Abstract. Weed communities, comprising 12 introduced species at constant starting densities and three species already present in the seed bank, were followed through three years of continuous winter wheat. The wheat and weeds were subjected to two treatments in a split‐plot factorial design, organic contrasting with conventional fertilizer, and ploughing plus hand‐roguing contrasting with minimum tillage plus herbicide. The minimum tilled plots developed in a uniform manner, and became dominated by very high densities of Anisantha sterilis. Agrostemma githago and Galium aparine also persisted in these plots at lower densities. The ploughed plots had a lower total density but a greater range of species. Stellaria media, Veronica persica and Avena fatua were the most common; other species occurred at lower densities. The major effect of fertilizer treatment was a greater initial increase by G. aparine on the organic, minimum tilled plots compared with the conventionally fertilized, minimum tilled plots. Species associated with minimum tillage were annuals with either no or a short term seed bank and autumn germination and rather predictable dynamics, whereas species that did well under ploughing were either spring germinating or had a persistent seed bank, implying greater annual variation in population size associated with weather conditions. There seemed no clear way to distinguish between those species which were abundant on the ploughed plots and those which were scarce under all conditions using readily accessible data.

Interactions between the weeds Bromussterilis L., Galium aparine L. and Papaver rhoeas L. were investigated over 3 years of continuous winter wheat (Triticum aestivum L.) across a factorial combination of organic and conventional fertilizer, and ploughing and hand‐roguing contrasted with minimum tillage and herbicide. The species were sown separately and together at 50 seeds m−2 per species at the start of the experiment in October 1989. In addition, there were weed‐free and background‐weed controls. Weed densities were monitored at roughly monthly intervals and crop yield recorded for three seasons. B. sterilis populations increased 10‐fold under minimum tillage, but declined under ploughing. Densities of P. rhoeas remained largely low. G. aparine increased on the organically fertilized minimum‐tillage plots, except where B. sterilis was present; the high densities of B. sterilis reduced the population size of G. aparine. Crop yield was influenced most strongly by the fertilizer treatment in the first season, but later the density of B. sterilis was by far the most important factor; the evidence of interactive effects of the different weed species on crop yield was weak at best. Interactive effects of arable weed species can be observed, but only at very high densities, and so are unlikely to be of widespread economic importance.

We report preliminary results of a series of experiments designed to explore the importance of interspecific competition within arable weed communities at different scales. Competition hierarchies were apparent from a pot experiment with different levels of nutrients and water. Two field experiments looked at Bromus sterilis, Galium aparine and Papaver rhoeas in winter wheat in the field, in a range of combinations and management treatments, and a fourth field experiment included a wider variety of species. There was little effect of fertilizer on population behaviour in the the field. Bromus increased around ten fold per year on minimum‐tilled plots, regardless of other treatments. Galium increased on organically‐fertilized and minimum‐tilled plots, but only in the absence of Bromus. Papaver densities remained low, but again were depressed in the presence of high densities of Bromus. Taken together, the experiments demonstrate the existence of competition between weed species. However, as the design of the experiment increased to include greater levels of environmental variation, so competition became more difficult to detect, and less useful for interpreting the results than knowledge of the biology of the individual species. At the scale of interest to the farmer, the level of competition is not a good predictor for weed population dynamics.

Bright-green luminescent clouds frequently occur at the surface of shallow waters of the Caribbean Sea. These clouds are produced by syllid polychaetes during courtship. Although temporal variation in the occurrence of these courtship displays has been documented throughout the diurnal and lunar cycle, other factors such as habitat type have not been well studied. In this study, we investigated how syllid courtship-display densities varied across 3 substrate types (grassbed, rubble, and coral) over a 3 day period. In line with previous studies, we found that syllid courtship displays occurred over seagrass and rubble substrates; however, we also found that display densities were significantly higher over shallow coral substrates than over either seagrass or rubble habitats. These findings reflect published observations and newly collected observational data from other locations throughout the Caribbean. Future work across species, time and regions is required in order to better understand the factors underlying syllid display densities.

Morphological similarities between skates of the genus Dipturus in the north‐eastern Atlantic and Mediterranean have resulted in longstanding confusion, misidentification and misreporting. Current evidence indicates that the common skate is best explained as two species, the flapper skate (Dipturus intermedius) and the common blue skate (D. batis). However, some management and conservation initiatives developed prior to the separation continue to refer to common skate (as ‘D. batis’). This taxonomic uncertainty can lead to errors in estimating population viability, distribution range, and impact on fisheries management and conservation status. Here, we demonstrate how a concerted taxonomic approach, using molecular data and a combination of survey, angler and fisheries data, in addition to expert witness statements, can be used to build a higher resolution picture of the current distribution of D. intermedius. Collated data indicate that flapper skate has a more constrained distribution compared to the perceived distribution of the ‘common skate’, with most observations recorded from Norway and the western and northern seaboards of Ireland and Scotland, with occasional specimens from Portugal and the Azores. Overall, the revised spatial distribution of D. intermedius has significantly reduced the extant range of the species, indicating a possibly fragmented distribution range.