The influence of seasonal migration on range size in temperate North American passerines

Seasonal migration has been alternately proposed to promote geographic range size in some contexts and to constrain it in others, but it remains unclear if migratory behavior has a general effect on range size. Because migration involves movement, most hypotheses about the relationship between migration and range size invoke an influence of migration on the process of dispersal-mediated range expansion. Intuitively, a positive relationship between migratory behavior and dispersal ability could bolster range expansion among migratory species, yet some biogeographic patterns suggest that long-distance migration may instead impede range expansion, especially in the temperate zone. We conducted a comparative analysis of the relationship between migratory behavior and range size by testing the effect of migratory status, migration distance and morphological dispersal ability on breeding range size among all temperate North American passerines. Further, we assessed whether these traits affect range expansion into suitable habitat by analyzing their relationship with range filling (the proportion of climatically-suitable area occupied, or ‘filled’ by a species). Contrary to previous studies, we found migration and dispersal ability to be poor predictors of range size and range filling in North America. Rather, most variation in range size is explained by latitude. Our results suggest that migratory behavior does not affect range size within the scale of a continent, and furthermore, that temperate North American passerines’ breeding ranges are not influenced by their dispersal abilities. To better understand why migratory behavior appears to promote range size in some contexts and constrain it in others, future studies should investigate how migratory behavior affects dispersal at the individual level, as well as the relationship between the evolution of migratory behavior and the breadth of species’ climatic niches.     

Incomplete datasets obscure associations between traits affecting dispersal ability and geographic range size of reef fishes in the Tropical Eastern Pacific

Dispersal is thought to be an important process determining range size, especially for species in highly spatially structured habitats, such as tropical reef fishes. Despite intensive research efforts, there is conflicting evidence about the role of dispersal in determining range size. We hypothesize that traits related to dispersal drive range sizes, but that complete and comprehensive datasets are essential for detecting relationships between species’ dispersal ability and range size. We investigate the roles of six traits affecting several stages of dispersal (adult mobility, spawning mode, pelagic larval duration (PLD), body size, aggregation behavior, and circadian activity), in explaining range size variation of reef fishes in the Tropical Eastern Pacific (TEP). All traits, except for PLD (148 species), had data for all 497 species in the region. Using a series of statistical models, we investigated which traits were associated with large range sizes, when analyzing all TEP species or only species with PLD data. Furthermore, using null models, we analyzed whether the PLD‐subset is representative of the regional species pool. Several traits affecting dispersal ability were strongly associated with range size, although these relationships could not be detected when using the PLD‐subset. Pelagic spawners (allowing for passive egg dispersal) had on average 56% larger range sizes than nonpelagic spawners. Species with medium or high adult mobility had on average a 25% or 33% larger range, respectively, than species with low mobility. Null models showed that the PLD‐subset was nonrepresentative of the regional species pool, explaining why model outcomes using the PLD‐subset differed from the ones based on the complete dataset. Our results show that in the TEP, traits affecting dispersal ability are important in explaining range size variation. Using a regionally complete dataset was crucial for detecting the theoretically expected, but so far empirically unresolved, relationship between dispersal and range size.     

What determines a species' geographical range? Thermal biology and latitudinal range size relationships in European diving beetles (Coleoptera: Dytiscidae)

1.  The geographical range sizes of individual species vary considerably in extent, although the factors underlying this variation remain poorly understood, and could include a number of ecological and evolutionary processes. A favoured explanation for range size variation is that this result from differences in fundamental niche breadths, suggesting a key role for physiology in determining range size, although to date empirical tests of these ideas remain limited.
2.  Here we explore relationships between thermal physiology and biogeography, whilst controlling for possible differences in dispersal ability and phylogenetic relatedness, across 14 ecologically similar congeners which differ in geographical range extent; European diving beetles of the genus Deronectes Sharp (Coleoptera, Dytiscidae). Absolute upper and lower temperature tolerance and acclimatory abilities are determined for populations of each species, following acclimation in the laboratory.
3.  Absolute thermal tolerance range is the best predictor of both species' latitudinal range extent and position, differences in dispersal ability (based on wing size) apparently being less important in this group. In addition, species' northern and southern range limits are related to their tolerance of low and high temperatures respectively. In all cases, absolute temperature tolerances, rather than acclimatory abilities are the best predictors of range parameters, whilst the use of independent contrasts suggested that species' thermal acclimation abilities may also relate to biogeography, although increased acclimatory ability does not appear to be associated with increased range size.
4.  Our study is the first to provide empirical support for a relationship between thermal physiology and range size variation in widespread and restricted species, conducted using the same experimental design, within a phylogenetically and ecologically controlled framework.     

Do species’ traits predict recent shifts at expanding range edges?

Although some organisms have moved to higher elevations and latitudes in response to recent climate change, there is little consensus regarding the capacity of different species to track rapid climate change via range shifts. Understanding species' abilities to shift ranges has important implications for assessing extinction risk and predicting future community structure. At an expanding front, colonization rates are determined jointly by rates of reproduction and dispersal. In addition, establishment of viable populations requires that individuals find suitable resources in novel habitats. Thus, species with greater dispersal ability, reproductive rate and ecological generalization should be more likely to expand into new regions under climate change. Here, we assess current evidence for the relationship between leading-edge range shifts and species' traits. We found expected relationships for several datasets, including diet breadth in North American Passeriformes and egg-laying habitat in British Odonata. However, models generally had low explanatory power. Thus, even statistically and biologically meaningful relationships are unlikely to be of predictive utility for conservation and management. Trait-based range shift forecasts face several challenges, including quantifying relevant natural history variation across large numbers of species and coupling these data with extrinsic factors such as habitat fragmentation and availability.     

The relationship between pelagic larval duration and range size in tropical reef fishes: a synthetic analysis

We address the conflict in earlier results regarding the relationship between dispersal potential and range size. We examine all published pelagic larval duration data for tropical reef fishes. Larval duration is a convenient surrogate for dispersal potential in marine species that are sedentary as adults and that therefore only experience significant dispersal during their larval phase. Such extensive quantitative dispersal data are only available for fishes and thus we use a unique dataset to examine the relationship between dispersal potential and range size. We find that dispersal potential and range size are positively correlated only in the largest ocean basin, the Indo-Pacific, and that this pattern is driven primarily by the spatial distribution of habitat and dispersal barriers. Furthermore, the relationship strengthens at higher taxonomic levels, suggesting an evolutionary mechanism. We document a negative correlation between species richness and larval duration at the family level in the Indo-Pacific, implying that speciation rate may be negatively related to dispersal potential. If increased speciation rate within a taxonomic group results in smaller range sizes within that group, speciation rate could regulate the association between range size and dispersal potential.     

Body size and feeding specificity: macrolepidoptera in Britain

Within a geographic assemblage, large-bodied species of macrolepidopteran moths tend, on average, to be less host-specific than small-bodied. Five possible explanations for this pattern are identified, based respectively on (i) phylogenetic relationships between species, (ii) latitudinal gradients in body size and feeding specificity, (iii) the relationship between range size and body size, (iv) larger body size as a buffer from environmental variation, and (v) the relationship between endophagous host associations and small body size. These mechanisms are tested using data for British macrolepidoptera and also evaluated using evidence from the literature at large. Although some of their assumptions are found to be justified, there is no significant support for any single mechanism. This lack of evidence for previously proposed mechanisms is discussed in the light of a recently proposed alternative explanation which combines theories of host quality and host defence mechanisms.     

A Multi-Clade Test Supports the Intermediate Dispersal Model of Biogeography

Background

Biogeography models typically focus on explaining patterns through island properties, such as size, complexity, age, and isolation. Such models explain variation in the richness of island biotas. Properties of the organisms themselves, such as their size, age, and dispersal abilities, in turn may explain which organisms come to occupy, and diversify across island archipelagos. Here, we restate and test the intermediate dispersal model (IDM) predicting peak diversity in clades of relatively intermediate dispersers.

Methodology

We test the model through a review of terrestrial and freshwater organisms in the western Indian Ocean examining the correlation among species richness and three potential explanatory variables: dispersal ability quantified as the number of estimated dispersal events, average body size for animals, and clade age.

Conclusions

Our study supports the IDM with dispersal ability being the best predictor of regional diversity among the explored variables. We find a weaker relationship between diversity and clade age, but not body size. Principally, we find that richness strongly and positively correlates with dispersal ability in poor to good dispersers while a prior study found a strong decrease in richness with increased dispersal ability among excellent dispersers. Both studies therefore support the intermediate dispersal model, especially when considered together. We note that many additional variables not here considered are at play. For example, some taxa may lose dispersal ability subsequent to island colonization and some poor dispersers have reached high diversity through within island radiations. Nevertheless, our findings highlight the fundamental importance of dispersal ability in explaining patterns of biodiversity generation across islands.     

A predictive model of avian natal dispersal distance provides prior information for investigating response to landscape change

1. Informative Bayesian priors can improve the precision of estimates in ecological studies or estimate parameters for which little or no information is available. While Bayesian analyses are becoming more popular in ecology, the use of strongly informative priors remains rare, perhaps because examples of informative priors are not readily available in the published literature. 2. Dispersal distance is an important ecological parameter, but is difficult to measure and estimates are scarce. General models that provide informative prior estimates of dispersal distances will therefore be valuable. 3. Using a world-wide data set on birds, we develop a predictive model of median natal dispersal distance that includes body mass, wingspan, sex and feeding guild. This model predicts median dispersal distance well when using the fitted data and an independent test data set, explaining up to 53% of the variation. 4. Using this model, we predict a priori estimates of median dispersal distance for 57 woodland-dependent bird species in northern Victoria, Australia. These estimates are then used to investigate the relationship between dispersal ability and vulnerability to landscape-scale changes in habitat cover and fragmentation. 5. We find evidence that woodland bird species with poor predicted dispersal ability are more vulnerable to habitat fragmentation than those species with longer predicted dispersal distances, thus improving the understanding of this important phenomenon. 6. The value of constructing informative priors from existing information is also demonstrated. When used as informative priors for four example species, predicted dispersal distances reduced the 95% credible intervals of posterior estimates of dispersal distance by 8-19%. Further, should we have wished to collect information on avian dispersal distances and relate it to species' responses to habitat loss and fragmentation, data from 221 individuals across 57 species would have been required to obtain estimates with the same precision as those provided by the general model.     

Habitat type predicts genetic population differentiation in freshwater invertebrates

A basic challenge in evolutionary biology is to establish links between ecology and evolution of species. One important link is the habitat template. It has been hypothesized, that the spatial and temporal settings of a habitat strongly influence the evolution of species dispersal propensity. Here, we evaluate the importance of the habitat type on genetic population differentiation of species using freshwater habitats as a model system. Freshwater habitats are either lentic (standing) or lotic (running). On average, lotic habitats are more stable and predictable over space and time than lentic habitats. Therefore, lentic habitats should favour the evolution of higher dispersal propensity which ensures population survival of lentic species. To test for such a relationship, we used extensive data on species' genetic population differentiation of lentic and lotic freshwater invertebrates retrieved from published allozyme studies. Overall, we analysed more than 150 species from all over the world. Controlling for several experimental, biological and geographical confounding effects, we always found that lentic invertebrates exhibit, on average, lower genetic population differentiation than lotic species. This pattern was consistent across insects, crustaceans and molluscs. Our results imply fundamental differences in genetic population differentiation among species adapted to either lentic or lotic habitats. We propose that such differences should occur in a number of other habitat types that differ in spatio-temporal stability. Furthermore, our results highlight the important role of lotic habitats as reservoirs for evolutionary processes and the potential for rapid speciation.     

Host specificity and geographic range in haematophagous ectoparasites

A negative interspecific correlation between the degree of habitat specialization and the size of a species' geographic range has been documented for several free living groups of organisms, providing support for the niche breadth hypothesis. In contrast, practically nothing is known about the geographic range sizes of parasitic organisms and their determinants. In the context of the niche breadth hypothesis, parasites represent ideal study systems, because of the well documented variation in host specificity among parasite species. Here, we investigated the relationship between host specificity (a measure of niche breadth) and geographic range size among flea species parasitic on small mammals, using data from seven distinct geographical regions. Two measures of host specificity were used: the number of host species used by a flea species, and a measure of the average taxonomic distance between the host species used by a flea; the latter index provides an evolutionary perspective on host specificity. After correcting for phylogenetic influences, and using either of our two measures of host specificity, the degree of host specificity of fleas was negatively correlated with the size of their geographic range in all seven regions studied here, with only one minor exception. Overall, these results provide strong support for the niche breadth hypothesis, although other explanations cannot be ruled out.     

Postglacial migration supplements climate in determining plant species ranges in Europe

The influence of dispersal limitation on species ranges remains controversial. Considering the dramatic impacts of the last glaciation in Europe, species might not have tracked climate changes through time and, as a consequence, their present-day ranges might be in disequilibrium with current climate. For 1016 European plant species, we assessed the relative importance of current climate and limited postglacial migration in determining species ranges using regression modelling and explanatory variables representing climate, and a novel species-specific hind-casting-based measure of accessibility to postglacial colonization. Climate was important for all species, while postglacial colonization also constrained the ranges of more than 50 per cent of the species. On average, climate explained five times more variation in species ranges than accessibility, but accessibility was the strongest determinant for one-sixth of the species. Accessibility was particularly important for species with limited long-distance dispersal ability, with southern glacial ranges, seed plants compared with ferns, and small-range species in southern Europe. In addition, accessibility explained one-third of the variation in species' disequilibrium with climate as measured by the realized/potential range size ratio computed with niche modelling. In conclusion, we show that although climate is the dominant broad-scale determinant of European plant species ranges, constrained dispersal plays an important supplementary role.     

How do low dispersal species establish large range sizes? The case of the water beetle Graphoderus bilineatus

Species’ dispersal abilities have been considered a major driving force in establishment and maintenance of large range sizes. However, recent studies question the general validity of this relationship because the relationship between dispersal ability and range size might in some cases be less important than species phylogeny or local spatial attributes. In this study we used the water beetle Graphoderus bilineatus a philopatric species of conservation concern in Europe as a model to explain large range size and to support effective conservation measures for such species that also have limited dispersal. We recorded the presence/absence of G. bilineatus and measured 14 habitat and 20 landscape variables at 228 localities in Estonia, Poland and Sweden within the core range of the species. Using information theory and average multivariate logistic regression models we determined that presence of G. bilineatus depended on landscape connectivity, distance to a possible source habitat, and stability of the site; however, specificity of habitat characteristics was not vital for the species. We reason that the large range of G. bilineatus is best explained by the historical combination of lakes, river systems and wetlands which used to be highly connected throughout the central plains of Europe. Our data suggest that a broad habitat niche can prevent landscape elements from becoming barriers for species like G. bilineatus. Therefore, we question the usefulness of site protection as conservation measures for G. bilineatus and similar philopatric species. Instead, conservation actions should be focused at the landscape level to ensure a long‐term viability of such species across their range.     

Climate envelope modelling reveals intraspecific relationships among flowering phenology, niche breadth and potential range size in Arabidopsis thaliana

Species often harbour large amounts of phenotypic variation in ecologically important traits, and some of this variation is genetically based. Understanding how this genetic variation is spatially structured can help to understand species' ecological tolerances and range limits. We modelled the climate envelopes of Arabidopsis thaliana genotypes, ranging from early- to late-flowering, as a function of several climatic variables. We found that genotypes with contrasting alleles at individual flowering time loci differed significantly in potential range size and niche breadth. We also found that later flowering genotypes had more restricted range potentials and narrower niche breadths than earlier flowering genotypes, indicating that local selection on flowering can constrain or enhance the ability of populations to colonise other areas. Our study demonstrates how climate envelope models that incorporate ecologically important genetic variation can provide insights into the macroecology of a species, which is important to understand its responses to changing environments.     

Dispersal ability correlates with range size in Amazonian habitat-restricted birds

Understanding how species attain their geographical distributions and identifying traits correlated with range size are important objectives in biogeography, evolutionary biology and biodiversity conservation. Despite much effort, results have been varied and general trends have been slow to emerge. Studying species pools that occupy specific habitats, rather than clades or large groupings of species occupying diverse habitats, may better identify ranges size correlates and be more informative for conservation programmes in a rapidly changing world. We evaluated correlations between a set of organismal traits and range size in bird species from Amazonian white-sand ecosystems. We assessed if results are consistent when using different data sources for phylogenetic and range hypotheses. We found that dispersal ability, as measured by the hand-wing index, was correlated with range size in both white-sand birds and their non-white-sand sister taxa. White-sand birds had smaller ranges on average than their sister taxa. The results were similar and robust to the different data sources. Our results suggest that the patchiness of white-sand ecosystems limits species’ ability to reach new habitat islands and establish new populations.     

Niche breadth explains the range size of European-centred butterflies,but dispersal ability does not

Aim

The breadth of ecological niches and dispersal abilities have long been discussed as important determinants of species' range sizes. However, studies directly comparing the relative effects of both factors are rare, taxonomically biased and revealed inconsistent results.

Location

Europe.

Time Period

Cenozoic.

Major Taxa

Butterflies, Lepidoptera.

Methods

We relate climate, diet and habitat niche breadth and two indicators of dispersal ability, wingspan and a dispersal tendency index, to the global range size of 369 European-centred butterfly species. The relative effects of these five predictors and their variation across the butterfly phylogeny were assessed by means of phylogenetic generalized least squares models and phylogenetically weighted regressions respectively.

Results

Climate niche breadth was the most important single predictor, followed by habitat and diet niche breadth, while dispersal tendency and wingspan showed no relation to species' range size. All predictors together explained 59% of the variation in butterfly range size. However, the effects of each predictor varied considerably across families and genera.

Main Conclusions

Range sizes of European-centred butterflies are strongly correlated with ecological niche breadth but apparently independent of dispersal ability. The magnitude of range size–niche breadth relationships is not stationary across the phylogeny and is often negatively correlated across the different dimensions of the ecological niche. This variation limits the generalizability of range size–trait relationships across broad taxonomic groups.     

Spatial dynamics of keystone predation

1. I investigated the effects of dispersal on communities of keystone predators and prey. I obtained two key results. 2. First, a strong trade-off between competitive ability and predator susceptibility allows consumer coexistence over a large resource productivity range, but it also lowers the predator-susceptible superior competitor's abundance and increases its risk of extinction. Thus, unexpectedly, dispersal plays a more important role in coexistence when predator-mediated coexistence is strong rather than weak. The interplay between the trade-off, small population sizes resulting from transient oscillations, and dispersal leads to qualitatively different species distributions depending on the relative mobilities of the consumers and predator. These differences yield comparative predictions that can be tested with data on trade-off strength, dispersal rates, and species distributions across productivity gradients. 3. Second, there is an asymmetry between species in their dispersal effects: the predator-resistant inferior competitor's dispersal has a large effect, but the predator-susceptible superior competitor's dispersal has no effect, on coexistence and species' distributions. The inferior competitor's dispersal also mediates the predator's dispersal effects: the predator's dispersal has no effect when the inferior competitor is immobile, and a large effect when it is mobile. The net outcome of the direct and indirect effects of the inferior competitor's dispersal is a qualitative change in the species' distributions from interspecific segregation to interspecific aggregation. 4. The important point is that differences between species in how they balance resource acquisition and predator avoidance can lead to unexpected differences in their dispersal effects. While consumer coexistence in the absence of dispersal is driven largely by the top predator, consumer coexistence in the presence of dispersal is driven largely by the predator-resistant inferior competitor.     

Whip it good! Geographic consistency in male songs and variability in female songs of the duetting eastern whipbird Psophodes olivaceus

Geographic variation in male bird songs has been studied extensively, but there have been few investigations of geographic variation in female songs or sex differences in patterns of geographic variation. We compared patterns of variation in male and female songs of eastern whipbirds Psophodes olivaceus by analyzing recordings from 16 populations across the species' geographic range in eastern Australia. We found remarkably different patterns of geographic variation between the sexes. Female eastern whipbird songs are easily categorized into discrete song types. Song types are shared between nearby females, but female songs show pronounced differences at a continental scale. In contrast, male eastern whipbird songs show high consistency throughout the species' geographic range. All recorded males share the ability to transpose the frequency of the introductory whistle and most recorded males share the ability to vary the direction of the slope of the terminal whip crack. For eight of nine measured variables, female songs show significantly higher levels of variation than male songs. We discuss whether sex differences in dispersal, song learning strategies, and song function may explain these sex differences in patterns of song variation. We suggest that eastern whipbirds have experienced a decoupling of male and female song learning strategies and that the songs of each sex have responded to different selective pressures in the context of countersinging interactions. We speculate that consistency in male songs throughout the geographic range of eastern whipbirds may arise through female preference for males that perform large bandwidth whip cracks.     

Role of larval host plants in the climate-driven range expansion of the butterfly Polygonia c-album

1. Some species have expanded their ranges during recent climate warming and the availability of breeding habitat and species' dispersal ability are two important factors determining expansions. The exploitation of a wide range of larval host plants should increase an herbivorous insect species' ability to track climate by increasing habitat availability. Therefore we investigated whether the performance of a species on different host plants changed towards its range boundary, and under warmer temperatures. 2. We studied the polyphagous butterfly Polygonia c-album, which is currently expanding its range in Britain and apparently has altered its host plant preference from Humulus lupulus to include other hosts (particularly Ulmus glabra and Urtica dioica). We investigated insect performance (development time, larval growth rate, adult size, survival) and adult flight morphology on these host plants under four rearing temperatures (18-28.5 degrees C) in populations from core and range margin sites. 3. In general, differences between core and margin populations were small compared with effects of rearing temperature and host plant. In terms of insect performance, host plants were generally ranked U. glabra > or = U. dioica > H. lupulus at all temperatures. Adult P. c-album can either enter diapause or develop directly and higher temperatures resulted in more directly developing adults, but lower survival rates (particularly on the original host H. lupulus) and smaller adult size. 4. Adult flight morphology of wild-caught individuals from range margin populations appeared to be related to increased dispersal potential relative to core populations. However, there was no difference in laboratory reared individuals, and conflicting results were obtained for different measures of flight morphology in relation to larval host plant and temperature effects, making conclusions about dispersal potential difficult. 5. Current range expansion of P. c-album is associated with the exploitation of more widespread host plants on which performance is improved. This study demonstrates how polyphagy may enhance the ability of species to track climate change. Our findings suggest that observed differences in climate-driven range shifts of generalist vs. specialist species may increase in the future and are likely to lead to greatly altered community composition.     

Evolutionarily accelerated invasions: the rate of dispersal evolves upwards during the range advance of cane toads

Human activities are changing habitats and climates and causing species' ranges to shift. Range expansion brings into play a set of powerful evolutionary forces at the expanding range edge that act to increase dispersal rates. One likely consequence of these forces is accelerating rates of range advance because of evolved increases in dispersal on the range edge. In northern Australia, cane toads have increased their rate of spread fivefold in the last 70 years. Our breeding trials with toads from populations spanning the species' invasion history in Australia suggest a genetic basis to dispersal rates and interpopulation genetic variation in such rates. Toads whose parents were from the expanding range front dispersed faster than toads whose parents were from the core of the range. This difference reflects patterns found in their field-collected mothers and fathers and points to heritable variance in the traits that have accelerated the toads' rate of invasion across tropical Australia over recent decades. Taken together with demonstrated spatial assortment by dispersal ability occurring on the expanding front, these results point firmly to ongoing evolution as a driving force in the accelerated expansion of toads across northern Australia.     

Low dispersal ability and habitat specificity promote extinctions in rare but not in widespread species: the Orthoptera of Germany

Local extinctions are often non‐randomly associated with range size, dispersal ability and habitat specificity, as well as body size, sexual dimorphism and phylogeny. We used a large data set of the Orthoptera species (bush crickets, crickets, grasshoppers) occurring in Germany and compared the number of occupied grid cells before 1980 to those occupied after 1980, corrected for monitoring intensity. The number of grid cells in which a species went extinct was non‐linearly related to the number of occupied grid cells per species. Using generalized linear modelling we analysed extinction in relation to national distribution (the number of occupied grid cells before 1980), dispersal ability (derived from a large body of literature concerning wing development, colonization dynamics and within‐habitat mobility), habitat specificity (moisture specialists versus generalists), potential reproduction (the number of ovarioles), the degree of sexual size dimorphism and phylogeny (twelve clades). Species with a large global range size also had a large national range size. Species with a large range experienced more total extinction events than species with smaller ranges but relatively fewer compared to range size. The latter relationship was largely shaped by the dispersal ability of the species: the interactions of range size×dispersal ability and range size×habitat specificity explained almost one third of the variation in the number of extinction events. Species with high dispersal ability went extinct in a similar number of grid cells irrespective of their range size. By contrast, species with low dispersal ability went extinct in proportion to their range size. Therefore, comparing the speed of extinction across species in the conventional way of extinction rates (that is the percentage of range contraction) might be flawed because it only applies to species with low dispersal ability. Sexual size dimorphism was not a significant predictor of extinction. Extinction was not concentrated on particular clades.