High mortality and enhanced recovery: modelling the countervailing effects of disturbance on population dynamics.

Disturbances cause high mortality in populations while simultaneously enhancing population growth by improving habitats. These countervailing effects make it difficult to predict population dynamics following disturbance events. To address this challenge, we derived a novel form of the logistic growth equation that permits time-varying carrying capacity and growth rate. We combined this equation with concepts drawn from disturbance ecology to create a general model for population dynamics in disturbance-prone systems. A river flooding example using three insect species (a fast life-cycle mayfly, a slow life-cycle dragonfly and an ostracod) found optimal tradeoffs between disturbance frequency vs. magnitude and a close fit to empirical data in 62% of cases. A savanna fire analysis identified fire frequencies of 3-4 years that maximised population size of a perennial grass. The model shows promise for predicting population dynamics after multiple disturbance events and for management of river flows and fire regimes.

Quantifying invertebrate resistance to floods: a global-scale meta-analysis.

Floods are a key component of the ecology and management of riverine ecosystems around the globe, but it is not clear whether floods have predictable effects on organisms that can allow us to generalize across regions and continents. To address this, we conducted a global-scale meta-analysis to investigate effects of natural and managed floods on invertebrate resistance, the ability of invertebrates to survive flood events. We considered 994 studies for inclusion in the analysis, and after evaluation based on a priori criteria, narrowed our analysis to 41 studies spanning six of the seven continents. We used the natural-log-ratio of invertebrate abundance before and within 10 days after flood events because this measure of effect size can be directly converted to estimates of percent survival. We conducted categorical and continuous analyses that examined the contribution of environmental and study design variables to effect size heterogeneity, and examined differences in effect size among taxonomic groups. We found that invertebrate abundance was lowered by at least one-half after flood events. While natural vs. managed floods were similar in their effect, effect size differed among habitat and substrate types, with pools, sand, and boulders experiencing the strongest effect. Although sample sizes were not sufficient to examine all taxonomic groups, floods had a significant, negative effect on densities of Coleoptera, Eumalacostraca, Annelida, Ephemeroptera, Diptera, Plecoptera, and Trichoptera. Results from this study provide guidance for river flow regime prescriptions that will be applicable across continents and climate types, as well as baseline expectations for future empirical studies of freshwater disturbance.

Acute renal failure from xanthine nephropathy during management of acute leukemia.

Tumor lysis syndrome is a potentially life-threatening complication of induction chemotherapy for treatment of lymphoproliferative malignancies. Serious complications of tumor lysis syndrome are rare with the preemptive use of allopurinol, rasburicase, and urine alkalinization. We report a case of oliguric acute renal failure due to bilateral xanthine nephropathy in an 11-year-old girl as a complication of tumor lysis syndrome during the treatment of T-cell acute lymphoblastic leukemia. Xanthine nephrolithiasis results from the inhibition of uric acid synthesis via allopurinol which increases plasma and urinary xanthine and hypoxanthine levels. Reports of xanthine nephrolithiasis as a cause of tumor lysis syndrome are rare in the absence of defects in the hypoxanthine-guanine phosphoribosyl transferase (HGPRT) enzyme. Xanthine nephropathy should be considered in patients who develop acute renal failure following aggressive chemotherapy with appropriate tumor lysis syndrome prophylaxis. Urine measurements for xanthine could aid in the diagnosis of patients with nephrolithiasis complicating tumor lysis syndrome. Allopurinal dosage should be reduced or discontinued if xanthine nephropathy is suspected.