Plankton lattices and the role of chaos in plankton patchiness

Spatiotemporal and interspecies irregularities in planktonic populations have been widely observed. Much research into the drivers of such plankton patches has been initiated over the past few decades but only recently have the dynamics of the interacting patches themselves been considered. We take a coupled lattice approach to model continuous-in-time plankton patch dynamics, as opposed to the more common continuum type reaction-diffusion-advection model, because it potentially offers a broader scope of application and numerical study with relative ease. We show that nonsynchronous plankton patch dynamics (the discrete analog of spatiotemporal irregularity) arise quite naturally for patches whose underlying dynamics are chaotic. However, we also observe that for parameters in a neighborhood of the chaotic regime, smooth generalized synchronization of nonidentical patches is more readily supported which reduces the incidence of distinct patchiness. We demonstrate that simply associating the coupling strength with measurements of (effective) turbulent diffusivity results in a realistic critical length of the order of 100 km, above which one would expect to observe unsynchronized behavior. It is likely that this estimate of critical length may be reduced by a more exact interpretation of coupling in turbulent flows

Functionally reversible impacts of disturbances on lake food webs linked to spatial and seasonal dependencies

Increasing human impact on the environment is causing drastic changes in disturbance regimes and how they prevail over time. Of increasing relevance is to further our understanding on biological responses to pulse disturbances (short duration) and how they interact with other ongoing press disturbances (constantly present). Because the temporal and spatial contexts of single experiments often limit our ability to generalize results across space and time, we conducted a modularized mesocosm experiment replicated in space (five lakes along a latitudinal gradient in Scandinavia) and time (two seasons, spring and summer) to generate general predictions on how the functioning and composition of multitrophic plankton communities (zoo-, phyto- and bacterioplankton) respond to pulse disturbances acting either in isolation or combined with press disturbances. As pulse disturbance, we used short-term changes in fish presence, and as press disturbance, we addressed the ongoing reduction in light availability caused by increased cloudiness and lake browning in many boreal and subarctic lakes. First, our results show that the top-down pulse disturbance had the strongest effects on both functioning and composition of the three trophic levels across sites and seasons, with signs for interactive impacts with the bottom-up press disturbance on phytoplankton communities. Second, community composition responses to disturbances were highly divergent between lakes and seasons: temporal accumulated community turnover of the same trophic level either increased (destabilization) or decreased (stabilization) in response to the disturbances compared to control conditions. Third, we found functional recovery from the pulse disturbances to be frequent at the end of most experiments. In a broader context, these results demonstrate that top-down, pulse disturbances, either alone or with additional constant stress upon primary producers caused by bottom-up disturbances, can induce profound but often functionally reversible changes across multiple trophic levels, which are strongly linked to spatial and temporal context dependencies. Furthermore, the identified dichotomy of disturbance effects on the turnover in community composition demonstrates the potential of disturbances to either stabilize or destabilize biodiversity patterns over time across a wide range of environmental conditions

Resource heterogeneity and community structure: A case study in Heliconia imbricata Phytotelmata

Complex or non-additive differences in the distribution and abundance of arthropod species inhabiting the water-filled bracts of Heliconia imbricata can be created by simple manipulations of resource levels. The primary resources for these assemblages are the corollas of the flowers that accumulate in the bracts. Removing or adding corollas to individual bracts changes the pattern in the abundance of arthropod species within each bract such that bracts with different treatments ultimately differ in composition and numerical associations among species. These results suggest that direct and indirect resource-mediated factors can structure or significantly affect the distribution and abundance of species in these and perhaps other assemblages. Thus, in natural communities, if resources are heterogeneous among patches (such as among the bracts in this study) structure in a given patch may be a function of the resource level of that patch and can differ significantly from neighboring patches that provide different resource levels.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47788/1/442_2004_Article_BF00665591.pd

Predictor of exertional hypoxemia: Dlco Vs. Dlco/va. a retrospective study.

Introduction: Diffusion capacity for carbon monoxide (DLCO) is used to measure the transfer of gas across alveolo-capillary membrane of the lung. It is unknown if this is the best test to predict hypoxemia as it does not account for alveolar volume. As such, the DLCO to VA ratio has been used to account for alveolar volume, which has been thought to be a more useful predictor of hypoxemia. However, prior studies looked only at certain subgroups of patients and often looked at tests that were separated by a fair bit of time. We investigated which test (the DLCO or the DLCO/VA) best predicts hypoxemia during exercise test (6-min walk or O2 dosing tests) done in patients with a variety of pulmonary disorders. Methods: We reviewed our pulmonary function tests (PFTs) database to identify patients that had PFTs and exercise test done on the same day. We evaluated diffusion capacity based on percent predicted of normal diffusion capacity. Hypoxemia was scored as present if the lowest oxygen saturation during exercise was ≤88%. Logistic regression was used to assess the predictive ability of both the DLCO and the DLCO/VA. We compared these predictors using the area under the curve of the ROC curve. The 2 AUCs were compared statistically using the nonparametric approach of DeLong. We then picked an optimal cutoff using Youden\u27s index so that the test characteristics of this cutoff could be evaluated. Results: Between March, 2013 and September, 2015, 1028 patients were identified that had both PFTs and exercise test on the same day. The DLCO and DLCOVA had an ROC AUC of 0.76 and 0.69 respectively, which were significantly different (p\u3c0.0001. Figure). To further investigate the predictive ability of DLCO vs DLCO/VA, we looked at the AUC for subsets of patients with the following diagnoses: COPD, CHF, ILD, Sleep apnea, and Pulmonary Hypertension. In all these subgroups, DLCO had a statistically significantly higher AUC than DLVA. Based on the optimal cutoff point for DLCO (45% predicted), and the DLVA (70 % of predicted), sensitivity (58.5% vs. 52%), specificity (83% vs. 80%), positive predictive value (64% vs. 58%) and negative predictive value (79.5% vs. 75.7%) were higher for DLCO as opposed to DLCO/VA, respectively. [Graph Presented]. Conclusion: Both DLCO and DLCO/VA can be used to identify patients at risk for exertional hypoxemia, but the DLCO is a better predictive test than DLCO/VA

Predictor of exertional hypoxemia: Dlco Vs. Dlco/va. a retrospective study.

Diffusion capacity for carbon monoxide (DLCO) is used to measure the transfer of gas across alveolo-capillary membrane of the lung. It is unknown if this is the best test to predict hypoxemia as it does not account for alveolar volume. As such, the DLCO to VA ratio has been used to account for alveolar volume, which has been thought to be a more useful predictor of hypoxemia. However, prior studies looked only at certain subgroups of patients and often looked at tests that were separated by a fair bit of time. We investigated which test (the DLCO or the DLCO/VA) best predicts hypoxemia during exercise test (6-min walk or O2 dosing tests) done in patients with a variety of pulmonary disorders. Methods: We reviewed our pulmonary function tests (PFTs) database to identify patients that had PFTs and exercise test done on the same day. We evaluated diffusion capacity based on percent predicted of normal diffusion capacity. Hypoxemia was scored as present if the lowest oxygen saturation during exercise was ≤88%. Logistic regression was used to assess the predictive ability of both the DLCO and the DLCO/VA. We compared these predictors using the area under the curve of the ROC curve. The 2 AUCs were compared statistically using the nonparametric approach of DeLong. We then picked an optimal cutoff using Youden\u27s index so that the test characteristics of this cutoff could be evaluated. Results: Between March, 2013 and September, 2015, 1028 patients were identified that had both PFTs and exercise test on the same day. The DLCO and DLCOVA had an ROC AUC of 0.76 and 0.69 respectively, which were significantly different (p\u3c0.0001. Figure). To further investigate the predictive ability of DLCO vs DLCO/VA, we looked at the AUC for subsets of patients with the following diagnoses: COPD, CHF, ILD, Sleep apnea, and Pulmonary Hypertension. In all these subgroups, DLCO had a statistically significantly higher AUC than DLVA. Based on the optimal cutoff point for DLCO (45% predicted), and the DLVA (70 % of predicted), sensitivity (58.5% vs. 52%), specificity (83% vs. 80%), positive predictive value (64% vs. 58%) and negative predictive value (79.5% vs. 75.7%) were higher for DLCO as opposed to DLCO/VA, respectively. [Graph Presented]. Conclusion: Both DLCO and DLCO/VA can be used to identify patients at risk for exertional hypoxemia, but the DLCO is a better predictive test than DLCO/VA