Bats benefit from beavers: a facilitative link between aquatic and terrestrial food webs

Bat populations are declining in many areas, partly because up to two-thirds of their wetland habitats have been lost. One natural agent creating wetlands is the beaver, which is recolonizing its former range. Beaver flowages are known for their high production of aquatic invertebrates. We tested the hypothesis that the high numbers of insects emerging from beaver flowages influences their use by foraging bats. We compared bat use and bat numbers above flowages of introduced Canadian beavers Castor canadensis and in nearby control ponds where beavers were absent. The two bat species detected, Eptesicus nilssoni and Myotis daubentoni, used beaver flowages more than non-beaver ponds. This is especially the case for Eptesicus nilssoni. Bats also seemed to forage in larger groups while above beaver ponds compared to the control ponds. Beaver flowages appeared to improve bat habitats. A plausible reason for this could be the high number of insects emerging from beaver ponds. Favouring the beaver in habitat management is a tool for creating suitable conditions for many other species, such as bats. In areas not suited for the beaver, insect production can be achieved by imitating the beaver with man-made impoundments. This is especially important in areas which have lost most of their wetlands.     

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.

     

Flight and echolocation behaviour of three vespertilionid bat species while commuting on flyways

This study compares the flight and echolocation behaviour of three vespertilionid bat species while they commute on flyways. We measured the bats’ spatial position relative to vertical background contours and relative to the ground while recording their echolocation behaviour. In Myotis daubentonii, we found a significant influence of spatial context on the position and dimensions of flyways as well as on echolocation behaviour. In gap situations, flyways tended to be narrower and located closer to background structures, flight speeds were lower and the bandwidth of echolocation signals was larger than in edge situations. Differences in background structure did not affect flight and echolocation behaviour. When commuting in the same gap situation flyway positions and dimensions for M. daubentonii and Myotis brandtii were similar but differed from those of Pipistrellus pipistrellus, which were slightly higher and further out than those used by the Myotis species. In M. brandtii, flyway positions and dimensions remained constant over 3 years. We found species-dependent differences in signal structure, but pulse interval and flight speed were similar across all species. The influence of available space on the position of flyways, on flight speed and on echolocation behaviour is discussed.     

Vegetative composition and community structure associated with beaver ponds in Canaan valley, West Virginia, USA

Beavers (Castor canadensis) can cause dramatic changes in vegetative composition and diversity. Although alterations by beaver have been studied extensively, little attention has been paid to the effects beaver impoundments have on rare plants. Effective conservation of riparian and wetland rare plant species must consider the responses of vegetation to changes in hydrology that can occur when beaver populations are present. The goal of this research was to establish the occurrence of locally rare plant species, examine community composition, and analyze vegetative community structure of vegetation associated with beaver ponds in Canaan Valley, West Virginia, USA. Species richness and diversity were similar between plots located inside beaver ponds and adjacent to beaver ponds (P > 0.05). Although no significant difference in rare plant species was detected among pond ages, the oldest ponds (>56 years) had twice as many rare species as the youngest ponds (≤6 years). The youngest ponds had higher overall mean species richness (S) than ponds 7–56 years old (P < 0.05), but S returned to similar levels in the oldest ponds. Of the 15 rare species observed, most were classified as obligate (9) or facultative wetland (4) species. The youngest ponds contained the fewest number of rare species. Multiple response permutation procedure (MRPP) analyses of community structure detected no relation between community composition and either pond age or size. However, both MRPP and non-metric multi-dimensional scaling showed proximity to pond was important in herbaceous community structure. Wetlands in beaver ponds also were shown to be distinct from adjacent wetland areas. Conservation of existing beaver populations is necessary so that the entire spectrum of pond ages is available for the maintenance of rare plant species and communities.     

Beavers affect carbon biogeochemistry: both short‐term and long‐term processes are involved

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Beavers (Castor canadensis) influence habitat for juvenile salmon in a large Alaskan river floodplain

Our aim was to determine how beavers affect habitats and food resources for juvenile salmon in the Kwethluk River in western Alaska.

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Habitat usage of Daubenton's bat (Myotis daubentonii), common pipistrelle (Pipistrellus pipistrellus), and soprano pipistrelle (Pipistrellus pygmaeus) in a North Wales upland river catchment

Distributions of Daubenton's bat (Myotis daubentonii), common pipistrelle, (Pipistrellus pipistrellus), and soprano pipistrelle (Pipistrellus pygmaeus) were investigated along and altitudinal gradient of the Lledr River, Conwy, North Wales, and presence assessed in relation to the water surface condition, presence/absence of bank‐side trees, and elevation. Ultrasound recordings of bats made on timed transects in summer 1999 were used to quantify habitat usage. All species significantly preferred smooth water sections of the river with trees on either one or both banks; P. pygmaeus also preferred smooth water with no trees. Bats avoided rough and cluttered water areas, as rapids may generate high‐frequency echolocation‐interfering noise and cluttered areas present obstacles to flight. In lower river regions, detections of bats reflected the proportion of suitable habitat available. At higher elevations, sufficient habitat was available; however, bats were likely restricted due to other factors such as a less predictable food source. This study emphasizes the importance of riparian habitat, bank‐side trees, and smooth water as foraging habitat for bats in marginal upland areas until a certain elevation, beyond which bats in these areas likely cease to forage. These small‐scale altitudinal differences in habitat selection should be factored in when designing future bat distribution studies and taken into consideration by conservation planners when reviewing habitat requirements of these species in Welsh river valleys, and elsewhere within the United Kingdom.     

Beavers alter stream macroinvertebrate communities in north-eastern Utah

1. Understanding changes in macroinvertebrate communities is important because they play a large role in stream ecosystem functioning, and they are an important food resource for fish. Beaver-induced changes to stream morphology could alter macroinvertebrate communities, which in turn could affect food webs and ecosystem function. However, studies investigating the effects of North American beaver activities on macroinvertebrates are rare in the inter-mountain west, an area with high potential for beaver-assisted restoration.
2. The aim of this study was to quantify differences in the macroinvertebrate community between unaltered segments of streams and within beaver ponds in north-eastern Utah, U.S.A. We assessed macroinvertebrate species richness, biomass, density, functional feeding group composition, mobility group composition, and macroinvertebrate habitat characteristics to test the hypothesis that macroinvertebrate communities will differ among habitat types (undammed stream segments and beaver ponds) in beaver-occupied streams.
3. Beaver pond communities significantly differed from lotic reach communities in many ways. Beaver ponds were less diverse with 25% fewer species. Although there was variability among streams, in general, beaver ponds had 75% fewer individuals and 90% lower total macroinvertebrate biomass compared to lotic reaches.
4. Regarding functional feeding groups, beaver ponds contained more engulfers, while lotic reaches contained more scrapers, filterers, and gatherers. For mobility groups, beaver ponds had more sprawlers, while lotic reaches had more clingers. Swimmers were also more prevalent in lotic reaches, although this is probably due to the abundance of Baetis within lotic reaches. More beaver pond taxa were classified as lentic-dwelling insects, while more lotic reach taxa were categorised as preferring lotic habitats.
5. The creation of ponds by beavers fundamentally altered the macroinvertebrate community in north-eastern Utah streams. Such changes to stream macroinvertebrate communities suggest that recolonisation of beavers across North America may be altering stream functioning and food webs. Our study highlights the need to further investigate the effects of beaver recolonisation on stream communities.

     

Tundra be dammed: Beaver colonization of the Arctic

Increasing air temperatures are changing the arctic tundra biome. Permafrost is thawing, snow duration is decreasing, shrub vegetation is proliferating, and boreal wildlife is encroaching. Here we present evidence of the recent range expansion of North American beaver (Castor canadensis) into the Arctic, and consider how this ecosystem engineer might reshape the landscape, biodiversity, and ecosystem processes. We developed a remote sensing approach that maps formation and disappearance of ponds associated with beaver activity. Since 1999, 56 new beaver pond complexes were identified, indicating that beavers are colonizing a predominantly tundra region (18,293 km²) of northwest Alaska. It is unclear how improved tundra stream habitat, population rebound following overtrapping for furs, or other factors are contributing to beaver range expansion. We discuss rates and likely routes of tundra beaver colonization, as well as effects on permafrost, stream ice regimes, and freshwater and riparian habitat. Beaver ponds and associated hydrologic changes are thawing permafrost. Pond formation increases winter water temperatures in the pond and downstream, likely creating new and more varied aquatic habitat, but specific biological implications are unknown. Beavers create dynamic wetlands and are agents of disturbance that may enhance ecosystem responses to warming in the Arctic.     

Does the morphology of beaver ponds alter downstream ecosystems?

Differences among lake morphologies often explain variation in characteristics of lentic ecosystems. Although beaver ponds also vary in morphology, previous studies have not examined the effects of such variation on downstream ecosystems. This study evaluated downstream effects of multiple beaver ponds in the Colorado Rocky Mountains during one low and one high-flow year. Beaver pond morphology was described as the natural log transformed ratio of beaver dam height (which determines hydraulic head) to pond surface area and related to pond spillover phytoplankton and characteristics of the ecosystem downstream (nutrient concentrations, limiting nutrients, periphyton, benthic organic matter (BOM), and benthic invertebrate consumers). Nitrate concentration increased systematically downstream of beaver ponds, but only in the low flow year when groundwater influences predominated. Effects of beaver ponds on soluble reactive phosphorus concentration depended on pond morphology, increasing downstream of small ponds with high dams, but only during the low-flow year. In situ experiments showed that neither beaver activity nor pond morphology predicted periphyton-limiting nutrients downstream. Both periphyton biomass and BOM decreased downstream of small ponds with high dams but pond morphology did not predict abundance of invertebrate grazers or detritus-feeding consumers. While suspension feeding invertebrates increased downstream from small ponds with high dams, variation in chlorophyll a from water spilling over beaver dams did not follow a similar pattern. We conclude that the effects of beaver ponds on downstream nutrients, resources and consumers are rarely systematic, but instead depend on variation in pond morphology and on annual hydrologic variation.     

Experimental evidence that the ecosystem effects of aquatic herbivory by moose and beaver may be contingent on water body type

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Lowland boreal forests characterization in Algonquin Provincial Park relative to beaver (Castor canadensis) foraging and edaphic factors

Beaver (Caster canadensis) foraging and edaphic conditions can modify the vegetational characteristics of woody plant community in lowland boreal forests. Effective management of these areas requires an understanding of the relative contribution of these factors in shaping the woody plant community structure. Our objective was to quantify the effects of herbivory by beavers and edaphic conditions on woody plant community organization of lowland boreal forests surrounding beaver ponds. Woody vegetation and soils were sampled at 15 ponds occupied by beavers and one other pond abandoned by them in southern Algonquin Park, Ontario. We measured spatial variation in plant diversity, foraging rates and sapling recruitment of trees and shrubs along gradients of beaver foraging intensity and soil moisture, P, K, Mg, and pH. Beavers fed preferentially on a small number of deciduous species and the number of cut stems declined sharply with increasing distance from ponds. Conifers increased in relative dominance to deciduous species in the presence of beavers. Plant species richness and stem and basal area diversity peaked at intermediate distances (about 25 m) from ponds. Sapling recruitment by non-preferred species was positively related to foraging intensity. Total stem abundance and basal area and sapling recruitment by four preferred species (Populus tremuloides, Acer rubrum, Acer saccharum and Corylus cornuta) were negatively related to foraging intensity. However, by including Alnus rugosa and Salix bebbiana (also preferred by beavers) these patterns changed, becoming positively related to foraging intensity. There was also a pronounced gradient in soil moisture, which also decreased with distance from ponds. The other measured edaphic variables did not vary consistently with distance from ponds. Sapling recruitment in mesic versus xeric species varied consistently with hydrid conditions along the moisture gradient, such that variation in moisture also could produce the observed pattern of plant diversity. Diversity patterns changed three years after beaver abandonment of a pond, though sapling recruitment patterns in preferred and non-preferred species around the abandoned pond were similar to the occupied ponds. These observations suggest spatial variation in woody plant richness and diversity could be determined by combined effects of both herbivory (disturbance by beavers) and variable responses of different species to edaphic conditions.     

Bat casualties by road traffic (Brno-Vienna)

We studied the impact of road E461, Brno-Vienna, on bat mortality, with the goal to predict this impact after the road has been reconstructed and turned into highway, R52. In the Czech territory, two proposed road sections of E461 were selected, 3.5 and 4.5 km long, and divided into segments 100 m in length. Bat carcasses were picked up from emergency stopping lanes, and bat activity was recorded by ultrasound detectors along the road and 100 m away on both sides from the central strip. From May to October 2007, 25 checks of bat mortality performed at weekly intervals revealed 119 bat carcasses representing 11 or 12 species.Pipistrellus nathusii, P. pygmaeus andMyotis daubentonii were the most frequent traffic casualties. The greatest mortality was documented from early July to mid-October, with a peak in September. Monitoring bat activity by ultrasound detectors (one night per month in May, June and September) yielded 12 bat species and 3 species couples (Myotis mystacinus/brandtii, M. emarginatus/alcathoe, Plecotus auritus/austriacus), mostly the same taxa as found dead on the road. Significantly greater bat numbers were revealed in the section where the road was situated between two artificial lakes, as compared to a road section without any lakes directly adjacent to the road. In the former section, significant correlation was found between the number of carcasses found and the activity detected, according to road segments.     

The effect of beaver (Castor fiber Linnaeus, 1758) activity on amphibian reproduction

The effect of beaver (Castor fiber Linnaeus, 1758) activity on amphibian reproduction was studied in the small river valleys in Novgorod oblast. At sites not subjected to beaver activity, the reproduction rate of amphibians was low. In spring the water in beaver ponds warms up quickly, which attracts amphibians for reproduction. The maximal abundance of tadpoles due to a high reproduction rate was observed in partially drained ponds. However, a high larvae mortality rate was often observed there. Tadpole survival in flooded and empty ponds depends on factors that are not controlled by beavers, such as geomorphology and climate.     

The Impact of Water Chemistry on Zooplankton Occurrence in Two Types (Field versus Forest) of Small Water Bodies

We examined the influence of water chemistry on zooplankton community structure in the unvegetated zone (open water) and among different types of macrophytes (helophytes and elodeids) in 12 ponds located in two types of catchment area (mid‐forest and mid‐field). An equal occurrence of rotifers and crustaceans was found in mid‐field ponds, while rotifers prevailed over crustaceans in mid‐forest ponds which may have been due to phytoflagellate prevalence, contributing to diminishing the diversity index. We found variation in physical‐chemical features between both types of ponds with higher trophic status, confirmed by eutrophy indicators (K. quadrata or B. longirwostris) frequent occurrence, in the case of mid‐field ponds. The type of water body (forest vs. field) was the best predictor of zooplankton species distribution using DCA analysis. Two groups of zooplankton species were distinguished: (1) related to the mid‐forest ponds (representatives of genera: Cephalodella, Lepadella, Lecane, Trichocerca), where zooplankton densities positively correlated with chlorophyll a and CDOC and (2) related to the mid‐field ponds (representatives of genera: Keratella, Bosmina or Ceriodaphnia). Spatial differentiation of zooplankton community structure was also recorded with lower species diversity attributed to the open water zone compared to vegetated areas. Crustacean densities rose along the heterogeneity gradient of a habitat (from the open water to the zone of elodeids), which indicates the best refuge conditions in the most complex habitat during the daylight‐hours in the ponds with fish presence. Rotifers (especially those equipped with morphological adaptations againt predators) remained in the open water despite the presence of fish. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Roost and hunting site fidelity of female and juvenile Daubenton's bat Myotis daubentonii (Kuhl, 1817) (Chiroptera: Vespertilionidae)

We investigated roosting and hunting site fidelity of Daubenton's bats Myotis daubentonii (Kuhl, 1817) in the Forêt de Soignes, an old-stand forest dominated by 150–200-year-old beeches, during the summers of 2003 and 2004. Roosting behaviour and hunting activity over ponds of adult females and juveniles were monitored using radio-telemetry. Eighteen roosts were located, all in natural cavities. The bats occupied a limited number of trees located in a specific and small roosting area. This roost aggregation was not linked to the distribution of hollow trees. Furthermore, whereas all 11 ponds in the study area were exploited by Daubenton's bats, monitored individuals were limited to two ponds to which they showed high fidelity. These two ponds were not the closest to the roosting area. Overall, these results show that at least for the time we conducted our experiment, female and juvenile Daubenton's bats are highly faithful to specific roosting and hunting grounds.     

Potential use of beaver Castor fiber L., 1758 dams by the thick-shelled river mussel Unio crassus Philipsson, 1788

ABSTRACT

The objective of this paper is to draw attention to a previously unrecognised habitat for Unio crassus Philipsson, 1788 (Bivalvia: Unionidae), namely beaver dam-and-pond complexes. The construction of beaver ponds will allow the colonisation of high energy streams by providing flow refuges during periods of high near-bed shear stress. The absence of freshwater mussels (Unionidae) in mountain streams may result from steep slopes, shear stress during floods, lack of food suspended in the water column (seston), and unfavourable conditions for the settlement and growth of juvenile mussels. Transportation of parasitic larvae on host fish is the main dispersal mechanism for the mussels. A possible constraint on the colonisation of beaver complexes by freshwater mussels is that beaver dams may hinder the upstream movement of their minnow hosts. In the surveyed beaver ponds, the first specimens of U. crassus were found in 2008. Single mussels were also found in subsequent years. It is uncertain whether the occurrence of U. crassus depends on the periodic support of the population from the main river, but the presence of beaver ponds is certain to have given it the opportunity of colonising new areas.     

The relevance of vegetation structures and small water bodies for bats foraging above farmland

Bats are known to forage and commute close to vegetation structures when moving across the agricultural matrix, but the role of isolated landscape elements in arable fields for bat activity is unknown. Therefore, we investigated the influence of small isolated ponds which lie within arable fields close to vegetation structures on the flight and foraging activity of bats. Additionally, we compared species-specific activity measures between forest edges and linear structures such as hedgerows. We repeatedly recorded bat activity using passive acoustic monitoring along 20 transects extending from the vegetation edge up to 200 m into the arable field (hereafter: edge-field interface) with a small pond present at five transects per edge type (linear vs. forest). Using generalized linear mixed effect models, we analyzed the effects of edge type, pond presence and the season on species-specific flight and foraging activity within the edge-field interface. We found a higher flight activity of Nyctalus noctula and Pipistrellus pygmaeus above the arable field when a pond was present. Furthermore, Pipistrellus nathusii and Pipistrellus pipistrellus foraged more frequently at forest edges than at linear structures (e.g. hedgerows). Additionally, we found three major patterns of seasonal variation in the activity of bats along the edge-field interface. This study highlights the species-specific and dynamic use of forest and hedgerow or tree line edges by bats and their importance for different bat species in the agricultural landscape. Further, additional landscape elements such as small isolated ponds within arable fields might support the activity of bats above the open agricultural landscape, thereby facilitating agroecosystem functioning. Therefore, additional landscape elements within managed areas should be restored and protected against the conversion into arable land and better linked to surrounding landscape elements in order to efficiently support bats within the agroecosystem.     

Dental incremental lines in some small species of the European vespertilionid bats

The dentine and cementum of the mammals exhibit incremental lines (IL) that may be seen as dark and light rings in properly prepared sections of teeth. Counting of IL provides a potential method to evaluate the absolute age of many wild species. The aim of the present study was to evaluate IL in small bat species and to test whether the number of IL is associated with the absolute age of bat when its minimal age was known based on ringing data. Teeth of 26 specimens of the following species were examined:Myotis daubentonii (n = 12),Barbastella barbastellus (n = 4),M. brandtii (n = 2),M. nattereri (n = 2),Pipistrellus nathusii (n = 2),Plecotus auritus (n = 2),M. dasycneme (n = 1),Vespertilio murinus (n = 1). Transverse morphological sections of canines, incisors and postcanine teeth were analysed by a light microscopy. In 4 cases, the minimal age of animals examined in this study was known. The IL were revealed in the dentine of 14 bats examined. The cementum of all animals was devoid of IL. The mean distance between the first and second juxtaposed IL ofM. daubentonii was 3.2 ± 0.2 mm, but it was significantly fewer among the subsequent adjacent lines. Due to a thinness of the IL, an accurate counting was considerably difficult in the canines containing more than 10 IL, as well as in the incisors and postcanine teeth with more than 3-6 IL. The IL of roots showed the most contrast, but they were almost obscured from view at the cingulum and crown. In bats of known-age, the numbers of IL were significantly lower than minimal age of those animals examined, and IL were either revealed only in certain teeth or absent entirely in all teeth. The present findings suggest that the number of the IL varies in different teeth and is strongly dependent on section level. Consequently, age determination in small bats using dental IL is doubtful and requires a reevaluation.     

Foraging habitats of bats in southern Finland

We determined the foraging habitats of the northern batEptesicus nilssonii (Keyserling et Blasius, 1839), Brandt’s batMyotis brandtii (Eversmann, 1845), whiskered batMyotis mystacinus (Kuhl, 1819), Daubenton’s batMyotis daubentonii (Kuhl, 1819) and brown long-eared batPlecotus auritus (Linnaeus, 1758) in southern Finland. Among these species, we compared the diversities of foraging habitats, linear feature preference and the bats’ tendencies to forage simultaneously.Eptesicus nilssonii was the most opportunistic, foraging in a wide range of habitats.Myotis daubentonii (94%) foraged mainly on water habitats, whileM. brandtii/mystacinus (89%) andP. auritus (66%) foraged mainly in forest habitats. The diversities of foraging habitats used byE. nilssonii andP. auritus were higher than those ofM. brandtii/mystacinus andM. daubentonii. Both E.nilssonii andP. auritus foraged mostly alone or in small numbers, whileM. brandtii/mystacinus tended to gather in large numbers to forage in the same habitat. Half ofE. nilssonii and 46% ofM. daubentonii foraged over linear features, while other species did not use linear features to such an extent. Management and conservation of foraging habitats are needed especially forM. brandtii/mystacinus andM. daubentonii, which are more specialized thanE. nilssonii and P. auritus.