Causes Of Geographic Variation Research Articles

Linking Leaf Functional Traits with Soil and Climate Factors in Forest Ecosystems in China.

Plant leaf functional traits can reflect the adaptive strategies of plants to environmental changes. Exploring the patterns and causes of geographic variation in leaf functional traits is pivotal for improving ecological theory at the macroscopic scale. In order to explore the geographical variation and the dominant factors of leaf functional traits in the forest ecosystems of China, we measured 15 environmental factors on 16 leaf functional traits in 33 forest reserves in China. The results showed leaf area (LA), carbon-to-nitrogen ratio (C/N), carbon-to-phosphorus ratio (C/P), nitrogen-to-phosphorus ratio (N/P), phosphorus mass per area (Pa) and nitrogen isotope abundance (δ15N)) were correlated with latitude significantly. LA, Pa and δ15N were also correlated with longitude significantly. The leaf functional traits in southern China were predominantly affected by climatic factors, whereas those in northern China were mainly influenced by soil factors. Mean annual temperature (MAT), mean annual precipitation (MAP) and mean annual humidity (MAH) were shown to be the important climate factors, whereas available calcium (ACa), available potassium (AK), and available magnesium (AMg) were shown to be the important climate factors that affect the leaf functional traits of the forests in China. Our study fills the gap in the study of drivers and large-scale geographical variability of leaf functional traits, and our results elucidate the operational mechanisms of forest-soil-climate systems. We provide reliable support for modeling global forest dynamics.

Be careful with ecological associations.

Ecological studies are observational studies commonly used in public health research. The main characteristic of this study design is that the statistical analysis is based on pooled (i.e., aggregated) rather than on individual data. Thus, patient-level information such as age, gender, income and disease condition are not considered as individual characteristics but as mean values or frequencies, calculated at country or community level. Ecological studies can be used to compare the aggregated prevalence and incidence data of a given condition across different geographical areas, to assess time-related trends of the frequency of a pre-defined disease/condition, to identify factors explaining changes in health indicators over time in specific populations, to discriminate genetic from environmental causes of geographical variation in disease, or to investigate the relationship between a population-level exposure and a specific disease or condition. The major pitfall in ecological studies is the ecological fallacy, a bias which occurs when conclusions about individuals are erroneously deduced from results about the group to which those individuals belong. In this paper, by using a series of examples, we provide a general explanation of the ecological studies and provide some useful elements to recognize or suspect ecological fallacy in this type of studies.

Racial Disparities In Excess All-Cause Mortality During The Early COVID-19 Pandemic Varied Substantially Across States.

The impact of the coronavirus disease 2019 (COVID-19) pandemic has been starkly unequal across race and ethnicity. We examined the geographic variation in excess all-cause mortality by race and ethnicity to better understand the impact of the pandemic. We used individual-level administrative data on the US population between January 2011 and April 2020 to estimate the geographic variation in excess all-cause mortality by race and Hispanic origin. All-cause mortality allows a better understanding of the overall impact of the pandemic than mortality attributable to COVID-19 directly. Nationwide, adjusted excess all-cause mortality during that period was 6.8 per 10,000 for Black people, 4.3 for Hispanic people, 2.7 for Asian people, and 1.5 for White people. Nationwide averages mask substantial geographic variation. For example, despite similar excess White mortality, Michigan and Louisiana had markedly different excess Black mortality, as did Pennsylvania compared with Rhode Island. Wisconsin experienced no significant White excess mortality but had significant Black excess mortality. Further work understanding the causes of geographic variation in racial and ethnic disparities-the relevant roles of social and environmental factors relative to comorbidities and of the direct and indirect health effects of the pandemic-is crucial for effective policy making.

Geographic variation in female body size and clutch size of the lizard Sceloporus variabilis (Squamata: Phrynosomatidae) in Mexico

AbstractThe body size and reproductive characteristics in populations of the same species is influenced by environmental and ecological factors. In this study, we analysed the relationship of environmental factors, morphological characters (body size and mass) and reproductive traits (clutch size) of females from 13 populations of Sceloporus variabilis. Results showed variation in snout‒vent length (SVL), body mass and clutch size among populations. An ANCOVA between SVL and clutch size showed an increase of the latter in females from Alvarado and Valle Nacional; ANCOVA between body mass and SVL revealed an increase in body mass in most populations. A canonical correlation analysis showed a positive relationship between SVL, body mass, and clutch size with elevation and precipitation, but not with temperature. Future studies should assess the effect of seasonality and food resource availability on reproductive investment among populations of S. variabilis to determine whether these characteristics are a function of differences in key ecological factors (e.g. availability of resources and seasonality) associated with each population, and determine the causes of geographic variation in morphological and life history characteristics among populations.

Geographical variation of social calls and vocal discrimination in male Himalayan leaf-nosed bats

Like birds and many other animals, bats produce diverse acoustic calls for social communication. Geographical variation in social acoustic signals and perceptual discrimination abilities are well studied in birds but largely unexplored in bats. In this study, we recorded male territorial calls of the great Himalayan leaf-nosed bat, Hipposideros armiger, from nine colonies at a large geographical scale and investigated the patterns and causes of geographical variation in acoustic signals. We also performed habituation−dishabituation playbacks to investigate whether males could discriminate between territorial calls of their own versus a foreign colony. Overall, our results showed significant geographical variation in calls across colonies. Neither climatic differences, morphological differences, geographical distances nor genetic distances between colonies explained the observed acoustic variation between colonies. A playback experiment indicated that males from eastern China were able to discriminate between calls of males from their own colony and those of males from a colony in southwestern China. This study provides the first experimental evidence that bats can discriminate geographical variation in social calls.

Geographic variation in marmots’ alarm calls causes different responses

Geographic variation in acoustic signals has been investigated for five decades to better understand the evolution of communication. When receivers are able to discriminate among signals and to react accordingly, geographic variation can have major impacts on the ability of conspecifics to communicate. Surprisingly, geographic variation in alarm calls and its consequences for the communication process have been so far neglected despite their crucial role on individual survival. Working with four wild populations of Alpine marmots (Marmota marmota), we found differences in the acoustic structure of their alarm calls. These differences cannot be explained by geographic or genetic distances but more likely by other mechanisms including random processes. Moreover, playback experiments provided evidence that receivers discriminate between alarm calls from their own versus other populations, with responses at lower intensity when the alarm calls played back originated from their own population. Research on the mechanistic causes of geographic variation and on the relationship between alarm call variation, familiarity, and intelligibility of signal and behavioral responses is now required to better understand how predation pressure, and more widely natural selection, could drive the evolution of communication. Dialects (i.e., geographic variation) can have major impacts on the ability of conspecifics to communicate. Surprisingly, dialects in alarm calls have been neglected despite their crucial role on survival of individuals. Alpine marmots have dialects in alarm calls and discriminate their own dialects from others, being more frightened by alarm calls from another population than by those from their own. Confronted with an unknown dialect, marmots may adopt a self-preserving strategy and choose to run away before assessing the danger.

The patterns and possible causes of global geographical variation in the body size of the greater horseshoe bat (Rhinolophus ferrumequinum)

AbstractAimGeographical variations in endotherm body size (e.g. Bergmann's rule/James's rule and Allen's rule) have long been tested. However, the patterns and causes of geographical variation in body size within bat species, especially within widespread hibernating species, are little known. Here, we evaluated the possible causes of geographical size variation patterns in the greater horseshoe bat (Rhinolophus ferrumequinum), a bat species widely distributed across the Palearctic.LocationPalearctic.MethodsWe collected body size data (body mass and forearm length) from 1,172 adult bats via direct measurements or from the literature. We used high‐resolution environmental data for the sampled sites. We applied multiple linear regressions and an information‐theoretic approach on separate female and male datasets to estimate the support for various hypotheses.ResultsTemperature and latitude failed to predict body mass in both females and males. The best model showed that populations with longer forearms in both sexes were associated with higher mean temperatures (in the warmest quarter) and lower mean temperatures (in the coldest quarter). The independent contribution of these temperature parameters to forearm length in both sexes was higher than that of all other variables.Main conclusionThe observed relationship between temperature and body mass was not consistent with James's rule, and thus failed to support the heat conservation hypothesis. Our results are consistent with the predictions of Allen's rule and indicated that direct heat dissipation from the wing may be the most likely mechanism underlying geographical variation in forearm length. We suggest that the evaluation of the relative importance of multiple causal mechanisms may improve our understanding of patterns of geographical variation in endotherms.

Polychromatism of populations of Corallus hortulanus (Squamata: Boidae) from the southern Amazon Basin, Brazil

The Amazon tree boa Corallus hortulanus is known for featuring a wide variation in color pattern and design markings. Although there are studies on its polychromatism, none of them addresses the geographic variation in the color pattern of this species. The aim of this study was to describe the chromatic variation found in the populations of C. hortulanus from the southern Amazon Basin and its relationship with geographic distribution of the species. Analysis of both design markings and color patterns on 112 C. hortulanus specimens from the southern Amazon Basin interfluves resulted in the identification of six distinct morphotypes. Grayish-brown coloration and elongated diamond-shaped patterns were the most frequent patterns. Two morphotypes showed a tendency of correlation with the geographical distribution of those species found in Madeira and Juruá Rivers. The small sample size does not allow for a robust conclusion on the possible cause of geographic variation. The distribution of morphological patterns of C. hortullanus in the Amazon Basin suggest that there is gene flow between populations, regardless of geographical distance and natural barriers. The variation in color pattern and markings may represent a phenotypic response to the characteristics of different habitats occupied by the species.

A systematic review of the magnitude and cause of geographic variation in unplanned hospital admission rates and length of stay for ambulatory care sensitive conditions

BackgroundUnplanned hospital admissions place a large and increasing strain on healthcare budgets worldwide. Many admissions for ambulatory care sensitive conditions (ACSCs) are thought to be preventable, a belief supported by significant geographic variations in admission rates. We conducted a systematic review of the evidence on the magnitude and correlates of geographic variation in ACSC admission rates and length of stay (LOS).MethodsWe performed a search of Medline and Embase databases for English language cross-sectional and cohort studies on 28th March 2013 reporting geographic variation in admission rates or LOS for patients receiving unplanned care across at least 10 geographical units for one of 35 previously defined ACSCs. Forward and backward citation searches were undertaken on all included studies. We provide a narrative synthesis of study findings. Study quality was assessed using a modified Newcastle-Ottawa scale.ResultsWe included 39 studies comprising 25 on admission rates and 14 on LOS. Studies generally compared admission rates between regions (e.g. states) and LOS between hospitals. Most of the published research was undertaken in the US, UK or Canada and often focussed on patients with pneumonia, COPD or heart failure. 35 (90 %) studies concluded that geographic variation was present. Primary care quality and secondary care access were frequently suggested as drivers of admission rate variation whilst secondary care quality and adherence to clinical guidelines were often listed as contributors to LOS variation. Several different methods were used to quantify variation, some studies listed raw data, failed to control for confounders and used naive statistical methods which limited their utility.ConclusionsThe substantial geographical variations in the admission rates and LOS of potentially avoidable conditions could be a symptom of variable quality of care and should be a concern for clinicians and policymakers. Policymakers targeting a reduction in unplanned admissions could introduce initiatives to improve primary care access and quality or develop alternatives to admission. Those attempting to curb unnecessarily long LOS could introduce care pathways or guidelines. Methodological work on the quantification and reporting of geographic variation is needed to aid inter-study comparisons.Electronic supplementary materialThe online version of this article (doi:10.1186/s12913-015-0964-3) contains supplementary material, which is available to authorized users.

Environment, but not genetic divergence, influences geographic variation in colour morph frequencies in a lizard.

BackgroundIdentifying the causes of intraspecific phenotypic variation is essential for understanding evolutionary processes that maintain diversity and promote speciation. In polymorphic species, the relative frequencies of discrete morphs often vary geographically; yet the drivers of spatial variation in morph frequencies are seldom known. Here, we test the relative importance of gene flow and natural selection to identify the causes of geographic variation in colour morph frequencies in the Australian tawny dragon lizard, Ctenophorus decresii.ResultsPopulations of C. decresii are polymorphic for male throat coloration and all populations surveyed shared the same four morphs but differed in the relative frequencies of morphs. Despite genetic structure among populations, there was no relationship between genetic similarity or geographic proximity and similarity in morph frequencies. However, we detected remarkably strong associations between morph frequencies and two environmental variables (mean annual aridity index and vegetation cover), which together explained approximately 45 % of the total variance in morph frequencies.ConclusionsSpatial variation in selection appears to play an important role in shaping morph frequency patterns in C. decresii. Selection associated with differences in local environmental conditions, combined with relatively low levels of gene flow, is expected to favour population divergence in morph composition, but may be counteracted by negative frequency-dependent selection favouring rare morphs.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-015-0442-x) contains supplementary material, which is available to authorized users.

Patterns and causes of geographic variation in bat echolocation pulses

Evolutionary biologists have a long-standing interest in how acoustic signals in animals vary geographically, because divergent ecology and sensory perception play an important role in speciation. Geographic comparisons are valuable in determining the factors that influence divergence of acoustic signals. Bats are social mammals and they depend mainly on echolocation pulses to locate prey, to navigate and to communicate. Mounting evidence shows that geographic variation of bat echolocation pulses is common, with a mean 5-10 kHz differences in peak frequency, and a high level of individual variation may be nested in this geographical variation. However, understanding the geographic variation of echolocation pulses in bats is very difficult, because of differences in sample and statistical analysis techniques as well as the variety of factors shaping the vocal geographic evolution. Geographic differences in echolocation pulses of bats generally lack latitudinal, longitudinal and elevational patterns, and little is known about vocal dialects. Evidence is accumulating to support the fact that geographic variation in echolocation pulses of bats may be caused by genetic drift, cultural drift, ecological selection, sexual selection and social selection. Future studies could relate geographic differences in echolocation pulses to social adaptation, vocal learning strategies and patterns of dispersal. In addition, new statistical techniques and acoustic playback experiments may help to illustrate the causes and consequences of the geographic evolution of echolocation pulse in bats.

Geographical variation in echolocation vocalizations of the Himalayan leaf‐nosed bat: contribution of morphological variation and cultural drift

Ecologists and evolutionary biologists have a long‐standing interest in the patterns and causes of geographical variation in animals’ acoustic signals. Nonetheless, the processes driving acoustic divergence are still poorly understood. Here, we studied the geographical variation in echolocation vocalizations (commonly referred to as echolocation ‘pulses’ given their short duration and relatively stereotypic nature, and to contrast them from the communicative vocalizations or ‘calls’) of a widespread bat species Hipposideros armiger in south China, and assessed whether the acoustic divergence was driven by either ecological selection, or cultural or genetic drift. Our results revealed that the peak frequency of echolocation pulses varied significantly across populations sampled, with the maximum variation of about 6 kHz. The peak frequency clustered into three groups: eastern and western China, Hainan and southern Yunnan. The population differences in echolocation pulses were not significantly related to the variation in climatic (mean annual temperature, mean annual relative humidity, and mean annual precipitable water) or genetic (genetic distance) factors, but significantly related to morphological (forearm length) variation which was correlated with mean annual temperature. Moreover, the acoustic differences were significantly correlated with geographical and latitudinal distance after controlling for ‘morphological distance’. Thus, neither direct ecological selection nor genetic drift contributed to the acoustic divergence observed in H. armiger. Instead, we propose that the action of both indirect ecological selection (i.e. selection on body size) as well as cultural drift promote, in part, divergence in echolocation vocalizations of individuals within geographically distributed populations.

Changes in Geographic Variation in the Use of Percutaneous Coronary Intervention for Stable Ischemic Heart Disease After Publication of the Clinical Outcomes Utilizing Revascularization and Aggressive Drug Evaluation (COURAGE) Trial

Clinical uncertainty is cited as a cause of geographic variation. However, little is known about the effect of comparative effectiveness research on variation. We examined whether geographic variation in the use of percutaneous coronary intervention (PCI) for stable ischemic heart disease (SIHD) declined after publication of the Clinical Outcomes Utilizing Revascularization and Aggressive Drug Evaluation (COURAGE) trial. We examined changes in utilization and geographic variation in 67 hospital referral regions using the State Inpatient Databases. We compared age- and sex-adjusted rates of PCI for SIHD before (2006) and after (2008) publication of the COURAGE trial and compared those with contemporaneous changes in PCI volume for acute coronary syndrome. A total of 272,659 PCIs for SIHD from 526 hospitals were included in the analysis. After the publication of the COURAGE trial, PCI volume for SIHD declined by 25% (P<0.001) and decreased by 12% for acute coronary syndrome (P<0.001). This was predominantly attributable to changes in hospital referral regions with the highest levels of utilization pre-COURAGE trial (35% decline in the highest tertile versus 18% in the lowest). As measured by the systematic component of variation, there was substantial geographic variation in the use of PCI for SIHD preceding the publication of the COURAGE trial. Variation declined by 28% (0.53 versus 0.40) after publication, but geographic variation remained higher for SIHD than acute coronary syndrome (0.40 versus 0.17). There was a substantial decline in the use of and geographic variation in PCI for SIHD after the publication of the COURAGE trial. However, geographic variation in the use of PCI for SIHD remained high.

When directional selection reduces geographic variation in traits mediating species interactions.

Although we often focus on the causes of geographic variation, understanding processes that act to reduce geographic variation is also important. Here, we consider a process whereby adaptive foraging across the landscape and directional selection exerted by a conifer seed predator, the common crossbill (Loxia curvirostra), potentially act to homogenize geographic variation in the defensive traits of its prey. We measured seed predation and phenotypic selection exerted by crossbills on black pine (Pinus nigra) at two sites in the Pindos Mountains, Greece. Seed predation by crossbills was over an order of magnitude higher at the site where cone scale thickness was significantly thinner, which was also the cone trait that was the target of selection at the high predation site. Additional comparisons of selection differentials demonstrate that crossbills exert selection on black pine that is consistent in form across space and time, and increases in strength with increasing seed predation. If predators distribute themselves in relation to the defensive traits of their prey and the strength of selection predators exert is proportional to the amount of predation, then predators may act to homogenize trait variation among populations of their prey in a process analogous to coevolutionary alternation with escalation.

Relatedness does not explain geographic variation in queen cooperation in the seed-harvester ant Messor pergandei

The desert seed-harvester ant Messor pergandei shows sharp regional differences in social structure: in central Arizona, queens initially form group nests but become aggressive following worker emergence and reduce to a single queen (secondary monogyny). In much of the rest of the species range, however, co-founding queens do not display aggression and retain multiple queens throughout the colony lifecycle (primary polygyny). One hypothesis to explain why queen behavior differs between regions is that relatedness among co-foundresses and, therefore, the potential for kin-selected cooperation, varies geographically. To test whether primary polygyny is associated with greater kin association, we used highly polymorphic microsatellites to estimate within-group relatedness for co-foundress associations in the field at two secondarily monogynous sites and five primarily polygynous sites. To determine whether queens can potentially use nestmate identity as a proxy for genetic relatedness, we compared these values to similarly sized samples of worker nestmates from adult colonies at the same sites. We found that foundresses do not preferentially form groups with relatives regardless of the ultimate fate of foundress groups. Mean relatedness values for co-foundresses did not differ significantly from zero irrespective of social structure. In contrast, adult colony worker nestmates were significantly positively related at all sites. These results indicate that kin-selected benefits are not likely to be responsible for the absence of fatal competition in the polygynous region; instead, the cause of geographic variation in queen cooperation must lie in ecological factors that alter the costs and benefits of retaining additional queens into colony maturity.

A postcode lottery for cardiac rhythm management?

British Journal of Cardiac NursingVol. 7, No. 3 CommentA postcode lottery for cardiac rhythm management?Andrew J Turley, Nicholas J LinkerAndrew J TurleySearch for more papers by this author, Nicholas J LinkerSearch for more papers by this authorAndrew J Turley; Nicholas J LinkerPublished Online:27 Sep 2013https://doi.org/10.12968/bjca.2012.7.3.132AboutSectionsView articleView Full TextPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareShare onFacebookTwitterLinked InEmail View article References Boriani G, Berti E, Biffi M et al. (2010) Implantable electrical devices for prevention of sudden cardiac death: data on implant rates from a ‘real world’ regional registry. Europace 12: 1224–1224 Crossref, Google ScholarCunningham D, Charles R, Cunningham M, de Lange A for HRUK Audit Group (2011) Cardiac Rhythm Management: UK National Clinical Audit 2010. http://www.devicesurvey.com (accessed 23February 2012) Google ScholarCunnington MS, Plummer CJ, McDiarmid AK, McComb JM (2008) The patient journey from symptom onset to pacemaker implantation. QJM 101: 955–955 Crossref, Google ScholarCunnington MS, Plummer CJ, McComb JM (2009) Delays and adverse clinical outcomes associated with unrecognized pacing indications. QJM 102: 485–485 Crossref, Google ScholarCunnington MS, Plummer CJ, McComb JM (2010) A survey of investigations performed prior to permanent pacemaker implantation. Age Ageing 39: 135–135 Crossref, Google ScholarDickstein K, Vardas PE, Auricchio A et al. (2010) 2010 Focused Update of ESC Guidelines on device therapy in heart failure: an update of the 2008 ESC Guidelines for the diagnosis and treatment of acute and chronic heart failure and the 2007 ESC guidelines for cardiac and resynchronization therapy. Developed with the special contribution of the Heart Failure Association and the European Heart Rhythm Association. Eur Heart J 31: 2677–87 Crossref, Google ScholarEpstein AE, DiMarco JP, Ellenbogen KA et al. (2008) ACC/AHA/HRS 2008 Guidelines for Device-Based Therapy of Cardiac Rhythm Abnormalities: A Report of the American College of Cardiology/ American Heart Association Task Force on Practice Guidelines (Writing Committee to Revise the ACC/AHA/NASPE 2002 Guideline Update for Implantation of Cardiac Pacemakers and Antiarrhythmia Devices) Developed in Collaboration With the American Association for Thoracic Surgery and Society of Thoracic Surgeons. J Am Coll Cardiol 51: e1–e62 Crossref, Google ScholarFerreira AM, Adragão P, Cavaco DM et al. (2008) Benefit of cardiac resynchronization therapy in atrial fibrillation patients vs. patients in sinus rhythm: the role of atrioventricular junction ablation. Europace 10: 809–809 Crossref, Google ScholarMcComb JM, Plummer CJ, Cunningham MW, Cunningham D (2009) Inequity of access to implantable cardioverter defibrillator therapy in England: possible causes of geographical variation in implantation rates. Europace 11: 1308–1308 Crossref, Google ScholarNational Institute for Health and Clinical Excellence (2006) Implantable Cardioverter Defibrillators for Arrhythmias [Technology appraisal 95] http://publications.nice.org.uk/implantable-cardioverter-defibrillators-for-arrhythmias-ta95. Google ScholarNational Institute for Health and Clinical Excellence (2007) Cardiac Resynchronization Therapy for the Treatment of Heart Failure [Technology appraisal 120] from http://publications.nice.org.uk/cardiac-resynchronization-therapy-for-the-treatment-of-heart-failure-ta120 Google ScholarScott PA, Turner NG, Chungh A, Morgan JM, Roberts PR (2009) Varying implantable cardio-verter defibrillator referral patterns from implanting and non-implanting hospitals. Europace 11: 1048–1048 Crossref, Google Scholar FiguresReferencesRelatedDetails 1 March 2012Volume 7Issue 3ISSN (online): 2052-2207 Metrics History Published online 27 September 2013 Published in print 1 March 2012 Information© MA Healthcare LimitedPDF download

Phenotypic Plasticity of Body Size in an Insular Population of a Snake

Difference in growth pattern is one of the proximate causes of geographic variation in body size. Such a difference in growth pattern could be explained by two extremes such as genetically determined outcome and phenotypic plasticity or by a combination of these. The Japanese four-lined snake (Elaphe quadrivirgata) on Yakushima Island, Japan, has small body size compared with snakes on the main islands. To examine whether the dwarfism of Yakushima snakes is a consequence of genetic modification or a direct phenotypic response to immediate environmental conditions, E. quadrivirgata from Yakushima and a main island (Shiga Prefecture in Honshu Island), were reared from hatching in a laboratory environment. Data of field surveys were used to examine feeding habits and growth in the wild. Free-ranging snakes on Yakushima had significantly smaller body size and lower growth rate than those in Shiga. Yakushima snakes consumed almost exclusively lizards, whereas frogs were the main prey for Shiga snakes. The proportion of snakes that contained food in their stomach was lower in Yakushima than in Shiga. Available information suggests that the dwarfism of Yakushima snakes cannot be explained by lower survivorship. At hatching, Yakushima snakes of both sexes were larger than Shiga snakes. However, Yakushima and Shiga snakes reached similar body size after approximately 1 year. Captive-reared snakes from the insular dwarf population can reach comparable size to those from the main island, indicating that the growth rate, and hence body size, of E. quadrivirgata is obviously highly plastic. Based on these results, I consider that the dwarfism of Yakushima snakes is attributable to a direct phenotypic response, presumably to food limitation, rather than to microevolutionary changes.

Explaining disparities in species richness between Mediterranean floristic regions: a case study inGladiolus(Iridaceae)

Aim The causes of geographical variation in species richness in clades that do not follow the latitudinal diversity gradient have rarely been investigated. Here, we examine spatial asymmetries of diversity in Gladiolus (Iridaceae), a large genus (> 260 species) that is present in two mediterranean climate biomes: the Cape of southern Africa (106 species) and the Mediterranean Basin (7 species). Despite convergence of climatic conditions between the two regions, the species density of Gladiolus is over one order of magnitude higher in the Cape than in the Mediterranean Basin. We investigate whether the diversity disparities observed in the genus are better explained by recent colonization of species-poor areas (temporal hypothesis) or by differential rates of diversification (evolutionary hypothesis). Location Africa, Madagascar and Eurasia Methods We employ a recently developed Bayesian method for the estimation of diversification rates and a biogeographical optimization approach within a phylogenetic framework. Results In Gladiolus, the ‘diversity anomaly’ between the two Mediterranean climate regions cannot be explained solely by the time available for speciation in the Cape, but is also due to locally reduced rates of diversification in the Mediterranean Basin. Furthermore, high overall diversity in southern Africa stems from an ancient origin in the Cape allied with high rates of diversification in the summer-rainfall region of the subcontinent. Main conclusions Both evolutionary and temporal hypotheses must be taken into account in order to explain the diversity anomaly between the Mediterranean Basin and the Cape. Our results suggest that regions at comparable latitudes and/or with similar climate may not converge in diversity levels due to heterogeneity of diversification rates and contrasting biogeographical histories.

Regional Variation in the Use of Implantable Cardioverter-Defibrillators for Primary Prevention

Although the use of implantable cardioverter-defibrillators (ICDs) for the primary prevention of sudden cardiac death varies by sex, race, and hospital, geographic variation in ICD use remains unexplored. Our objective was to quantify regional variations in the utilization of primary prevention ICDs in the United States, and to evaluate if an association exists between utilization and physician supply or the proportion of patients meeting the trial inclusion criteria. This is a cross-sectional analysis among the Medicare, fee-for-service population from the National Cardiovascular Data Registry. Using hospital referral regions, we calculated the age-, sex-, and race-adjusted rates of ICD placement for each region and assessed the correlation between these rates and (1) physician supply and (2) the proportion of patients meeting trial inclusion criteria. Substantial variation was found across quintiles of rate ratios of ICD implantation, ranging from 0.39 to 1.77 (compared with a national mean rate of 1.0). This ratio was not correlated with the supply of cardiologists (R(2)=0.01), electrophysiologists (R(2)=0.01), or with the proportion of patients meeting trial inclusion criteria (R(2)<0.01). Over all, 13% of all patients receiving ICDs did not meet trial criteria. Marked geographic variation in the use of primary prevention ICDs exists across the United States that is not correlated with physician supply. Although >1 in 10 patients received ICDs outside of trial criteria, this potential overuse did not explain the variation. Future studies should consider underuse or misuse of primary prevention ICDs as causes of geographic variation.

Inequity of access to implantable cardioverter defibrillator therapy in England: possible causes of geographical variation in implantation rates

There is marked geographical variation in implantable cardioverter defibrillator (ICD) implantation rates in England. This study examined factors which might explain this variation. Detailed data relating to 1510 patients who received an implanted defibrillator and who were reported to a national pacemaker and implantable defibrillator registry in 2002 were examined and correlated with factors which have been suggested as affecting ICD implantation. None of the factors examined, which included factors related both to the need for ICD implantation and service provision, in addition to socio-economic deprivation, was found to correlate with regional ICD implantation rates. There appears to have been no systematic planning of ICD services. Whether this has led to the marked regional variation and in inequity of service provision is not clear.