Abiotic and biotic processes in lakes recovering from acidification: the relative roles of metal toxicity and fish predation as barriers to zooplankton re‐establishment

1. Recovery of acidified aquatic systems may be affected by both abiotic and biotic processes. However, the relative roles of these factors in regulating recovery may be difficult to determine. Lakes around the smelting complexes near Sudbury, Ontario, Canada, formerly affected by acidification and metal exploration, provide an excellent opportunity to examine the factors regulating the recovery of aquatic communities. 2. Substantial recovery of zooplankton communities has occurred in these lakes following declines in acidity and metal concentrations, although toxicity by residual metals still appears to limit survival for many species. Metal bioavailability, not simply total metal concentrations, was very important in determining effects on zooplankton and was associated with a decrease in the relative abundance of cyclopoids and Daphnia spp., resulting in communities dominated by Holopedium gibberum. 3. As chemical habitat quality has improved and fish, initially yellow perch and later piscivores (e.g. smallmouth bass, walleye), have invaded, biotic effects on the zooplankton are also becoming apparent. Simple fish assemblages dominated by perch appear to limit the survival of some zooplankton species, particularly Daphnia mendotae. 4. Both abiotic (residual metal contamination) and biotic (predation from planktivorous fish) processes have very important effects on zooplankton recovery. The re‐establishment of the zooplankton in lakes recovering from stress will require both improvements in habitat quality and the restoration of aquatic food webs.     

The noncosmopolitanism paradigm of freshwater zooplankton: insights from the global phylogeography of the predatory cladoceran Polyphemus pediculus (Linnaeus, 1761) (Crustacea,Onychopoda)

A major question in our understanding of eukaryotic biodiversity is whether small bodied taxa have cosmopolitan distributions or consist of geographically localized cryptic taxa. Here, we explore the global phylogeography of the freshwater cladoceran Polyphemus pediculus (Linnaeus, 1761) (Crustacea, Onychopoda) using two mitochondrial genes, cytochrome c oxidase subunit I and 16s ribosomal RNA, and one nuclear marker, 18s ribosomal RNA. The results of neighbour‐joining and Bayesian phylogenetic analyses reveal an exceptionally pronounced genetic structure at both inter‐ and intra‐continental scales. The presence of well‐supported, deeply divergent phylogroups across the Holarctic suggests that P. pediculus represents an assemblage of at least nine, largely allopatric cryptic species. Interestingly, all phylogenetic analyses support the reciprocal paraphyly of Nearctic and Palaearctic clades. Bayesian inference of ancestral distributions suggests that P. pediculus originated in North America or East Asia and that European lineages of Polyphemus were established by subsequent intercontinental dispersal events from North America. Japan and the Russian Far East harbour exceptionally high levels of genetic diversity at both regional and local scales. In contrast, little genetic subdivision is apparent across the formerly glaciated regions of Europe and North America, areas that historical demographic analyses suggest that were recolonized just 5500–24 000 years ago.     

Interactive effects of multiple stressors and restoration priorities in a mined Appalachian watershed

We surveyed benthic macroinvertebrate communities, water chemistry, and thermal regime in the Cheat River, WV, USA in an attempt to quantify the interactive effects of multiple stressors on ecological condition and identify priorities for restoration in this mined Appalachian watershed. We used a novel approach, which combined use of the West Virginia Stream Condition Index (WVSCI) to quantify ecological losses and community similarity analysis to assign specific levels of ecological loss to AMD, thermal effluent, and their interaction. Finally, we developed an ecological currency to quantify the relative benefits of a restoration program that focused either on AMD remediation or heat reduction and to identify spatially explicit restoration priorities. Variation in ecological condition was strongly correlated to variation in water quality when AMD and heat stress occurred in isolation. Acute inputs of AMD or heat caused predictable reductions in condition followed by rapid recovery downstream. However, benthic communities failed to recover from combined inputs of heat and AMD even when these stressors occurred at relatively low levels. Over the course of an entire year, AMD alone was over two times more responsible than heat alone for ecological loss. Consequently, AMD is the dominant factor limiting ecological condition and should be the primary target for restoration. Nevertheless, an AMD × heat interaction also was responsible for extensive ecological loss in lower reaches of the river. Consequently, full restoration of the lower Cheat River mainstem will require an approach that integrates AMD remediation with effective management of thermal effluent. Our results provide some of the first field evidence of the interactive effects of multiple stressors on biological communities in a mined watershed. This approach may be valuable for quantifying impacts from multiple interacting stressors and for prioritizing restoration efforts in other mined watersheds. Handling editor: S. M. Adams     

Mass effects,clonality, and phenology but not seed traits predict species success in colonizing restored grasslands

Preserved grasslands commonly host species‐rich plant communities but a large part of the grasslands were plowed up in the past. Their restoration often requires a long time and initial restoration measures might trigger ecosystem recovery, which is then followed by spontaneous colonization. We evaluate the establishment success of target grassland species, which were not sown but established spontaneously in the restored grasslands of Bílé Karpaty Mts., SE Czech Republic. According to their key functional traits and incidence in the landscape (mass effect; acquired from the results of a grid mapping project in the region), we examined the frequency of species and their mean cover in 82 restored grasslands. The best predictor of species frequency in the grasslands was their mass effect, followed by a high capacity for clonal growth and late phenology. Seed dispersal traits (seed mass, terminal velocity, epizoochory ranking index) and plant height had no significant effect. Specific leaf area was positively correlated with mass effect. Species having a high cover in the restored grasslands had a high capacity for clonal growth. In the preparation of seed mixtures, we should therefore consider that nonclonal species relying on regeneration from seeds will be generally less able to reproduce and should be promoted by artificial sowing. At the same time, species common in the landscape, which spread well clonally, and those with a late phenology, might be expected to colonize restored meadows on their own, so that sowing them is not necessary.