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The mountain yellow-legged frog (Rana muscosa) was once a common inhabitant of the Sierra Nevada (California, USA), but has declined precipitously during the past century due in part to the introduction of nonnative fish into naturally fishless habitats. The objectives of the current study were to describe (1) the effect of fish removal from three lakes (located in two watersheds) on the small, remnant R. muscosa populations inhabiting those lakes, and (2) the initial development of metapopulation structure in each watershed as R. muscosa from expanding populations in fish-removal lakes dispersed to adjacent habitats. At all three fish-removal lakes, R. muscosa population densities increased significantly following the removal of predatory fish. The magnitude of these increases was significantly greater than that observed over the same time period in R. muscosa populations inhabiting control lakes that remained in their natural fishless condition. Following these population increases, R. muscosa dispersed to adjacent suitable (but unoccupied) sites, moving between 200 and 900 m along streams or across dry land. Together, these results suggest that large-scale removal of introduced fish could result in at least partial reversal of the decline of R. muscosa. Continued monitoring of R. muscosa at the fish-removal sites will be necessary to determine whether the positive effects of fish eradication are sustained over the long-term, especially in light of the increasingly important role played by an emerging infectious disease (chytridiomycosis, caused by Batrachochytrium dendrobatidis) in influencing R. muscosa populations.

Nonnative fishes have been introduced into naturally fishless mountain lakes worldwide, often with negative consequences for native fauna. In this study, I used data collected during a census of native herpetofauna, nonnative trout, and habitat characteristics at all lentic water bodies in Yosemite National Park (n=2655) to quantify the effect of trout introductions and habitat on the distribution of four amphibian species and two reptile species. Impacts of trout on amphibians and reptiles were characterized using generalized additive models that included as predictor variables fish presence/absence, amphibian presence/absence (only in models for the two reptile species), elevation, water depth, littoral zone and shoreline substrate composition, relative survey date, and location. All species showed significant associations with habitat characteristics, and elevation and water depth appeared particularly important in influencing distributions. In addition, distributions of the mountain yellow-legged frog (Rana muscosa) and Pacific treefrog (Hyla regilla) were strongly negatively associated with the presence of nonnative trout while those of the Yosemite toad (Bufo canorus) and Sierra newt (Taricha torosa sierrae) were unrelated to trout presence. The distribution of the mountain garter snake (Thamnophis elegans elegans) was strongly negatively associated with the presence of nonnative trout and positively associated with the presence of native amphibians. Regression results for the Sierra garter snake (Thamnophis couchi couchi) were similar except that the direct effect of nonnative trout was considerably weaker. Together, these results indicate that trout introductions have resulted in considerable alteration of Yosemite's herpetofauna. Long-term studies will be necessary to determine whether removal of nonnative trout populations, where possible, would allow these impacts to be partially reversed.

Abstract. In many animal species, females lay eggs within male territories. Research on female choice in such species has shown that females often assess male or territory quality indirectly on the basis of male characters that are correlated with male or territory quality. Researchers have given much less attention to the possibility that females can assess male or territory quality directly based on the survival of previous broods. This study demonstrates that in the bicolour damselfish, a species with exclusive male parental care of eggs, females use the survival of previously-laid eggs to avoid nests that have a low probability of offspring survival. Females mate repeatedly during a reproductive cycle and although they generally show high nest fidelity, this fidelity is broken when a nest loses an entire brood to nocturnally feeding brittlestars. Experimental removal of broods and addition of brittlestar odours to nests demonstrate that brittlestar odours are sufficient to cause females to avoid nests. Females may also respond to visual cues associated with brood loss. In addition, clutches laid in nests after nocturnal complete-brood losses are much less likely to survive than clutches laid in nests that have not suffered nocturnal complete-brood losses. Therefore, by avoiding nests from which brittlestars have recently removed eggs, females increase the probability of future egg survival.

Female mate choice and patterns of clutch loss were investigated in a natural population of the bicolor damselfish, Stegastes partitus, in an attempt to link criteria used by females in mate choice with male or territory characteristics that enhance egg survival. Previous studies of mate choice in fish species with paternal care have demonstrated the importance of male size and the brood size defended by males in determining female choice. In the present study, neither male size nor brood size influenced male mating success. Of the measured male and territory characteristics, females chose males solely on the basis of their courtship rate. The lack of a female preference for large males and for males with relatively larger broods appeared to result from the patterns of clutch loss. Egg-hatching success was unrelated to either male size or brood size. Future work will determine whether males with high courtship rates provide superior parental care.

An analytic study was carried out to determine the applicability of the concept of thermal stress fragmentation to the UO 2 -Na fuel-coolant interaction. Major emphasis was put on the fracture mechanics approach to assess whether or not the solidifying UO 2 would fracture under the thermally-induced stresses. It was found that the stress levels were sufficient to generate K I values substantially in excess of the UO 2 fracture toughness K IC . Thus, rapid instantaneous propagation of inherent flaws is anticipated.