Search

ABSTRACT Aim In times of biodiversity crisis, it is extremely important to understand diversity gradients. In particular, the study of the diversity of ecological functions is a key issue for the management of ecosystem integrity. Here we identify areas of low functional diversity of the native fish fauna in European drainage basins and we determine the relative importance of three underlying mechanisms: environmental filtering, geographic isolation and climatic history. Location The European continent. Methods Based on 14 morphological traits that are closely related to fish function (habitat and dietary niches), three independent functional diversity indices [functional richness (FR), functional evenness (FE), functional divergence (FD)] were calculated for 128 European drainage basins with a total of 230 fish species. The indices were standardized for species richness using null models. The patterns of the standardized indices are described and three potentially underlying mechanisms are tested using variance partitioning and multi-linear regression models. Results FR and FD were highest in eastern European drainage basins and in Great Britain and lowest in the Mediterranean. FE patterns were less pronounced. All observed patterns were mainly governed by geographic isolation and present environmental conditions. Within the environmental conditions, average annual temperature and precipitation were good predictors for functional diversity. The role of habitat diversity and size was negligible. Main conclusions Geographic isolation coupled with harsh environmental conditions such as extreme temperatures and low precipitation, as in Mediterranean regions, can lead to low FR and FD. This can be explained by extinction that could not be compensated by re-colonization and high speciation. Due to their high functional redundancy, communities in these areas might better withstand further species extinctions on a small scale. Over the short term, however, their often extremely low FR suggests a less flexible functioning that can hinder their ability to withstand today's rapid environmental and anthropogenic threats. [ABSTRACT FROM AUTHOR]

The effect of group size on the routine metabolic rate and activity of the two shoaling percids, Eurasian perch and ruffe , was studied by using twin-flow intermittent respirometry and time-lapse video techniques. In both species, we found a clear group effect. In isolated fish, oxygen consumption was as much as twice that in groups of eight fish, with intermediate values in groups of four fish. The routine metabolic rate was highest during twilight in both species, irrespective of group size. Eurasian perch consumed more oxygen and were more active during the day than during the night, whereas the oxygen consumption and activity of ruffe were higher during the night than during the day. With increasing group size, the differences between day and night decreased and the diel cycle was less pronounced. Individual fish may benefit from the presence of conspecifics through a calming effect that reduces their energetic costs. We advise that the social behavior of a species be more thoroughly considered when planning behavioral, growth, and respiration experiments. Because bioenergetic model parameters for many species are based on data gained from isolated fish, we conclude that without considering group size the results of bioenergetic modeling may be seriously biased. [ABSTRACT FROM AUTHOR]