of North America in relation to latitude. Location North America north of Mexico. Methods The study area was divided into 313 equal‐area quadrats (241 × 241 km). Faunal data for all continental mammals were compiled for these quadrats, which were divided among five latitudinal zones. These zones were comparable in terms of latitudinal and longitudinal span, climatic gradients and elevational gradients. We used the natural logarithm of the Jaccard index (lnJ) to measure species turnover between pairs of quadrats within each latitudinal zone. The slope of lnJ in relation to distance was compared among latitudinal zones. We used partial regression to partition the variance in lnJ into the components uniquely explained by distance and by environmental differences, as well as jointly by distance and environmental differences. Results Mammalian faunas of North America differ more from each other at lower latitudes than at higher latitudes. Regression models of lnJ in relation to distance, climatic difference and topographic difference for each zone demonstrated that these variables have high explanatory power that diminishes with latitude. Beta diversity is higher for zones with higher mean annual temperature, lower seasonality of temperature and greater topographic complexity. For each latitudinal zone, distance and environmental differences explain a greater proportion of the variance in lnJ than distance, climate or topography does separately. Main conclusions The latitudinal gradient in beta diversity of North American mammals corresponds to a macroclimatic gradient of decreasing mean annual temperature and increasing seasonality of temperature from south to north. Most of the variance in spatial turnover is explained by distance and environmental differences jointly rather than distance, climate or topography separately. The high predictive power of geographical distance, climatic conditions and topography on spatial turnover could result from the direct effects of physical limiting factors or from ecological and evolutionary processes that are also influenced by the geographical template.     

Regional patterns of nematode assemblages in the Arctic deep seas

Surface primary productivity and carbon flux in the Arctic Seas are higher along the warm Spitsbergen Water Current than along the ice-infested East Greenland Current. These contrasting oceanographic conditions are reflected in the deep-sea environment and may shape nematode assemblages. However, the paucity of samples in the Arctic deep seas precludes any regional scale assessment. In the present study, nematode assemblages were investigated in relation to a range of environmental variables along the 2,000 m isobath between latitudes 72°N and 79°N for both East and Western margins of the northern North Atlantic. Results showed that both margins had distinct environmental characteristics, with respect to chloroplastic pigments, sediment water content, sediment-bound organic matter, phospholipids and particulate proteins. Nematode assemblages varied according to these environmental changes. Along the more oligotrophic western margin, chloroplastic pigments increased towards the North, while the other environmental variables, nematode abundances and species richness decreased. In contrast, along the eastern margin, we observed higher quantities of organic matter and particulate protein, which supported higher abundance and species richness. Nematode assemblages along both margins varied according to food availability with species composition more variable in areas with lower amounts. Seventy percent of the species occurred in both margins indicating a low turnover of species. The present results support the hypothesis of a positive latitudinal gradient across the North Atlantic and further suggest that contemporary climate and recent ecological processes may predict nematode diversity patterns at larger scales.     

Patterns of functional diversity across an extensive environmental gradient: vertebrate consumers, hidden treatments and latitudinal trends

Over the last two decades, although much has been learned regarding the multifaceted nature of biodiversity, relatively little is known regarding spatial variation in constituents other than species richness. This is particularly true along extensive environmental gradients such as latitude. Herein, we describe latitudinal gradients in the functional diversity of New World bat communities. Bat species from each of 32 communities were assigned to one of seven functional groups. Latitudinal gradients existed for the richness, diversity and scaled‐dominance of functional groups. No significant patterns were observed for evenness of functional groups. Measures of functional diversity were different in magnitude and increased towards the equator at a faster rate than expected given the underlying spatial variation in species richness. Thus, latitudinal gradient in species richness alone do not cause the latitudinal gradient in functional diversity. When variation in species composition of the regional fauna of each community was incorporated into analyses, many differences between observed and simulated patterns of functional diversity were not significant. This suggests that those processes that determine the composition of regional faunas strongly influence the latitudinal gradient in functional diversity at the local level. Nonetheless, functional diversity was lower than expected across observed sites. Community‐wide responses to variation in the quantity and quality of resources at the local level probably contribute to differences in functional diversity at local and regional scales and enhance beta diversity.     

Faster Speciation and Reduced Extinction in the Tropics Contribute to the Mammalian Latitudinal Diversity Gradient

The increase in species richness from the poles to the tropics, referred to as the latitudinal diversity gradient, is one of the most ubiquitous biodiversity patterns in the natural world. Although understanding how rates of speciation and extinction vary with latitude is central to explaining this pattern, such analyses have been impeded by the difficulty of estimating diversification rates associated with specific geographic locations. Here, we use a powerful phylogenetic approach and a nearly complete phylogeny of mammals to estimate speciation, extinction, and dispersal rates associated with the tropical and temperate biomes. Overall, speciation rates are higher, and extinction rates lower, in the tropics than in temperate regions. The diversity of the eight most species-rich mammalian orders (covering 92% of all mammals) peaks in the tropics, except that of the Lagomorpha (hares, rabbits, and pikas) reaching a maxima in northern-temperate regions. Latitudinal patterns in diversification rates are strikingly consistent with these diversity patterns, with peaks in species richness associated with low extinction rates (Primates and Lagomorpha), high speciation rates (Diprotodontia, Artiodactyla, and Soricomorpha), or both (Chiroptera and Rodentia). Rates of range expansion were typically higher from the tropics to the temperate regions than in the other direction, supporting the “out of the tropics” hypothesis whereby species originate in the tropics and disperse into higher latitudes. Overall, these results suggest that differences in diversification rates have played a major role in shaping the modern latitudinal diversity gradient in mammals, and illustrate the usefulness of recently developed phylogenetic approaches for understanding this famous yet mysterious pattern.     

Latitudinal gradients in niche breadth: empirical evidence from haematophagous ectoparasites

Aim  We searched for relationships between latitude and both the geographic range size and host specificity of fleas parasitic on small mammals. This provided a test for the hypothesis that specialization is lower, and thus niche breadth is wider, in high-latitude species than in their counterparts at lower latitudes.
Location  We used data on the host specificity and geographic range size of 120 Palaearctic flea species (Siphonaptera) parasitic on small mammals (Soricomorpha, Lagomorpha and Rodentia). Data on host specificity were taken from 33 regions, whereas data on geographic ranges covered the entire distribution of the 120 species.
Methods  Our analyses controlled for the potentially confounding effects of phylogenetic relationships among flea species by means of the independent-contrasts method. We used regressions and structural equation modelling to determine whether the latitudinal position of the geographic range of a flea covaried with either the size of its range or its host specificity. The latter was measured as the number of host species used, as well as by an index providing the average (and variance in) taxonomic distinctness among the host species used by a flea.
Results  Geographic range size was positively correlated with the position of the centre of the range; in other words, fleas with more northerly distributions had larger geographic ranges. Although the number of host species used by a flea did not vary with latitude, both the mean taxonomic distinctness among host species used and its variance increased significantly towards higher latitudes.
Main conclusions  The results indicate that niche breadth in fleas, measured in terms of both its spatial (geographic range size) and biological (host specificity) components, increases at higher latitudes. These findings are compatible with the predictions of recent hypotheses about latitudinal gradients.     

Mollusk species diversity in the Southeastern Pacific: why are there more species towards the pole?

The most ubiquitous and well recognized diversity pattern at large spatial scales is the latitudinal increase in species richness near the equator and decline towards the poles. Although several exceptions to this pattern have been documented, shallow water mollusks, the most specious group of marine invertebrates, are the epitome of the monotonic decline in species diversity toward higher latitudes along the Pacific and Atlantic coasts of North America. Here we analyze the geographic diversity of 629 mollusk species along the Pacific South American shelf. Our analyses are based on the most complete database of invertebrates assembled for this region of the world, consisting of latitudinal ranges of over 95% of all described mollusks between 10° and 55°S. Along this coast, mollusk diversity did not follow the typical latitudinal trend. The number of species remained constant and relatively low at intermediate latitudes and sharply increased toward higher latitudes, south of 42°S. This trend was explained by changes in shelf area, but not by sea surface temperature, unlike the pattern documented for Northern Hemisphere mollusks. Direct sampling of soft bottom communities along the gradient suggests that regional trends in species richness are produced by increased alpha diversity, and not only by artifacts produced by the increase in sampling area. We hypothesize that increased shelf area south of 42°S, geographic isolation produced by divergence of major oceanic currents, and the existence of refugia during glaciations, enabled species diversification. Radiation could have been limited by narrow continental shelves between 10°–42°. Asymmetries in latitudinal diversity trends between hemispheres show that there is not a single general factor determining large-scale diversity patterns.     

Environmental filtering explains a U‐shape latitudinal pattern in regional β‐deviation for eastern North American trees

The underlying drivers of β‐diversity along latitudinal gradients have been unclear. Previous studies have focused on β‐diversities calculated at a local scale and shed limited light on regional β‐diversity. We tested the much‐debated effects of range size vs. environmental filtering on the β‐gradient using data from the US Forest Inventory Analysis Program. We showed that the drivers of the β‐gradient were scale dependent. At the local scale species spatial patterns contributed little to the β‐gradient, whereas at the regional scale spatial patterns dominated the gradient and a U‐shape latitudinal relationship for the standardised β‐diversity deviation was revealed. The relationship can be explained by spatial variation in climate and soil texture, thus supporting the environmental filtering hypothesis. But it is inconsistent with Rapoport's rule about the effect of range size on β‐gradient. These results resolve the debate on whether species spatial distributions contribute to β‐gradient and attest the importance of environmental filtering in determining regional β‐diversity.     

Gap formation and species diversity in Japanese beech forests: a test of the intermediate disturbance hypothesis on a geographic scale

To evaluate whether the intermediate-disturbance hypothesis applies on regional scales, the relationship between the species diversity and gap formation regime of beech forests was examined. The mean gap size and the variation of gap sizes showed no correlation with species diversity. The mean windstorm interval varied widely, but geographical trends, such as latitudinal gradient, were not observed. However, locations that sustained an intermediate frequency of disturbance had the highest species diversity. Although a latitudinal gradient of disturbance was not apparent, the intermediate-disturbance hypothesis was partly supported on a geographic scale. The most predictable model for species diversity was a multiple regression model composed of two factors, the windstorm interval and the cumulative temperature of the growing season. The fact that the temperature was of greater importance than the disturbance interval indicates that the most important factor in predicting forest species diversity is the amount of available energy on a geographic scale.     

Hydrological stability drives both local and regional diversity patterns in rock pool metacommunities

A main challenge associated with macro ecological gradients such as the latitudinal diversity gradient (LDG) is that proxies of potential underlying processes are often correlated at large scales. One way to reliably identify contributing processes is to show that they can lead to similar responses at local scales. Using a set of invertebrate communities from rock pool clusters along a latitudinal gradient in Australia, we investigated the importance of hydrological stability for explaining both local and regional diversity patterns in this habitat. Results show that, at both local and regional scales, habitat stability in terms of the frequency and length of inundations was strongly correlated to local alpha diversity in individual pools and to gamma diversity at the level of pool clusters. Additionally, partitioning beta diversity into components of nestedness and species turnover revealed that communities in unstable habitats were nested subsets of communities in more stable habitats. Overall, this study provides convincing mechanistic support for the climate stability hypothesis as a potential explanation for the LDG in this system. Results also indicate that when there is enough time for dispersal and colonization, regional processes can be relatively unimportant compared to local processes to explain large scale diversity patterns.     

Digest: The contribution of historical climate events in shaping the modern latitudinal diversity gradient of ancient reptiles

It is recognized that biodiversity changes across the planet latitudinally; however, the timing of and reasons for diversity loss at higher latitudes are not well understood. Meseguer and Condamine investigate phylogenies and fossil evidence of reptilian species and determine that global warming and cooling events allowed asymmetric extinction and dispersion across latitudes, suggesting a hypothesis where climate profoundly shapes the latitudinal diversity gradient in certain taxa.