Isolation controls reestablishment mechanisms and post-drying community structure in an intermittent stream.

Biota in disturbance-prone landscapes have evolved a variety of strategies to persist long term, either locally (resistance) or by regional recolonization (resilience). Habitat fragmentation and isolation can limit the availability of recolonization pathways, and thus the dynamics of post-disturbance community reestablishment. However, empirical studies on how isolation may control the mechanisms that enable community recovery remain scarce. Here, we studied a pristine intermittent stream (Chalone Creek, Pinnacles National Park, California) to understand how isolation (distance from a perennial pool) alters invertebrate community recolonization after drying. We monitored benthic invertebrate reestablishment during the rewetting phase along a ~2-km gradient of isolation, using mesh traps that selected for specific recolonization pathways (i.e., drift, flying, swimming/crawling, and vertical migration from the hyporheic). We collected daily emigration samples, surveyed the reestablished benthic community after 6 weeks, and compared assemblages across trap types and sites. We found that isolation mediated migration dynamics by delaying peak vertical migration from the hyporheic by ca. 1 day on average per 250 m of dry streambed. The relative importance of reestablishment mechanisms varied longitudinally-with more resistance strategists (up to 99.3% of encountered individuals) in the upstream reaches, and increased drift and aerial dispersers in the more fragmented habitats (up to 17.2% and 18%, respectively). Resistance strategists persisting in the hyporheic dominated overall (88.2% of individuals, ranging 52.9%-99.3% across sites), but notably most of these organisms subsequently outmigrated downstream (85.6% on average, ranging 52.1%-96% across sites). Thus, contrary to conventional wisdom, resistance strategists largely contributed to downstream resilience as well as to local community recovery. Finally, increased isolation was associated with a general decrease in benthic invertebrate diversity, and up to a 3-fold increase in the relative abundance of drought-resistant stoneflies. Our results advance the notion that understanding spatial context is key to predicting post-disturbance community dynamics. Considering the interaction between disturbance and fragmentation may help inform conservation in ecosystems that are subject to novel environmental regimes.

Drought and nutrient pollution produce multiple interactive effects in stream ecosystems.

Drought and nutrient pollution can affect the dynamics of stream ecosystems in diverse ways. While the individual effects of both stressors are broadly examined in the literature, we still know relatively little about if and how these stressors interact. Here, we performed a mesocosm experiment that explores the compounded effects of seasonal drought via water withdrawals and nutrient pollution (1.0 mg/L of N and 0.1 mg/L of P) on a subset of Ozark stream community fauna and ecosystem processes. We observed biological responses to individual stressors as well as both synergistic and antagonistic stressor interactions. We found that drying negatively affected periphyton assemblages, macroinvertebrate colonization, and leaf litter decomposition in shallow habitats. However, in deep habitats, drought-based increases in fish density caused trophic cascades that released algal communities from grazing pressures; while nutrient enrichment caused bottom-up cascades that influenced periphyton variables and crayfish growth rates. Finally, the combined effects of drought and nutrient enrichment interacted antagonistically to increase survival in longear sunfish; and stressors acted synergistically on grazers causing a trophic cascade that increased periphyton variables. Because stressors can directly and indirectly impact biota-and that the same stressor pairing can act differentially on various portions of the community simultaneously-our broad understanding of individual stressors might not adequately inform our knowledge of multi-stressor systems.

Modeling effects of disturbance across life history strategies of stream fishes.

A central goal of population ecology is to establish linkages between life history strategy, disturbance, and population dynamics. Globally, disturbance events such as drought and invasive species have dramatically impacted stream fish populations and contributed to sharp declines in freshwater biodiversity. Here, we used RAMAS Metapop to construct stage-based demographic metapopulation models for stream fishes with periodic, opportunistic, and equilibrium life history strategies and assessed their responses to the effects of invasion (reduced carrying capacity), extended drought (reduced survival and fecundity), and the combined effects of both disturbances. Our models indicated that populations respond differentially to disturbance based on life history strategy. Equilibrium strategists were best able to deal with simulated invasion. Periodic strategists did well under lower levels of drought, whereas opportunistic strategists outperformed other life histories under extreme seasonal drought. When we modeled additive effects scenarios, these disturbances interacted synergistically, dramatically increasing terminal extinction risk for all three life history strategies. Modeling exercises that examine broad life history categories can help to answer fundamental ecological questions about the relationship between disturbance resilience and life history, as well as help managers to develop generalized conservation strategies when species-specific data are lacking. Our results indicate that life history strategy is a fundamental determinant of population trajectories, and that disturbances can interact synergistically to dramatically impact extinction outcomes.

A review and synthesis of late Pleistocene extinction modeling: progress delayed by mismatches between ecological realism, interpretation, and methodological transparency.

Late Pleistocene extinctions occurred globally over a period of about 50,000 years, primarily affecting mammals of > or = 44 kg body mass (i.e., megafauna) first in Australia, continuing in Eurasia and, finally, in the Americas. Polarized debate about the cause(s) of the extinctions centers on the role of climate change and anthropogenic factors (especially hunting). Since the late 1960s, investigators have developed mathematical models to simulate the ecological interactions that might have contributed to the extinctions. Here, we provide an overview of the various methodologies used and conclusions reached in the modeling literature, addressing both the strengths and weaknesses of modeling as an explanatory tool. Although late Pleistocene extinction models now provide a solid foundation for viable future work, we conclude, first, that single models offer less compelling support for their respective explanatory hypotheses than many realize; second, that disparities in methodology (both in terms of model parameterization and design) prevent meaningful comparison between models and, more generally, progress from model to model in increasing our understanding of these extinctions; and third, that recent models have been presented and possibly developed without sufficient regard for the transparency of design that facilitates scientific progress.

Sensitivity of NMR residual dipolar couplings to perturbations in folded and denatured staphylococcal nuclease.

The invariance of NMR residual dipolar couplings (RDCs) in denatured forms of staphylococcal nuclease to changes in denaturant concentration or amino acid sequence has previously been attributed to the robustness of long-range structure in the denatured state. Here we compare RDCs of the wild-type nuclease with those of a fragment that retains a folded OB-fold subdomain structure despite missing the last 47 of 149 residues. The RDCs of the intact protein and of the truncation fragment are substantially different under conditions that favor folded structure. By contrast, there is a strong correlation between the RDCs of the full-length protein and the fragment under denaturing conditions (6 M urea). The RDCs of the folded and unfolded forms of the proteins are uncorrelated. Our results suggest that RDCs are more sensitive to structural changes in folded than unfolded proteins. We propose that the greater susceptibility of RDCs in folded states is a consequence of the close packing of the polypeptide chain under native conditions. By contrast, the invariance of RDCs in denatured states is more consistent with a disruption of cooperative structure than with the retention of a unique long-range folding topology.

[Value and justification of urine dip-sticks in the diagnosis of postoperative urinary infections in urology]. / Intérêt et justification de la bandelette urinaire dans le diagnostic des infections urinaires post-opératoires en urologie.

OBJECTIVE: To assess the diagnostic value of urine dip-sticks for postoperative urinary tract infections. MATERIAL AND METHODS: A prospective study was performed on 165 patients undergoing radical prostatectomy, open prostatectomy for BPH or transurethral resection of the prostate or bladder. Postoperative bacteriuria was investigated by using Multistix urine dip-sticks and was verified by urine culture. The presence of nitrites was the only parameter of the dip-stick taken into account. RESULTS: The overall infection rate was 9.7% (range: 7.3% to 16%). The dip-stick showed extremely poor sensitivity and specificity of 36.3% and 57.8%, respectively (p = 0.03). The main bacterial species isolated were: Escherichia coli (63%) and Enterococcus faecalis (27%). CONCLUSION: The lack of diagnostic reliability of urine dip-sticks no longer justifies the use of these tests for the diagnosis of postoperative infection. Urine culture, with documented efficacy, remains the reference examination.

Total and free serum prostate specific antigen levels during the first month of acute prostatitis.

OBJECTIVES: The level of total prostate specific antigen (PSA) rises in acute prostatitis. The PSA fraction responsible for this increase and the evolution of the free/total PSA ratio are little known at the present time. We therefore carried out a prospective study of the evolution of total and free PSA levels and the free-to-total PSA ratio for one month after diagnosis of acute prostatitis. PATIENTS AND METHODS: Between January 1999 and February 2001, 31 consecutive patients (mean age 51 years) were treated for acute prostatitis. No patient had a history of prostate cancer or of recent prostatitis. Measurement of C-reactive protein (CRP), total PSA and free PSA was done at days 0, 3, 10 and 30. RESULTS: During the first month of acute prostatitis and under an adapted antibiotherapy, CRP progressively decreased and returned to normal levels at about day 10. Total PSA level increased up to day 3 and then gradually decreased until at least the end of the first month. The level of free PSA decreased up to day 10 and was still low at one month, leading to a decrease in the free-to-total PSA ratio which was reached its lowest level at day 10 and was still low at one month. CONCLUSION: The increased level of total PSA in acute prostatitis is secondary to the proportional increase in bound serum PSA and decrease in free PSA. Free PSA was still low at one month, maintaining a low free-to-total PSA ratio.

A trauma education workshop on posttraumatic stress.

Adapting successfully in life involves successful management of stress. Posttraumatic stress presents a significant challenge for successful adaptation, one that is often misunderstood, devalued, dismissed, or denied. This article presents a brief and potentially effective method of group education about posttraumatic stress for "victims" of posttraumatic stress, significant others, and health worker. Appropriate use of group education for posttraumatic stress, it is argued, offers empowering meaning and purpose, and faith and hope for healing and well-being.