Species-range Size Distribution Research Articles

Species-range-size distributions: Integrating the effects of speciation, transformation, and extinction.

The species‐range size distribution is a product of speciation, transformation of range‐sizes, and extinction. Previous empirical studies showed that it has a left‐skewed lognormal‐like distribution. We developed a new mathematical framework to study species‐range‐size distributions, one in which allopatric speciation, transformation of range size, and the extinction process are explicitly integrated. The approach, which we call the gain‐loss‐allopatric speciation model, allows us to explore the effects of various speciation scenarios. Our model captures key dynamics thought to lead to known range‐size distributions. We also fitted the model to empirical range‐size distributions of birds, mammals, and beetles. Since geographic range dynamics are linked to speciation and extinction, our model provides predictions for the dynamics of species richness. When a species‐range‐size distribution initially evolves away from the range sizes at which the likelihood of speciation is low, it tends to cause diversification slowdown even in the absence of (bio)diversity dependence in speciation rate. Using the mathematical model developed here, we give a potential explanation for how observed range‐size distributions emerge from range‐size dynamics. Although the framework presented is minimalistic, it provides a starting point for examining hypotheses based on more complex mechanisms.

Latitudinal Diversity Gradients and Rapoport Effects in Chinese Endemic Woody Seed Plants

The distribution of plant species diversity has long been a major focus on biogeography. Yet, the universality of the popular Rapoport’s rule remains controversial for endemic plants, as previous studies have focused more on broad-ranged species. Here, we collected data for 4418 endemic woody seed plant species across China, including trees, shrubs, and lianas, to explore the latitudinal patterns of species range size and richness, and test the relevant biogeographic law. The species range size distribution was examined for conformity with Rapoport’s rule using four methods (i.e., Steven’s, Pagel’s, the mid-point, and the across-species method). Spatial patterns of species richness along latitudinal gradient were also investigated by parabolic regression. Results showed that species range size increased with latitude for all species as well as by trees, shrubs and lianas, especially assessed by Pagel’s method. Species richness was highest at low latitude, where species range size was smallest, and decreased with increasing latitude. The species range size and richness of shrubs were maximum, followed by trees then lianas. These findings prove that Rapoport’s rule is strongly supported by latitudinal patterns of species distribution in Chinese endemic woody seed plants.

Altitudinal range-size distribution of breeding birds and environmental factors for the determination of species richness: An empirical test of altitudinal Rapoport's rule and non-directional rescue effect on a local scale.

Range-size distributions are important for understanding species richness patterns and led to the development of the controversial Rapoport’s rule and Rapoport-rescue effect. This study aimed to understand the relationship between species richness and range-size distribution in relation to environmental factors. The present study tested the following: (1) altitudinal Rapoport’s rule, and a subsequent test on climatic and ambient energy hypotheses, (2) non-directional rescue effect, and a subsequent test on effect of environmental factors associated with the distribution of narrowest to widest-range species. Altitudinal species range-size distribution increased with increasing altitude and showed a negative relationship with climatic variables. These results support the altitudinal Rapoport’s rule and climatic hypothesis; however, they do not fully support the ambient energy hypothesis. Results from testing the non-directional rescue effect showed that the inflow intensity of species from both directions (high and low elevations) affected species richness. And we found that the species with intermediate range-size, rather than narrowest or widest range-size were the main cause of a mid-peak of species richness and the non-directional rescue effect. Additionally, the richness of species with intermediate range-size was highly related to minimum temperature, habitat heterogeneity, or primary productivity. Although altitudinal range-size distribution results were similar to the phenomenon of altitudinal Rapoport’s rule, the mid-peak pattern of species richness could not be explained by the underlying mechanism of Rapoport’s-rescue effect; however, the non-directional rescue effect could explain a mid-peak pattern of species richness along altitudinal gradient.

Extension of the gambin model to multimodal species abundance distributions

Abstract Species abundance distributions (SADs) are one of the most widely used tools in macroecology, and it has become increasingly apparent that many empirical SADs can best be described as multimodal. However, only a few SAD models have been extended to incorporate multiple modes and no software packages are available to fit multimodal SAD models. In this study, we present an extension of the gambin SAD model to multimodal SADs. We derive the maximum likelihood equations for fitting the bimodal gambin distribution and generalize this approach to fit gambin models with any number of modes. We present these new functions, along with additional functions to aid in the analysis of multimodal SADs, within an updated r package (“gambin”; version 2.4.0) that enables the fitting, plotting and evaluating of gambin models with any number of modes. We use a mixture of simulations and empirical datasets to test our new models, including tests of the sensitivity of the model parameters to the number of individuals and the number of species in a sample. We show that the new multimodal gambin models perform well under a variety of circumstances, and that the application of these new models to empirical SAD and other macroecological (e.g., species range size distributions) datasets can provide interesting insights. The updated software package is simple to use and provides straightforward yet flexible statistical analyses of multimodality in SAD‐type datasets.

A review of the Polystira clade--the Neotropic's largest marine gastropod radiation (Neogastropoda: Conoidea: Turridae sensu stricto).

The Polystira clade (here comprising Polystira and Pleuroliria) is a poorly known but hyper-diverse clade within the neogastropod family Turridae (sensu stricto). It has extensively radiated within the tropics and subtropics of the Americas, to which it is endemic. In this paper we present a synthetic overview of existing information on this radiation together with new information on estimated species diversity, systematic relationships, a species-level molecular phylogenetic analysis and preliminary macroecological and diversification analyses, to serve as a platform for further study. We currently estimate that about 300 species (122 extant) are known from its 36 million year history but this number will undoubtedly increase as we extend our studies. We discuss the relationships of Polystira to other Neotropical Turridae (s.s.) and examine the taxonomy and systematics of the geologically oldest described members of the clade. To aid taxonomic description of shells we introduce a new notation for homologous major spiral cords. Focusing on key publications, we discuss in detail the changing historical understanding of the taxonomy of the clade and the relationships of its component genus-level taxa: Polystira Woodring, 1928, Pleuroliria de Gregorio, 1890, Josephina Gardner, 1945 and Oxytropa Glibert, 1955. We designate a neotype for Pleurotoma (Pleuroliria) supramirifica de Gregorio, 1890, to stabilize our understanding of this, the type species of Pleuroliria. Application of the name Oxytropa is restricted to the type species. The genus Polystira is conchologically re-described and for the first time we synthesize available information on the anatomy, feeding and toxinology, reproduction and life history, larval modes and life habits, and geographic and bathymetric ranges of its species. We give an updated list of the 19 formally described living species and present the pitfalls of the currently poor species-level taxonomy of Polystira using case examples. We present a molecular phylogenetic analysis of 22 extant species using three mitochondrial gene fragments (COI, 12S rRNA and 16S rRNA). This reveals undescribed species and indicates that Recent genetic clades ('biospecies') are consistent with finely divided conchological 'morphospecies'. Historically, there has been a slow realisation of the high species diversity of the Polystira clade and we consider that this may be due to inadequate precision of morphological description of shells and a lack of clear homology statements. We suggest how these both might be improved. Finally, using a data compilation based on museum specimens we examine species range-size distributions and species abundance distributions for 85 of the 112 extant western Atlantic species that we have delimited to date. Our results indicate that the majority of species are rare and have short geographic ranges; only a few are wide-ranging and abundant. This has important implications for surveys of biodiversity.

Intermediate geographic range facilitates speciation in European tree species

The possible influence of geographic range size on speciation remains a controversial subject in evolutionary ecology, with theory and data supporting positive, negative and bell-shaped relationships between speciation probability and ancestor range size. In this study, a surrogate of the speciation-range size relationship of extant European tree species (22 genera, 11 families) is obtained by comparing the range-size distribution of candidate ancestors (i.e.species which are thought to have originated new species) with that of relatives, controlling phylogenetic inertia and macroecological sampling bias. In this comparison, species range size is measured qualitatively using six categories. The candidate ancestors included seem to have speciated mainly through allopatric speciation, with fewer instances of hybridogenesis by allopolyploidy. The results show that speciation is significantly facilitated for species with intermediate range size. In the European tree flora, this pattern could be the result of multiple causes, including intermediate dispersal ability at these ranges. Descendant tree species tend to have narrow geographic ranges, a trend which arguably comes from limited dispersal ability in this case. Low dispersal ability could be common in new species as a consequence of widespread adaptation to stable habitats isolated by geographic barriers (“island habitats”) during allopatric speciation. This mechanism could be widespread among regional biotas and would facilitate narrow ranges in new species. This would provide a simple explanation to the observed abundance of narrow ranges in most macroecological species-range size distributions.

ARE RANGE-SIZE DISTRIBUTIONS CONSISTENT WITH SPECIES-LEVEL HERITABILITY?

The concept of species-level heritability is widely contested. Because it is most likely to apply to emergent, species-level traits, one of the central discussions has focused on the potential heritability of geographic range size. However, a central argument against range-size heritability has been that it is not compatible with the observed shape of present-day species range-size distributions (SRDs), a claim that has never been tested. To assess this claim, we used forward simulation of range-size evolution in clades with varying degrees of range-size heritability, and compared the output of three different models to the range-size distribution of the South American avifauna. Although there were differences among the models, a moderate-to-high degree of range-size heritability consistently leads to SRDs that were similar to empirical data. These results suggest that range-size heritability can generate realistic SRDs, and may play an important role in shaping observed patterns of range sizes.

Spatial Patterns of Endemic Plants in California

California endemic vascular plant range patterns were quantified using a flora-based geodatabase technique that defined species range by geographic area and elevation band. Resulting species spatial patterns are reported for 228 geographic units. Over 60% of the endemic species range size distributions were found to have range sizes less than 10,000 km2. The largest endemic taxon range was 275,749 km2, or 67% of the state. California endemic plant richness distribution patterns are summarized by 228 geographic units, and reported by various criteria. California's Central Coast Ranges, Sierra Nevada foothills, high elevation Sierra Nevada Mountains, Channel Islands, San Jacinto Mountains, Napa and Lake Counties, Inyo Mountains, sections of the Mojave Desert, and San Bernardino Mountains were all identified as areas with unique endemic plant attributes. We compared endemic species richness between map units in zones containing similar topography and climate, and found that area only weakly correlated with species richness, suggesting other factors have stronger influence on endemism in continental California. The findings have implications for developing conservation plans that target endemic species. In particular, we identify areas of the state, previously de-emphasized, that deserve greater recognition based on the characteristics of their restricted endemic plants. This analysis underestimates the level of endemism near the borders with Oregon and Baja California because of the artificial limitation of the database to the boundaries of the state of California. However, range distribution estimates produced from digital renditions of floral keys proved effective in this study, an inexpensive approach that could be implemented in other regions of the world for which floras have been published.

Compositional similarity and the distribution of geographical range size for assemblages of native and non‐native species in urban floras

ABSTRACTThere is evidence that, within a region, non‐native species introduced from nearby sources (extralimital native) promote homogenization and non‐native species introduced from distant sources (exotic) promote differentiation of species composition. A possible explanation for these associations is that they are related to differences in the distribution of geographical range size. We test this by examining geographical ranges, delineated within a defined region, for assemblages of vascular plants in eight urban floras in the USA. Across floras, native species had the largest, least variable ranges and the greatest proportion of shared species. Exotic species had the most variable ranges with concentrations of species with small and large ranges and the lowest proportion of shared species. Extralimital natives had concentrations of species with intermediate‐sized ranges and intermediate proportions of shared species. These results suggest that patterns of compositional similarity were associated with the relative strength and equality of two opposing patterns within species range size distributions: species with small vs. large ranges. In general, concentrations of species with small ranges promoted low levels and concentrations of species with large ranges promoted high levels of compositional similarity. However, patterns documented for exotic species will likely continue to develop, possibly taking on new forms, depending on how geographical distributions and the rate of introductions of exotic species change over time. Our findings also suggest that processes underlying these patterns have operated at two spatiotemporal scales. The first scale reflects historical consequences of anthropogenic activities occurring within regional extents that have promoted the introduction of extralimital natives; the second scale reflects modern consequences of anthropogenic activities operating at an increasingly global extent that have promoted the introduction of exotic species.

The structure of global species–range size distributions: raptors & owls

ABSTRACTAims To determine the shape of global species–range size distributions, the influence on these of island species, threatened species and patterns of latitudinal variation in range sizes, and the fit to logit‐normal distributions.Location Global.Methods We take the spatial distributions of the raptors and owls of the world as exemplar data sets, document the shapes of their species–range size distributions, the influence of particular groups of species and of latitudinal variation in range sizes on these shapes, and the fit of these distributions to a variety of models.Results The global species–range size distributions of both raptors and owls are extremely right skewed on untransformed axes. They are not lognormally distributed, as has commonly been stated for species–range size distributions, nor logit‐normally distributed as has been suggested might be the case. For raptors, departures from either a lognormal or a logit‐normal are little mitigated by excluding groups of species that might be thought to distort the observed species–range size distribution, nor by the latitudinal gradient in geographical range size. For owls, the effects of excluding island and threatened species are more marked, with the fit of the species–range size distribution to a lognormal or a logit‐normal becoming much closer.Conclusions A simple general description of the shape of species–range size distributions remains elusive. This constitutes a significant constraint on the development of theory as to how they are determined. Whilst in principle the fit of any given mechanistic model can be tested against one or more empirical data sets, whatever their form, a simple general mathematical description of species–range size distributions would make the process of rapidly testing the appropriateness of mechanistic models more straightforward.

Nested subset analysis and taxa-range size distributions of pedological assemblages: implications for biodiversity studies

A common pattern of taxa distribution has been termed nested subsets by ecologists. Species present in any particular biological assemblage tend also to be present in larger assemblages. The same is true for the so called species–range size distribution: locally abundant species tend to be widespread, whereas locally rare species tend to be narrowly distributed. According to several ecologists, this pattern could be described by a power law. In this paper we show that regularities tested with our data (soil types = pedotaxa, and soilscapes = pedological assemblages) are surprisingly similar to those in ecological literature. For this purpose several soil data sets, as well as techniques utilised in mathematical ecology, including Atmar and Patterson’s Nested Calculator Program have been used. Many of these common patterns appear at different spatial scales suggesting that mechanisms such as nestedness, taxa-range size distributions and species–area relationships among others could be scale invariant, as some ecologists claim. Our results show that nestedness and scale-independent taxa-range size distributions are not exclusive properties of biological assemblages, but can be found in a broader class of earth systems. Pedodiversity analysis also has practical implications for designing reserves for biological and pedological conservation.

Nested subset analysis and taxa-range size distributions of pedological assemblages: implications for biodiversity studies

A common pattern of taxa distribution has been termed nested subsets by ecologists. Species present in any particular biological assemblage tend also to be present in larger assemblages. The same is true for the so called species–range size distribution: locally abundant species tend to be widespread, whereas locally rare species tend to be narrowly distributed. According to several ecologists, this pattern could be described by a power law. In this paper we show that regularities tested with our data (soil types = pedotaxa, and soilscapes = pedological assemblages) are surprisingly similar to those in ecological literature. For this purpose several soil data sets, as well as techniques utilised in mathematical ecology, including Atmar and Patterson’s Nested Calculator Program have been used. Many of these common patterns appear at different spatial scales suggesting that mechanisms such as nestedness, taxa-range size distributions and species–area relationships among others could be scale invariant, as some ecologists claim. Our results show that nestedness and scale-independent taxa-range size distributions are not exclusive properties of biological assemblages, but can be found in a broader class of earth systems. Pedodiversity analysis also has practical implications for designing reserves for biological and pedological conservation.

Species range size distributions for some marine taxa in the Atlantic Ocean. Effect of latitude and depth

The range size distributions of 6643 species in ten different fish and invertebrate taxa dwelling in pelagic (latitudinal range sizes) and benthic (latitudinal and depth range sizes) habitats on both sides of the Atlantic Ocean (80 ∞ N - 70 ∞ S) were studied. The objectives were to analyse: (1) the range size distribution patterns for the various taxa and whether they have right/left skewed or lognormal distributions; (2) the geographical species distributions, to ascertain whether the distribution ranges change with latitude (Rapoport’s rule); and (3) the relationship between the depth ranges of benthic species and their maximum depth of occurrence and how depth range size distributions change with latitude. The pelagic taxa exhibited larger range sizes than did the benthic taxa, continental slope/rise species excepted. On the other hand, the boundaries between geographical provinces for both benthic taxa and pelagic taxa tended to occur in association with major oceanographic processes. The shape of the latitudinal range frequency distributions (LRFDs) of the pelagic organisms were distinctly left-skewed, and the LRFDs for most taxa were significantly different from lognormal. There was no common pattern for the distributions of the benthic organisms, which were lognormal in Cephalopoda, Stomatopoda, and Crustacea Decapoda and tended to be left-skewed and significantly different from lognormal in Pisces. The applicability of Rapoport’s rule was not clearly inferable from the results, and the rule appears to be conditioned by the location of biogeographical boundaries and the endemism rate in the different biogeographical provinces. A clear increase in depth range size with maximum depth range was observable for benthic species, confirming previous studies. Species’ depth range distributions displayed a discernible latitudinal pattern, right-skewed at high latitudes and left-skewed at low latitudes. The location of biogeographical boundaries, and endemism rate by biogeographical province were considered to be the factors most useful in explaining species’ distribution patterns and their conformity or nonconformity to Rapoport’s rule. © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 80 , 437‐455.

On the heritability of geographic range sizes.

Within taxonomic groups, most species are restricted in their geographic range sizes, with only a few being widespread. The possibility that species-level selection on range sizes contributes to the characteristic form of such species-range size distributions has previously been raised. This would require that closely related species have similar range sizes, an indication of "heritability" of range sizes at the species level. Support for this view came from a positive correlation between the range sizes of closely related pairs of fossil mollusc species. We extend this analysis by considering the relationship between the geographic range sizes of 103 pairs of contemporary avian sister species. Range sizes in these sister species show no evidence of being more similar to each other than expected by chance. A reassessment of the mollusc data also suggests that the high correlation was probably overestimated because of the skewed nature of range size data. The fact that sister species tend to have similar life histories and ecologies suggests that any relationship between range sizes and biology is likely to be complicated and will be influenced by historical factors, such as mode of speciation and postspeciation range size transformations.

The distribution of species range size: a stochastic process.

The major role played by environmental factors in determining the geographical range sizes of species raises the possibility of describing their long-term dynamics in relatively simple terms, a goal which has hitherto proved elusive. Here we develop a stochastic differential equation to describe the dynamics of the range size of an individual species based on the relationship between abundance and range size, derive a limiting stationary probability model to quantify the stochastic nature of the range size for that species at steady state, and then generalize this model to the species-range size distribution for an assemblage. The model fits well to several empirical datasets of the geographical range sizes of species in taxonomic assemblages, and provides the simplest explanation of species-range size distributions to date.

Dynamics of speciation and diversification in a metapopulation.

We develop a simple framework for modeling speciation and diversification as a continuous process of accumulation of genetic (or morphological) differences accompanied by species and subpopulation extinction and/or range expansion. This framework can be used to approach a number of questions such as species-area distribution, species-range size distribution, the rate of ecological turnover, asymmetries of range division between sister species, waiting time until speciation and extinction, the relationship between the geographic range size and the probability of speciation, the relationships between subpopulation-level parameters and metapopulation-level parameters, and the effects of taxonomic level on these rates, distributions, and parameters. We illustrate some of these applications using numerical simulations. We develop approximations describing the dependence of the number of different taxonomic units, their average range size, and the rate of their turnover on the system size, the rate of fixation of genetic (or morphological) changes in local demes, and the rate of local extinction and colonization.

DYNAMICS OF SPECIATION AND DIVERSIFICATION IN A METAPOPULATION

We develop a simple framework for modeling speciation and diversification as a continuous process of accumulation of genetic (or morphological) differences accompanied by species and subpopulation extinction and/or range expansion. This framework can be used to approach a number of questions such as species-area distribution, species–range size distribution, the rate of ecological turnover, asymmetries of range division between sister species, waiting time until speciation and extinction, the relationship between the geographic range size and the probability of speciation, the relationships between subpopulation-level parameters and metapopulation-level parameters, and the effects of taxonomic level on these rates, distributions, and parameters. We illustrate some of these applications using numerical simulations. We develop approximations describing the dependence of the number of different taxonomic units, their average range size, and the rate of their turnover on the system size, the rate of fixation of genetic (or morphological) changes in local demes, and the rate of local extinction and colonization.Corresponding Editor: H. A. Orr

Species‐range size distributions in Britain

The detailed forms of species‐range size distributions in Britain are determined and contrasted for ten taxonomic assemblages (liverworts, vascular plants, molluscs [aquatic and terrestrial], dragonflies, macro‐moths. butterflies, birds [breeding and wintering], mammals). All are strongly right‐skewed when range sizes are untransformed. A logarithmic transformation fails to normalise the distribution for all but one group, and the distributions for several groups are not readily normalised at all. Taxa with larger median range sizes have species‐range size distributions that are less strongly right‐skewed. The median observed range sizes of species in each of the taxonomic groups fall, in terms of decreasing range size, in the sequence wintering birds < breeding birds < mammals < butterflies < terrestrial molluscs < dragonflies < aquatic molluscs < vascular plants < moths < liverworts. Despite the difficulties in deriving a simple and sensible mechanistic model for range size distributions, this is likely to be the most important next step towards understanding their forms.

Species-range size distributions: products of speciation, extinction and transformation

One basic summary of the spatial pattern of biodiversity across the surface of the Earth is provided by a species–range size distribution, the frequency distribution of the numbers of species exhibiting geographic ranges of different sizes. Although widely considered to be approximately lognormal, increasingly it appears that across a variety of groups of organisms this distribution systematically departs from such a form. Whatever its detailed shape, however, the distribution must arise as a product of three processes, speciation, extinction and transformation (the temporal dynamics of the range sizes of species during their life times). Considering the role potentially played by each of these processes necessitates drawing on information from a diverse array of research fields, and highlights the possible role of geographic range size as a common currency uniting them.

Age, area and avian diversification

Using coarse resolution data on the spatial distribution of the entire New World avifauna, we test for phylogenetic patterns in the mean and total geographic range sizes of taxa. The analyses reveal that (i) the species-range size distribution is only approximately normalized, and remains significantly left-skewed, under logarithmic transformation. Most variance in range sizes is explained at the level of species within genera; (ii) there is no effect of the age of taxa on mean clade range size, although older taxa are more likely to have larger total range sizes; (iii) there is some evidence that taxa comprising more species have larger total range sizes; (iv) there is little or no evidence for a relationship between rate of cladogenesis and range size. The results suggest that geographic range size is a labile trait, at least for New World birds, and that the influence of evolutionary history is only weakly detectable in the range size variation of extant taxa, at least at the scale of analysis used here. In addition to these conclusions, two general and important procedural issues emerge.