Seasonal and long-term variations in the body size of planktonic copepods in the northern Baltic Sea

Seasonal and long-term variations in the body size of planktonic copepods were studied in the northern Baltic Sea. The influence of temperature, salinity and phytoplankton concentration to the body size of Eurytemora affinis, Acartia bifilosa and Limnocalanus macrurus (Calanoida) was examined at three sea areas, differing in their hydrographical and trophic conditions (an archipelago area and an enclosed bay on the SW coast of Finland in 1992 and at an open sea station in the Gulf of Bothnia in 1991). There was an inverse relationship between copepod body length and temperature, while there was a direct effect of phytoplankton concentration. According to multiple regression analysis, the relative importance of these factors varied according to species, developmental stage and study area. In the archipelago area, copepod body size was mainly determined by temperature, while in the open Gulf of Bothnia, phytoplankton concentration was usually more important. Interannual variation in the summer body length of E. affinis and A. bifilosa was examined using samples collected over 18 years (1967 to 1984) in the archipelago area. In this analysis, the inverse relationship between water temperature and copepod body size disappeared; in E. affinis the average female length correlated positively with summer temperature. We suggest that the length and timing of the study period greatly influence the investigator's view of the factors regulating copepod body size.     

Sexual selection and the tail ornaments of North American barn swallows

Summary In this study conducted in southeastern Ontario, Canada, we manipulated the length of outer tail feathers (streamers) of male barn swallows (Hirundo rustica) shortly after they returned to four small breeding colonies in the spring. Both streamers on most males in these colonies were experimentally either lengthened or shortened by 20 mm and as a result 10 randomly chosen males of each category had their streamer lengths manipulated before the fertile period of their mate. Males with elongated streamers had a significantly shorter pre-laying period (from arrival until first egg date) than those with shortened streamers and we interpret this as indicating that they obtained their mates more rapidly. Females mated to elongated males had significantly longer tails and laid their first egg significantly earlier than those mated to shortened males; no other indices of reproductive success differed between these two experimental groups. These results provide some support for previous work suggesting that females prefer males with longer streamers and thus that streamer length in this species is under the influence of sexual selection. We also found that males with longer natural streamers were significantly more likely to break them and that males were much more likely to break their streamers than were females. Since males participate in incubation in North America but not in Europe, we suggest that the aerodynamic disadvantages of streamer breakage that result from incubation attentiveness are at least partly responsible for the shorter streamer length of males in North America. Offprint requests to: R. Montgomerie     

Dominance,prior occupancy,and winter residency in the great tit (Parus major)

Summary This study reports an aviary experiment aimed at determining what affects social dominance in the great tit (Parus major), especially why older birds (adults) in nature normally dominate younger ones (juveniles). When birds were matched with respect to age, prior residency determined dominance. Without a difference in prior residency older birds dominated younger ones. However, when juvenile birds had a prior residency advantage over adult birds, they often became dominant. This was especially so when the juvenile bird was large relative to the adult bird. When a resident juvenile male was also consorted by a female, he became dominant over an adult male on most occasions. An experiment where the dominant bird was removed and later returned to the aviary failed to produce more than one shift in dominance. However, the proportion of reversals in dominance interactions increased with separation time. It is argued that the fact that dominance depends on prior residency selects for winter residency in the great tit.Offprint requests to: H.G. Smith     

Diel vertical migration and feeding patterns of Mysis mixta (Crustacea,Mysidacea) in the Baltic Sea

The extent of the nocturnal vertical migration of Mysis mixta Lilljeborg varied between early July and late October (of 1985 and 1986) in a coastal area of the Baltic Sea. Migration was more restricted in early July and late October. Seasonal changes in surface light levels and transparency were sufficient to explain the observed differences. Mysids avoided light levels above 10^-4 lux throughout the study period. Smaller juveniles migrated higher up than larger juveniles and adults. A two-layered distribution with part of the population close to the bottom was observed at night. Zooplankton were more abundant in water layers above the main concentration of mysids. M. mixta fed on phytoplankton, detritus, copepods, cladocerans, rotifers and tintinnids. Diel changes in gut fluorescence indicated a higher intake of phytoplankton at night, but levels were low compared to primarily herbivorous zooplankton. Comparisons of stomach contents of mysids caught at the bottom in the evening and in the water column at night showed a higher ingestion of zooplankton at night and of detritus during the day. Mysids caught at the bottom at night had an intermediate diet. Copepods and cladocerans constituted between 90 and 100% of ingested material by weight in all mysid groups.     

Organochlorine pollutants in Scots pine needles--biological and site related variation within a forest stand

To study the biological variation in the content of some persistent organic pollutants, viz hexachlorobenzene (HCB), alpha- and gamma-hexachlorocyclohexane (alpha- and gamma-HCH), and 1,1,1-trichloro-2,2-bis-(4-chlorophenyl)-ethane (DDT) were analysed in needles from Scots pine trees growing at an isolated peninsula south of Stockholm, Sweden. The concentration variations of each compound was evaluated by a nested analysis of variance (ANOVA) with sampling site specific compass direction, individual tree, and sampling height as factors. Two pair-wise post hoc tests were used to test significant results from the ANOVA. The hexachlorocyclohexanes showed no significant differences between sampling site, trees or sampling height. DDT concentration was significantly lower at the sampling site with the densest vegetation compared to at least three of the other sampling sites. HCB was significantly lower at the lowest sampling height (0.5 m).     

Synthesis of effects in four Arctic subregions

An assessment of impacts on Arctic terrestrial ecosystems has emphasized geographical variability in responses of species and ecosystems to environmental change. This variability is usually associated with north-south gradients in climate, biodiversity, vegetation zones, and ecosystem structure and function. It is clear, however, that significant east-west variability in environment, ecosystem structure and function, environmental history, and recent climate variability is also important. Some areas have cooled while others have become warmer. Also, east-west differences between geographical barriers of oceans, archipelagos and mountains have contributed significantly in the past to the ability of species and vegetation zones to relocate in response to climate changes, and they have created the isolation necessary for genetic differentiation of populations and biodiversity hot-spots to occur. These barriers will also affect the ability of species to relocate during projected future warming. To include this east-west variability and also to strike a balance between overgeneralization and overspecialization, the ACIA identified four major sub regions based on large-scale differences in weather and climate-shaping factors. Drawing on information, mostly model output that can be related to the four ACIA subregions, it is evident that geographical barriers to species re-location, particularly the distribution of landmasses and separation by seas, will affect the northwards shift in vegetation zones. The geographical constraints--or facilitation--of northward movement of vegetation zones will affect the future storage and release of carbon, and the exchange of energy and water between biosphere and atmosphere. In addition, differences in the ability of vegetation zones to re-locate will affect the biodiversity associated with each zone while the number of species threatened by climate change varies greatly between subregions with a significant hot-spot in Beringia. Overall, the subregional synthesis demonstrates the difficulty of generalizing projections of responses of ecosystem structure and function, species loss, and biospheric feedbacks to the climate system for the whole Arctic region and implies a need for a far greater understanding of the spatial variability in the responses of terrestrial arctic ecosystems to climate change.     

A net loss: policy instruments for commercial cod fishing in Sweden

This paper describes the overfishing of the seas, in particular for cod in Sweden. It discusses policy instruments such as individual quotas, labelling and marine reserves. A tentative conclusion is that something needs to be done to the very structure of the policy instruments used. Information on stock depletion is available but goes unheeded and is counteracted by fishermen who want to fish more and who are routinely supported by "the political establishment" who appear to be most concerned about (short-term) employment. The whole debate is taking place before the eyes of a general public that does not care sufficiently and difficult international bureaucracy. In this situation, the most important changes may be to strengthen both the rights and the duties of the fishermen. The integrity of fish stocks must be given absolute priority, but it is also important to motivate the fishermen with a greater stake and interest in the stock by giving them quotas that have, as far as possible, the characteristics of property.