Urease activity in the gastrointestinal tract of the European hare (<Emphasis Type="Italic">Lepus europaeus</Emphasis>)

The intensity of urea recycling in the wild herbivorous European hare has been investigated. The intensity of urease activity in the gastrointestinal tract has been selected as a convenient quantitative measure of nitrogen recycling. High urease activity was detected in the large intestine; it was higher than the previously detected activity in other mammals with postgastric fermentation: pigs, rats, and rabbits. The strong seasonal dynamics of urease activity has been noted: it increases during winter diet consumption, which is poor in available nitrogen.     

Nitrogen budget of a subarctic stream altered by beaver (Castor canadensis)

Beaver (Castor canadensis) influence stream ecosystems through their wood cutting and dam building activities. To quantify this influence we have used measured rates of nitrogen dynamics to construct a nitrogen budget for a section of a second order stream in eastern Québec and a beaver dam in that stream. The budget demonstrates the importance of sediment accumulations and an expanded wetted area to the annual nitrogen economy and to pathways of nitrogen cycling. Major changes after impoundment (per unit area) include a reduction in allochthonous nitrogen and an increase in nitrogen fixation by sediment microbes. Overall, the beaver-modified section accumulated 10³ times more nitrogen than before alteration. The ecosystem implications of beaver activity suggest that current concepts of patterns and processes in running waters require modification.Research support by NSF grant DEB 81-05677 and the Woods Hole Oceanographic Institution. this is Contribution No. 5565 from the Woods Hole Oceanographic Institution and No. 88 from the Institution's Matamek Research Station     

Seasonal variations of the digestive tract of the Eurasian beaver <Emphasis Type="Italic">Castor fiber</Emphasis>

Forage availability for wild rodents varies with season. In turn, the composition of food can affect morphometric parameters of the digestive tract. This study was performed in Eurasian beavers (Castor fiber) whose population was close to extinction in most Eurasian countries, but has now increased. Due to the previous low number of studies, information about the effect of forage availability on the digestive tract morphology has previously been lacking. This study was performed using beavers captured from the natural environment during three seasons of different forage availability: winter, summer and autumn. It was found that the diet of the beaver varied during the year; in winter it was dominated by woody material consisting of willow shoots, whereas in summer the diet was primarily herbs, grass and leaves. Season also affected the mass of digested contents of the digestive tract. The digestive content increased in the caecum and colon in winter and autumn, when poor-quality food dominated the beaver’s diet. The results indicated that the digestive tract parameters of beavers varied based on the composition of available forage.     

Activity of beavers as an ecological factor that affects the benthos of small rivers - a case study in the Żylica River (Poland)

The Eurasian beaver (Castor fiber) has a greater impact on local ecosystems than other herbivores, and the affected area exceeds the range of its presence. Its activity may change or create new habitats by modifying the availability of the biotic and abiotic resources available not only to beavers, but also to other groups of animals. Our aim was to study how beaver activity affects the benthos composition in a small river and in a beaver pond. The way in which beavers function in the case of small rivers has received little attention. The study showed a lower density of benthos above the dam (beaver pond - 1467 ind./m²) compared to the river (3147 ind./m²). Below the dam, the diversity of Trichoptera and Coleoptera was greater, while Diptera were more abundant in the beaver pond. Betidae were a constant component in the benthos assemblages and were most abundant in the beaver pond. Collectors-gatherers and predators were the most numerous in the beaver pond. Decreasing percentages of collectors-gatherers were observed with an increased abundance of collectors-filterers and shredders in the river. All of the ratio values except the P/T FFG (Predators to total of all other groups) were lower in the beaver pond compared to the river. The % EPT (Ephemeroptera Plecoptera and Trichoptera) was also greater in the beaver pond. Small differences in the physicochemical properties of the water and organic matter content in the bottom sediments were found both above and below the beaver dam.     

Population-genetic structure of beaver (Castor fiber L., 1758) communities and estimation of effective reproductive size Ne of an elementary population

The absence of panmixia at all hierarchical levels of the European beaver communities down to individual families implies a complex organization of the population-genetic structures of the species, in particular, a large intergroup component of gene diversity in the populations. Testing this assumption by analysis of 39 allozyme loci in the communities of reintroduced beaver from the Vyatka river basin (Kirov oblast) has shown that only the beaver colonies exhibit high intergroup gene diversity (Gst = 0.32) whereas this parameter is much lower when estimated among beaver groups from individual Vyatka River tributaries and among localities of one of the tributaries (0.07 and 0.11, respectively). The data suggesting genetic heterogeneity among individual settles within colonies have been obtained. The factors affecting the structure of the beaver communities of the lower hierarchical ranks are considered: the common origin, founder effect, selection, gene drift, assortative mating, and social and behavior features of the species. The conclusion is drawn that the founder effect could be the primary factor of population differentiation only at the time of their formation. The heterogeneity among colonies and among settles is maintained largely by isolation of colonies from one another. The strong interspecific competition for food resources, which is behaviorally implemented in the species at the level of minimal structural units (individual settles) creates a profound and unique population-genetic subdivision of the species. These results substantiate the suggestion that an elementary population (micropopulation) of European beaver is a colony, i.e., a set of related settles of different types. Based on ecological and genetic parameters, the effective reproductive size Ne of the minimum beaver population was estimated to be equal to three animals. This extremely low value of effective reproductive population size largely explains the high tolerance of European beaver to inbreeding and striking viability of the species, which from the early 19th century has been for more than hundred years on the brink of survival in the condition which would made any other mammalian species vanish from the Earth.     

Quantitative relationships between various representatives of gastrointestinal microflora of experimental animals (rats) in normal conditions and after immunosuppression with imuran

The influence of imuran (an analog of nitrogen ioprin) on the quantitative relationship between lactobacilli, bifidobacteria, bacteroids and aerobic autoflora in different sections of the gastrointestinal tract of white rats was studied under experimental conditions. On days 7-14-30 after the introduction of imuran into the gastrointestinal tract dysbacteriosis developed; it was characterized by a decrease in the number of lactobacilli and asporogenic anaerobic microflora and an increase in the number of aerobic microorganisms. By days 60-90 the content of aerobic microbes in all sections of the gastrointestinal tract was still elevated, while the rapid restoration of the number of bacteroids took place. Therefore, immunosuppression therapy with imuran may give rise to autoinfectious complications caused by different representatives of infective microflora.     

The importance of spatial scale in habitat selection by European beaver

We evaluated habitat selection by European beaver Castor fiber L. across a spatial gradient from local (within the family territory) to a broad, ecoregional scale. Based on aerial photography, we assessed the habitat composition of 150 beaver territories along the main water bodies of the Vistula River delta (northern Poland) and compared these data with 183 randomly selected sites not occupied by the species. The beavers preferred habitats with high availability of woody plants, including shrubs, and avoided anthropogenically modified habitats, such as arable lands. Within a single family territory, we observed decreasing woody plant cover with increasing distance from a colony centre, which suggests that beaver habitat preferences depend on the assessment of both the abundance and spatial distribution of preferred habitat elements. We tested the importance of spatial scale in beaver habitat selection with principal coordinates of neighbour matrices analysis, which showed that the geographical scale explained 46.7% of the variation in habitat composition, while the local beaver density explained only 10.3% of this variability. We found two main spatial gradients that were related to the broad spatial scale: first, the most important gradient was related to the largest distances between beaver sites and was independent of woody plant cover and the local beaver site density. The second most important gradient appeared more locally and was associated with these variables. Our results indicate that European beaver habitat selection was affected by different scale‐related phenomena related 1) to central place foraging behaviour, which resulted in the clumped distribution of woody plants within the territory, and 2) local population density and woody plant cover. Finally, 3) habitat selection occurs independently across the largest spatial scale studied (e.g. between watersheds), which was probably due to the limited natal dispersal range of the animals.     

Population-Genetic Structure of Beaver (Castor fiber L., 1758) Communities and Estimation of Effective Reproductive Size N e of an Elementary Population

The absence of panmixia at all hierarchical levels of the European beaver communities down to individual families implies a complex organization of the population-genetic structures of the species, in particular, a large intergroup component of gene diversity in the populations. Testing this assumption by analysis of 39 allozyme loci in the communities of reintroduced beaver from the Vyatka river basin (Kirov oblast) has shown that only the beaver colonies exhibit high intergroup gene diversity (G _st = 0.32) whereas this parameter is much lower when estimated among beaver groups from individual Vyatka River tributaries and among localities of one of the tributaries (0.07 and 0.11, respectively). The data suggesting genetic heterogeneity among individual settles within colonies have been obtained. The factors affecting the structure of the beaver communities of the lower hierarchical ranks are considered: the common origin, founder effect, selection, gene drift, assortative mating, and social and behavior features of the species. The conclusion is drawn that the founder effect could be the primary factor of population differentiation only at the time of their formation. The heterogeneity among colonies and among settles is maintained largely by isolation of colonies from one another. The strong interspecific competition for food resources, which is behaviorally implemented in the species at the level of minimal structural units (individual settles) creates a profound and unique population-genetic subdivision of the species. These results substantiate the suggestion that an elementary population (micropopulation) of European beaver is a colony, i.e., a set of related settles of different types. Based on ecological and genetic parameters, the effective reproductive size N _e of the minimum beaver population was estimated to be equal to three animals. This extremely low value of effective reproductive population size largely explains the high tolerance of European beaver to inbreeding and striking viability of the species, which from the early 19th century has been for more than hundred years on the brink of survival in the condition which would made any other mammalian species vanish from the Earth.     

Estimates of underwater and aerial visual acuity in the European beaver <Emphasis Type="Italic">Castor fiber</Emphasis> L. based on morphological data

The eye optics and topographic distribution of ganglion cells were studied using whole mount preparations from European beaver Castor fiber L. The beaver eye optics provides emmetropia in air and hypermetropia in water. The optometrical measurements predict retinal resolution of the beaver eye around 17′ in air and 9′ in water. In air, retinal resolution corresponds to the real visual acuity, whereas in water, visual acuity is below the retinal resolution because of the non-precise focusing.     

Adiaspiromycosis in a European beaver from Sweden

An infection with the rare mycosis Chrysosporium parvum was diagnosed in a European beaver (Castor fiber) shot in northern Sweden. The animal was in normal body condition and no signs of disease were observed. In the lungs a large number of nodules, up to 5 mm diameter, were observed. A large number of adiaspores were observed in the interstitium of the lungs and in the mediastinal lymph node. A chronic inflammatory reaction dominated by mononuclear leukocytes and giant cells was observed around the spores. This is the first report of adiaspiromycosis (Chrysosporium parvum) in the European beaver.     

Impact of Beaver Dams on Abundance and Distribution of Anadromous Salmonids in Two Lowland Streams in Lithuania

European beaver dams impeded movements of anadromous salmonids as it was established by fishing survey, fish tagging and redd counts in two lowland streams in Lithuania. Significant differences in abundancies of other litophilic fish species and evenness of representation by species in the community were detected upstream and downstream of the beaver dams. Sea trout parr marked with RFID tags passed through several successive beaver dams in upstream direction, but no tagged fish were detected above the uppermost dam. Increase in abundances of salmonid parr in the stream between the beaver dams and decrease below the dams were recorded in November, at the time of spawning of Atlantic salmon and sea trout, but no significant changes were detected in the sections upstream of the dams. After construction of several additional beaver dams in the downstream sections of the studied streams, abundance of Atlantic salmon parr downstream of the dams decreased considerably in comparison with that estimated before construction.     

Echinococcus multilocularis in a European beaver from Switzerland

Infection with the larval stage of the cestode parasite Echinococcus multilocularis was diagnosed in a European beaver (Castor fiber) in central Switzerland. The animal was hit, run over by a car, and died of trauma. It was in normal body condition and no signs of disease were seen. At necropsy, multiple cystic structures up to 1 cm in diameter were found in the liver adjacent to the hilus. Within the parasite vesicles, multiple protoscolices were visible. The species was determined to be Echinococcus multilocularis by upon polymerase chain reaction and direct immunofluorescence with MAbG11-FITC. This is the first report of Echinococcus multilocularis in European beaver.     

Effects of season and reproductive state on lipid intake and fatty acid composition of gastrointestinal tract contents in the European hare

We investigated lipid content and fatty acid (FA) composition of gastrointestinal tract contents in free-living, herbivorous European hares (Lepus europaeus). Mean crude fat content in hare stomachs and total gastrointestinal (GI) tracts was higher than expected for typical herbivore forages and peaked in late fall when hares massively deposited body fat reserves. Changes of FA proportions in different parts of the GI-tract indicated a highly preferential absorption of polyunsaturated fatty acids (PUFA). A further reduction of PUFA content in the caecum, along with the appearance of odd-chained FAs in caecum, caecotrophes, and colon content, pointed to a biohydrogenation of PUFA in the hare’s hindgut. GI-tract contents showed significant seasonal changes in their FA composition. Among PUFA, α-linolenic acid peaked in spring while linoleic acid was predominant in late summer and fall, which probably reflected changes in the plant composition of forage. However, independent of seasonal changes, GI-tracts of lactating females showed a significantly (+33%) higher content of linoleic acid, a FA that is known to increase reproductive performance in European hares. This finding suggests that lactating females actively selected dietary plants rich in linoleic acid, a PUFA that may represent a limited resource for European hares.     

Interrelationship of the cardiovascular and digestive systems in the genesis of experimental atherosclerosis]

In chronic experiments (up to 2 years) on dogs on atherogenic diets the motor activity of the gastrointestinal tract, cholesterol, the phospholipid level in the blood and in the intestinal secretion as well as the morphology of the small intestine and the vascular system were examined. At the early stages of atherosclerosis (up to 4 months) the rise of the blood cholesterol level was followed by an increase in the periods of the activity of the gastrointestinal tract, a rise of cholesterol discharge by the small intestine, and the development of the hypertrophic process in the mucous membrane. At the later stages a change in the mucous membrane of the small intestine was observed with development of a dystrophic-atrophic process, a disturbance of motor activity of the gastrointestinal tract and of the correlations between the cholesterol content in the blood and its discharge by the small intestine. This period was characterized by a high and persistent hypercholesterolemia and pronounced atherosclerotic changes in the vascular system.     

Sequence diversity of the MHC DRB gene in the Eurasian beaver (Castor fiber)

Major histocompatibility complex (MHC) genes, coding molecules which play an important role in immune response, are the most polymorphic genes known in vertebrates. However, MHC polymorphism in some species is limited. MHC monomorphism at several MHC class I and II loci was previously reported for two neighbouring northern European populations of the Eurasian beaver (Castor fiber) and reduced selection for polymorphism has been hypothesized. Here, we analysed a partial sequence of the second exon of the MHC II DRB locus from seven relict European and Asian beaver populations. We detected 10 unique alleles among 76 beavers analysed. Only a western Siberian population was polymorphic, with four alleles detected in 10 individuals. Each of the remaining populations was fixed for a different allele. Sequences showed considerable divergence, suggesting the long persistence of allelic lineages. A significant excess of nonsynonymous substitutions was detected at the antigen binding sites, indicating that sequence evolution of beaver DRB was driven by positive selection. Current MHC monomorphism in the majority of populations may be the result of the superimposition of the recent bottleneck on pre-existing genetic structure resulting from population subdivision and differential pathogen pressure.     

Reintroduction of beavers <Emphasis Type="Italic">Castor fiber</Emphasis> may improve habitat quality for vespertilionid bats foraging in small river valleys

Beavers strongly modify their environment by not only building dams and creating ponds, which slow the water flow, but also by selective cutting and removing of trees, which change the spatial structure of the forest. We aimed to test the hypothesis that beaver activity promotes new foraging sites for insectivorous bats. The beaver’s influence can be especially significant on aerial hawkers that prefer moderate structural clutter, like the Pipistrellus species (by creating new canopy gaps), and on water-surface foragers, like Myotis daubentonii (by creating ponds with smooth water surface). The study was conducted on small streams in forest areas of northern Poland, which were colonized by the European beaver (Castor fiber). Bat activity was recorded with a Pettersson D-980 ultrasound detector on line transects. The number of bat passes was significantly higher in the stream sections modified by beavers (flooded and subjected to intensive tree cutting) than in the unmodified sections (for Pipistrellus nathusii, Pipistrellus pipistrellus, Pipistrellus pygmaeus, Nyctalus noctula, and all species lumped together). Contrary to our expectations, the activity of the Myotis species was significantly lower on the transect with the largest beaver ponds, possibly due to the blanket of duckweed (Lemnaceae), which is known to produce clutter echoes, thereby reducing prey detection by echolocating M. daubentonii.     

Beaver activity increases aquatic subsidies to terrestrial consumers

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The influence of Eurasian beaver Castor fiber activity on fish assemblages in small steppe rivers in Russia

In recent decades, the Eurasian beaver (Castor fiber) has once again become the keystone species in small river ecosystems in Russia. In many places, beaver activity has resulted in a significant change in lotic habitats, affecting the diversity, density, and biomass of aquatic organisms, including fish. While many studies have considered the ecosystem impacts of beavers, relatively few have focused on understanding the influence of beaver activity on steppe rivers. We conducted the first quantitative study of beaver impacts on fish assemblages in beaver-influenced and beaver-free sites on two small steppe rivers in the Don River basin in Russia. The presence of beavers altered the habitats in small steppe rivers and affected the diversity, density, and biomass of fish. A comparison of the number of species, density, and biomass of fish in six types of river habitats showed that these parameters were lower in beaver ponds than at riverine sites without beaver activity. Three fish species primarily preferred a single habitat type. Barbatula barbatula was found in riffles, Misgurnus fossilis in old beaver ponds, and Eudontomyzon mariae in abandoned beaver ponds. Beavers impacted fish distribution and density by changing dissolved oxygen, pH, and water current velocity. Overall, our results showed that the presence of beavers led to a temporary homogenization of fish habitats at a local scale in the valleys of small steppe rivers because beavers occupied these rivers only for a short period. However, habitat heterogeneity may increase if the beaver population stays stable or expands in the future.

     

The effect of beaver facilitation on Common Teal: pairs and broods respond differently at the patch and landscape scales

Avian species respond to ecological variability at a range of spatial scales and according to life history stage. Beaver dams create wetland systems for waterbirds that are utilized throughout different stages of the breeding season. We studied how beaver‐induced variability affected mobile pairs and more sedentary broods along with the production of Common Teal Anas crecca at the patch and landscape scale on their breeding grounds. Beavers Castor spp. are ecosystem engineers that enhance waterfowl habitats by impeding water flow and creating temporary flooding. Two landscapes in southern Finland with (Evo) and without (Nuuksio) American Beavers Castor canadensis were used in this study. To investigate the patch‐scale effect, pair and brood densities along with brood production were first compared at beaver‐occupied lakes and non‐beaver lakes in the beaver landscape. Annual pair and brood densities/km shoreline and brood production were compared between beaver and non‐beaver landscapes. Facilitative effects of beaver activity were manifest on brood density at both patch and landscape scales: these were over 90% and 60% higher in beaver patches and landscapes, respectively. An effect of beaver presence on pair density was only seen at the landscape level. Pair density did not strongly affect brood production, as shown earlier for relatively mildly density‐dependent Teal populations. Because the extent of beaver flooding was a crucial factor affecting annual Teal production in the study area, we infer beaver activity has consequences for the local Teal population. Ecosystem engineering by the beaver could therefore be considered a restoration tool in areas where waterfowl are in need of high‐quality habitats.     

Temporal changes in digestive enzyme activities in the gastrointestinal tract of European eel (Anguilla anguilla) (Linneo 1758) following feeding

Changes occurring after feeding in the digestive enzyme activities of European eel were investigated to provide some insights into the digestive physiology of this fish. Total and specific proteases, amylase and lipase activities were measured using standard biochemical assays over a 24 h cycle in fed eels, compared to starved ones, under the same rearing conditions. In the gastrointestinal tract of fed eels quantitative changes started 4 h after feeding and continued later on; conversely, in starved eels enzyme activities remained unchanged over time. In fed eels, total and specific protease activities showed an overall increasing trend in the intestine, while in the stomach they progressively decreased to values 22–50% lower than those measured at the pre-feeding time; this behaviour probably reflected the progression of digesta along the intestinal tract. The prolonged secretory response of European eel to food ingestion proved its extended activity in the digestive process.