Mowing in agri-environmental schemes (AES) and rare species of Vertigo snails: hope for grasslands but a threat to snails

Four Vertigo species are covered by special forms of protection under Annex II of the Habitats Directive. The habitats of these snails are currently rare in Europe. Since typical conservation practices are ineffective for this ecosystem, support mechanisms for measures maintaining biodiversity have been incorporated into agriculture in the form of agri-environmental schemes (AES). However, an inappropriately designed AES may threaten the survival of populations of globally endangered species such as Vertigo moulinsiana (Dupuy) as mowing and swath removal dates coincide with the snails’ activity period in the upper parts of the mown plants, the majority of their population will be removed from the area along with the harvested swath. In addition, mowing instantaneously and radically alters the habitat’s microclimate. The policy of mowing the total area thus leads to unprecedented habitat homogenisation across the landscape, especially when machine mowers are used. In the case of V. moulinsiana, the best approach would be not to mow the whole area but to leave a part unmown where these snails could live unhindered. Instead of machines, traditional mowing could be implemented, which entails cutting at a greater height above the sedge clump level. This would not destroy the tussock structure and would allow the habitat to recreate itself. In combination with the designation of unmown refuges, the effects of this approach could be quite beneficial to the snails.

Response of freshwater mussel recruitment to hydrological changes in a eutrophic floodplain lake

Although eutrophication of freshwaters is a natural process, the human impact often leads to inland waters becoming overloaded with nutrients, impoverishing many valuable and vanishing habitats, such as floodplain lakes. These changes need to be reversed if the occurrence of endangered aquatic species is to be restored. In this paper we analyse the impact of a change in the water regime of a naturally eutrophic floodplain lake, which harbours a large diversity of Unionidae (large freshwater mussels), a globally threatened taxonomic group that provides important ecosystem functions and services. We found that a slight increase in the discharge from this waterbody, following the construction of an additional outflow pipe, positively influenced recruitment in three of the five mussel species inhabiting the lake. We also found that, after the construction of this additional outflow, the niches of juveniles of Anodonta cygnea and Unio spp. changed, revealing differences in their hydrological requirements. Our results suggest that, as in lotic habitats, complex hydraulic parameters are highly significant to unionid mussels in lentic conditions.

Intraseasonal asynchrony as a factor boosting isolation within a metapopulation: The case of the clouded apollo

This article discusses the influence of phenology-related intraseasonal asynchrony on metapopulation dynamics and stability. As the part played by intraseasonal asynchrony is as yet unclear and poorly described, greater account of it should be taken in both metapopulation research and conservation practice. The subpopulations of the Parnassius mnemosyne metapopulation studied here are strongly isolated because of the phenological shift between them, despite the relatively small physical distances between them. This isolation is the result of a significant temporal shift in the species' flight periods in the main metapopulation centers: in some seasons its flight times in the different subpopulations did not overlap at all. The predicted results of such strong intraseasonal asynchrony are not altogether clear. On the one hand, they reduce the vulnerability of the entire metapopulation to the effects of short-term random disasters. On the other, the ever-greater isolation of subpopulations may cause the metapopulation to become a nonequilibrium one, which will have a serious impact on its long-term survival.

On the reintroduction of the endangered thick-shelled river mussel Unio crassus: The importance of the river's longitudinal profile

Freshwater mussels of the order Unionida provide important ecosystem functions and services. Unfortunately, some previously widespread species are now seriously endangered. To restore the historical range of the population of Unio crassus in the Biała River, southern Poland, the species was reintroduced into a series of 'stepping stones' joining two remnant populations. During the first phase of the study, the relationships between the abundance of U. crassus, physical habitat, and water quality were studied to assess reintroduction potential. In general, chemical water quality improved upstream from the existing population, favouring the decision for reintroduction, whereas morphological variables worsened. Mussel abundance was correlated negatively with the elevation and slope of channel, organic matter contents, and pH (exceeding 8.0), but positively with silt presence, water conductivity, and concentrations of HCO₃^-, Ca²⁺, and NO₃^-. During the second phase, adult individuals were introduced into one type of functional habitat-marginal channel sectors with still water and fine sediment. Despite the initial very high rate of reproduction in some parts of the upper reach of the river, the juveniles were ultimately recruited only in the lower part of the restored range, resulting in a very rapid change in recruitment at a channel slope of 1.8‰. Recruitment was positively related to silt content, conductivity, and Ca²⁺ and HCO₃^- ions, negatively to channel elevation and slope, and water pH. The host fish species showed no correlation with abiotic habitat features within the studied reach. These results imply that most of the habitat traits related to U. crassus occurrence depended on the river's longitudinal profile, not on the chemical water quality, and that final success of introduction should be evaluated after several years.