Downstream resource leakage a necessary condition for the stress-gradient hypothesis in processing chain commensalisms

The stress-gradient hypothesis (SGH) in ecology predicts that the strength and frequency of positive interspecific interactions, including processing chain commensalisms (PCCs), increase with environmental stress. Although observed in some empirical PCC studies, a recent theoretical study of PCCs using a consumer-resource-type model found that, given the model's assumptions, the SGH never occurs. To investigate if this is a true reflection of PCCs or merely an artefact of the model, in this study, we modified this earlier model formulation by incorporating generalized, monotonically increasing resource uptake functions in place of linear functions, and added a term to represent the spontaneous leakage of the downstream resource to the environment. Mathematical analyses of the model revealed two key insights: 1) the specific algebraic forms of the functional responses of the species in a PCC do not affect the long-term behaviour of the system; 2) the SGH can occur in a facilitative interaction only if the consumer-independent leakage rate of the downstream resource exceeds the consumer-independent input rate. The first insight shows that the outcomes of consumer-resource interactions are robust to details of the functional responses when the functional responses are monotonically increasing, while the second insight shows that the SGH is not a universal feature of positive interactions but instead holds only under a well-defined set of conditions which may vary between PCC interactions and the environmental contexts in which they take place

Does repeated pleural culture increase the diagnostic yield of Mycobacterium tuberculosis from tuberculous pleural effusion in HIV-negative individuals?

Despite recent advances in methods for culturing Mycobacterium tuberculosis (MTB), the diagnostic yield of tuberculous pleural effusion (TBPE) remains unsatisfactory. However, unlike repeated sputum cultures of pulmonary tuberculosis, little is known about the role of repeated pleural cultures. We examined whether repeated pleural cultures are associated with increased MTB yield from TBPE.A multicenter, retrospective cohort study was performed from January 2012 to December 2015 in South Korea. Patients were categorized into two groups: single- or repeated-culture groups. The diagnostic yield of MTB and clinical, radiological, and pleural fluid characteristics were evaluated.Among the 329 patients with TBPE, 77 (23.4%) had repeated cultures and 252 (76.5%) had a single culture. Pleural culture was performed twice in all 77 patients in the repeated-culture group at a 1-day interval (inter-quartile range, 1.0-2.0). In the repeated-culture group, the yield of MTB from the first culture was 31.2%, which was similar to that in the single-culture group (31.2% vs. 29.8%, P = 0.887). However, the yield of MTB from the second culture (10/77, 13.0%) was more than that from the first. These results may be attributable to the insufficient immune clearance for MTB invasion into the pleural space between the first and second cultures. Over time, the yield of the second cultures decreased from 17.4% to 6.7% and then 6.3%. Finally, the overall yield of MTB in the repeated- and single-culture groups was 44.2% and 29.8% respectively (P < 0.001).The results showed that repeated pleural cultures increased MTB yield from TBPE in human immunodeficiency virus-negative individuals. Furthermore, repeated cultures may increase yield when carried out for two consecutive days

Habitat adaptation mediates the influence of leaf traits on canopy productivity: evidence from a tropical freshwater swamp forest

Functional traits offer generalizability to the prediction of ecosystem processes such as production, and community-weighted mean trait values are increasingly used for such predictions. However, the underlying causal direction between traits and ecosystem processes are often indirect and sometimes even tenuous. In this study, we aimed to uncover underlying causal mechanisms between traits, habitat adaptation and canopy productivity. We used canopy production data estimated from leaf litter traps, and trait and habitat association data obtained from 40 permanent vegetation plots in the Nee Soon catchment in Singapore, which contains a heterogeneous mix of freshwater swamp and dry-land tropical forests. Mean canopy production across the catchment was estimated to be 768 g m−2 year−1, which is similar to other tropical dry-land forests in the region. Fortnightly per-basal-area canopy production was found to be consistently lower in swamp than non-swamp plots, and positively correlated with monthly mean temperature. Structural equation models fitted to data of canopy production, leaf traits, plot type (swamp versus non-swamp), basal areas and habitat adaptations of 69 tree species– plot combinations suggested that tree species possessing leaf traits associated with more conservative resource acquisition strategies, viz., low specific leaf area, high leaf C:N ratio, and thicker leaves, are better adapted to stressful, waterlogged swamp conditions, but that this adaptation also reduces canopy—and likely total—net primary productivity. These observations suggest that the stressful conditions of waterlogged, anoxic swamp habitats significantly reduce the rate at which nutrients are cycled by communities found in such environments

Does repeated pleural culture increase the diagnostic yield of <i>Mycobacterium tuberculosis</i> from tuberculous pleural effusion in HIV-negative individuals?

<div><p>Background</p><p>Despite recent advances in methods for culturing <i>Mycobacterium tuberculosis</i> (MTB), the diagnostic yield of tuberculous pleural effusion (TBPE) remains unsatisfactory. However, unlike repeated sputum cultures of pulmonary tuberculosis, little is known about the role of repeated pleural cultures. We examined whether repeated pleural cultures are associated with increased MTB yield from TBPE.</p><p>Methods</p><p>A multicenter, retrospective cohort study was performed from January 2012 to December 2015 in South Korea. Patients were categorized into two groups: single- or repeated-culture groups. The diagnostic yield of MTB and clinical, radiological, and pleural fluid characteristics were evaluated.</p><p>Results</p><p>Among the 329 patients with TBPE, 77 (23.4%) had repeated cultures and 252 (76.5%) had a single culture. Pleural culture was performed twice in all 77 patients in the repeated-culture group at a 1-day interval (inter-quartile range, 1.0–2.0). In the repeated-culture group, the yield of MTB from the first culture was 31.2%, which was similar to that in the single-culture group (31.2% vs. 29.8%, P = 0.887). However, the yield of MTB from the second culture (10/77, 13.0%) was more than that from the first. These results may be attributable to the insufficient immune clearance for MTB invasion into the pleural space between the first and second cultures. Over time, the yield of the second cultures decreased from 17.4% to 6.7% and then 6.3%. Finally, the overall yield of MTB in the repeated- and single-culture groups was 44.2% and 29.8% respectively (P < 0.001).</p><p>Conclusions</p><p>The results showed that repeated pleural cultures increased MTB yield from TBPE in human immunodeficiency virus-negative individuals. Furthermore, repeated cultures may increase yield when carried out for two consecutive days.</p></div

Biochemical changes in sequential examinations of 77 cases in the repeated pleural culture group.

<p>Biochemical changes in sequential examinations of 77 cases in the repeated pleural culture group.</p

Baseline characteristics of 329 patients with TBPE.

<p>Baseline characteristics of 329 patients with TBPE.</p

Flowchart of study: Selection of study participants.

<p>Flowchart of study: Selection of study participants.</p

Positive culture rate of overall and second pleural culture according to time interval between first and second culture and changes in pleural fluid characteristics.

<p>Positive culture rate of overall and second pleural culture according to time interval between first and second culture and changes in pleural fluid characteristics.</p

Predictors of MTB cultivation in patients with tuberculous pleural effusion via first and second pleural culture.

<p>Predictors of MTB cultivation in patients with tuberculous pleural effusion via first and second pleural culture.</p