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1.
    
Understanding the origins of species richness patterns is a fundamental goal in ecology and evolutionary biology. Much research has focused on explaining two kinds of species richness patterns: (i) spatial species richness patterns (e.g. the latitudinal diversity gradient), and (ii) clade-based species richness patterns (e.g. the predominance of angiosperm species among plants). Here, I highlight a third kind of richness pattern: trait-based species richness (e.g. the number of species with each state of a character, such as diet or body size). Trait-based richness patterns are relevant to many topics in ecology and evolution, from ecosystem function to adaptive radiation to the paradox of sex. Although many studies have described particular trait-based richness patterns, the origins of these patterns remain far less understood, and trait-based richness has not been emphasised as a general category of richness patterns. Here, I describe a conceptual framework for how trait-based richness patterns arise compared to other richness patterns. A systematic review suggests that trait-based richness patterns are most often explained by when each state originates within a group (i.e. older states generally have higher richness), and not by differences in transition rates among states or faster diversification of species with certain states. This latter result contrasts with the widespread emphasis on diversification rates in species-richness research. I show that many recent studies of spatial richness patterns are actually studies of trait-based richness patterns, potentially confounding the causes of these patterns. Finally, I describe a plethora of unanswered questions related to trait-based richness patterns.  相似文献   

2.
    
When the morphological diversity of a clade of species is quantified as the among-species variance in morphology, that diversity is a joint consequence of the phylogenetic structure of the clade (i.e., temporal pattern of speciation events) and the rates of change in the morphological traits of interest. Extrinsic factors have previously been linked to variation in the rate of morphological change among clades. Here, we ask whether species co-occurrence is positively correlated with the rate of change in several ecologically relevant morphological characters using the North American freshwater fish clade Percina (Teleostei: Etheostomatinae). We constructed a time-calibrated phylogenetic tree of Percina from mtDNA sequence data, gathered data on eight morphological characters from 37 species, used a principal components analysis to identify the primary axes of morphological variation, and analyzed 16,094 collection records to estimate species co-occurrence. We then calculated standardized independent contrasts (SIC) of the morphological traits (rate of change) at each node, estimated ancestral species co-occurrence, and quantified the correlation between species co-occurrence and rate of morphological change. We find that morphology changes more quickly when co-occurrence is greater in Percina . Our results provide strong evidence that co-occurrence among close relatives is linked to the morphological diversification of this clade.  相似文献   

3.
    
The identification of adaptations and key innovations has long interested biologists because they confer on organisms the ability to exploit previously unavailable ecological resources and respond to novel selective pressures. Although it can be extremely difficult to test for the effects of a character on the rate of lineage diversification, the convergent evolution of a character in multiple lineages provides an excellent opportunity to test for the effect of that character on lineage diversification. Here, I examine the effect of parity mode on the diversification of vipers, which have independently evolved viviparity in at least 13 lineages. I find strong statistical evidence that viviparous species diversify at a greater rate than oviparous species and correlate major decreases in the diversification rate of oviparous species with periods of global cooling, such as the Oligocene. These results suggest that the evolution of viviparity buffered live-bearing species against the negative effects of global climate change during the Cenozoic, and was a key innovation in the evolution and diversification of live-bearing vipers.  相似文献   

4.
    
Mass extinctions have altered the trajectory of evolution a number of times over the Phanerozoic. During these periods of biotic upheaval a different selective regime appears to operate, although it is still unclear whether consistent survivorship rules apply across different extinction events. We compare variations in diversity and disparity across the evolutionary history of a major Paleozoic arthropod group, the Eurypterida. Using these data, we explore the group's transition from a successful, dynamic clade to a stagnant persistent lineage, pinpointing the Devonian as the period during which this evolutionary regime shift occurred. The late Devonian biotic crisis is potentially unique among the “Big Five” mass extinctions in exhibiting a drop in speciation rates rather than an increase in extinction. Our study reveals eurypterids show depressed speciation rates throughout the Devonian but no abnormal peaks in extinction. Loss of morphospace occupation is random across all Paleozoic extinction events; however, differential origination during the Devonian results in a migration and subsequent stagnation of occupied morphospace. This shift appears linked to an ecological transition from euryhaline taxa to freshwater species with low morphological diversity alongside a decrease in endemism. These results demonstrate the importance of the Devonian biotic crisis in reshaping Paleozoic ecosystems.  相似文献   

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6.
    
The hypothesis of punctuated equilibrium proposes that most phenotypic evolution occurs in rapid bursts associated with speciation events. Several methods have been developed that can infer punctuated equilibrium from molecular phylogenies in the absence of paleontological data. These methods essentially test whether the variance in phenotypes among extant species is better explained by evolutionary time since common ancestry or by the number of estimated speciation events separating taxa. However, apparent \"punctuational\" trait change can be recovered on molecular phylogenies if the rate of phenotypic evolution is correlated with the rate of speciation. Strong support for punctuational models can arise even if the underlying mode of trait evolution is strictly gradual, so long as rates of speciation and trait evolution covary across the branches of phylogenetic trees, and provided that lineages vary in their rate of speciation. Species selection for accelerated rates of ecological or phenotypic divergence can potentially lead to the perception that most trait divergence occurs in association with speciation events.  相似文献   

7.
    
Size is among the most important traits of any organism, yet the factors that control its evolution remain poorly understood. In this study, we investigate controls on the evolution of organismal size using a newly compiled database of nearly 25,000 foraminiferan species and subspecies spanning the past 400 million years. We find a transition in the pattern of foraminiferan size evolution from correlation with atmospheric pO2 during the Paleozoic (400–250 million years ago) to long‐term stasis during the post‐Paleozoic (250 million years ago to present). Thus, a dramatic shift in the evolutionary mode coincides with the most severe biotic catastrophe of the Phanerozoic (543 million years ago to present). Paleozoic tracking of pO2 was confined to Order Fusulinida, whereas Paleozoic lagenides, miliolids, and textulariids were best described by the stasis model. Stasis continued to best describe miliolids and textulariids during post‐Paleozoic time, whereas random walk was the best supported mode for the other diverse orders. The shift in evolutionary dynamics thus appears to have resulted primarily from the selective elimination of fusulinids at the end of the Permian Period. These findings illustrate the potential for mass extinction to alter macroevolutionary dynamics for hundreds of millions of years.  相似文献   

8.
    
The evolution of seed size among angiosperms reflects their ecological diversification in a complex fitness landscape of life‐history strategies. The lineages that have evolved seeds beyond the upper and lower boundaries that defined nonflowering seed plants since the Paleozoic are more dispersed across the angiosperm phylogeny than would be expected under a neutral model of phenotypic evolution. Morphological rates of seed size evolution estimated for 40 clades based on 17,375 species ranged from 0.001 (Garryales) to 0.207 (Malvales). Comparative phylogenetic analysis indicated that morphological rates are not associated with the clade's seed size but are negatively correlated with the clade's position in the overall distribution of angiosperm seed sizes; clades with seed sizes closer to the angiosperm mean had significantly higher morphological rates than clades with extremely small or extremely large seeds. Likewise, per‐clade taxonomic diversification rates are not associated with the seed size of the clade but with where the clade falls within the angiosperm seed size distribution. These results suggest that evolutionary rates (morphological and taxonomic) are elevated in densely occupied regions of the seed morphospace relative to lineages whose ecophenotypic innovations have moved them toward the edges.  相似文献   

9.
    
Morphological cladograms of vertebrates are often inferred from greater numbers of characters describing the skull and teeth than from postcranial characters. This is either because the skull is believed to yield characters with a stronger phylogenetic signal (i.e., contain less homoplasy), because morphological variation therein is more readily atomized, or because craniodental material is more widely available (particularly in the palaeontological case). An analysis of 85 vertebrate datasets published between 2000 and 2013 confirms that craniodental characters are significantly more numerous than postcranial characters, but finds no evidence that levels of homoplasy differ in the two partitions. However, a new partition test, based on tree‐to‐tree distances (as measured by the Robinson Foulds metric) rather than tree length, reveals that relationships inferred from the partitions are significantly different about one time in three, much more often than expected. Such differences may reflect divergent selective pressures in different body regions, resulting in different localized patterns of homoplasy. Most systematists attempt to sample characters broadly across body regions, but this is not always possible. We conclude that trees inferred largely from either craniodental or postcranial characters in isolation may differ significantly from those that would result from a more holistic approach. We urge the latter.  相似文献   

10.
    
Declining diversification rates over time are a well-established evolutionary pattern, often interpreted as indicating initial rapid radiation with filling of ecological niche space. Here, we test the hypothesis that island radiations may show constant net diversification rates over time, due to continued expansion into new niche space in highly dispersive taxa. We investigate diversification patterns of four passerine bird families originating from the Indo-Pacific archipelagos, and link these to biogeographic patterns to provide independent indications of niche filling. We find a declining diversification rate for only one family, the Paradisaeidae (41 species). These are almost completely restricted to New Guinea, and have on average smaller species ranges and higher levels of species richness within grid cells than the other three families. In contrast, we cannot reject constant diversification rates for Campephagidae (93 species), Oriolidae (35 species), and Pachycephalidae (53 species), groups that have independently colonized neighboring archipelagos and continents. We propose that Paradisaeidae have reached the diversity limit imposed by their restricted distribution, whereas high dispersal and colonization success across the geologically dynamic Indo-Pacific archipelagos may have sustained high speciation rates for the other three families. Alternatively, increasing extinction rates may have obscured declining speciation rates in those three phylogenies.  相似文献   

11.
    
Taxa differ widely in numbers of species, which may be due either to chance alone or to factors that cause differences in speciation and extinction rates between taxa. To test whether an observed distribution of species over taxa differs from the distribution expected from chance alone, one must take into account that neither speciation nor extinction rates are known. This paper introduces a way to estimate speciation and extinction probabilities from the distribution of extant species over families and to test whether the observed distribution is different from expected. Application of this procedure to the distributions of bird, hexapod, primate, and angiosperm species over taxa provides statistical evidence of differences in rates of cladogenesis between taxa.  相似文献   

12.
Is gradual microevolutionary change within species simultaneously the source of macroevolutionary differentiation between species? Since its first publication, Darwin''s original idea that phenotypic differences between species develop gradually over time, as the accumulation of small selection-induced changes in successive generations has been challenged by palaeontologists claiming that, instead, new species quickly acquire their phenotypes to remain virtually unchanged until going extinct again. This controversy, widely known as the ‘punctuated equilibrium’ debate, remained unresolved, largely owing to the difficulty of distinguishing biological species from fossil remains. We analysed body masses of 2143 existing mammal species on a phylogeny comprising 4510 (i.e. nearly all) extant species to estimate rates of gradual (anagenetic) and speciational (cladogenetic) evolution. Our Bayesian estimates from mammals as well as separate sub-clades such as primates and carnivores suggest that gradual evolution is responsible for only a small part of body size variation between mammal species.  相似文献   

13.
    
The anterior cervical vertebrae form the skeletal connection between the cranial and postcranial skeletons in higher tetrapods. As a result, the morphology of the atlas‐axis complex is likely to be shaped by selection pressures acting on either the head or neck. The neoceratopsian (Reptilia:Dinosauria) syncervical represents one of the most highly modified atlas‐axis regions in vertebrates, being formed by the complete coalescence of the three most anterior cervical vertebrae. In ceratopsids, the syncervical has been hypothesized to be an adaptation to support a massive skull, or to act as a buttress during intraspecific head‐to‐head combat. Here, we test these functional/adaptive hypotheses within a phylogenetic framework and critically examine the previously proposed methods for quantifying relative head size in the fossil record for the first time. Results indicate that neither the evolution of cranial weaponry nor large head size correlates with the origin of cervical fusion in ceratopsians, and we, therefore, reject both adaptive hypotheses for the origin of the syncervical. Anterior cervical fusion has evolved independently in a number of amniote clades, and further research on extant groups with this peculiar anatomy is needed to understand the evolutionary basis for cervical fusion in Neoceratopsia.  相似文献   

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15.
    
Phenotypic integration and modularity describe the strength and pattern of interdependencies between traits. Integration and modularity have been proposed to influence the trajectory of evolution, either acting as constraints or facilitators. Here, we examine trends in the integration and modularity of pectoral fin morphology in teleost fishes using geometric morphometrics. We compare the fin shapes of the highly diverse radiation of acanthomorph fishes to lower teleosts. Integration and modularity are measured using two‐block partial least squares analysis and the covariance ratio coefficient between the radial bones and lepidotrichia of the pectoral fins. We show that the fins of acanthomorph fishes are more tightly integrated but also more morphologically diverse and faster evolving compared to nonacanthomorph fishes. The main pattern of shape covariation in nonacanthomorphs is concordant with the main trajectory of evolution between nonacanthomorphs and acanthomorphs. Our findings support a facilitating role for integration during the acanthomorph diversification. Potential functional consequences and developmental mechanisms of fin integration are discussed.  相似文献   

16.
    
The tempo and mode of species diversification and phenotypic evolution vary widely across the tree of life, yet the relationship between these processes is poorly known. Previous tests of the relationship between rates of phenotypic evolution and rates of species diversification have assumed that species richness increases continuously through time. If this assumption is violated, simple phylogenetic estimates of net diversification rate may bear no relationship to processes that influence the distribution of species richness among clades. Here, we demonstrate that the variation in species richness among plethodontid salamander clades is unlikely to have resulted from simple time-dependent processes, leading to fundamentally different conclusions about the relationship between rates of phenotypic evolution and species diversification. Morphological evolutionary rates of both size and shape evolution are correlated with clade species richness, but are uncorrelated with simple estimators of net diversification that assume constancy of rates through time. This coupling between species diversification and phenotypic evolution is consistent with the hypothesis that clades with high rates of morphological trait evolution may diversify more than clades with low rates. Our results indicate that assumptions about underlying processes of diversity regulation have important consequences for interpreting macroevolutionary patterns.  相似文献   

17.
    
Most extant species are in clades with poor fossil records, and recent studies of comparative methods show they have low power to infer even highly simplified models of trait evolution without fossil data. Birds are a well‐studied radiation, yet their early evolutionary patterns are still contentious. The fossil record suggests that birds underwent a rapid ecological radiation after the end‐Cretaceous mass extinction, and several smaller, subsequent radiations. This hypothesized series of repeated radiations from fossil data is difficult to test using extant data alone. By uniting morphological and phylogenetic data on 604 extant genera of birds with morphological data on 58 species of extinct birds from 50 million years ago, the “halfway point” of avian evolution, I have been able to test how well extant‐only methods predict the diversity of fossil forms. All extant‐only methods underestimate the disparity, although the ratio of within‐ to between‐clade disparity does suggest high early rates. The failure of standard models to predict high early disparity suggests that recent radiations are obscuring deep time patterns in the evolution of birds. Metrics from different models can be used in conjunction to provide more valuable insights than simply finding the model with the highest relative fit.  相似文献   

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19.
    
Studies of evolutionary correlations commonly use phylogenetic regression (i.e., independent contrasts and phylogenetic generalized least squares) to assess trait covariation in a phylogenetic context. However, while this approach is appropriate for evaluating trends in one or a few traits, it is incapable of assessing patterns in highly multivariate data, as the large number of variables relative to sample size prohibits parametric test statistics from being computed. This poses serious limitations for comparative biologists, who must either simplify how they quantify phenotypic traits, or alter the biological hypotheses they wish to examine. In this article, I propose a new statistical procedure for performing ANOVA and regression models in a phylogenetic context that can accommodate high‐dimensional datasets. The approach is derived from the statistical equivalency between parametric methods using covariance matrices and methods based on distance matrices. Using simulations under Brownian motion, I show that the method displays appropriate Type I error rates and statistical power, whereas standard parametric procedures have decreasing power as data dimensionality increases. As such, the new procedure provides a useful means of assessing trait covariation across a set of taxa related by a phylogeny, enabling macroevolutionary biologists to test hypotheses of adaptation, and phenotypic change in high‐dimensional datasets.  相似文献   

20.
    
Herbivory is rare among birds and is usually thought to have evolved predominately among large, flightless birds due to energetic constraints or an association with increased body mass. Nearly all members of the bird order Anseriformes, which includes ducks, geese, and swans, are flighted and many are predominately herbivorous. However, it is unknown whether herbivory represents a derived state for the order and how many times a predominately herbivorous diet may have evolved. Compiling data from over 200 published diet studies to create a continuous character for herbivory, models of trait evolution support at least five independent transitions toward a predominately herbivorous diet in Anseriformes. Although a nonphylogenetic correlation test recovers a significant positive correlation between herbivory and body mass, this correlation is not significant when accounting for phylogeny. These results indicate a lack of support for the hypothesis that a larger body mass confers an advantage in the digestion of low‐quality diets but does not exclude the possibility that shifts to a more abundant food source have driven shifts toward herbivory in other bird lineages. The exceptional number of transitions toward a more herbivorous diet in Anseriformes and lack of correlation with body mass prompts a reinterpretation of the relatively infrequent origination of herbivory among flighted birds.  相似文献   

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