The influence of large wood on brown trout (Salmo trutta) behaviour and surface foraging

1. Changes in riparian vegetation owing to forest harvesting may affect the input of large wood, a major structural element, to streams. Studies of large wood impacts on stream fish have focused on population‐level responses, whereas little attention has been given to how wood affects fish behaviour. 2. In a laboratory stream experiment, we tested how two size classes of brown trout, Salmo trutta, (mean size of 85 and 125 mm), alone and together, responded to a gradient of large wood in terms of activity, foraging on terrestrial drift and interactions between conspecifics. 3. The results showed that the presence of large wood significantly reduced the overall activity of the fish, the number of agonistic interactions between individuals and the proportion of captured prey. However, activity decreased relatively more than the proportion of captured prey, resulting in a significant positive net effect of wood on the number of prey captures per time spent active (PTA). This indicates that trout living in habitats with high wood density may have a higher net energy gain than trout living in habitats with less wood. 4. There were no observable size‐class differences in the benefits of large wood or in the utilisation of surface‐drifting terrestrial prey. 5. These results suggest that the presence of large wood may be an important factor shaping stream communities and that a lack of structural complexity may decrease energy gain, increase agonistic interactions and, consequently, lower the production of brown trout.     

The Physiology of the Lichen Peltigera aphthosa, with Special Reference to the Blue-green Phycobiont (Nostoc sp.)

Variations in the morphology and physiology were noted when parts of the Peltigera aphthosa Willd. thallus differing in age were examined. The many small cephalodia on the growing apex of the lichen showed a lower heterocyst frequency (14%) than those on the rest of the thallus (21–22%), which was reflected in the nitrogenase activity. In contrast, highest levels of photosynthesis (¹⁴CO₂ uptake and O₂ evolution) were noted at the growing apex. while respiration rates were fairly stable over the thallus. The water-holding capacity was greatest in the midparts. Cephalodial biomass represented an average of 2.6% of total thallus biomass. while the number and size of these structures varied considerably. A minor part of the total carbon fixation (¹⁴CO₂) and net oxygen evolution (O₂ electrode) was performed by the blue-green phycobiont (Nostoc) in light. A rapid excretion of ammonia from isolated cephalodia was noticed, which together with a comparatively constant C:N ratio throughout the thallus indicated a rapid transport of metabolites facilitated by close physical contact (electron microscopy).