Prey switching in Rhyacophila dorsalis (Trichoptera) alters with larval instar

1. Ontogenetic shifts in predator behaviour can affect the assessment of food‐web structure and the development of predator–prey models. Previous studies have shown that the diel activity pattern and functional response differed between larval instars of the carnivorous caddis, Rhyacophila dorsalis. The present study examines switching by larvae of R. dorsalis presented with different proportions of two prey types; either small (length 2–4 mm) and large (5–8 mm) Chironomus larvae for second, third, fourth and fifth instars of R. dorsalis; or Baetis rhodani (9–12 mm) and large Chironomus larvae for fourth and fifth instars. Experiments were performed in stream tanks with one Rhyacophila larva per tank and 200 prey arranged in nine different combinations of the two prey types (20 : 180, 40 : 160, 60 : 140, 80 : 120, 100 : 100, 120 : 80, 140 : 60, 160 : 40 and 180 : 20). Prey were replaced as they were eaten. A model predicted the functional response in the absence of switching and provided a null hypothesis against which any tendency to switch could be tested. 2. There was no prey switching in the second and third instars, with both instars always showing a preference for small over large Chironomus larvae. Prey switching occurred in the fourth and fifth instars. As the relative abundance of one prey type increased in relation to the alternative, the proportion eaten of the former prey changed from less to more than expected from its availability, the relationship being described by an S‐shaped curve. In the experiments with small and large Chironomus, the two instars switched to large larvae when their percentage of the total available prey exceeded 29% and 37% for fourth and fifth instars, respectively. In the experiments with Baetis and large Chironomus, both instars switched to Baetis larvae when their percentage of the total available prey exceeded 36%. 3. Non‐switching in second and third instars was related to their feeding strategies, both instars preferring smaller prey items. When the fourth and fifth instars foraged actively at night, they preferred larger over small Chironomus larvae, but when they behaved as ambush predators at dusk, they captured the more active Baetis larvae in preference to the more sedentary large Chironomus larvae and only switched to the latter when they were >64% of the available prey.     

The critical thermal limits for the stone loach, Noemacheilus barbatulus, from three populations in north-west England

1. The chief objective was to determine the upper and lower thermal limits for feeding and survival in the stone loach, Noemacheilus barbatulus, using juveniles (total length 30–45 mm, live weight 0.25–0.80 g) from one population and adults (total length 77–100 mm, live weight 3.6–7.9 g) from three populations. 2. Fish were acclimatized to constant temperatures of 3, 7, 10, 15, 20, 25 and 27°C; then the temperature was changed at a rate of 1°C/30min to determine the critical limits for feeding, survival over 7 days (incipient lethal temperature), or survival for 10 min or less (ultimate lethal temperature). The rate of 1°C/30min was the optimum value from preliminary experiments, using nine rates from 0.5°C/48h to 18°Ch^?1. As values for adults were not significantly different between populations, they were pooled to provide arithmetic means (with 95% CL) for the thermal limits at each acclimation temperature. 3. Feeding limits increased with acclimation temperature to upper and lower mean values of 28.0 ± 0.15°C and 5.1 ± 0.55°C for adults, 25.0 ± 0.54°C and 6.1 ± 0.92°C for juveniles. Incipient lethal levels defined a tolerance zone within which stone loach survive for a considerable time; upper limits increased with acclimation temperature to reach a maximum plateau of 29.1 ± 0.18°C for adults and 29.0 ± 0.40°C for juveniles; lower limits also increased from near 0°C to 3.0 ± 0.40°C for adults and juveniles. Upper limits for the ultimate lethal level increased with acclimation temperature to a maximum plateau of 33.5°C for adults (95% CL ± 0.19) and juveniles (95% CL ± 0.40), whilst the lower limits increased from near 0°C to 2.5 ± 0.30°C. At acclimation temperatures below 20°C, upper incipient and ultimate lethal values were significantly lower for juveniles than those for adults. 4. The thermal tolerance of stone loach was higher than that of juvenile Atlantic salmon or brown trout, one or both of these species often being dominant in streams with stone loach.     

Victorian gardeners and botanical nomenclature

ELLIOTT, B., 1992. Victorian gardeners and botanical nomenclature. A review of the debate over the relative importance of English over Latin names for plants is presented.     

Fluorescence microscopy of mycobacteria in pleural effusions

The diagnostic advantage of fluorescence microscopy (FM) of Papanicolaou-stained cytological specimens obtained by bronchoscopy has been described previously. This study was designed to evaluate the method's diagnostic benefit in cytological preparations of pleural effusions in cases of active pulmonary tuberculosis. In contrast to bronchial material there is no advantage in cytological evaluation of pleural effusions by FM.