Habitat use by singing voles and tundra voles in the southern Yukon

Summary We investigated how far competitive interactions influence the use of habitats and relative abundance of two species of Microtus in the southwestern Yukon. We worked in the ecotone between alpine tundra and subalpine shrub tundra where populations of singing voles (Microtus miurus) and tundra voles (M. oeconomus) overlap little.We removed tundra voles from shrub tundra on one live-trapping area to look at the effect on the contiguous population of singing voles in alpine tundra. The removal of tundra voles did not affect the distribution or relative abundance of singing voles. The spatial distribution of these species and their movements within habitats suggest that they have a strong habitat preference.Populations of small mammals in the area are extremely dynamic and the relative importance of competitive interactions may change as density varies. At present we have no evidence that competition affects habitat use in M. miurus.     

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.     

Combined effects of environmental factors and predator–prey interactions on zooplankton assemblages in five high alpine lakes

The examination of a yearly cycle of plankton density (rotifer and microcrustacean) and of 419 stomach contents of four species of salmonid fishes, arctic charr, Salvelinus alpinus, brown trout, Salmo trutta, rainbow trout, Onchorynchus mykiss and lake trout, Salvelinus namaycush, living in five high altitude lakes in the French Alps, shows an impact of abiotic variates and the effects of predation on the composition of zooplankton assemblages. The lakes studied may be divided in two groups. The colder, Muzelle and Puy Vachier, are characterised by a low level of food resources, an important impact of predation, and the near absence of planktonic crustaceans. The second group, consisting of Lakes Les Pisses, Petarel and Palluel, is characterised by a low density rotifer assemblage and a more abundant crustacean population controlled by a low level of fish predation.     

Quantitative analysis of freshwater ostracode assemblages in southwestern Yukon Territory,Canada

Relations between modern ostracode assemblages and environmental variables from lakes in the southwest Yukon and northern British Columbia were explored. A total of 29 freshwater species representing 8 genera were identified from the sediments of 36 lakes, with the number of species ranging between 3 and 8 per lake. Species widespread throughout the study area include Cyclocypris ampla, Candona candida, Cypria turneri, Cypria ophtalmica, and Candona protzi. The Mg/Ca ratio is an important factor determining the ostracode species composition of a lake. Species richness is at a maximum when the lake water has intermediate values of conductivity. Lakes in which one species clearly dominates the assemblage (‰>‰70% relative abundance) have water saturated with respect to CaCO₃. Mg/Ca ratio, depth and Sr are the environmental factors that are most highly correlated with species distributions in this region.     

The relationship between fecundity and adult body weight in Homeotherms

Summary Bythotrephes cederstroemii Schoedler, a predatory freshwater zooplankter (Crustacea: Cladocera), was first found in the Laurentian Great Lakes in December 1984. The first individuals were from Lake Huron, followed in 1985 with records from Lakes Erie and Ontario. By late August, 1986 the species had spread to southern Lake Michigan (43°N). Bythotrephes has not previously been reported from North America, but has been restricted to a northern and central Palearctic distribution. Its dramatic and widespread rise in abundance in Lake Michigan was greatest in offshore regions. Bythotrephes appears to be invading aggressively, but avoiding habitats presently occupied by glacio-marine relict species that became established in deep oligotrophic North American lakes after the Wisconsin glaciation. Because it is a voracious predator its invasion may lead to alterations in the native zooplankton fauna of the Great Lakes. It offers the chance to study how invading plankton species join an existing community. Judging from its persistence and success in deep European lakes, Bythotrephes may now become a permanent member of zooplankton communities in the Nearctic.     

Climate‐associated tundra thaw pond formation and range expansion of boreal zooplankton predators

Most of the freshwater component of the Earth's surface is composed of shallow tundra ponds. These high latitude ecosystems have been exposed to a variety of abiotic disturbances associated with recent environmental change. However, the biological significance of these changes remains poorly understood. Here, we characterize the abiotic disturbance to the shallow tundra ponds of northwest Alaska. We used historical aerial imagery to determine that up to 53% of the sampled ponds have formed during the recent warmer decades (since the 1970s). We discovered that two top predator species (phantom midges of the genus Chaoborus) of the freshwater zooplankton have recently undergone range expansion, forming widespread (a scale of hundreds of km) stable tundra populations. We assessed the population persistence of these boreal predators by longitudinal sampling over 14 yr. Recent thaw ponds had significantly dissimilar zooplankton communities to communities of ponds that formed before 1950. Both predator and herbivore species differed by age of pond. Younger pond ages and warmer surface temperatures were the significant predictors of the presence of temperate Chaoborus americanus in tundra ponds. Ponds containing tundra populations of C. americanus and C. cf. flavicans were associated with recent formation (83–90%). Recent ponds in river valleys appeared more important than recent ponds near roads as colonization corridors for C. americanus. Only 24% of the tundra keystone predator, Heterocope septentrionalis, populations were from recent ponds. Our results suggest that climate‐associated disturbance can lead to a widespread stable range expansion of boreal species despite the propinquity of older ponds with top‐down control exerted by an endemic keystone predator.     

The ecological niches of <Emphasis Type="Italic">Bythotrephes</Emphasis> and <Emphasis Type="Italic">Leptodora:</Emphasis> lessons for predicting long-term effects of invasion

We here exploit two large datasets on zooplankton in Norwegian lakes, spanning a wide range of geographical, physical, chemical and biological properties, to assess the ecological niches and habitats of Bythotrephes longimanus and Leptodora kindtii. The species overlapped geographically, yet co-occurred only in a limited number of lakes. Bythotrephes inhabited virtually all types of lakes, except alpine localities and productive lakes dominated by cyprinid communities where the hyaline Leptodora was most abundant. The zooplankton communities also differed in Bythotrephes and Leptodora lakes, probably both reflecting different predatory regimes, but also water quality and other lake-specific properties. We found no evidence for species being excluded by the presence of Bythotrephes, rather the diversity in general was higher in lakes with these predators present compared with those without. We found, however, a very close association between Bythotrephes and Daphnia galeata and to some extent also between Bythotrephes and D. longispina, suggesting that these species also may benefit from Bythotrephes invasion. Both Bythotrephes and Leptodora species occur naturally in this region, and knowledge about the ecological preferences and the zooplankton community composition in Bythotrephes—and Leptodora lakes will provide valuable information about the long-term effects of Bythotrephes invasion and potential interaction with of Leptodora as top invertebrate predator.     

Patterns in the Distribution of Cladocerans (Crustacea: Branchiopoda) in Lakes Across a North–south Transect in Alaska, USA

The remains of cladocerans were examined from the surface sediments of 51 freshwater sites along a north–south transect spanning Alaska. We identified 27 cladoceran taxa from the sediments, consisting primarily of littoral chydorid species. Variations in cladoceran assemblages were related to measured physical and chemical variables using multivariate techniques. Redundancy analysis (RDA) indicated that lake depth, total phosphorus (TP), and altitude all had a significant influence in determining the composition of cladoceran assemblages. Cladoceran communities in tundra and forest-tundra lakes, which were relatively shallow and nutrient-poor, had relatively low abundances of pelagic Cladocera, and were primarily composed of several littoral chydorid species. Among pelagic cladoceran species, there was a distinct shift in dominance from the Bosminidae in lakes in the southern boreal forest region to Daphniidae in lakes in the northern boreal forest. Daphnia dominated lakes had significantly higher total phosphorus, specific conductivity, and calcium concentrations than lakes dominated by Eubosmina. Overall, the relative importance of physical and chemical factors in structuring cladocerans is similar to other previously studied regions, and suggests the Cladocera may be useful as ecological and paleoenvironmental indicators in this region.     

Ciliate community structure and interactions within the planktonic food web in two alpine lakes of contrasting transparency

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Invertebrate zooplankton predator composition and diversity in tropical lentic waters

Invertebrate zooplankton predators are generally less diverse in average species numbers in tropical than in temperate lakes and reservoirs. Predatory Copepoda which comprise the majority of limnetic predators are particularly low in species numbers in the tropics. Predatory Cladocera are confined to the North Temperate zone. Chaoborus appears to be cosmopolitan. Among Rotifera, only the cosmopolitan predator Asplanchna occurs in tropical waters while the other common limnetic carnivorous genus Ploesoma is restricted to higher latitudes. Hydracarina, and insects besides Chaoborus, are generally restricted to the littoral and appear to be more diverse in the tropics. Lakes Awasa and Zwai, Ethiopia, are almost devoid of predators in the limnetic, which is invaded by a littoral chydorid Alona diaphana. Low diversity of lake types and low production of tropical zooplankton could restrict predator diversity too. Very low diversity of invertebrate predators in the limnetic and higher diversity in the littoral may characterize tropical lakes in contrast to temperate lakes, which have more invertebrate predators in the limnetic and perhaps relatively less in the littoral. Tropical zooplankton in freshwaters, appears to be a very immature community. Hence opportunistic species can readily invade the limnetic and even dominate in isolated situations as has been shown for Alona davidi, Hydracarina and some other unconventional forms.     

Higher temperatures enhance the effects of invasive sportfish on mountain zooplankton communities

1. Decades of introductions of exotic sportfish to mountain lakes around the world have impoverished them biologically, and this may be exacerbated by global warming. We assessed the current status of invasive salmonids and native zooplankton communities in 34 naturally fishless lakes along an elevational gradient, which served as an environmental proxy for the expected effects of climate change. 2. Our main goal was to explore how climate‐related variables influence the effects of stocked salmonids on the total biomass, species richness and taxonomic composition of zooplankton. We predicted that warmer conditions would dampen the negative predatory effects of exotic brook trout (Salvelinus fontinalis) on zooplankton communities because more temperate lakes contain a greater diversity of potentially tolerant species. 3. Instead, we discovered that the persistence of stocked brook trout in the warmer lakes significantly amplified total zooplankton biomass and species richness. In colder and deeper lakes, zooplankton were relatively unaffected by S. fontinalis, which however persisted better in alpine lakes than at lower elevations after stocking practices were halted over two decades ago. Warmer lake conditions and higher concentrations of dissolved organic carbon (DOC) were significant primary drivers of zooplankton species turnover, both favouring greater species diversity. 4. Our findings of an ecological surprise involving potential synergistic positive effects of climate warming and exotic trout on native zooplankton communities presents a conundrum for managers of certain national mountain parks. Present mandates to eradicate non‐native trout and return the mountain lakes to their naturally fishless state may conflict with efforts to conserve biodiversity under a rapidly changing climate.     

Zooplankton Migration in Three Lakes of Western New York

We examined the diel vertical migration (DVM) of zooplankton in three lakes of western New York; Lakes Conesus, Lime, and McCargo. In all three lakes, the dipteran predator Chaoborus was a more dramatic migrator than any of the cladocerans or copepods. In contrast, another invertebrate predator, Leptodora, seemed to have the least vertical dispersal. In Conesus Lake, following the evening ascent and upper-water night-positioning of Chaoborus flavicans, Daphnia pulicaria expanded its own vertical range of dispersal thereby decreasing its degree of overlap with Chaoborus. The vertical distribution of Diaptomus sicilis was mostly below that of Daphnia pulicaria, thus reducing possible competition for food resources. Poor oxygen conditions in the lower waters of Lakes Lime and McCargo restricted all zooplankton (except Chaoborus) to an epilimnetic zone where the regions of niche overlap and predation were narrowed. Such annually-induced restrictions on vertical dispersal are probably common features of numerous stratified lakes with hypolimnetic reducing conditions. No fixed pattern of vertical dispersal or migration is likely in lakes where stratification and non-stratification follow each other seasonally. Vertical migration does provide some flexibility in niche separation, but the potential for chaotic behavior in interacting predators and prey may confound simple explanations of DVM.     

Atypical swimbladders of lake charr, Salvelinus namaycush, from Great Slave Lake, Northwest Territories, Canada

Swimbladder walls of lake charr, Salvelinus namaycush, from Great Slave Lake (GSL), Northwest Territories, Canada, were unusually thick for the species. The thinnest sections of the GSL bladders (mean = 2.44mm, range = 1.1–4.4mm) were significantly thicker (P = 0.001) than lake charr swimbladders collected from two small Province of Ontario lakes (means = 0.65 and 0.92mm), whose populations were assumed to be representative of the species. Variance in wall thickness was also greater in GSL lake charr than in charr from two small lakes (P < 0.02). Within individuals, some of the GSL bladder walls were markedly irregular in thickness, but whether these anomalies exist in situ or were artifacts of preservation remains uncertain. The bulk of the tissue in the thickest sections of the GSL swimbladders was in the tunica serosa (outer layer). The extent of the modification of the GSL swimbladders is extraordinary for northern fishes in postglacial lakes.     

Limnological characteristics of subtropical Lakes Phewa, Begnas, and Rupa in Pokhara Valley, Nepal

Limnological characteristics were studied and analyzed in the subtropical Lakes Phewa, Begnas, and Rupa of Pokhara Valley, Nepal, from 1993 to 1997. The annual water temperature ranged from 12° to 29°C in all lakes. Lake Phewa and Lake Begnas were monomictic and anoxic in the hypolimnion during thermal stratification from April to September. Dissolved oxygen was drastically depleted in April and/or May in shallow Lake Rupa when the macrophyte community began to decompose. NH₄ ⁺-N accumulated below 5 m during March–September when dissolved oxygen was depleted in Lakes Phewa and Begnas. The PC : PP ratio was higher, but the PC : PN and PN : PP ratios were close to the Redfield ratio (106C : 16N : 1P) in Lakes Phewa and Begnas, denoting that P was limited. Annual net primary production showed that the lakes were productive but will tend to become heterotrophic in the future. The seasonal variation of chlorophyll a concentration was high, but its annual variation was low. Ceratium hirundinella and Peridinium spp. in Lake Phewa, Microcystis aeruginosa and Aulacoseira granulata in Lake Begnas, and Tabellaria fenestra in Lake Rupa were the dominant species. The zooplankton population and species varied irregularly. On the basis of chlorophyll a concentration in the euphotic zone and phytoplankton species composition, the lakes seem to be oligoeutrophic and to have some characteristics of temperate lakes rather than tropical lakes. Received: April 26, 1999 / Accepted: September 20, 1999     

Erratum to: How do UV radiation, temperature, and zooplankton influence the dynamics of alpine phytoplankton communities?

Plankton in mountain lakes are confronted with generally higher levels of incident ultraviolet radiation (UVR), lower temperatures, and shorter growing seasons than their lower elevation counterparts. The direct inhibitory effects of high UVR and low temperatures on montane phytoplankton are widely recognized. Yet little is known about the indirect effects of these two abiotic factors on phytoplankton, and more specifically whether they alter zooplankton grazing rates which may in turn influence phytoplankton. Here, we report the results of field microcosm experiments that examine the impact of temperature and UVR on phytoplankton growth rates and zooplankton grazing rates (by adult female calanoid copepods). We also examine consequent changes in the absolute and relative abundance of the four dominant phytoplankton species present in the source lake (Asterionella formosa, Dinobryon sp., Discostella stelligera, and Fragilaria crotonensis). All four species exhibited higher growth rates at higher temperatures and three of the four species (all except Dinobryon) exhibited lower growth rates in the presence of UVR versus when shielded from UVR. The in situ grazing rates of zooplankton had significant effects on all species except Asterionella. Lower temperatures significantly reduced grazing rates on Fragilaria and Discostella, but not Dinobryon. While UVR had no effect on zooplankton grazing on any of the four species, there was a significant interaction effect of temperature and UVR on zooplankton grazing on Dinobryon. Discostella and Dinobryon increased in abundance relative to the other species in the presence of UVR. Colder temperatures, the presence of zooplankton, and UVR all had consistently negative effects on rates of increase in overall phytoplankton biomass. These results demonstrate the importance of indirect as well as direct effects of climate forcing by UVR and temperature on phytoplankton community composition in mountain lakes, and suggest that warmer climates and higher UVR levels may favor certain species over others.     

A description of pelagic zooplankton in the large lakes of the Todzha Depression (Bolshoi Yenisey River basin, Tuva)

The zooplankton structure of large lakes (Noyon-Khol’, Shuram-Khol’, Borzu-Khol’, Many-Khol’, Kadysh, and Todzha) of the Todzha Depression has been studied. A comparison of the species composition, abundance, and biomass of zooplankton in the lakes was made. Rotifers have the largest species diversity: from 10 to 16 species, with Conochilus sp., Collotheca sp., Kellicottia longispina (Kellicott), and Asplanchna priodonta Gosse being the most abundant. Copepods are represented mostly by Arctodiaptomus paulseni (Sars), Eudiaptomus graciloides (Lilljeborg), Cyclops scutifer Sars, and Mesocyclops leuckarti Claus. Daphnia galeata Sars and Bosmina longispina Leydig are the dominant cladoceran species. It is shown that the zooplankton communities of the lakes in the Todzha Depression are characterized by a high degree of species composition similarity. Factors forming the taxonomic structure of pelagic zooplankton in the system of these lakes are displayed.     

<Emphasis Type="Italic">Bythotrephes</Emphasis> invasion elevates trophic position of zooplankton and fish: implications for contaminant biomagnification

We estimated the effects of Bythotrephes longimanus invasion on the trophic position (TP) of zooplankton communities and lake herring, Coregonus artedi. Temporal changes in lacustrine zooplankton communities following Bythotrephes invasion were contrasted with non-invaded reference lakes, and along with published information on zooplankton and herring diets, formed the basis of estimated changes in TP. The TP of zooplankton communities and lake herring increased significantly following the invasion of Bythotrephes, whereas TP in reference lakes decreased (zooplankton) or did not change significantly (lake herring) over a similar time frame. Elevated TP following Bythotrephes invasion was most prominent in lakes that also supported the glacial relict, Mysis diluvania, suggesting a possible synergistic interaction between these two species on zooplankton community composition. Our analysis indicated that elevated TPs of zooplankton communities and lake herring are not simply due to the presence of Bythotrephes, but rather reflect changes in the zooplankton community induced by Bythotrephes; namely, a major reduction in the proportion of herbivorous cladoceran biomass and a concomitant increase in the proportion of omnivorous and/or predatory copepod biomass in invaded lakes. We demonstrated that increases in TP of the magnitude reported here can lead to substantial increases in fish contaminant concentrations. In light of these results, we discuss potential mechanisms that may be responsible for the disconnect between empirical and theoretical evidence that mid-trophic level species invasions (e.g., Bythotrephes) elevate contaminant burdens of consumer species, and provide testable hypotheses to evaluate these mechanisms.     

Benthic and pelagic food resources for zooplankton in shallow high-latitude lakes and ponds

1. Shallow lakes and ponds are a major component of the northern landscape and often contain a high zooplankton biomass despite clear waters that are poor in phytoplankton. 2. In this study we quantified zooplankton food sources and feeding rates in the shallow waters of two contrasting high‐latitude biomes: subarctic forest tundra (Kuujjuarapik, Quebec) and high arctic polar desert (Resolute, Nunavut). Five substrate types were tested (beads, bacteria, picophytoplankton, filamentous plankton and microbial mats). Special attention was given to the role of benthos, a component that is usually poorly integrated into models of aquatic foodwebs. 3. Consistent with observations elsewhere in the circumpolar region, high concentrations of adult macrozooplankton occurred in all sites (up to 17 100 crustaceans m^?3) while phytoplankton concentrations and primary productivity were low. The communities were composed of multiple species, including Daphnia middendorfiana, Hesperodiaptomus arcticus, Leptodiaptomus minutus, Artemiopsis stefanssoni and Branchinecta paludosa. 4. Detritus made 89–98% of the planktonic resource pool and bacteria contributed the highest biomass (up to 29 mg C m^?3) of the planktonic food particles available to zooplankton. Benthic resources were dominated by microbial mats that grew in nutrient‐rich conditions at the base of the ponds and which dominated overall ecosystem biomass and productivity. 5. All species were flexible in their feeding but there were large, order of magnitude differences in clearance rates among taxa. These differences likely resulted from different grazing strategies among cladocerans, copepods and fairy shrimps, and possibly also from adaptation to specific food types and size ranges that occur locally in these waters. 6. The subarctic cladocerans Ceriodaphnia quadrangula and D. middendorfiana, and the arctic fairy shrimp B. paludosa were observed to graze directly on the microbial mats and the feeding experiments confirmed their assimilation of benthic substrates. The other zooplankton species showed a more pelagic feeding mode but were capable of using microbial mat filaments, thus may be indirectly linked to benthic processes via resuspension. 7. Our study indicates that the classical aquatic food web in which phytoplankton provide the sole production base for grazers does not apply to northern shallow lakes and ponds. Instead, microbial mats increase the physical complexity of these high latitude ecosystems and likely play a role in sustaining their high zooplankton biomass.     

长白山高山苔原带蛾类物种组成及其时间动态

长白山高山苔原带环境条件恶劣,通过对高山苔原带蛾类研究,揭示蛾类物种组成以及时间变化,可为研究蛾类对苔原极端生境的适应能力,以及蛾类在维持苔原带生态平衡中的作用提供依据。2005-2007年和2019年,每年的6、7、8月,在长白山高山苔原带利用灯诱采集蛾类标本,分析蛾类的物种组成以及时间动态。共采集蛾类1585头,隶属于13科126种,夜蛾科（Noctuidae）为优势类群,绿组夜蛾（Anaplectoides prasina）和一色兜夜蛾（Cosmia unicolor）为优势种,稀有种较多。蛾类的种-多度分布接近生态位优先假说。7月份蛾类的物种数、个体数最多,丰富度指数、多样性指数都最高,但均匀度指数却最低。不同种类对时间的反应表现出一定的差异,黄绿组夜蛾（Anaplectoides virens）对8月,厉切夜蛾（Euxoa lidia）对6月的适应力相对较强。各物种的顺序日期存在一定的差异性,只有10种蛾类在3个月份都被采集到。研究表明,长白山高山苔原带蛾类的多样性较低,成虫活跃期较短;不同类群的蛾类在苔原环境中显示出差异化的适应性,夜蛾科的适应能力超过其它类群,尺蛾科（Geometridae）的适应性相对较低,蛾类对时间的变化反应比较敏感。     

Intraspecific variation in diet, growth, and morphology of landlocked Galaxias maculatus during its larval period: the role of food availability and predation risk

Food availability and predation risk have been shown to affect phenotypes during early life history of fishes. Galaxias maculatus, a small fish widely distributed around the southern hemisphere, clearly exhibits a complex trade-off between feeding and predation avoidance during growth over the larval period. We studied the effect of different environmental variables on diet, growth, mortality, and morphology through field surveys and data revision in the literature for limnetic G. maculatus larvae in five oligotrophic lakes of Patagonia. Both number of food categories and prey ingested by larvae were directly related to zooplankton density. Larval growth rate was related with zooplankton density and temperature. Lakes with high zooplankton densities and low predation risk had larvae with deeper bodies and shorter caudal peduncles, while in lakes with less food and high predation risk larvae were slender with shallower bodies and longer peduncles. Food availability and predation risk seem to operate on the swimming performance of G. maculatus larvae through the slenderness of the body and the length of the caudal peduncle. The observed phenotypic variation in growth and morphology could be a key feature that has allowed this species to successfully colonize a wide variety of environments in the southern hemisphere.