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We examined effects of disturbance timing on resistance and resilience of epilithic algal communities growing in fast— (29 cm/s) and slow— (12 cm/s) current outdoor experimental stream channels in Kentucky, USA that were either left undisturbed (control) over 33 d following a simulated spate, or were subjected to an additional spate after either 9, 18, 27, 33 d. On day 33, all channels were subjected to a final spate to assess effects of short—term disturbance history on resistance, independently of seasonal influences. Succession proceeded from a sparsely populated community dominated by a small, monoraphid diatom (Achnanthes minutissima) immediately after the initial spate, to dominance by dense floating mats of filamentous green algae (Zygnematales: Mougeotia and Spirogyra) and Synedra spp. by day 21—24. Resistance was generally lower in slow—current communities, both in terms of cell—density reduction and displacement of taxonomic structure, than in fast—current communities. Resistance in slow—current communities varied temporally, with communities least resistant on day 18, when community composition and physiognomy was changing rapidly, and on day 33, when green algal mats began to senesce. On day 33, slow—current communities that had not been recently disturbed (control, D9) exhibited greatest spate—induced loss of algal biomass. Additionally, slow—current communities with high pre—disturbance phaeophytin content (an indicator of algal senescence) also changed most in diatom assemblage structure across the final spate. No such relationship was noted in fast current, suggesting that autogenic factors influenced communities in slow current more than those in fast. Resilience was higher in slow—current communities than in fast current, with disturbed communities reaching biomass and taxonomic structure similar to controls after 3—9 d. High resilience in slow current resulted from enhanced reproduction in some populations following spate—induced biomass reduction and presumed release from nutrient and light limitation, and low shear stress relative to fast—current channels where biomass accrual was limited by current. Interactions between disturbance timing, successional state, and habitat affect the susceptibility of epilithic algal communities to disturbance and likely influence temporal and spatial heterogeneity in stream ecosystems.

We compared rates and directions of benthic aquatic macroinvertebrate succession following eight spates of varying magnitude that occurred in different seasons over 3 yr in Sycamore Creek, a Sonoran Desert stream. A consistent cycle of seasonal change in assemblage composition occurred each year, little altered by spates. Changes reflected variations in presence or absence rather than relative abundance of taxa. Seasonal patterns were confirmed by plotting temporal changes in densities of common taxa. Invertebrate abundance (mostly oligochaetes and mayflies) peaked in spring. "Summer" dominants included gastropod Physella virgata and the caddisfly larva Cheumatopsyche arizonensis. Assemblages composition remained relatively consistent during spring over 3 yr when high discharge was prolonged, whereas there was a major change in autumn community structure between 1984 and 1986, probably, reflecting low discharge during a drought in 1986. Drying apparently influenced assemblage composition more than spates, possibly by altering habitat availability and the intensity of biotic interactions as surface stream volume shrank. Assemblage resistance to disturbance by spates was variable. Similarly, resistance of individual common taxa varied within and among taxa, and like assemblage resistance, was not simply a function of spate magnitude or timing (season). Resilience was generally high. Succession rate (degree of change in assemblage composition) decline during succession in all but spring sequences, which displayed no consistent trend. The two summer sequences had highest initial succession rates (in first 30 d postspate), possibly reflecting higher water temperatures, as also exhibited late—successional increases in succession rate. Spatial variation in assemblage composition was uncorrelated with any physical variable measured. Factors known to influence ecosystem—level processes such as primary productivity (e.g., inorganic nitrogen flux, days since spate) also affected community—level aspects such as aquatic invertebrate assemblage composition in Sycamore Creek. Discharge and water temperature had lesser but detectable effects, and probably contributed to the marked seasonality in assemblage composition. Further comparisons of collective properties of ecosystems and communities within other biomes may identify "common denominators" that characterize responses to disturbance and environmental change. This will remove the different perceptions about stability we gain by using response variables that are assessed only at a community or ecosystem level.

Purpose In low–tumor burden follicular lymphoma (FL), maintenance rituximab (MR) has been shown to improve progression-free survival when compared with observation. It is not known whether MR provides superior long-term disease control compared with re-treatment rituximab (RR) administered on an as-needed basis. E4402 (RESORT) was a randomized clinical trial designed to compare MR against RR. Patients and Methods Eligible patients with previously untreated low–tumor burden FL received four doses of rituximab, and responding patients were randomly assigned to either RR or MR. Patients receiving RR were eligible for re-treatment at each disease progression until treatment failure. Patients assigned to MR received a single dose of rituximab every 3 months until treatment failure. The primary end point was time to treatment failure. Secondary end points included time to first cytotoxic therapy, toxicity, and health-related quality of life (HRQOL). Results A total of 289 patients were randomly assigned to RR or MR. With a median follow-up of 4.5 years, the estimated median time to treatment failure was 3.9 years for patients receiving RR and 4.3 years for those receiving MR (P = .54). Three-year freedom from cytotoxic therapy was 84% for those receiving RR and 95% for those receiving MR (P = .03). The median number of rituximab doses was four patients receiving RR and 18 for those receiving MR. There was no difference in HRQOL. Grade 3 to 4 toxicities were infrequent in both arms. Conclusion In low–tumor burden FL, a re-treatment strategy uses less rituximab while providing disease control comparable to that achieved with a maintenance strategy.