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1.
Freshwater mussels of the order Unionoida have life cycles that include larval attachment to and later metamorphosis on suitable host fishes. Information on the trophic relationship between unionoid larvae and their host fishes is scarce. We investigated the trophic interaction between fish hosts and encysted larvae of two species of freshwater mussels, Margaritifera margaritifera and Unio crassus, using stable isotope analyses of larvae and juvenile mussels as well as of host fish gill and muscle tissues before and after infestation. Due to different life histories and durations of host‐encystment, mass and size increase in M. margaritifera during the host‐dependent phase were greater than those of U. crassus. δ 13C and δ 15N signatures of juvenile mussels approached isotopic signatures of fish tissues, indicating a parasitic relationship between mussels and their hosts. Shifts were more pronounced for M. margaritifera, which had a five‐fold longer host‐dependent phase than U. crassus. The results of this study suggest that stable isotope analyses are a valuable tool for characterizing trophic relationships and life history strategies in host–parasite systems. In the case of unionoid mussels, stable isotopic shifts of the larvae are indicative of the nutritional versus phoretic importance of the host. 相似文献
2.
Our aim was to determine how beavers affect habitats and food resources for juvenile salmon in the Kwethluk River in western Alaska. 相似文献
3.
Limnology - Populations of most freshwater mussels (Unionidae) are declining worldwide; these includes Sinanodonta spp., which inhabit artificial ponds in Japan. The detection of environmental DNA... 相似文献
4.
- 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.
- 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.
- 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.
- 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.
- 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.
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5.
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 km 2) 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. 相似文献
6.
A threatened but under-studied component offreshwater biodiversity in North America is thenative freshwater mussels (Bivalvia:Unionoidea: Margaritiferidae and Unionidae). Genetic data suggest that these mussel speciesgenerally exhibit levels of variability similarto other invertebrates. We surveyed allozymevariation in the Louisiana Pearlshell, Margaritifera hembeli (Margaritiferidae), athreatened freshwater mussel. Five examinedpopulations are monomorphic for 25 allozymeloci, the first report of a native freshwatermussel species with extensive allozymemonomorphism. Low genetic diversity appears tobe characteristic of margaritiferids, as anANOVA indicated that mussels of the familyMargaritiferidae have significantly lowerlevels of heterozygosity than the mussels ofthe family Unionidae. Margaritiferids havestrong habitat preferences and modification ofhabitat leads to rapid loss of populations.Although bottlenecks are known to cause lowgenetic variability, margaritiferids mayexhibit meta-population structure withextinction/re-colonization dynamics leading tolow genetic variability. Margaritiferidsgenerally exhibit a patchy distribution with acolonization rate that is approximately twicethat of extinction. Tests of themetapopulation hypothesis will requireadditional allozyme population genetic data aswell as hypervariable microsatellite loci. 相似文献
8.
North American beavers ( Castor canadensis) were introduced to Tierra del Fuego Island in 1946 for their fur, and have since spread across the archipelago and onto
the South American mainland. We assessed the impact of invasive beavers on streams of these forested watersheds by quantifying
the trophic basis of production (TBP) and consumptive organic matter flows of benthic macroinvertebrate assemblages. TBP was
determined in two streams: clear- and black-water. Stable isotopes were used across four streams to further elucidate food
web structure and dominant pathways. TBP and stable isotopes showed that terrestrially derived organic matter (amorphous detritus,
leaves, and wood) supported a majority of secondary production in the benthic food webs at all sites (forested reaches, beaver
ponds, and sections downstream of ponds with foraged riparian zones). The magnitude of these flows was enhanced in beaver-modified
sites compared with forested habitats (4.0–5.3× increase g AFDM m −2 year −1 in pond habitats, 1.1–2.1× increase in downstream habitats). Diatoms were the only autochthonous resource identified in macroinvertebrate
guts, but their contribution to secondary production was small. Consumptive flows mirrored trends in TBP (i.e., dominance
of terrestrial sources and greater magnitude in beaver ponds). Collector–gatherer consumption of amorphous detrital material
dominated food web flows in all habitats, but was higher in beaver ponds relative to other habitats. Food web structure was
simplified in beaver ponds; only two of the five possible functional groups contributed >1% of total organic matter flow in
ponds (collector–gatherers and predators). Consumptive flows to predators increased in ponds, and stable isotopes of nitrogen
and carbon (δ 15N and δ 13C) corroborated a relatively greater importance of predators (greater trophic distance), as well as less diversity of basal
resources (less variation in δ 13C) in ponds. Our findings indicate that invasive beaver’s engineering activities resulted in greater flows of terrestrial
organic matter subsidies to in-stream food webs, which had a relatively greater change in the clear-water than in the black-water
stream. Owing to the fact that these streams were naturally dependent on allochthonous resources for a majority of production
and material flows, changes wrought by beavers to streams in forested environments are probably less than in watersheds with
inherently greater dependence on autochthonous production such as the adjacent steppe biome. 相似文献
9.
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. 相似文献
10.
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. 相似文献
12.
Today, land use impacts a major proportion of all streams. Here, landscape features in corridors along streams and water chemical factors were analyzed in relation to recruitment of the threatened freshwater pearl mussel ( Margaritifera margaritifera) and its host fish the brown trout ( Salmo trutta). Mussel recruitment and trout density were negatively related to forest clear-cuts. Mussel recruitment was negatively related to water color and turbidity. Therefore, the threats to the mussel may be severe, as low mussel recruitment may be caused by direct effects on the juvenile mussels and indirect effects on the host fish. High proportions of lakes and ponds were found to be positive for recruitment and for trout, and deciduous forest was positively related to trout. The combination of investigations at different scales at the landscape level and at in-stream levels may be applicable to find threats to other threatened species. The results indicate that forestry activities may negatively affect recruitment of freshwater pearl mussels and its host fish. Reductions of forestry activities and the retaining of intact quantity and quality of the riparian zones next to streams, both for the mussel and its host fish may be important conservation measures to restore freshwater pearl mussel populations. 相似文献
14.
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. 相似文献
15.
Our study found that beaver activity affects macroinvertebrate assemblages of both beaver ponds and downstream sites. The
percentage composition of the invertebrate faunae of beaver ponds was strikingly different from the invertebrate faunae of
upstream forested and downstream sites. The number of EPT (ephemeropteran, plecopteran, trichopteran) taxa in the upstream
forested sites in all streams was higher than in beaver pond and downstream sites. Statistically significant differences were
found in absolute and relative abundances of EPT and Chironomidae between different streams sites. The absolute and relative
abundance of pollution-sensitive EPT was significantly higher in forested sites than in beaver pond and downstream sites in
all measured streams. Beaver ponds had a significantly higher absolute and relative abundance of Chironomidae compared with
upstream forested and downstream sites. We found that Plecoptera and Coleoptera were absent from beaver pond sites. The absolute
abundance of Plecoptera was significantly higher in upstream forested sites than in downstream sites in all three streams.
Gatherers were the dominant functional feeding group in relative abundance in all three habitat types. The percentage of gatherers
was higher in beaver ponds than in forested and downstream sites. 相似文献
16.
SUMMARY 1. Exotic zebra mussels, Dreissena polymorpha, occur in southern U.S. waterways in high densities, but little is known about the interaction between native fish predators and zebra mussels. Previous studies have suggested that exotic zebra mussels are low profitability prey items and native vertebrate predators are unlikely to reduce zebra mussel densities. We tested these hypotheses by observing prey use of fishes, determining energy content of primary prey species of fishes, and conducting predator exclusion experiments in Lake Dardanelle, Arkansas. 2. Zebra mussels were the primary prey eaten by 52.9% of blue catfish, Ictalurus furcatus; 48.2% of freshwater drum, Aplodinotus grunniens; and 100% of adult redear sunfish, Lepomis microlophus. Blue catfish showed distinct seasonal prey shifts, feeding on zebra mussels in summer and shad, Dorosoma spp., during winter. Energy content (joules g −1) of blue catfish prey (threadfin shad, Dorosoma petenense; gizzard shad, D. cepedianum; zebra mussels; and asiatic clams, Corbicula fluminea) showed a significant species by season interaction, but shad were always significantly greater in energy content than bivalves examined as either ash-free dry mass or whole organism dry mass. Fish predators significantly reduced densities of large zebra mussels (>5 mm length) colonising clay tiles in the summers of 1997 and 1998, but predation effects on small zebra mussels (≤5 mm length) were less clear. 3. Freshwater drum and redear sunfish process bivalve prey by crushing shells and obtain low amounts of higher-energy food (only the flesh), whereas blue catfish lack a shell-crushing apparatus and ingest large amounts of low-energy food per unit time (bivalves with their shells). Blue catfish appeared to select the abundant zebra mussel over the more energetically rich shad during summer, then shifted to shad during winter when shad experienced temperature-dependent stress and mortality. Native fish predators can suppress adult zebra mussel colonisation, but are ultimately unlikely to limit population density because of zebra mussel reproductive potential. 相似文献
17.
Species introductions threaten ecosystem function worldwide, and interactions among introduced species may amplify their impacts. Effects of multiple invasions are still poorly studied, and often, the mechanisms underlying potential interactions among invaders are unknown. Despite being a remote and well‐conserved area, the southern portion of South America has been greatly impacted by invasions of both the American beaver ( Castor canadensis) and Brown Trout ( Salmo trutta fario). Here, we compared growth, condition, diet, and stable isotopes of sulfur δ 34S, nitrogen δ 15N, and carbon δ 13C for stream‐living Brown Trout from streams with ( n = 6) and without ( n = 6) beaver in Tierra del Fuego, Chile. We show that beaver may facilitate the success of trout by positively influencing fish growth. Beaver indirectly provide greater food subsidies (i.e., macroinvertebrate abundances) by modifying the local aquatic environment through active dam and lodge building suggesting a one‐way positive interaction. Trout in beaver‐influenced streams occupied a slightly higher trophic level with more depleted sulfur and carbon isotopic ratios suggesting that food web pathways rely on secondary production from autochthonous origin. Trout in beaver‐influenced streams had a wider dietary breadth with diptera and amphipoda as the prey items providing most of the energy, whereas in streams without beaver, trichoptera were the main source of energy for trout. Ultimately, we find that these two species, which have never co‐occurred naturally, bring about the same ecosystem function and the beneficial influences in their native ranges as in invaded systems. 相似文献
18.
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. 相似文献
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