Robust scaling in ecosystems and the meltdown of patch size distributions before extinction

Ecology Letters (2011) 14: 29–35Robust critical systems are characterized by power laws which occur over a broad range of conditions. Their robust behaviour has been explained by local interactions. While such systems could be widespread in nature, their properties are not well understood. Here, we study three robust critical ecosystem models and a null model that lacks spatial interactions. In all these models, individuals aggregate in patches whose size distributions follow power laws which melt down under increasing external stress. We propose that this power-law decay associated with the connectivity of the system can be used to evaluate the level of stress exerted on the ecosystem. We identify several indicators along the transition to extinction. These indicators give us a relative measure of the distance to extinction, and have therefore potential application to conservation biology, especially for ecosystems with self-organization and critical transitions.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/79378/1/j.1461-0248.2010.01553.x.pd

Regularity Properties and Pathologies of Position-Space Renormalization-Group Transformations

We reconsider the conceptual foundations of the renormalization-group (RG) formalism, and prove some rigorous theorems on the regularity properties and possible pathologies of the RG map. Regarding regularity, we show that the RG map, defined on a suitable space of interactions (= formal Hamiltonians), is always single-valued and Lipschitz continuous on its domain of definition. This rules out a recently proposed scenario for the RG description of first-order phase transitions. On the pathological side, we make rigorous some arguments of Griffiths, Pearce and Israel, and prove in several cases that the renormalized measure is not a Gibbs measure for any reasonable interaction. This means that the RG map is ill-defined, and that the conventional RG description of first-order phase transitions is not universally valid. For decimation or Kadanoff transformations applied to the Ising model in dimension $d \ge 3$, these pathologies occur in a full neighborhood $\{ \beta > \beta_0 ,\, |h| < \epsilon(\beta) \}$ of the low-temperature part of the first-order phase-transition surface. For block-averaging transformations applied to the Ising model in dimension $d \ge 2$, the pathologies occur at low temperatures for arbitrary magnetic-field strength. Pathologies may also occur in the critical region for Ising models in dimension $d \ge 4$. We discuss in detail the distinction between Gibbsian and non-Gibbsian measures, and give a rather complete catalogue of the known examples. Finally, we discuss the heuristic and numerical evidence on RG pathologies in the light of our rigorous theorems.Comment: 273 pages including 14 figures, Postscript, See also ftp.scri.fsu.edu:hep-lat/papers/9210/9210032.ps.

Behind the confession: Relating false confession, interrogative compliance, personality traits, and psychopathy

The present study further supports the established notion that personality traits contribute to the phenomenon of false confessions and compliance in an interrogative setting. Furthermore, the study provides an investigation into the more recent interest in the potential effect of psychopathic traits in this context. A sample of university students (N = 607) completed questionnaires measuring psychopathic traits, interrogative compliance, and the big five personality factors. Of these, only 4.9% (n=30) claimed to have falsely confessed to an academic or criminal offense, with no participant taking the blame for both types of offense. Across measures the big five personality traits were the strongest predictors of compliance. The five personality traits accounted for 17.9 % of the total variance in compliance, with neuroticism being the strongest predictor, followed by openness and agreeableness. Psychopathy accounted for 3.3% of variance, with the lifestyle facet being the only significant predictor. After controlling for the big five personality factors, psychopathy only accounted for a small percentage of interrogative compliance, indicating that interrogators should take into account a person’s personality traits during the interrogation.N/

Cardiorespiratory fitness in outpatients with bipolar disorder versus matched controls: An exploratory study

AbstractBackground Patients with bipolar disorder (BD) are approximately twice as likely to die prematurely due cardiovascular diseases (CVD) than the general population. Cardiorespiratory fitness (CRF) is an important health outcome measure, predictive for CVD and premature mortality. Aims The aim of the current study was to compare the CRF of outpatients with BD versus age-, gender-, and body mass index (BMI)-matched healthy controls (HC). A secondary aim was to assess potential correlates of CRF. Methods All participants underwent a maximal incremental exercise test to measure the maximum oxygen uptake (VO2max, the golden standard assessment of cardiorespiratory fitness), wore a Body Sensewear Armband for 5 subsequent days to assess their physical activity behavior and completed the Positive-and-Negative-Affect-Schedule (PANAS). Results Outpatients with BD (n=20; 47.8±7.6years) had a significantly lower VO2max compared with HC (n=20; 47.8±7.6years) (26.0±7.3 versus 30.4±6.5 ml/min/kg, P=0.047). A higher VO2max was correlated with younger age, higher active energy expenditure, higher PANAS positive and lower PANAS negative affect scores and a lower antipsychotic medication dose. Limitations The limited sample and cross-sectional design preclude definitive conclusions. Conclusions Compared with HC, outpatients with BD have reduced CRF levels of approximately 4.4 ml/min/kg. In the general population such reductions are associated with a 20% increased premature mortality risk. Interventions targeting CRF in BD are required. Although more research is needed, clinicians should consider the utility of objective assessments of CRF for risk stratification in outpatient settings

Endogenous dopa and dopamine responses to dietary salt loading in salt-sensitive rats

We measured daily urinary excretion rates of dopamine and dopa during dietary salt loading and natriuretic responses to exogenous dopamine in Dahl salt-sensitive (DS), Dahl salt-resistant (DR) and Sprague-Dawley rats. Excretion rates of dopa increased approximately sixfold during salt loading in all rat strains. Maximal urinary dopa responses were attained within 1 day of salt loading. Daily excretion rates of dopamine also increased about five- to sixfold in DS and DR rats and about twofold in Sprague-Dawley rats, with maximal dopamine responses attained by day 5. Dopamine infusion (3 μg/kg per min) increased urinary sodium excretion by 406 ± 132% (mean ± s.e.m.) in Sprague-Dawley rats but only 267 ± 131% and 147 ± 80% in DS and DR rats (P \u3c 0.05 for Sprague-Dawley versus Dahl rats). The results demonstrate that salt loading markedly and rapidly increases dopa excretion in rats. Considering values for dopamine excretion in other rat strains, the results suggest that Dahl rats have increased formation of dopamine for a given amount of dopa delivery to the kidney and that this abnormality is unrelated to salt-sensitive hypertension in DS rats. The results also provide in vivo support for the view that the responsiveness of renai dopamine receptors mediating natriuresis is related to production of endogenous dopamine in the kidney. © Current Science Ltd

Dual roles for cholesterol in mammalian cells

The structural features of sterols required to support mammalian cell growth have not been fully defined. Here, we use mutant CHO cells that synthesize only small amounts of cholesterol to test the capacity of various sterols to support growth. Sterols with minor modifications of the side chain (e.g., campesterol, β-sitosterol, and desmosterol) supported long-term growth of mutant cells, but sterols with more complex modifications of the side chain, the sterol nucleus, or the 3-hydroxy group did not. After 60 days in culture, the exogenous sterol comprised >90% of cellular sterols. Inactivation of residual endogenous synthesis with the squalene epoxidase inhibitor NB-598 prevented growth in β-sitosterol and greatly reduced growth in campesterol. Growth of cells cultured in β-sitosterol and NB-598 was restored by adding small amounts of cholesterol to the medium. Surprisingly, enantiomeric cholesterol also supported cell growth, even in the presence of NB-598. Thus, sterols fulfill two roles in mammalian cells: (i) a bulk membrane requirement in which phytosterols can substitute for cholesterol and (ii) other processes that specifically require small amounts of cholesterol but are not enantioselective