Spatial stratification of host-seeking Diptera in boreal forests of northern Europe.

The stratification of haematophagous Diptera was assessed in two boreal forests in northern Sweden by placing traps baited with carbon dioxide at 1.5 m, 5.0 m and 10.0 m above the ground. More than 40 000 specimens were captured, including 617 biting midges (Ceratopogonidae), 4029 mosquitoes (Culicidae) and 36 092 black flies (Simuliidae). Catches at the various trap heights reflected the general vertical distribution of the preferred hosts, with mammalophilic flies predominating (68.6%) in catches at 1.5 m and ornithophilic flies (42.4%) in catches at 10.0 m; however, most flies that use host birds at ground level were caught in the lowest traps (e.g. 85.1% of Simulium annulus were collected at 1.5 m). Within-species variation in vertical patterns between forests suggests plasticity in responses to environmental factors such as vegetative structure.

Bird hosts, blood parasites and their vectors--associations uncovered by molecular analyses of blackfly blood meals.

The level of host specificity of blood-sucking invertebrates may have both ecological and evolutionary implications for the parasites they are transmitting. We used blood meals from wild-caught blackflies for molecular identification of parasites and hosts to examine patterns of host specificity and how these may affect the transmission of avian blood parasites of the genus Leucocytozoon. We found that five different species of ornithophilic blackflies preferred different species of birds when taking their blood meals. Of the blackflies that contained avian blood meals, 62% were infected with Leucocytozoon parasites, consisting of 15 different parasite lineages. For the blackfly species, there was a significant association between the host width (measured as the genetic differentiation between the used hosts) and the genetic similarity of the parasites in their blood meals. The absence of similar parasite in blood meals from blackflies with different host preferences is interpreted as a result of the vector-host associations. The observed associations between blackfly species and host species are therefore likely to hinder parasites to be transmitted between different host-groups, resulting in ecologically driven associations between certain parasite lineages and hosts species.

Ecosystem functioning in stream assemblages from different regions: contrasting responses to variation in detritivore richness, evenness and density.

1. The diversity of species traits in a biological assemblage varies not only with species richness, but also with species evenness and organism density, which together influence the concentration of traits within functional guilds. Potential trait diversity at local scales is also constrained by the regional species pool. Implications of such variation for spatio-temporal variability in biodiversity-ecosystem functioning relationships are likely to be complex, but are poorly understood. 2. In microcosm experiments conducted at laboratories in Sweden, Ireland and Romania, we investigated effects of species richness, evenness and density of stream-living detritivores on two related processes: detritivore leaf-processing efficiency (LPE) and growth. Assemblage composition varied among laboratories: one taxonomic order (Plecoptera) was studied in Sweden, whereas two orders, encompassing wider trait variation, were studied in Romania (Trichoptera and Plecoptera) and Ireland (Trichoptera and Isopoda). 3. Relationships between density and both LPE and growth ranged from negative to positive across the study species, highlighting the potential for density-dependent variation in process rates to alter ecosystem functioning, but indicating that such effects depend on species identity. 4. LPE varied with species diversity in the two more heterogeneous assemblages, but whereas LPE in the Romanian study was generally enhanced as richness increased, LPE in the Irish study increased only in less-even polycultures dominated by particular species. Transgressive overyielding was detected in the Irish experiment, indicating complementary resource use and/or facilitation (complementarity). These mechanisms could not be distinguished from the selection effect in the Romanian study. 5. Growth was elevated in Romanian species mixtures, reflecting positive complementarity, but lower than expected growth in some Swedish mixtures was associated with negative complementarity, indicating interspecific interference competition. 6. Our results emphasize the potential importance of detritivore diversity for stream ecosystem functioning, but both the effects of diversity on the studied processes, and the mechanisms underlying those effects, were specific to each assemblage and process. Such variability highlights challenges in generalizing impacts of diversity change for functional integrity in streams and other ecosystems in which the occurrence of important species traits fluctuates over relatively small spatio-temporal scales.

Habitat selection of larval brook lampreys (Lampetra planeri, Bloch) in a South Swedish stream.

The burrowing larvae of the brook lamprey Lampetra planeri (Bloch) were shown by discriminant analysis to inhabit stream sites having certain qualities. Although a few larvae occurred in far-from-optimal habitats, most larvae selected those with low current velocity, low water depth, a low number of particles in the 0.5-1 mm range, and with low chlorophyll α content. Other factors normally positively attributed to larval lamprey distribution such as organic content, shade, and presence of algae did not improve the discriminant model. The last factor even showed a negative correlation. Stream bed stability was considered to be of great importance although it was not possible to estimate quantitatively.

Stream drift as a consequence of disturbance by invertebrate predators : Field and laboratory experiments.

We carried out an experimental field study in a Swedish stream in order to determine whether mobile predators enhance the drift of stream insects. We increased the density of nymphs of the predaceous perlid stonefly, Dinocras cephalotes, in an experimental section of a stream up to densities in another more densely populated part of the same stream. The drift of several benthic species increased significantly compared to a control section where D. cephalotes were rare. Experiments carried out in September showed a strongly elevated drift response in nymphs of the mayfly Baetis rhodani only, whereas May experiments resulted in increased drift in B. rhodani as well as the amphipod Gammarus pulex, the stonefly Leuctra fusca, chironomids, and the total number of drifting animals. In September, we found that the drift response of Baetis rhodani to predator disturbance was dependent on the size of mayfly nymphs; small nymphs appeared in greater numbers in the drift nets than did large nymphs. A subsequent laboratory analysis of drift lengths of B. rhodani nymphs supported the hypothesis that small nymphs travel in the drift for longer than do large nymphs, particularly in darkness. We suggest that morphological constraints in vision or swimming performance, or both, cause small nymphs to drift longer. In May, size-dependent drift was less obvious, probably because the size of the nymphs was considerably greater than in September.

Anti-predator adaptations in a neustonic insect (Velia caprai).

The risk of a Velia caprai (Heteroptera: Veliidae) individual to fall victim to brown trout (Salmo trutta) was demonstrated experimentally to be markedly lower when several bugs were simultaneously exposed to the trout. V. caprai was found distasteful to brown trout, and a high proportion was ejected alive after being captured. We suggest that school formation in V. caprai lowers the risk of predation because frequent predator-prey encounters may assist in retention of the avoidance learned by the predator. Individual behavioural responses to attacks were variable and the frequency of expansion skating and thanatosis was temperature dependent. Thanatosis postures were either symmetric with the legs pressed to the body or irregular.

Records of Cucullanus truttae (Fabricius, 1794) (Nematoda: Cucullanidae) from Swedish brook lampreys, Lampetra planeri (Bloch).

Adult nematodes of the family Cucullanidae, parasitic in the abdominal cavity of the brook lamprey, Lampetra planeri (Bloch) from the River Stensån, south Sweden are described and illustrated. According to the morphometry, these nematodes belong to the species Cucullanus truttae (Fabricius, 1794)--a common intestinal parasite of salmonid fishes. The name Dacnitis stelmioides Vessichelli, 1910 is considered to be a synonym of the latter. The role of lampreys in the life-cycle of C. truttae is discussed: although lampreys are either intermediate hosts or serve only as transport hosts for larvae of this parasite, the nematode larvae can attain maturity in this host.

[Ambulatory 24-hour blood pressure monitoring. A comparative study of oscillometric and auscultatory blood pressure measurement]. / Ambulant 24-timers-blodtryksmonitorering. En sammenlignende undersøgelse af oscillometrisk og auskultatorisk blodtryksmåling.

The purpose of this study was to investigate the compatibility between oscillometric and auscultatory methods, and to determine whether one is preferable to the other for ambulatory 24 h blood pressure monitoring. We used an A & D TM 2421 blood pressure monitoring device. Our investigation included 281 patients with suspected hypertension or undergoing treatment for hypertension. We were able to compare 18,790 paired measurements. The difference (auscultatoric--oscillometric) in paired single readings between the two methods was 1.4 +/- 19 mmHg (mean +/- SD) for systolic and -2.4 +/- 18 mmHg for diastolic readings. The difference for 24 h monitoring amounted to 0.7 +/- 4 mmHg for systolic and -2.2 +/- 6 mmHg for diastolic measurements. The auscultatory method showed a uniformed distribution of errors throughout the 24 h, whereas the oscillometric method had fewer errors in the evenings, but more during working hours. A weak correlation between the difference and systolic blood pressure levels, age and pulse pressure was found. Difference in diastolic blood pressure correlated only weakly with the level of pulse pressure. Although we found a considerable SD on single readings, there was a good agreement between the mean values for the 24 h monitoring for the two methods. The findings suggest that, for this equipment, the oscillometric method is preferable for 24 h ambulatory blood pressure monitoring because it provides a much higher rate of successful readings.

Fixation of femoral neck fracture. Prospective comparison of von Bahr screws, Gouffon screws, and Hessel pins.

We report a prospective study of 214 patients with femoral neck fractures operated on with multiple pinning. The fractures were randomly allocated to fixation with either von Bahr screws or Hessel pins in 1983 and 1984 or von Bahr or Gouffon screws in 1984 and 1985. After 2 years, the failure rate was one third in the von Bahr and the Gouffon screw groups and one half in the Hessel pin group. We conclude that the nonthreaded Hessel pin is inferior to the von Bahr and Gouffon screws for fixation of femoral neck fractures.

Long-term results with the Bankart and Bristow-Latarjet procedures: recurrent shoulder instability and arthropathy.

We retrospectively analyzed 26 shoulders in 24 patients 16 to 20 years (mean, 17.5 years) after a Bankart repair and compared these with a prospective series of 30 shoulders in 28 patients 15 years (mean, 15.1 years) after a Bristow-Latarjet repair for recurrent anterior dislocation of the shoulder. At follow-up one patient in each group had undergone revision surgery for recurrent instability. Two patients in the Bankart group had spontaneous stabilization of postoperative instability. Further, one patient in this group had had one subluxation during the follow-up period. In the Bristow group one patient reported 3 recurrences 3 years postoperatively. This patient has had no further redislocations during the past 12 years. Subluxations occurred occasionally several times in 2 patients in the Bristow group, but these patients were satisfied with the procedures at follow-up. No patient in the Bankart group had apprehension at follow-up. Eight patients in the Bristow group had subjective and/or objective apprehension. Throwing ability after surgery in the dominant shoulder was considered normal in 8 of 12 patients in the Bristow series and in 1 of 11 patients in the Bankart series. In the Bankart group 17 patients were "very satisfied" with the operative result, 7 were "satisfied," and 1 was "dissatisfied." The corresponding figures for the Bristow group were 24 who were very satisfied and 5 who were satisfied. Dislocation arthropathy was found in 16 of 26 Bankart shoulders (14 mild and 2 moderate) and in 9 of 30 Bristow shoulders (5 mild, 3 moderate, and 1 severe). The Bankart procedure seemed to be more successful than the Bristow-Latarjet repair when stability at follow-up was considered. However, when other criteria, as well as the patients' assessment of the operative result, are included, both methods can be recommended without any major differences.