I assessed the impact of both drift-feeding (Salmo trutta, brown trout) and benthic-feeding (Cottus gobio, bullhead) fish on a benthic assemblage during a 1-month-long field experiment. I used enclosures containing cobble/gravel substrata with 6-mm mesh net that allowed invertebrates to drift freely in and out of enclosures. Four treatments, arranged in a factorial design, were tested: a predator-free control, bullheads only (2.67 bullheads/m, two per enclosure), brown trout only (2.67 brown trout/m, two per enclosure), and bullheads and brown trout together (2.67 fish/m, one of each). Bullheads reduced the densities of seven invertebrate taxa (Gammarus pulex amphipods, Baetis rhodani mayfly nymphs, Leuctra spp. stonefly nymphs, Polycentropus spp. caddis larvae, Pacifastacus leniusculus signal crayfishes, Simuliidae, blackfly larvae, and Limnephilidae, caddis larvae) whereas brown trout only affected one taxon (B. rhodani). The weaker effect of brown trout on benthic prey was probably related to its heavy reliance on terrestrial prey. Dietary analyses showed that more than 80% of prey consumed by brown trout were terrestrial animals, whereas bullhead only consumed benthic prey. Neither bullhead nor brown trout affected the absolute number of immigrating or emigrating invertebrates in enclosures, but bullhead affected the per capita emigration rates of G. pulex. Direct predation by bullhead was more important than avoidance behaviour (drift) in determining densities of six of the seven taxa; only G. pulex densities were equally affected by avoidance behaviour and direct predation. Direct predation by brown trout was also more important in determining densities of B. rhodani. The presence of bullhead raised periphyton biomass, presumably mediated via their consumption of grazers. Brown trout had no effect on periphyton biomass and these results indicate that the presence of alternative prey, in this case terrestrial animals, may have repercussions for fish-benthic macroinvertebrate-periphyton interactions and may potentially explain some of the variable impacts of fish on benthic macroinvertebrates that have been reported in the literature.

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In high‐elevation streams of western Colorado, mayflies (Baetis bicaudatus) develop faster, but mature at a smaller size where trout are present compared to streams where fish are absent. These life history traits reduce the time of larval exposure to trout predation, but cost reduced fecundity. We designed a field experiment involving manipulation of whole streams to determine whether these changes were caused by the presence of brook trout, and specifically, whether they could be triggered by trout chemical cues. In 1999 and 2000, we introduced water from containers with brook trout (Salvelinus fontinalis) into five naturally fishless streams, and fishless stream water into five adjacent control streams, to determine whether these cues alone could induce the mayfly life history traits we have observed in natural trout streams. As in previous small‐scale experiments, the size at which mayflies matured declined significantly in streams with added trout chemicals but did not change in streams with fishless water only. Thus, life history traits similar to those observed in the field were induced within the natural variability inherent in streams. These results demonstrate the strength of this predator–prey interaction and indicate that brook trout are an important agent of natural selection on mayfly life history traits.

Regional and global metabolic rates for glucose were estimated using 18F-fluorodeoxyglucose and positron emission tomography in 10 patients with a clinical likelihood of striatonigral degeneration (2 men and 8 women; mean age, 61.8 +/- 6.9 years; mean disease duration, 4.7 +/- 2.2 years; mean Hoehn and Yahr score, 3.5 +/- 0.8). Measures of brain glucose metabolism in these patients were compared with those for 10 age-matched normal volunteers, 10 disease severity-matched patients with Parkinson's disease (PD), and 10 disease duration-matched patients with PD. Normalized glucose metabolism was significantly reduced in the caudate (p < 0.03) and putamen (p < 0.003) as compared with that in normal and PD control subjects, and discriminated patients with striatonigral degeneration from control subjects (p < 0.002). Putamenal hypometabolism in patients with striatonigral degeneration correlated significantly with quantitative ratings of motor disability (p < 0.02). These results suggest that quantitative 18F-fluorodeoxyglucose positron emission tomography techniques may be useful in supporting a diagnosis of striatonigral degeneration in life, and in objectively assessing disease severity and potential therapeutic interventions.