RESUMO
Understanding the spatial scales at which organisms can adapt to strong natural and human-induced environmental gradients is important. Salinization is a key threat to biodiversity, ecosystem functioning and the provision of ecosystem services of freshwater systems. Clusters of naturally saline habitats represent ideal test cases to study the extent and scale of local adaptation to salinization. We studied local adaptation of the water flea Daphnia magna, a key component of pond food webs, to salinity in two contrasting landscapes-a dense cluster of sodic bomb crater ponds and a larger-scale cluster of soda pans. We show regional differentiation in salinity tolerance reflecting the higher salinity levels of soda pans versus bomb crater ponds. We found local adaptation to differences in salinity levels at the scale of tens of metres among bomb crater pond populations but not among geographically more distant soda pan populations. More saline bomb crater ponds showed an upward shift of the minimum salt tolerance observed across clones and a consequent gradual loss of less tolerant clones in a nested pattern. Our results show evolutionary adaptation to salinity gradients at different spatial scales, including fine-tuned local adaptation in neighbouring habitat patches in a natural landscape.
Assuntos
Ecossistema , Tolerância ao Sal , Animais , Biodiversidade , Daphnia , Água Doce , SalinidadeRESUMO
Climate change-related heatwaves are major threats to biodiversity and ecosystem functioning. However, our current understanding of the mechanisms governing community resistance to and recovery from extreme temperature events is still rudimentary. The spatial insurance hypothesis postulates that diverse regional species pools can buffer ecosystem functioning against local disturbances through the immigration of better-adapted taxa. Yet, experimental evidence for such predictions from multi-trophic communities and pulse-type disturbances, like heatwaves, is largely missing. We performed an experimental mesocosm study to test whether species dispersal from natural lakes prior to a simulated heatwave could increase the resistance and recovery of plankton communities. As the buffering effect of dispersal may differ among trophic groups, we independently manipulated the dispersal of organisms from lower (phytoplankton) and higher (zooplankton) trophic levels. The experimental heatwave suppressed total community biomass by having a strong negative effect on zooplankton biomass, probably due to a heat-induced increase in metabolic costs, resulting in weaker top-down control on phytoplankton. While zooplankton dispersal did not alleviate the negative heatwave effects on zooplankton biomass, phytoplankton dispersal enhanced biomass recovery at the level of primary producers, providing partial evidence for spatial insurance. The differential responses to dispersal may be linked to the much larger regional species pool of phytoplankton than of zooplankton. Our results suggest high recovery capacity of community biomass independent of dispersal. However, community composition and trophic structure remained altered due to the heatwave, implying longer-lasting changes in ecosystem functioning.
Assuntos
Ecossistema , Plâncton , Animais , Zooplâncton/fisiologia , Biodiversidade , Biomassa , Fitoplâncton/fisiologia , Cadeia AlimentarRESUMO
Growing evidence suggests that global climate change promotes the dominance of mixotrophic algae especially in oligotrophic aquatic ecosystems. While theory predicts that mixotrophy increases trophic transfer efficiency in aquatic food webs, deleterious effects of some mixotrophs on consumers have also been reported. Here, using a widespread mixotrophic algal genus Dinobryon, we aimed to quantify how colonial taxa contribute to secondary production in lakes. We, therefore, studied the dietary effects of Dinobryon divergens on Cladocera (Daphnia longispina) and Copepoda (Eudiaptomus gracilis), representing two main taxonomic and functional groups of zooplankton. In feeding experiments, we showed that Dinobryon was largely grazing resistant and even inhibited the uptake of the high-quality reference food in Daphnia. Eudiaptomus could to some extent compensate with selective feeding, but a negative long-term food quality effect was also evident. Besides, Eudiaptomus was more sensitive to the pure diet of Dinobryon than Daphnia. Low lipid content and high C:P elemental ratio further supported the low nutritional value of the mixotroph. In a stable isotope approach analysing a natural plankton community, we found further evidence that carbon of Dinobryon was not conveyed efficiently to zooplankton. Our results show that the increasing dominance of colonial mixotrophs can result in reduced dietary energy transfer to consumers at higher trophic levels. In a wider perspective, global climate change favours the dominance of some detrimental mixotrophic algae which may constrain pelagic trophic transfer efficiency in oligotrophic systems, similarly to cyanobacteria in eutrophic lakes.
Assuntos
Ecossistema , Zooplâncton , Animais , Cadeia Alimentar , Qualidade dos Alimentos , LagosRESUMO
When habitats are lost, species are lost in the region as a result of the sampling process. However, it is less clear what happens to biodiversity in the habitats that remain. Some have argued that the main influence of habitat loss on biodiversity is simply due to the total amount of habitat being reduced, while others have argued that fragmentation leads to fewer species per site because of altered spatial connectance among extant habitats. Here, we use a unique data set on invertebrate species in ponds spanning six decades of habitat loss to show that both regional and local species richness declined, indicating that species loss is compounded by habitat loss via connectivity loss, and not a result of a sampling process or changes in local environmental conditions. Overall, our work provides some of the clearest evidence to date from a longitudinal study that habitat loss translates into species loss, even within the remaining habitats.
Assuntos
Biodiversidade , Ecossistema , Estudos Longitudinais , LagoasRESUMO
Considering the ongoing loss of aquatic habitats, anthropogenic ponds are gaining importance as substitute habitats. It is therefore important to assess their functioning in comparison to their natural precursors. Here we assess the biodiversity value of sodic bomb crater ponds by comparing their gamma diversity to that of natural reference habitats, astatic soda pans, and assess their importance on the landscape level by studying alpha and beta diversity. We studied aquatic organisms ranging from algae to vertebrates in a dense cluster of 54 sodic bomb crater ponds in Central Europe. Despite the overall small area of the pond cluster, gamma diversity was comparable to that found in surveys of natural habitats that encompassed much wider spatial and temporal scales. We also found a considerable number of species shared with reference habitats, indicating that these anthropogenic habitats function as important refuge sites for several species that are associated with the endangered soda pans. Moreover, we found a number of regionally or worldwide rare species. Among the components of beta diversity, species replacement dominated community assembly. Individual ponds contributed similarly to beta diversity in terms of replacement, being equally important for maintaining high gamma diversity and emphasising the role of the pond network rather than individual ponds. This pattern was seen in all studied groups. Bomb crater ponds therefore acted as important contributors to aquatic biodiversity. Considering the tremendous losses of ponds throughout Europe, anthropogenic ponds should be taken into consideration in nature conservation, especially when occurring in pond networks.
RESUMO
Directional dispersal by wind and other dispersal agents may generate spatial patterns in passively dispersing metacommunities which cannot be detected by classical eigenvector methods based on Euclidean distances. We analysed zooplankton communities (Rotifera, Cladocera, Copepoda) in a cluster of soda pans distributed over a short spatial scale of 18 km and tested explicitly for directional signals in their spatial configuration. The study area is exposed to a prevailing northwestern wind direction. By applying asymmetric eigenvector maps (AEM), we were able to identify corresponding directionality in the spatial structure of communities. Furthermore, the match between community composition and environmental conditions exhibited a spatial pattern consistent with the prevailing wind corridor, with best match found downwind the dominant wind direction. We also found that classical eigenvector methods based on Euclidean distances underestimated the role of spatial processes in our data. Our study furthermore shows that dispersal limitation may constrain community assembly in highly mobile organisms even at spatial scales below 5 km.
RESUMO
The degree of dietary specialization has a fundamental impact on the ecological function and interactions of suspension feeders. While niche differentiation by food particle size is common among obligate suspension feeders, its role is not evident in facultative ones. In this study, we aimed at providing new insights on the matter by focusing on sympatric mysid species. As mysids use different mechanisms for raptorial and filter-feeding, they represent a more adequate model system than for example, the more extensively studied copepods. We made morphological measurements on the 4 coexisting invasive Ponto-Caspian mysid species to determine the areas and mesh sizes of their filters. We also quantified their clearance rates on the microalga Cryptomonas sp. in a laboratory experiment to reveal how morphological differences manifest in their overall filtering capacity. We found relatively small but consistent differences in the primary filter area among the species, indicating that morphological constraints due to the enclosed position of the setae might limit the possibility for differentiation. The primary filter mesh sizes were small in all 4 species (0.69-2.73 µm) with moderate but consistent intraspecific differences, suggesting that the benefit of being able to capture small particles might outweigh the pressure for differentiation. The observed clearance rates were in accordance with the morphological characteristics of the species, highlighting that auxiliary filters (present in one of the species, Limnomysis benedeni) are needed to increase filtering capacity considerably. Our study confirmed that food particle size can contribute to the niche differentiation of facultative filter feeders, but also indicated that they can tolerate a higher overlap than obligate ones. The observed differences were related to the habitat preferences and predatory potentials of the species, suggesting that complementarity among the different niche axes might further facilitate their coexistence.
RESUMO
Understanding the diet preferences and food selection of invasive species is crucial to better predict their impact on community structure and ecosystem functioning. Limnomysis benedeni, a Ponto-Caspian invasive mysid shrimp, is one of the most successful invaders in numerous European river and lake ecosystems. While existing studies suggest potentially strong trophic impact due to high predation pressure on native plankton communities, little is known of its food selectivity between phyto- and zooplankton, under different food concentrations. Here, we therefore investigated the feeding selectivity of L. benedeni on two commonly occurring prey organisms in freshwaters, the small rotifer zooplankton Brachionus calyciflorus together with the microphytoplankton Cryptomonas sp. present in increasing densities. Our results demonstrated a clear shift in food selection, with L. benedeni switching from B. calyciflorus to Cryptomonas sp. already when the two prey species were provided in equal biomasses. Different functional responses were observed for the two food types, indicating somewhat different foraging mechanisms for each food type. These findings provide experimental evidence on the feeding flexibility of invasive mysid shrimps and potential implications for trophic interactions in invaded ecosystems.
RESUMO
Freshwater ecosystems are increasingly affected by rising annual mean temperatures and heatwaves. While heatwaves are expected to have more immediate effects than mean temperature increases on local communities, comparative experimental studies are largely lacking. We conducted a 1-month mesocosm experiment to test the effect of different warming treatments, constantly raised temperatures (+3°C) and recurring heatwaves (+6°C), on plankton communities. We specifically tested how shifts in zooplankton trait composition and functional groups are reflected in ecosystem function (top-down control on primary producers). We found that heatwaves had a stronger and more immediate effect on zooplankton trait composition (specifically on body length and body mass) and functional groups. Heatwaves led to the decrease of small-bodied grazers (i.e., Rotifera) and the dominance of larger omnivorous Copepoda, and these shifts resulted in weaker top-down control, leading to elevated phytoplankton biomass. Altogether, our results highlight the importance of the indirect effects of heatwaves via inducing shifts in zooplankton functional groups and trait composition, which may lead to algal blooms.
RESUMO
Temporary ponds are among the most sensitive aquatic habitats to climate change. Their microbial communities have crucial roles in food webs and biogeochemical cycling, yet how their communities are assembled along environmental gradients is still understudied. This study aimed to reveal the environmental drivers of diversity (OTU-based richness, evenness, and phylogenetic diversity) and community composition from a network of saline temporary ponds, soda pans, in two consecutive spring seasons characterized by contrasting weather conditions. We used DNA-based molecular methods to investigate microbial community composition. We tested the effect of environmental variables on the diversity of prokaryotic (Bacteria, Cyanobacteria) and microeukaryotic functional groups (ciliates, heterotrophic flagellates and nanoflagellates, fungi, phytoplankton) within and across the years. Conductivity and the concentration of total suspended solids and phosphorus were the most important environmental variables affecting diversity patterns in all functional groups. Environmental conditions were harsher and they also had a stronger impact on community composition in the dry spring. Our results imply that these conditions, which are becoming more frequent with climate change, have a negative effect on microbial diversity in temporary saline ponds. This eventually might translate into community-level shifts across trophic groups with changing local conditions with implications for ecosystem functioning.
Assuntos
Cianobactérias , Ecossistema , Filogenia , Cadeia Alimentar , Águas Salinas , BiodiversidadeRESUMO
Very little is known about the feeding of naupliar and juvenile life stages of omnivorous fairy shrimps (Crustacea: Anostraca). Here, we aim to reveal whether the fairy shrimp Branchinecta orientalis is an ontogenetic omnivore and at which age and ontogenetic stage they gain the ability to feed on zooplankton. We assess how food uptake rates change with age until reaching maturity by providing algae (pico- and nanoplanktonic unicellular algae) and zooplankton (rotifers and copepod nauplii) as food in individual experiments. We found that the fairy shrimp B. orientalis started to feed on both types of algal prey immediately after hatching. Nanoplanktonic algae likely represented the most important food source until reaching maturity. Moreover, fairy shrimps started to feed on zooplankton already when they were 7 days old. Slow-moving rotifers gradually gained importance in the fairy shrimp diet with time. Our results reveal an ontogenetic change in the prey spectrum of fairy shrimp. The systematic shift towards omnivory likely affects both phyto- and zooplankton community composition, possibly contributing to temporal changes in food web dynamics in fairy shrimp habitats, and temporary ponds, which may warrant more detailed investigations in future studies. Supplementary Information: The online version contains supplementary material available at 10.1007/s10750-022-05132-z.
RESUMO
The widespread salinisation of freshwater ecosystems poses a major threat to the biodiversity, functioning, and services that they provide. Human activities promote freshwater salinisation through multiple drivers (e.g., agriculture, resource extraction, urbanisation) that are amplified by climate change. Due to its complexity, we are still far from fully understanding the ecological and evolutionary consequences of freshwater salinisation. Here, we assess current research gaps and present a research agenda to guide future studies. We identified different gaps in taxonomic groups, levels of biological organisation, and geographic regions. We suggest focusing on global- and landscape-scale processes, functional approaches, genetic and molecular levels, and eco-evolutionary dynamics as key future avenues to predict the consequences of freshwater salinisation for ecosystems and human societies.
Assuntos
Ecossistema , Água Doce , Biodiversidade , Evolução Biológica , Mudança Climática , HumanosRESUMO
Pleistocene glaciations had a tremendous impact on the biota across the Palaearctic, resulting in strong phylogeographic signals of range contraction and rapid postglacial recolonization of the deglaciated areas. Here, we explore the diversity patterns and history of two sibling species of passively dispersing taxa typical of temporary ponds, fairy shrimps (Anostraca). We combine mitochondrial (COI) and nuclear (ITS2 and 18S) markers to conduct a range-wide phylogeographic study including 56 populations of Branchinecta ferox and Branchinecta orientalis in the Palaearctic. Specifically, we investigate whether their largely overlapping ranges in Europe resulted from allopatric differentiation in separate glacial refugia followed by a secondary contact and reconstruct their postglacial recolonization from the inhabited refugia. Our results suggest the existence of distinct refugia for the two species, with genetic divergence among intraspecific lineages consistent with late Pleistocene glacial cycles. While B. ferox lineages originated from Mediterranean refugia, the origin of B. orientalis lineages was possibly located on the Pannonian Plain. We showed that most dispersal events predominantly happened within 100 km, coupled with several recent long-distance events (> 1000 km). Hence the regional habitat density of suitable habitats in Central Europe is possibly a key to the co-existence of the two species. Overall, our study illustrates how isolation in combination with stochastic effects linked to glacial periods are important drivers of the allopatric differentiation of Palaearctic taxa.
Assuntos
Anostraca/genética , DNA Mitocondrial/genética , Evolução Molecular , Variação Genética , Animais , Ecossistema , Deriva Genética , Haplótipos , Modelos Genéticos , Filogenia , Filogeografia , Lagoas , Dinâmica Populacional , Processos EstocásticosRESUMO
Lakes in the Alps represent a considerable fraction of nutrient-poor lakes in Central Europe, with unique biodiversity and ecosystem properties. Although some individual lakes are well studied, less knowledge is available on large-scale patterns essential to general understanding of their functioning. Here, we aimed to describe crustacean zooplankton communities (Cladocera, Copepoda) and identify their environmental drivers in the pelagic zone of 54 oligotrophic lakes in the montane region of the Alps (400-1200 m) in Austria, Germany, and Switzerland, covering a spatial scale of 650 km. Moreover, we aimed to provide data on the distribution and ecological requirements of the North American invader Bythotrephes longimanus in its Central European native range. Communities were mainly dominated by widespread species typical of lowland habitats, and only a few true specialists of oligotrophic alpine lakes were present. The most frequent taxa were the Daphnia longispina complex and Eudiaptomus gracilis, with 48 and 45 occurrences, respectively. Species richness decreased with altitude and increased with lake area. The main structuring factors of community composition were chlorophyll a concentration and depth, which drove an apparent separation of mesotrophic and oligotrophic communities. Bythotrephes had 13 occurrences, showing a preference for deep oligotrophic lakes. Its presence was not coupled with lower crustacean species richness, as was repeatedly observed in North America. Additionally, it frequently co-occurred with the other large predatory cladoceran, Leptodora kindtii. B. longimanus might be considered a truly montane species in Central Europe, given its absence in lowland and alpine lakes.
RESUMO
Lakes in the Alps represent a considerable fraction of nutrient-poor lakes in Central Europe, with unique biodiversity and ecosystem properties. Although some individual lakes are well-studied, less knowledge is available on large-scale patterns essential to generalise the understanding of their functioning. Here, we aimed to describe crustacean zooplankton communities (Cladocera, Copepoda) and identify their environmental drivers in the pelagic zone of 54 oligotrophic lakes in the montane region of the Alps (400-1200 m) in Austria, Germany, and Switzerland, covering a spatial scale of 650 km. Moreover, we aimed to provide data on the distribution and ecological requirements of the North American invader Bytotrephes longimanus in its Central European native range. Communities were mainly dominated by widespread species typical of lowland habitats, and only a few true specialists of oligotrophic alpine lakes were present. The most frequent taxa were the Daphnia longispina complex and Eudiaptomus gracilis, with 48 and 45 occurrences, respectively. Species richness decreased with altitude and increased with lake area. The main structuring factors of community composition were chlorophyll a concentration and depth, which drove an apparent separation of mesotrophic and oligotrophic communities. Bytotrephes had 13 occurrences, showing a preference for deep oligotrophic lakes. Its presence was not coupled with lower crustacean species richness as it was repeatedly observed in North America. Additionally, it frequently co-occurred with the other large predatory cladoceran, Leptodora kindtii. B. longimanus might be considered a truly montane species in Central Europe, given its absence in lowland and alpine lakes.