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PubMed2007

Larval feeding induced defensive responses in tobacco: comparison of two sibling species of Helicoverpa with different diet breadths.

Plants respond differently to damage by different herbivorous insects. We speculated that sibling herbivorous species with different host ranges might also influence plant responses differently. Such differences may be associated with the diet breadth (specialization) of herbivores within a feeding guild, and the specialist may cause less intensive plant responses than the generalist. The tobacco Nicotinana tabacum L. is the common host plant of a generalist Helicoverpa armigera (Hübner) and a specialist H. assulta Guenée (Lepidoptera, Noctuidae). The induced responses of tobacco to feeding of these two noctuid herbivores and mechanical wounding were compared. The results showed that the feeding of the specialist H. assulta and the generalist H. armigera resulted in the same inducible defensive system, but response intensity of plants was different to these two species. Inductions of jasmonic acid (JA), lipoxygenase (LOX), and proteinase inhibitors (PIs) were not significantly different concerning these two species, but H. assulta caused the less intensive foliar polyphenol oxidase (PPO) increase, more intensive nicotine and peroxidase (POD) increases in tobacco than H. armigera. The defensive response of plant to herbivores with different diet breadth seems to be more complicated than we expected, and the specialist does not necessarily cause less intensive plant responses than the generalist.

Animals↗
PubMed2003

Local species immigration, extinction, and turnover of butterflies in relation to habitat area and habitat isolation.

Temporal dynamics of insect communities in terrestrial habitat fragments have been rarely studied. Here it was tested whether immigration, extinction, and turnover of butterfly species change with area and isolation of 31 calcareous grasslands. The area ranged from 0.03 to 5.14 ha, the isolation index from 2,100 to 86,000 (edge-to-edge distance 55-1,894 m). In both study years (1996, 2000), the total number of individuals (16,466, 15,101) and species (60, 54) sampled across all sites were similar and number of species increased with area in both years indicating an equilibrium. Rates of extinction (38% for habitat specialists vs. 20% for generalists) and turnover (51% vs. 35%) were higher, and rates of immigration (11% vs. 30%) were lower for habitat specialists than for generalists. Extinction and turnover rates decreased with increasing fragment size for both specialist ( n=25 species) and generalist ( n=36) butterflies, but specialists showed a significantly steeper decrease with increasing fragment size than generalists. Immigration rates increased with area. As a result, species number of habitat specialists declined in small habitats but not in large habitats between 1996 and 2000. No significant impact of habitat isolation on the butterfly community was found. The data suggest that large habitat fragments are of special importance for the conservation of the specialized, most endangered butterfly species. Habitat isolation appears to be less important, as butterflies can cope with the habitat mosaic in our study region.

Animals↗
PubMed2006

Asymmetric specialization and extinction risk in plant-flower visitor webs: a matter of morphology or abundance?

A recently discovered feature of plant-flower visitor webs is the asymmetric specialization of the interaction partners: specialized plants interact mainly with generalized flower visitors and specialized flower visitors mainly with generalized plants. Little is known about the factors leading to this asymmetry and their consequences for the extinction risk of species. Previous studies have proposed random interactions proportional to species abundance as an explanation. However, the simulation models used in these studies did not include potential biological constraints. In the present study, we tested the potential role of both morphological constraints and species abundance in promoting asymmetric specialization. We compared actual field data of a Mediterranean plant-flower visitor web with predictions of Monte Carlo simulations including different combinations of the potential factors structuring the web. Our simulations showed that both nectar-holder depth and abundance were able to produce asymmetry; but that the expected degree of asymmetry was stronger if based on both. Both factors can predict the number of interaction partners, but only nectar-holder depth was able to predict the degree of asymmetry of a certain species. What is more, without the size threshold the influence of abundance would disappear over time. Thus, asymmetric specialization seems to be the result of a size threshold and, only among the allowed interactions above this size threshold, a result of random interactions proportional to abundance. The simulations also showed that asymmetric specialization could not be the reason that the extinction risk of specialists and generalists is equalized, as suggested in the literature. In asymmetric webs specialists clearly had higher short-term extinction risks. In fact, primarily generalist visitors seem to profit from asymmetric specialization. In our web, specialists were less abundant than generalists. Therefore, including abundance in the simulation models increased the difference between specialists and generalists even more.

Adaptation, Biological↗
PubMed2003

A correlation between macronutrient balancing and insect host-plant range: evidence from the specialist caterpillar Spodoptera exempta (Walker).

In an earlier study, we showed that the ingestive responses of the generalist caterpillar Spodoptera littoralis to foods imbalanced in their protein:carbohydrate content is similar to generalist locusts, but differs from that of specialist-feeding locusts. Here we further pursued the comparison by repeating the experiments using a closely related specialist caterpillar, Spodoptera exempta. First, caterpillars were allowed to self-compose a diet of preferred protein:carbohydrate balance by mixing between nutritionally complementary foods. Then, they were confined to one of five imbalanced foods, in which we measured the trade-off between over- and under-ingesting the two nutrients. On complementary foods, the caterpillars actively regulated their protein and carbohydrate intake. In the no-choice experiment, those fed excess-protein foods ingested small surpluses of protein compared with generalist feeders, thus showing a pattern of nutrient balancing similar to that observed in specialist locusts. Utilisation data indicated that ingested excesses and deficits were to some extent offset by differential utilisation. Evidence also showed that post-ingestive responses of the specialist S. exempta were less flexible than those observed in the generalist S. littoralis, a pattern which is again in accordance with comparisons of acridids differing in their host-plant range.

Animals↗
PubMed2005

Nutrient-limited food webs with up to three trophic levels: feasibility, stability, assembly rules, and effects of nutrient enrichment.

Community structure is controlled, among multiple factors, by competition and predation. Using the R* rule and graphical analysis, we analyse here the feasibility, stability and assembly rules of resource-based food webs with up to three trophic levels. In particular, we show that (1) the stability of a food web with two plants and two generalist herbivores does not require that plants' resource exploitation abilities trade-off with resistance to the two herbivores, and (2) food webs with two plants and either one generalist herbivore and a carnivore or two generalist herbivores and two generalist carnivores are not feasible because of cascade competition between top consumers. The relative strength of species interactions and the relative impacts of plants and herbivores on factors which control their growth also play a critical role. We discuss how community structure constrains assembly rules and yields cascades of extinctions in food webs.

Animals↗
PubMed1998

Do physicians modify their prehospital management of patients in response to a public campaign on chest pain?

The goals of this study were to analyze the impact of a public campaign on chest pain on physicians involved in the prehospital care of patients with this symptom, in terms of physician delay, rates of immediate hospitalization, and of transportation by ambulance. Prehospital delays and decisions for all 866 patients with chest pain managed by the community and generalist physicians or by emergency physicians, who presented to the emergency department of a teaching hospital during the 12 months of the campaign, were compared with those of all 749 patients with similar presentations during the 12 months before it. When community and generalist physicians were involved, median (110 minutes) physician delay did not decrease during the campaign, whereas it decreased from 65 to 56 minutes (p <0.003) when emergency physicians were involved. Rates of immediate hospitalization (73%) and of transportation by ambulance (47%) of patients managed by community and generalist physicians were unaffected by the campaign, whereas they increased from 96% and 89%, respectively, to 98% (p = 0.09) and 94% (p <0.02) when emergency physicians were involved. Similar observations were made in patients with confirmed acute myocardial infarction and unstable angina and remained highly significant after adjustment for differences in clinical characteristics. Thus, community and generalist physicians did not significantly modify their prehospital management of patients with chest pain despite a public campaign. To be successful, guidelines on the matter have to be developed with the active participation of these physicians.

Aged↗
PubMed1998

Effects of caregiver specialty on cost and clinical outcomes following hospitalization for heart failure.

In 614 consecutive hospitalizations with the primary discharge diagnosis of diagnosis-related group (DRG) 127 (heart failure and shock), we sought to assess the effect of caregiver specialty (generalist, n = 217; cardiologist, n = 397) on hospital costs, length of stay, and in-hospital mortality. Patients treated by cardiologists were younger (68 vs 71 years) and less likely to have hypertension (52% vs 61%), but were more likely to be men (61% vs 44%), require an intensive care stay (13% vs 5%), have coronary artery disease (49% vs 23%), have a left ventricular ejection fraction <40% (74% vs 49%), and have lower systolic (132 vs 146 mm Hg) and diastolic (76 vs 81 mm Hg) blood pressures on admission. Predictors of acute disease severity were similarly distributed between the 2 groups. No difference was found between patients treated by cardiologists versus those treated by generalists with respect to crude or adjusted hospital cost, length of stay, and in-hospital mortality. However, in subsets of patients who required intensive care during hospitalization (n = 64), as well as those who did not (n = 550), care by cardiologists was associated with a lower adjusted hospital cost. Any potential cost savings that could have accrued from care by cardiologists was, however, negated by the higher proportion of patients treated by cardiologists who required intensive care during hospitalization. We conclude that when differences in clinical variables are adjusted, care by cardiologists versus generalists is associated with similar or lower hospital cost for patients with DRG 127. Our findings challenge the notion that in-patient care provided by specialists is more expensive than that provided by generalists.

Adult↗
PubMed2001

The effect of a hospitalist service with nurse discharge planner on patient care in an academic teaching hospital.

PURPOSE: To evaluate the impact of implementing a hospitalist service with a nurse discharge planner in an academic teaching hospital. SUBJECTS AND METHODS: Inpatient medicine service was provided by hospitalists, general internists, and specialists. Service personnel were identical except that the hospitalist service also had a nurse discharge planner. Hospitalists attended 4 months per year (compared with the 1 month by most other attending physicians) and had no outpatient responsibilities during the ward months. Patients were admitted alternately based on resident call schedule. Major outcomes included average costs of hospitalization, length of stay, and resource utilization. Quality measures included inpatient mortality, 30-day readmission rates, and satisfaction of patients, residents and students. RESULTS: Hospitalist-attended services had lower mean (+/- SD) inpatient costs per patient ($4289 +/- $6512) compared with specialist-staffed services ($6066 +/- $7550, P < 0.0001), with a trend toward lower costs when compared with generalist-attended services ($4850 +/- $7027, P = 0.11). Hospitalist services had shorter mean lengths of stay (4.4 +/- 4.0 days), compared with generalists (5.2 +/- 5.2 days) and specialists (6.0 +/- 5.5 days, P < 0.0001 for hospitalists vs. both groups). Readmission rates were similar in all groups. Mortality rates were higher in the specialist group [5.0% (44 of 874)] compared with hospitalists [2.2% (18 of 829)] and generalists [2.6% (20 of 761), P = 0.002 for specialists vs. both groups, P = 0.09 for generalists vs hospitalists]. Satisfaction results were uniformly high in all groups, with no significant differences. CONCLUSION: Hospitalist services with a nurse discharge planner were associated with lower average cost and shorter average length of hospital stay, without any apparent compromise in clinical outcomes or patient satisfaction.

Adult↗
PubMed1996

Preserving the patient referral process in the managed care environment.

Referrals are a central component of the American health care system, defining the relationship among generalists, patients, and specialists. The dynamics of the referral process as they existed in a fee-for-service medical environment will evolve under managed care, but retain the basic "Try-out" approach of the generalist and "Rule-out" approach of the specialist. A managed care, contract-based health care system alters some of the assumptions on which the referral relationship has been structured. A four-step approach to assuring quality interactions among patient, generalist, and specialist within the managed care environment is described, including: (1) engage; (2) anticipate; (3) feedback; and (4) reassess. When the referral process is structured as suggested, it can be evaluated for quality and efficacy. Armed with mutual respect and understanding, the forces that polarized specialist and generalist care in the 1980s can be redirected to enhancing patient care in the 1990s.

Communication↗
PubMed1997

Who should teach medical students surgery?

BACKGROUND: Medical schools are undergoing major curricular reform, partly in attempts to increase the number of graduates pursuing careers in the generalist disciplines. These reforms have often resulted in a shortening of the surgery clerkship, decreasing students' experiences in several domains important to the generalist. METHODS: A seven-question survey of clerkship directors of US medical schools was administered to measure the magnitude of curriculum change during the past 5 years affecting the surgery and family practice clerkships. The survey also addressed attitudes about the purpose of the surgery clerkship. RESULTS: There was an 80% (103 of 129) response rate. Between 1989 and 1994, surgery clerkships decreased on average from 11 to 10.2 weeks (P <0.05) while family practice clerkships increased from 4.2 to 6.8 weeks (P <0.05). Ninety-one percent of clerkship directors felt the primary goal of the clerkship should be to train generalists. CONCLUSIONS: The length of the surgery clerkship has decreased at several institutions. In order to ensure an appropriate educational experience for medical students, surgeons must participate actively in curriculum reform within medical schools and highlight their unique role in training generalists.

Clinical Clerkship↗
PubMed1988

Maturation of the immune response: a computational model.

Experimental studies of the effect on antibody affinity of antigen dose and time after immunization show that average affinity increases progressively with time after immunization, and that this increase is greater at lower doses of antigen. In this paper we describe a polyclonal computer model of the immune system that yields all the essential phenomena of affinity maturation, including dose-dependency. Our main findings are (1) the dose-dependency relationship is not produced when typical assumptions regarding B-cell populations and binding reactions are employed, and (2) it is possible to reproduce this dependency by assuming two classes of lymphocytes: generalists and specialists. Generalists have a low threshold for response and produce antibody of low effectiveness, whereas specialists have a high threshold for response, and produce highly effective antibody. We make an analogy between the generalists and a pioneer species in ecological succession, and suggest how the generalists may contribute to a more effective defense against real infections.

Antibody Affinity↗
PubMed2004

Phytoseiid mites on unsprayed apple trees in Oregon, and other western states (USA): distributions, life-style types and relevance to commercial orchards.

In unsprayed apple trees in eastern Oregon, Galendromus flumenis (Chant), Galendromus occidentalis (Nesbitt), Typhlodromus caudiglans Schuster and Metaseiulus citri (Garman and McGregor) were common phytoseiid mites; common plant-feeding mites were the eriophyid, Aculus schlechtendali Nalepa, the brown mite, Bryobia rubrioculus (Scheuten) and Eotetranychus spp.; apple rust mites seemed to be the primary prey for phytoseiids; the spider mites, Tetranychus urticae Koch and Panonychus ulmi (Koch) were scarce except for a few local outbreaks; the stigmaeid Zetzellia mali (Ewing) was at 10% of sites and its densities were inversely related to phytoseiid densities; phytoseiids were absent at some sites, particularly at high elevations where winters are severe. In seven Oregon ecoregions, G. flumenis was often at lower elevations in valleys with moderate winters; T. caudiglans was often at higher elevations; G. occidentalis was often at intermediate elevations, in young trees, and near where pesticides were used; it dominated in unsprayed trees only in almost treeless, sage-covered areas; M. citri was usually in older apple trees near agriculture. In mixed phytoseiid populations, M. citri, a generalist, and G. occidentalis, a specialist, occurred more often than expected; G. occidentalis was mostly found with T. caudiglans, a generalist; G. flumenis, a generalist, occurred less with others, possibly because it competes with both specialists and generalists. Analyses of species' distributions with multiple regression and genetic models gave explanatory r2s of 0.019-0.318. Of 29 variables, altitude of site, intensity of agricultural management, tree age, plant types, and Z. mali levels helped explain phytoseiid species presence. In the western USA, G. flumenis dominated in middle-southern latitudes; T. caudiglans dominated in the north near the Canadian border; G. occidentalis dominated in middle latitudes in parts of Washington, Idaho, Montana, and Wyoming; M. citri was at a few sites in these four states. Distributional and independent variable data were used to predict species presence at sites in Oregon with a 70% success rate. We discuss phytoseiid life-style types, community dynamics, presence in organic/conventional orchards, and trends as more selective IPM methods are used in apple orchards.

Animals↗
PubMed2003

Induction of hypericins and hyperforins in Hypericum perforatum in response to damage by herbivores.

Plants respond to herbivore and pathogen attack by a variety of direct and indirect mechanisms that include the induction of secondary metabolites. The phytomedicinal plant Hypericum perforatum L. produces two different classes of secondary metabolites: hyperforins, a family of antimicrobial acylphloroglucinols; and hypericins, a family of phototoxic anthraquinones exhibiting antimicrobial, antiviral, and antiherbivore properties in vitro. To determine whether these compounds are part of the herbivore-specific inducible plant defense system, we used an in vitro detached assay to assess the effects of specialist and generalist herbivore damage on the levels of hypericins and hyperforin. Greenhouse-grown H. perforatum plant sections were challenged with the specialist, Chrysolina quadrigemina, or with one of the following generalist feeders: Spilosoma virginica, Spilosoma congrua, or Spodoptera exigua. Feeding by the specialist beetle or mechanical wounding caused little change in phytochemical levels in plant tissue, whereas the small amount of feeding by the generalists caused 30-100% increases in hypericins and hyperforin as compared to control levels. Although the leaf damage index of the specialist feeding was 2.7 times greater, C. quadrigemina had little effect on H. perforatum chemical defenses in response to feeding damage in comparison to generalist feeding.

Adaptation, Physiological↗
PubMed2002

Single-species models for many-species food webs.

Most species live in species-rich food webs; yet, for a century, most mathematical models for population dynamics have included only one or two species. We ask whether such models are relevant to the real world. Two-species population models of an interacting consumer and resource collapse to one-species dynamics when recruitment to the resource population is unrelated to resource abundance, thereby weakening the coupling between consumer and resource. We predict that, in nature, generalist consumers that feed on many species should similarly show one-species dynamics. We test this prediction using cyclic populations, in which it is easier to infer underlying mechanisms, and which are widespread in nature. Here we show that one-species cycles can be distinguished from consumer resource cycles by their periods. We then analyse a large number of time series from cyclic populations in nature and show that almost all cycling, generalist consumers examined have periods that are consistent with one-species dynamics. Thus generalist consumers indeed behave as if they were one-species populations, and a one-species model is a valid representation for generalist population dynamics in many-species food webs.

Animals↗
PubMed2003

Physician specialization and antiretroviral therapy for HIV.

BACKGROUND: Since the introduction of the first protease inhibitor in January 1996, there has been a dramatic change in the treatment of persons infected with HIV. The changing nature of HIV care has important implications for the types of physicians that can best care for patients with HIV infection. OBJECTIVE: To assess the association of specialty training and experience in the care of HIV disease with the adoption and use of highly active antiretroviral (ARV) therapy (HAART). DESIGN: Observational cohort study of patients under care for HIV infection and their physicians. PATIENTS AND SETTING: This analysis used data collected from a national probability sample of noninstitutionalized persons with HIV infection participating in the HIV Costs and Service Utilization Study and their primary physicians. We analyzed 1,820 patients being cared for by 374 physicians. MEASUREMENTS: Rates of HAART use at 12 months and 18 months after the approval of the first protease inhibitor. RESULTS: Forty percent of the physicians were formally trained in infectious diseases (ID), 38% were general medicine physicians with self-reported expertise in the care of HIV, and 22% were general medicine physicians without self-reported expertise in the care of HIV. The majority of physicians (69%) reported a current HIV caseload of 50 patients or more. In multivariable models controlling for patient characteristics, there were no differences between generalist experts and ID physicians in rates of HAART use in December 1996. When compared to ID physicians, however, patients being treated by non-expert general medicine physicians were less likely to be on HAART (odds ratio [OR], 0.32; 95% confidence interval [95% CI], 0.17 to 0.61). Patients being treated by low-volume physicians were also much less likely to be on HAART therapy than those treated by high-volume physicians (OR, 0.26; 95% CI, 0.14 to 0.48). These findings were attenuated by June 1997, suggesting that over time, the broader physician community successfully adopted HAART therapy. This finding is consistent with prior research on the diffusion of innovations. CONCLUSIONS: Similar proportions of patients treated by expert generalists and ID specialists were on appropriate HAART therapy by December 1996 and July 1997. Patients treated by non-expert generalists, most of whom were the lowest-volume physicians, were much less likely to be on appropriate ARV therapy in the earlier time period. Our findings demonstrate that expert generalists who develop specialized expertise are able to provide care of quality comparable to that of specialists.

Adult↗
PubMed2002

An analysis of oral surgical dental visits by provider type, 1996.

OBJECTIVE: The choice by consumers of the professional from whom they receive specific types of care is influenced by many factors. This study examines the roles that socioeconomic and racial factors play in deciding whether a generalist or oral and maxillofacial surgeon provides routine exodontia care in a community. STUDY DESIGN: The 1996 Medical Expenditure Panel Survey sampled 10,500 households consisting of 21,571 individuals. The combined full-year 1996 response rate of the Medical Expenditure Panel Survey sample through the third round was 70%. An analysis was undertaken of surgical dental services and type of provider for each of several socioeconomic and demographic categories. All estimates and statistics reported were computed, taking into account the complex sampling design of the Medical Expenditure Panel Survey, with the use of the software package SUDAAN. RESULTS: Data analyzed in this study reveal that the majority of oral surgical visits for all patients are to a generalist and not an oral and maxillofacial surgeon. In addition, nonwhite patients, patients from lower-income households, and patients with less education are more likely to receive surgical care from a generalist than from a specialist. On the other hand, white patients, patients from higher-income households, and patients with more education are more likely to receive surgical care from a specialist than from a generalist. CONCLUSIONS: Socioeconomic status and race seem to play a role in whether patients receive oral surgical care from a general dentist or an oral and maxillofacial surgeon.

Adolescent↗
PubMed2004

Diet breadth and its relationship with genetic diversity and differentiation: the case of southern beech aphids (Hemiptera: Aphididae).

Herbivorous insect species with narrow diet breadth are expected to be more prone to genetic differentiation than insect species with a wider diet breadth. However, a generalist can behave as a local specialist if a single host-plant species is locally available, while a specialist can eventually behave as a generalist if its preferred host is not available. These problems can be addressed by comparing closely related species differing in diet breadth with overlapping distributions of insect and host populations. In this work, diet breadth, genetic diversity and population differentiation of congeneric aphid species from southern beech forests in Chile were compared. While at the species level no major differences in genetic diversity were found, a general trend towards higher genetic diversity as diet breadth increased was apparent. The aphid species with wider diet breadth, Neuquenaphis edwardsi (Laing), showed the highest genetic diversity, while the specialist Neuquenaphis staryi Quednau & Remaudière showed the lowest. These differences were less distinct when the comparisons were made in the same locality and over the same host. Comparison of allopatric populations indicates that genetic differentiation was higher for the specialists, Neuquenaphis similis Hille Ris Lambers and N. staryi, than for the generalist N. edwardsi. Over the same host at different locations, genetic differentiation among populations of N. edwardsi was higher than among populations of N. similis. The results support the assumption that specialists should show more pronounced genetic structuring than generalists, although the geographical distribution of host plants may be playing an important role.

Animals↗
PubMed2003

Herbivore responses to plant secondary compounds: a test of phytochemical coevolution theory.

Literature data were collected on the floristic distribution and toxicity of phytochemicals to herbivores and on herbivore specialization in order to test phytochemical coevolution theory. The theory makes four predictions that can be tested with this information. Herbivores can adapt to novel, more toxic chemicals by becoming specialists, or they can become generalists but at the cost of lower feeding success on any particular host. Thus, the first two predictions are as follows: herbivores should do better on chemicals that are present in their normal host, and this pattern should be stronger for specialists than for generalists. The "escape and radiation" aspect of the theory holds that if a plant taxon with a novel defense chemical diversifies, the chemical will become widespread. Eventually, herbivores will adapt to and disarm it. So the third prediction is that more widespread chemicals are less toxic than more narrowly distributed ones. Because generalists should not do as well as specialists on chemicals disarmed by the latter, the fourth prediction is that the third prediction should be more true for generalists than specialists and should depend on presence/absence of the chemical in the normal host. Multiple regressions of toxicity (herbivore mortality and final weight) on three predictor variables (chemical presence/absence in the normal host, specialism, and chemical floristic distribution) and relevant interactions were used to test these predictions. Chemical presence/absence in the normal host, the interaction between this variable and specialism, and chemical floristic distribution had significant effects on both measures of toxicity, supporting the first three predictions of the model. Support for the fourth prediction (a three-way interaction among all predictor variables) was evident for final weight but not mortality, perhaps because growth is more responsive to toxicity differences than survival. In short, the phytochemistry literature provides broad support for the phytochemical coevolution model.

Adaptation, Physiological↗