Rapoport's Rule Research Articles

Is thermal limitation the primary driver of elevational distributions? Not for montane rainforest ants in the Australian Wet Tropics.

Terrestrial ectotherms are likely to be especially sensitive to rising temperatures over coming decades. Thermal limits are used to measure climatic tolerances that potentially affect ectotherm distribution. While there is a strong relationship between the critical thermal maximum (CTmax) of insects and their latitudinal ranges, the nature of this relationship across elevation is less clear. Here we investigated the combined relationships between CTmax, elevation and ant body mass, given that CTmax can also be influenced by body mass, in the World Heritage-listed rainforests of the Australian Wet Tropics. We measured the CTmax and body mass of 20 ant species across an elevational gradient from 350 to 1000m a.s.l. Community CTmax did not vary systematically with increasing elevation and there was no correlation between elevation and elevational ranges of species. However, body mass significantly decreased at higher elevations. Despite the negative correlation between CTmax and body mass at the community level, there was no significant difference in CTmax of different-sized ants within a species. These findings are not consistent with either the climatic variability hypothesis, Rapoport's rule or Bergmann's rule. Models indicated that elevation and body mass had limited influences on CTmax. Our results suggest that the distribution of most montane ants in the region is not strongly driven by thermal limitation, and climate change will likely impact ant species differently. This is likely to occur primarily through changes in rainfall via its effects on vegetation structure and therefore thermal microhabitats, rather than through direct temperature changes.

Interrelations of global macroecological patterns in wing and thorax size, sexual size dimorphism, and range size of the Drosophilidae

Support for macroecological rules in insects is mixed, with potential confounding interrelations between patterns rarely studied. We here investigate global patterns in body and wing size, sexual size dimorphism and range size in common fruit flies (Diptera: Drosophilidae) and explore potential interrelations and the predictive power of Allen's, Bergmann's, Rensch's and Rapoport's rules. We found that thorax length (r2 = 0.05) and wing size (r2 = 0.09) increased with latitude, supporting Bergmann's rule. Contrary to patterns often found in endothermic vertebrates, relative wing size increased towards the poles (r2 = 0.12), a pattern against Allen's rule, which we attribute to selection for increased flight capacity in the cold. Sexual size dimorphism decreased with size, evincing Rensch's rule across the family (r2 = 0.14). Yet, this pattern was largely driven by the virilis–repleta radiation. Finally, range size did not correlate with latitude, although a positive relationship was present in a subset of the species investigated, providing no convincing evidence for Rapoport's rule. We further found little support for confounding interrelations between body size, wing loading and range size in this taxon. Nevertheless, we demonstrate that studying several traits simultaneously at minimum permits better interpretation in case of multiple, potentially conflicting trends or hypotheses concerning the macroecology of insects.

Rapoport's rule and determinants of species range size in snakes

AbstractAimUnderstanding determinants of species' range size is paramount to explaining global ecological patterns and estimating extinction risk of species. Here, we examined whether a sample of 536 snake species exhibits a latitudinal gradient of range size in support of Rapoport's rule, and determined predictors of range size from a set of environmental and biological factors.LocationGlobal.MethodsBased on a priori hypotheses about the effects of latitude, environmental and biological factors on species' range, we calculated mid‐latitudes of species ranges, and collected data on environmental factors (altitude, temperature, precipitation, size and number of ecoregions occupied) and biological traits (body size, fecundity, habitat breadth and species age) to construct multivariate models of snake range size. We used a recently published dated consensus phylogeny to determine minimum adequate models of range size using phylogenetic generalized least squares models and establish correlations between range size and time since species' description.ResultsRange size increased significantly with latitude, consistent with Rapoport's rule, especially across mid‐ and high latitudes in the Northern Hemisphere. Habitat breadth, body size and altitudinal range had a significant positive effect on range size, with minor negative effects on range size from mean altitude and reproductive output. Biological variables explained more variation in range size than environmental variables. Species' range size had a significant effect on species' description, with larger‐ranged species having been described earlier.Main conclusionsPrediction of range size in lesser‐known species such as snakes relies on a suite of factors. Species with restricted habitat breadth, small body size and at high altitudes generally have smaller ranges, and are thus likely to have higher extinction risk. [Correction added on 10 October 2017, after first online publication: The preceding sentence has been rephrased for clarity.] Our work illustrates that it is these species we are likely to under‐report in extinction risk assessments.

Thermal barriers constrain microbial elevational range size via climate variability.

Range size is invariably limited and understanding range size variation is an important objective in ecology. However, microbial range size across geographical gradients remains understudied, especially on mountainsides. Here, the patterns of range size of stream microbes (i.e., bacteria and diatoms) and macroorganisms (i.e., macroinvertebrates) along elevational gradients in Asia and Europe were examined. In bacteria, elevational range size showed non-significant phylogenetic signals. In all taxa, there was a positive relationship between niche breadth and species elevational range size, driven by local environmental and climatic variables. No taxa followed the elevational Rapoport's rule. Climate variability explained the most variation in microbial mean elevational range size, whereas local environmental variables were more important for macroinvertebrates. Seasonal and annual climate variation showed negative effects, while daily climate variation had positive effects on community mean elevational range size for all taxa. The negative correlation between range size and species richness suggests that understanding the drivers of range is key for revealing the processes underlying diversity. The results advance the understanding of microbial species thermal barriers by revealing the importance of seasonal and diurnal climate variation, and highlight that aquatic and terrestrial biota may differ in their response to short- and long-term climate variability.

Following Rapoport's Rule: the geographic range and genome size of bacterial taxa decline at warmer latitudes.

We sought to test whether stream bacterial communities conform to Rapoport's Rule, a pattern commonly observed for plants and animals whereby taxa exhibit decreased latitudinal range sizes closer to the equator. Using a DNA sequencing approach, we explored the biogeography of biofilm bacterial communities in 204 streams across a ∼1000 km latitudinal gradient. The range sizes of bacterial taxa were strongly correlated with latitude, decreasing closer to the equator, which coincided with a greater than fivefold increase in bacterial taxonomic richness. The relative richness and range size of bacteria were associated with spatially correlated variation in temperature and rainfall. These patterns were observed despite enormous variability in catchment environmental characteristics. Similar results were obtained when restricting the same analyses to native forest catchments, thereby controlling for spatial biases in land use. We analysed genomic data from ∼500 taxa detected in this study, for which data were available and found that bacterial communities at cooler latitudes also tended to possess greater potential metabolic potential. Collectively, these data provide the first evidence of latitudinal variation in the range size distributions of freshwater bacteria, a trend which may be determined, in part, by a trade-off between bacterial genome size and local variation in climatic conditions.

Support for the elevational Rapoport's rule among seed plants in Nepal depends on biogeographical affinities and boundary effects.

As one of the most important hypotheses on biogeographical distribution, Rapoport's rule has attracted attention around the world. However, it is unclear whether the applicability of the elevational Rapoport's Rule differs between organisms from different biogeographical regions. We used Stevens’ method, which uses species diversity and the averaged range sizes of all species within each (100 m) elevational band to explore diversity‐elevation, range‐elevation, and diversity‐range relationships. We compared support for the elevational Rapoport's rule between tropical and temperate species of seed plants in Nepal. Neither tropical nor temperate species supported the predictions of the elevational Rapoport's rule along the elevation gradient of 100–6,000 m a.s.l. for any of the studied relationships. However, along the smaller 1,000–5,000 m a.s.l. gradient (4,300 m a.s.l. for range‐elevation relationships) which is thought to be less influenced by boundary effects, we observed consistent support for the rule by tropical species, although temperate species did not show consistent support. The degree of support for the elevational Rapoport's rule may not only be influenced by hard boundary effects, but also by the biogeographical affinities of the focal taxa. With ongoing global warming and increasing variability of temperature in high‐elevation regions, tropical taxa may shift upward into higher elevations and expand their elevational ranges, causing the loss of temperate taxa diversity. Relevant studies on the elevational Rapoport's rule with regard to biogeographical affinities may be a promising avenue to further our understanding of this rule.

The roles of elevation and local environmental factors as drivers of diatom diversity in subarctic streams

Summary High latitude and altitude freshwater systems are highly sensitive to the effects of global warming and associated environmental changes. Diatoms are widely used as sentinels of environmental change, yet knowledge of diatom community patterns in high latitude and altitude streams remains limited. The aim of this study was to examine alpha and beta diversity of diatoms in subarctic streams in Finland and Norway, and to determine the importance of local environmental factors and elevation in shaping their community patterns. We also aimed at testing, for the first time, whether microbes conform to Rapoport's elevational rule, which states that species occurring at higher elevations have generally larger elevational ranges than species at lower elevations. Three streams (44 sites in total) with an altitudinal gradient of 21–877 m a.s.l. were sampled. Generalized linear models, hierarchical partitioning, and a boosted regression tree method were used to identify drivers of diatom species richness. We ran Mantel tests, and calculated initial similarities and elevational halving distances to examine beta diversity. There were no apparent richness–elevation relationships within streams. Across all study streams, the water depth was the most important factor for richness, with additional influences by stone size, conductivity, pH and elevation. Diatoms in subarctic streams did not conform to Rapoport's elevational rule. Community similarity decreased significantly with elevational distance while distance decay was weaker with environmental distance. Our results suggest that diatom alpha and beta diversity along stream elevational gradients are shaped by interacting local environmental factors such as water depth and substrate size, indicating vulnerability of diatoms to physical disturbances, and regional factors such as dispersal and geographical variables. Diatom diversity patterns do not seem to concur with patterns often observed for larger organisms as no consistent elevational patterns in richness or range sizes were found.

Correlates of range size variation in the Australian seed‐plant flora

AbstractAimTo map and analyse range size variation in the terrestrial seed‐plant flora of Australia in relation to latitude, habitat availability, climate and soils, and to compare mean range size between biomes and growth forms.LocationAustralia.MethodsRange sizes were estimated from herbarium records using alpha‐hulls for 19,227 species and mapped into a set of 0.5° × 0.5° grid cells across Australia. Ordinary‐least squares regressions were used to test for relationships between mean range size, latitude and habitat availability. Simultaneous autoregressive models (SAR) with spatial error terms were used in a multi‐model framework to assess the role of aridity, mean annual temperature (MAT), soil pH, depth and total P concentration in shaping range size variation. Species‐level differences between growth forms (graminoids, herbs, trees, shrubs, climbers) and biomes were assessed using one‐way analysis of variance (ANOVA).Results68% of Australian seed‐plant species have ranges which cover < 1% of the continent. Generally, large ranges are characteristic of graminoids and herbs and are associated with arid and grassland biomes. The smallest ranges were found in Mediterranean ecosystems in the SW corner of the continent, and were typically shrub species. Range size peaked at mid‐latitudes and was not consistently smaller at lower latitudes (contrary to Rapoport's Rule). Increasing aridity, MAT and soil pH were strong predictors of large range size; however, soil depth and P content had little influence in SAR models.Main conclusionsAridity and temperature are the primary drivers of range size variation in the Australian flora. Trait syndromes which promote colonization and survival in arid and grassland habitats (e.g. C4 photosynthesis, wind pollination) have allowed grasses and herbs to occupy large areas of the continent. Ranges were not smaller, on average, in the tropics due to the concentration of large‐ranged species in the widespread arid biome in the centre of the continent.

Orchid Species Richness along Elevational and Environmental Gradients in Yunnan, China.

The family Orchidaceae is not only one of the most diverse families of flowering plants, but also one of the most endangered plant taxa. Therefore, understanding how its species richness varies along geographical and environmental gradients is essential for conservation efforts. However, such knowledge is rarely available, especially on a large scale. We used a database extracted from herbarium records to investigate the relationships between orchid species richness and elevation, and to examine how elevational diversity in Yunnan Province, China, might be explained by mid-domain effect (MDE), species–area relationship (SAR), water–energy dynamics (WED), Rapoport’s Rule, and climatic variables. This particular location was selected because it is one of the primary centers of distribution for orchids. We recorded 691 species that span 127 genera and account for 88.59% of all confirmed orchid species in Yunnan. Species richness, estimated at 200-m intervals along a slope, was closely correlated with elevation, peaking at 1395 to 1723 m. The elevational pattern of orchid richness was considerably shaped by MDE, SAR, WED, and climate. Among those four predictors, climate was the strongest while MDE was the weakest for predicting the elevational pattern of orchid richness. Species richness showed parabolic responses to mean annual temperature (MAT) and mean annual precipitation (MAP), with maximum richness values recorded at 13.7 to 17.7°C for MAT and 1237 to 1414 mm for MAP. Rapoport’s Rule also helped to explain the elevational pattern of species richness in Yunnan, but those influences were not entirely uniform across all methods. These results suggested that the elevational pattern of orchid species richness in Yunnan is collectively shaped by several mechanisms related to geometric constraints, size of the land area, and environments. Because of the dominant role of climate in determining orchid richness, our findings may contribute to a better understanding of the potential effects of climate change on orchid diversity, and the development of conservation strategies for orchids.

Rapoport's Rule: Do climatic variability gradients shape range extent?

The trend of increasing latitudinal range sizes of species towards higher latitudes, known as Rapoport's Rule, has been highly controversial in the literature since it was first proposed by Stevens in 1989. We contend that the question of interest is not whether general global patterns occur, nor whether they support or refute Rapoport's Rule, but whether the mechanism thought to underlie such patterns, the Climatic Variability Hypothesis, is supported. The Climatic Variability Hypothesis suggests that taxa originating from environmentally variable habitats, such as those at high latitudes and altitudes, should evolve wider environmental tolerances, and consequently establish wider distributions along climate gradients than taxa originating from relatively stable habitats. We applied a novel approach, incorporating measures of temperature variability across habitats within species' ranges into models of range size distributions, to determine whether the Climatic Variability Hypothesis applied to three clades of medium‐sized ectotherms (lizards) distributed over Australia. Our results show that the Climatic Variability Hypothesis is supported, even in taxa that do not exhibit a traditional Rapoport Effect, due to complex, non‐unidirectional climatic gradients in our study area. The results highlight the strong impact of climatic variability on species' physiological tolerances and their associated geographic distributions.

Macroecological patterns of archaeal ammonia oxidizers in the Atlantic Ocean.

Macroecological patterns are found in animals and plants, but also in micro‐organisms. Macroecological and biogeographic distribution patterns in marine Archaea, however, have not been studied yet. Ammonia‐oxidizing Archaea (AOA) show a bipolar distribution (i.e. similar communities in the northernmost and the southernmost locations, separated by distinct communities in the tropical and gyral regions) throughout the Atlantic, detectable from epipelagic to upper bathypelagic layers (<2000 m depth). This tentatively suggests an influence of the epipelagic conditions of organic matter production on bathypelagic AOA communities. The AOA communities below 2000 m depth showed a less pronounced biogeographic distribution pattern than the upper 2000 m water column. Overall, AOA in the surface and deep Atlantic waters exhibit distance–decay relationships and follow the Rapoport rule in a similar way as bacterial communities and macroorganisms. This indicates a major role of environmental conditions in shaping the community composition and assembly (species sorting) and no, or only weak limits for dispersal in the oceanic thaumarchaeal communities. However, there is indication of a different strength of these relationships between AOA and Bacteria, linked to the intrinsic differences between these two domains.

Macroecology of North American suckers (Catostomidae): tests of Bergmann's and Rapoport's rules.

Discerning spatial macroecological patterns in freshwater fishes has broad implications for community assembly, ecosystem dynamics, management, and conservation. This study explores the potential interspecific covariation of geographic range (Rapoport's rule) and body size (Bergmann's rule) with latitude in North American sucker fishes (Cypriniformes: Catostomidae). While numerous tests of Rapoport's and Bergmann's rules are documented in the literature, comparatively few of these studies have specifically tested for these patterns, and none have incorporated information reflecting shared ancestry into analyses of North American freshwater fish through a hierarchical model. This study utilized a hierarchical modeling approach with Bayesian inference to evaluate the role that evolution has played in shaping these distributional corollaries. Rapoport's rule was supported at the tribe level but not across family and subfamily groupings. Particularly within the Catostominae subfamily, two tribes reflected strong support for Rapoport's rule while two suggested a pattern was present. Conversely, Bergmann's rule was not supported in Catostomidae. This study provides additional information regarding the pervasiveness of these "rules" by expanding inferences in freshwater fishes and specifically addressing the potential for these macroecological patterns to play a role in the distribution of the understudied group Catostomidae.

Distribution, diversity gradients and Rapoport's elevational rule in the black scavenger flies of the Swiss Alps (Diptera: Sepsidae)

Abstract Elevational gradients influence the distribution and abundance of species drastically and can lead to variation in community composition. Although coprophagous flies are of ecological and economic importance, their biodiversity and distribution are largely neglected. We studied the impact of steep elevational gradients and geography on the distribution of sepsid flies in the Swiss Alps. Sepsidae are a family of acalyptrate flies strongly associated with decaying organic matter and vertebrate dung, and characterised by a high extent of sympatry in their breeding substrates. Historical, haphazardly sampled specimens from 116 locations covering an elevational range from 200 to 2000 m were available in ethanol collections of various Swiss museums. Nineteen species encompassing all native genera (Meroplius, Nemopoda, Saltella, Sepsis and Themira) were recorded. Local species richness increased linearly with elevation, while area‐corrected regional species richness of elevational belts increased asymptotically. Species occurring at higher altitudes had lower wing loadings and greater elevational ranges than lowland species, supporting Rapoport's elevational rule. Despite compositional similarities, the sepsid communities of the northern lowlands differed significantly from the alpine sepsid fauna. The southern lowlands were particularly differentiated in community composition due to a number of presumably thermophilic species that predominantly occur south of the Alps. Relative abundances of several species were thus strongly affected by elevation and climatic variables. We illustrate the impact of elevational gradients and geography on a community of closely related, often sympatric species, and discuss potential mechanisms of niche partitioning via temporal succession, thermal adaptation and differential resource use.

Do turtles follow the rules? Latitudinal gradients in species richness, body size, and geographic range area of the world's turtles.

Understanding how and why biodiversity is structured across the globe has been central to ecology, evolution, and biogeography even before those disciplines took their modern forms. Three global-scale patterns in particular have been the focus of research and debate for decades: latitudinal gradients in species richness (richness decreases with increasing latitude), body size (body size increases with increasing latitude in endotherms; Bergmann's rule), and geographic range size (range size increases with increasing latitude; Rapoport's rule). Despite decades of study, the generality and robustness of these trends have been debated, as have their underlying causes. Here we investigate latitudinal gradients in species richness, body size, and range size in the world's turtles (Testudines), and add more evidence that these rules do not seem to apply across all taxa. We show that turtle diversity actually peaks at 25° north, a highly unusual global pattern. Turtles also fail to follow Bergmann's Rule, and may show the converse (larger at lower latitudes), though trends are weak. Turtles also show a complex relationship between latitude and range size that does not directly follow Rapoport's rule. Body size and geographic range size are significantly correlated, and multiple abiotic and biotic variables help explain the relationships between latitude and species diversity, body size, and range size. Although we show that turtles do not strictly follow some classic biogeographical rules, we also call for further in-depth research to investigate potential causal mechanisms for these atypical patterns.

Can we derive macroecological patterns from primary Global Biodiversity Information Facility data?

AbstractAimTo determine whether the method used to build distributional maps from raw data influences the representation of two principal macroecological patterns: the latitudinal gradient in species richness and the latitudinal variation in range sizes (Rapoport's rule).LocationWorld‐wide.MethodsAll available distribution data from the Global Biodiversity Information Facility (GBIF) for those fish species that are members of orders of fishes with only marine representatives in each order were extracted and cleaned so as to compare four different procedures: point‐to‐grid (GBIF maps), range maps applying an α‐shape [GBIF‐extent of occurrence (EOO) maps], the MaxEnt method of species distribution modelling (GBIF‐MaxEnt maps) and the MaxEnt method but restricted to the area delimited by the α‐shape (GBIF‐MaxEnt‐restricted maps).ResultsThe location of hotspots and the latitudinal gradient in species richness or range sizes are relatively similar in the four procedures. GBIF‐EOO maps and most GBIF‐MaxEnt‐maps provide overestimations of species richness when compared with those present in a priori well‐surveyed cells. GBIF‐EOO maps seem to provide more reasonable world macroecological patterns. MaxEnt can erroneously predict the presence of species in environmentally similar cells of another hemisphere or in other regions that lie outside the range of the species. Limiting this overpredictive capacity, as in the case of GBIF‐MaxEnt‐restricted maps, seems to mimic the frequency of observations derived from a simple point‐to‐grid procedure, with the utility of this procedure consequently being limited.Main conclusionsIn studies of macroecological patterns at a global scale, the simple α‐shape method seems to be a more parsimonious option for extrapolating species distributions from primary data than are distribution models performed indiscriminately and automatically with MaxEnt. GBIF data may be used in macroecological patterns if original data are cleaned, autocorrelation is corrected and species richness figures do not constitute obvious underestimations. Efforts therefore should focus on improving the number and quality of records that can serve as the source of primary data in macroecological studies.

Latitudinal concordance between biogeographic regionalization, community structure, and richness patterns: a study on the reptiles of China.

Latitudinal patterns in species richness may be affected by both continuous variations in macroecological factors as well as discrete change between biogeographic regions. We examined whether latitudinal reptilian richness and community structure in China were best explained by three macroecological patterns (mid-domain effects, Rapoport's rule effects, or environmental correlates) within or across the ranges of biogeographic realms. The results showed that (1) there was a weak mid-domain effect within the Oriental Realm. However, the mid-domain effect was detected neither at the overall regional scale nor in the Palaearctic Realm. (2) Rapoport's rule was only weakly supported for reptilian fauna in China at lower latitudinal areas. (3) Environmental variables were more strongly correlated with species' latitudinal community structure and richness patterns at the scale of biogeographic realms. Based on the faunal similarity of reptilian community across latitudinal bands, we proposed a latitudinal delineation scheme at 34° N for dividing East Asia into Oriental and Palaearctic biogeographic realms. At last, at the functional group level, we also evaluated the relevant ecological patterns for lizard and snake species across different latitudinal bins, showing that the distributions of lizards presented strong mid-domain effects at the latitudinal ranges within the Oriental Realm and over the whole range but did not support Rapoport's rule. In comparison, snake species supported Rapoport's rule at low latitudinal zones but did not present any remarkable mid-domain effects at any spatial extents. In conclusion, biogeographic realms are an appropriate scale for studying macroecological patterns. Reptilian latitudinal richness patterns of China were explained by a combination of environmental factors and geometric constraints, while the latitudinal community structure patterns were greatly affected by environmental gradients. Functional guilds present differentiated macroecological patterns along the latitudinal gradients.

Nonlinear thermal gradients shape broad‐scale patterns in geographic range size and can reverse Rapoport's rule

AbstractAimSpecies living at latitudes that have greater annual temperature variations are expected to achieve broader geographic ranges than species living at latitudes that have smaller annual temperature variations, generating a positive relationship between range size and latitude (Rapoport's rule). However, this prediction fails to take into account the greater latitudinal extent of tropical temperatures relative to those at higher latitudes. Here we model the contributions of the broader latitudinal extent of equal‐temperature habitats at low latitudes and the greater annual temperature variation at high latitudes to the range size–latitude relationship, and test whether the latitudinal variation in geographic range size in marine bivalves can be explained by models that account for both annual temperature variation and the steepness of latitudinal thermal gradients.LocationWestern Pacific, eastern Pacific and western Atlantic.MethodsWe use a null model where geographic ranges are placed on the ocean surface independently of thermal gradients, and a range‐expansion model where the minimum and maximum temperatures encompassed by the geographic range of a species (macroecological thermal ranges) are positively related to annual temperature minima and maxima at the location where the species originated. We compare results with a database containing 40,820 occurrences of 4760 marine bivalve species.ResultModels incorporating temperature‐limited range expansion along realistic thermal gradients predict an inverse relationship between range size and latitude, in opposition to Rapoport's rule. The distribution patterns of marine bivalves match this prediction.Main conclusionsThe poleward trend in latitudinal range size is determined by the nonlinearity of the latitudinal gradient of temperature minima and maxima and less by the latitudinal gradient of the local seasonal range in temperatures. Although tropical species do have narrower macroecological thermal ranges than high‐latitude species, the nearly constant temperatures over wide areas of the tropics allow tropical species to achieve broad latitudinal ranges.

Ecological and evolutionary drivers of range size in Coenagrion damselflies.

Geographic range size is a key ecological and evolutionary characteristic of a species, yet the causal basis of variation in range size among species remains largely unresolved. One major reason for this is that several ecological and evolutionary traits may jointly shape species' differences in range size. We here present an integrated study of the contribution of ecological (dispersal capacity, body size and latitudinal position) and macroevolutionary (species' age) traits in shaping variation in species' range size in Coenagrion damselflies. We reconstructed the phylogenetic tree of this genus to account for evolutionary history when assessing the contribution of the ecological traits and to evaluate the role of the macroevolutionary trait (species' age). The genus invaded the Nearctic twice independently from the Palearctic, yet this was not associated with the evolution of larger range sizes or dispersal capacity. Body size and species' age did not explain variation in range size. There is higher flight ability (as measured by wing aspect ratio) at higher latitudes. Species with a larger wing aspect ratio had a larger range size, also after correcting for phylogeny, suggesting a role for dispersal capacity in shaping the species' ranges. More northern species had a larger species' range, consistent with Rapoport's rule, possibly related to niche width. Our results underscore the importance of integrating macroecology and macroevolution when explaining range size variation among species.

Rapoport's rule revisited: geographical distributions of human languages.

One of the most well studied ecological patterns is Rapoport's rule, which posits that the geographical extent of species ranges increases at higher latitudes. However, studies to date have been limited in their geographic scope and results have been equivocal. In turn, much debate exists over potential links between Rapoport's rule and latitudinal patterns in species richness. Humans collectively speak nearly 7000 different languages, which are spread unevenly across the globe, with loci in the tropics. Causes of this skewed distribution have received only limited study. We analyze the extent of Rapoport's rule in human languages at a global scale and within each region of the globe separately. We test the relationship between Rapoport's rule and the richness of languages spoken in different regions. We also explore the frequency distribution of language-range sizes. The language-range area distribution is strongly right-skewed, with 87% of languages having range areas less than 10,000 km2, and only nine languages with range areas over 1,000,000 km2. At a global scale, language-range extents and areas are positively correlated with latitude. At a global scale and in five of the six regions examined, language-range extent and language-range area are strongly correlated with language richness. Our results point to group boundary formation as a critical mediator of the relationship between Rapoport's rule and diversity patterns. Where strong group boundaries limit range overlap, as is the case with human languages, and range sizes increase with latitude, latitudinal richness gradients may result.

Regional and Elevational Patterns in Vascular Epiphyte Richness on an East Asian Island

AbstractThe distribution of species on mountains has been related to various predictor variables, especially temperature. Thermal specialization—presumed to be more pronounced on tropical mountains than on temperate mountains—accounts for the elevational pattern of species richness and varies between organisms and geographic areas. In this study, the elevational and regional distribution patterns of 331 epiphyte species in Taiwan were explored using 39,084 botanic collections, mostly from herbaria. Species richness showed a peak in elevation at 500–1500 m. This peak could not be explained by a null model, the mid‐domain effect, suggesting that environmental variables accounted mostly for the distribution of species on the mountains. Next, species distributions were modeled to assess epiphyte regional and elevational distribution patterns. The model results not only corroborated the position of the mid‐elevation peak in richness, but also identified two mountain areas on the island with exceptionally high species richness. These areas of high epiphyte diversity coincide with areas of high rainfall in relation to the direction of the prevailing winds. Moreover, a subsequent exploratory ordination analysis showed a varied thermal preference between epiphyte subcategories (hemiepiphytes, dicotyledons, orchids, and ferns). In contrast to predictions by the elevational Rapoport's rule, ordination analysis also showed that the degree of thermal specialization increased with elevation, suggesting that highland species may be especially vulnerable to global warming.