Host plant quality, spatial heterogeneity, and the stability of mite predator–prey dynamics

Population dynamics models suggest that both the over-all level of resource productivity and spatial variability in productivity can play important roles in community dynamics. Higher productivity environments are predicted to destabilize consumer–resource dynamics. Conversely, greater heterogeneity in resource productivity is expected to contribute to stability. Yet the importance of these two factors for the dynamics of arthropod communities has been largely overlooked. I manipulated nutrient availability for strawberry plants in a multi-patch experiment, and measured effects of overall plant quality and heterogeneity in plant quality on the stability of interactions between the phytophagous mite Tetranychus urticae and its predator Phytoseiulus persimilis. Plant size, leaf N content and T. urticae population growth increased monotonically with increasing soil nitrogen availability. This gradient in plant quality affected two correlates of mite population stability, population variability over time (i.e., coefficient of variation) and population persistence (i.e., proportion of plant patches colonized). However, the highest level of plant quality did not produce the least stable dynamics, which is inconsistent with the “paradox of enrichment”. Heterogeneity in plant productivity had modest effects on stability, with the only significant difference being less variable T. urticae densities in the heterogeneous compared to the corresponding homogeneous treatment. These results are generally congruent with metapopulation theory and other models for spatially segregated populations, which predict that stability should be governed largely by relative movement rates of predators and prey—rather than patch quality

Clinical evaluation of eight different D-dimer tests for the exclusion of deep venous thrombosis in primary care patients

D-dimer tests are an essential element in the diagnostic work-up of deep venous thrombosis (DVT). However, the poor standardization amongst assays necessitates clinical validation before implementation in daily practice. We therefore evaluated the analytical and diagnostic performance of eight D-dimer tests in a representative group of 290 prospectively identified consecutive primary care patients with suspected DVT. Seven quantitative D-dimer assays, and a qualitative test, Simplify, were evaluated. Correlation between assays was generally poor and several assays showed a significant bias in the method comparison. Nevertheless, the Vidas D-dimer, Innovance D-dimer (CA1500 and BCS), Pathfast D-dimer, and HemosIL HS500 (ACL TOP), all displayed 100% (95% CI: 85-100%) sensitivity. Tina-quant (Modular), AQT90 D-dimer, and Liatest (STA®) D-dimer tests showed a slightly lower sensitivity of 95% (78-100%). and the Simplify test reached a sensitivity of 91% (72-99%) that was further improved in combination with a clinical decision rule to 95% (76-100%). In concert with the low (8.2%) prevalence of proximal DVT, diagnosed by compression ultrasonography, in our study, all test reached a negative predictive value (NPV) of at least 99%. The user friendliness of the assays differed mainly by stability of reagents, calibration frequency, time required to obtain a test result and costs of a test. In conclusion, despite considerable analytical differences, in our low-risk population all tests evaluated displayed an excellent NPV. In combination with a validated clinical decision rule to identify low-risk patients, even a straightforward POC solution could safely and cost-efficiently rule out DVT