Biomic Specialization and Speciation Rates in Ruminants (Cetartiodactyla, Mammalia): A Test of the Resource-Use Hypothesis at the Global Scale
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The resource-use hypothesis proposed by E.S. Vrba predicts that specialist species have higher speciation and extinction rates than generalists because they are more susceptible to environmental changes and vicariance. In this work, we test some of the predictions derived from this hypothesis on the 197 extant and recently extinct species of Ruminantia (Cetartiodactyla, Mammalia) using the biomic specialization index (BSI) of each species, which is based on its distribution within different biomes. We ran 10000 Monte Carlo simulations of our data in order to get a null distribution of BSI values against which to contrast the observed data. Additionally, we drew on a supertree of the ruminants and a phylogenetic likelihood-based method (QuaSSE) for testing whether the degree of biomic specialization affects speciation rates in ruminant lineages. Our results are consistent with the predictions of the resource-use hypothesis, which foretells a higher speciation rate of lineages restricted to a single biome (BSI = 1) and higher frequency of specialist species in biomes that underwent high degree of contraction and fragmentation during climatic cycles. Bovids and deer present differential specialization across biomes; cervids show higher specialization in biomes with a marked hydric seasonality (tropical deciduous woodlands and schlerophyllous woodlands), while bovids present higher specialization in a greater variety of biomes. This might be the result of divergent physiological constraints as well as a different biogeographic and evolutionary history.Keywords:
Biome
Genetic algorithm
Vicariance
Biome
Settlement (finance)
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Abstract Molecular dating techniques require the use of calibrations, which are usually fossil or geological vicariance-based. Fossil calibrations have been criticised because they result only in minimum age estimates. Based on a historical biogeographic perspective, I suggest that vicariance-based calibrations are more dangerous. Almost all analytical methods in historical biogeography are strongly biased towards inferring vicariance, hence vicariance identified through such methods is unreliable. Other studies, especially of groups found on Gondwanan fragments, have simply assumed vicariance. Although it was previously believed that vicariance was the predominant mode of speciation, mounting evidence now indicates that speciation by dispersal is common, dominating vicariance in several groups. Moreover, the possibility of speciation having occurred before the said geological event cannot be precluded. Thus, geological calibrations can under- or overestimate times, whereas fossil calibrations always result in minimum estimates. Another major drawback of vicariant calibrations is the problem of circular reasoning when the resulting estimates are used to infer ages of biogeographic events. I argue that fossil-based dating is a superior alternative to vicariance, primarily because the strongest assumption in the latter, that speciation was caused by the said geological process, is more often than not the most tenuous. When authors prefer to use a combination of fossil and vicariant calibrations, one suggestion is to report results both with and without inclusion of the geological constraints. Relying solely on vicariant calibrations should be strictly avoided.
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Biome conservatism is often regarded as common in diversifying lineages, based on the detection of low biome shift rates or high phylogenetic signal. However, many studies testing biome conservatism utilise a single-biome-per-species approach, which may influence the detection of biome conservatism. Meta-analyses show that biome shift rates are significantly lower (less than a tenth), when single biome occupancy approaches are adopted. Using New Zealand plant lineages, estimated biome shifts were also significantly lower (14–67% fewer biome shifts) when analysed under the assumption of a single biome per species. Although a single biome approach consistently resulted in lower biome shifts, it detected fewer instances of biome conservatism. A third of clades (3 out of 9) changed status in biome conservatism tests between single and multiple biome occupancy approaches, with more instances of significant biome conservatism when using a multiple biome occupancy approach. A single biome approach may change the likelihood of finding biome conservatism because it assumes biome specialisation within species, falsely recognises some biome shift types and fails to include other biome shift types. Our results indicate that the degree of biome fidelity assumed has a strong influence on analyses assessing biome shift rates, and biome conservatism testing. We advocate analyses that allow species to occupy multiple biomes.
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Conservatism
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Abstract Aim Recent studies in southern Africa identified past biome stability as an important predictor of biodiversity. We aimed to assess the extent to which past biome stability predicts present global biodiversity patterns, and the extent to which projected climatic changes may lead to eventual biome changes in areas with constant past biome. Location Global. Taxon Spermatophyta; terrestrial vertebrates. Methods Biome constancy was assessed and mapped using results from 89 dynamic global vegetation model simulations, driven by outputs of palaeoclimate experiments spanning the past 140 ka. We tested the hypothesis that terrestrial vertebrate diversity is predicted by biome constancy. We also simulated potential future vegetation, and hence potential future biome patterns, and quantified and mapped the extent of projected eventual future biome change in areas of past constant biome. Results Approximately 11% of global ice‐free land had a constant biome since 140 ka. Apart from areas of constant Desert, many areas with constant biome support high species diversity. All terrestrial vertebrate groups show a strong positive relationship between biome constancy and vertebrate diversity in areas of greater diversity, but no relationship in less diverse areas. Climatic change projected by 2100 commits 46%–66% of global ice‐free land, and 34%–52% of areas of past constant biome (excluding areas of constant Desert) to eventual biome change. Main conclusions Past biome stability strongly predicts vertebrate diversity in areas of higher diversity. Future climatic changes will lead to biome changes in many areas of past constant biome, with profound implications for biodiversity conservation. Some projected biome changes will result in substantial reductions in biospheric carbon sequestration and other ecosystem services.
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Global biodiversity
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Generalist species are becoming increasingly dominant in European bird communities. This has been taken as evidence of biotic homogenization, whereby generalist ‘winners’ systematically replace specialist ‘losers’. We test this pattern by relating changes in the average specialization of UK bird communities to changes in the density of species with different degrees of habitat specialization. Although we find the expected decline in community specialization, this was driven by a combination of a strong increase in the density of the most generalist quartile of species and declines in the density of moderately generalist species. Contrary to expectation, specialist species increased slightly over the 18‐year study period but had little effect on the overall trend in community specialization. Our results indicate that the apparent homogenization of UK bird communities is not driven by the replacement of specialists by generalists, but instead by the changing fortunes of generalist species.
Homogenization
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Biome
Environmental change
Global Change
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The file contains BIOME 6000 reconstructions of vegetation at 0, 6, and 21ka at individual sites, where the original published nomenclature for individual regions has been converted to a globally-applicable standardized classification (BIOME 6000 Consolidated Name). Two other standardized classifications are also given: common biome names between BIOME 6000 and the BIOME 4.2 model (BIOME 4.2 BIOME 6000 common names) and the megabiome scheme used by Harrison and Bartlein (2012) (MegaBiome Scheme 2). Additional information to translate BIOME 4.2 outputs into either BIOME 6000 Consolidated Names or BIOME 4.2 BIOME 6000 common names is also given.
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이 연구는 지금까지 초등교사 정체성으로서 대별되어 왔던 generalist 관점과 specialist 관점의 논쟁점을 살피고, 특정 정체성에 우위를 두고자 했다. 이를 위해 먼저 specialist 관점과 generalist 관점을 비교하였다. 이때, 두 관점은 정체성 초점이 각각‘교과’와 ‘학급(아동)’으로 달랐다. 이로부터 specialist는 교과교육전문가로, generalist는 학급/아동교육전문가로 개념화했다. 다음으로 이렇게 차이가 존재하는 두 관점이 초등교사 정체성에 동시적으로 영향을 주게 된 원인을 찾고자 했다. 그 결과, 초등교육에는 교과(학문) 중심주의, 국가기반(주도) 제도주의, 아동 중심주의 이론이 동시적으로 작용하고 있었다. 이러한 상황은 초등교사가 교과와 아동 모두를 동등하게 자신의 주요 역할로서 받아들이는 아이러니를 생성시켰다. 그러나 초등학교의 목적, 초등교직 체제, 초등교사의 실제적 역할로 인해 초등교육은 학급담임제에 기반을 두고, 초등교사는 generalist(학급/아동교육전문가)로서 자기 정체성을 형성할 가능성이 높음을 알 수 있었다.
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