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...ariables) were created based on hypotheses generatedsfrom field observations, natural history knowledge and potential competing hypothesessfrom the scientific literature.sWe used logistic regression (=-=Hosmer and Lemeshow 2000-=-) to developsquantitative models. Appropriate logistic regression models were run in SYSTAT tospredict species richness (n=32), and wood frog (n=30), bullfrog (n=32) and pickerel frogs(n=32) breeding ...

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...presented in this study are based on amphibiansspecies breeding presence, unless otherwise noted.sWe developed and tested apriori models using model selection with Akaike'ssInformation Criteria (AIC, =-=Burnham and Anderson 2002-=-) to predict 1) sites with highsamphibian species richness and 2) bullfrog, wood frog and pickerel frog breeding sites.sWe used AIC model selection because it allowed us to compare the weight of evide...

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...unt Desert Islands0 2.5 5sI I % ~ o r n e t e r ssFigure 1.1. Location of amphibian study sites in Acadia National Park, Mount DesertsIsland, Maine.s<8 ha in size and <2 m maximum depth at low water, =-=Cowardin et al. 1979-=-) comprises32% of the total wetland area and over 40% of the 9,000 wetland units represented bysNational Wetlands Inventory (NWI) maps (Calhoun et al. 1994).sBeaver, although historically present on M...

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...sfully. Insaddition to being influenced by local variables at breeding sites, some species maysrequire a wetland landscape that provides additional habitat or resources for foraging orsoverwintering (=-=Dunning et al. 1992-=-). For example, Northern leopard frogs (Ranaspipiens) require shallow water bodies with open canopies for breeding (Werner andsGlennemeier 1999), grassy meadows or wetlands for summer foraging and per...

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...ductionsDistributions of pond-breeding amphibian species may shift naturally over time insresponse to changes both within ponds and in the landscape surrounding breeding pondss(Pechmann et al. 199 1, =-=Alford and Richards 1999-=-, Skelly et al. 1999, Skelly 200 1). If wesare to develop effective conservation strategies, we must understand how amphibiansspecies and populations respond to natural, as well as anthropogenic, pert...

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..., creating a consistent hydroperiod length tosensure successful wood frog metamorphosis (Paton and Crouch 2002).sAs the pemlanence of wetlands increases, so too does the suite of potentialspredators (=-=Wellborn et al. 1996-=-), which may serve as a tradeoff in determining overallsreproductive success at abandoned beaver sites. Wood frog egg mass numbers suggeststhat, despite increased predation by invertebrate predators i...

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...n 1994,sMuller-Schwarze and Sun 2003). Beaver activity varies spatially and temporally, therebyscreating a shifting mosaic of wetlands and an increase in wetland heterogeneity at theslandscape scale (=-=Naiman et al. 1986-=-, Remillard et al. 1987, Naiman et al.1988, Snodgrasss1997). Studies assessing the spatial and temporal dynamics of beaver disturbance onsplant community composition and structure, and on the distribu...

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... order to conserve pond-breeding amphibian species richness and populations, asdiversity of wetlands with regard to hydroperiod, as well as connectivity of sites in theslandscape, must be maintained (=-=Semlitsch 2000-=-, Snodgrass et al. 2000). As beaversrecolonize areas of their former range, they are increasing the available number ofswetlands and decreasing inter-wetland distance, which enhances wetland connectiv...

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...equire shallow water bodies with open canopies for breeding (Werner andsGlennemeier 1999), grassy meadows or wetlands for summer foraging and permanentslakes or streams for overwintering habitat (see =-=Pope et al. 2000-=-). Pickerel frogs (Ranaspalustris), a closely related species, frequent stream corridors, lake and pond shores andsother wet areas during the summer (Gibbs 1998, Hunter et al. 1999), and breedingspopu...

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...ms for overwintering habitat (see Pope et al. 2000). Pickerel frogs (Ranaspalustris), a closely related species, frequent stream corridors, lake and pond shores andsother wet areas during the summer (=-=Gibbs 1998-=-, Hunter et al. 1999), and breedingspopulations of this species may be influenced by the availability of suitable wetlandsforaging habitat in the surrounding landscape.sTo assess the relative importan...

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...nd landscape-scale variables in predicting amphibiansspecies richness in agricultural, urban and developing landscapes (Richter and Azouss1995, Hecnar and M'Closkey 1998, Kolozsvary and Swihart 1999, =-=Lehtinen et al. 1999-=-,sFindlay et al. 2001, Guerry and Hunter 2002). Similar multiple-scale studies are absentsfrom regions where direct anthropogenic disturbance, in the form of habitat loss andsfragmentation, is minimal...

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... predictor of highsamphibian species richness; connections through linear stream corridors providesfavorable conditions for amphibian movement by maintaining moist microclimates andsherbaceous cover (=-=Reh and Seitz 1990-=-, Gibbs 1998). Beaver may play a crucial role insenhancing connectivity by reducing the distance between suitable sites. A 68% decreasesin median inter-wetland distance due to beaver disturbance has b...

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...elative importance of local and landscape-scale variables in predicting amphibiansspecies richness in agricultural, urban and developing landscapes (Richter and Azouss1995, Hecnar and M'Closkey 1998, =-=Kolozsvary and Swihart 1999-=-, Lehtinen et al. 1999,sFindlay et al. 2001, Guerry and Hunter 2002). Similar multiple-scale studies are absentsfrom regions where direct anthropogenic disturbance, in the form of habitat loss andsfra...

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...ond-breeding amphibian species may shift naturally over time insresponse to changes both within ponds and in the landscape surrounding breeding pondss(Pechmann et al. 199 1, Alford and Richards 1999, =-=Skelly et al. 1999-=-, Skelly 200 1). If wesare to develop effective conservation strategies, we must understand how amphibiansspecies and populations respond to natural, as well as anthropogenic, perturbations atsboth po...

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... dry year (2001, driest year on record, l895-2OOl), the earliest ofsthese sites to dry was not until July 3 1 ", creating a consistent hydroperiod length tosensure successful wood frog metamorphosis (=-=Paton and Crouch 2002-=-).sAs the pemlanence of wetlands increases, so too does the suite of potentialspredators (Wellborn et al. 1996), which may serve as a tradeoff in determining overallsreproductive success at abandoned ...

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...rica has investigated thesrelative importance of local and landscape-scale variables in predicting amphibiansspecies richness in agricultural, urban and developing landscapes (Richter and Azouss1995, =-=Hecnar and M'Closkey 1998-=-, Kolozsvary and Swihart 1999, Lehtinen et al. 1999,sFindlay et al. 2001, Guerry and Hunter 2002). Similar multiple-scale studies are absentsfrom regions where direct anthropogenic disturbance, in the...

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...palatable to fish, andsmay actually require fish to suppress invertebrate predators in order to successfullysexploit wetlands at the permanent end of the hydroperiod gradient (Kruse and Franciss1977, =-=Werner and McPeek 1994-=-). In contrast, wood frogs are highly vulnerable to fishspredation and have active larvae that rely on rapid development and early metamorphosissto utilize short-hydroperiod wetlands with few predator...

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...andschange riparian areas to wetland basins; the results of these changes in the landscapesaffect geomorphology and can persist for centuries in the absence of beaver (Ruedemannsand Schoonmaker 1938, =-=Ives 1942-=-, Naiman et al. 1986). With reduced trapping duringsthe 20'" century, beaver returned, or were reintroduced, to many areas within their formersrange and actively recolonized available habitat (Naiman ...

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...a (including fish, birds, reptiles, mammals, and aquaticsinvertebrates) have been conducted (McDowell and Naiman 1986, Remillard et al. 1987,sDubuc et al. 1990, Brown et al. 1996, McCall et al. 1996, =-=Snodgrass and Meffe 1998-=-).sHowever, studies examining relationships between beaver activity and amphibian speciessrichness and distribution have been limited, and have not shown strong relationships.sStudies in Oregon and So...

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...beaver disturbance may besimportant for maintaining pond-breeding amphibian species richness in northern forestedslandscapes, we caution against assuming that isolated wetlands are less valuable (sees=-=Semlitsch and Bodie 1998-=-). Isolated wetlands provide unique (often temporary andsfishless) wetland habitat that supports species that may not exist in other wetlands, orsmay persist in lower abundances. Further research is n...

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...al.s1983). In contrast, unburned areas are dominated by spruce-fir coniferous forests. Sincesaspen, birch and other early successional tree species are a favored food source for beavers(Jenkins 1979, =-=Johnston and Naiman 1990-=-b, Fryxell and Doucet 1993), forestsregeneration in the burned area provided an abundant food supply that would favorsbeaver population growth.sBeaver Colonization PatternssBeaver colonized pre-existi...

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...unity composition and structure, and on the distribution and communitysstructure of a variety of animal taxa (including fish, birds, reptiles, mammals, and aquaticsinvertebrates) have been conducted (=-=McDowell and Naiman 1986-=-, Remillard et al. 1987,sDubuc et al. 1990, Brown et al. 1996, McCall et al. 1996, Snodgrass and Meffe 1998).sHowever, studies examining relationships between beaver activity and amphibian speciessric...

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...opy sitesswould reduce the number of suitable wood frog breeding sites in the landscape and mightsalso affect populations of other pond-breeding amphibian species (Chapter 1, Skelly et al.s1999,2002, =-=Halverson et al. 2003-=-). Large sites with permanent beaver colonies and asstable water level and hydroperiod may not be as likely to experience large shifts insamphibian assemblages over time. However, sites that are perio...

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...ing the course ofsamphibian larval sampling in 2000 and 2001, were used to confirm the data from 1999.sWe assumed that the presence of fish would exclude predation sensitive species (e.g.swood frogs, =-=Hopey and Petranka 1994-=-). Therefore, we did not distinguish betweenspredatory and non-predatory fish in our analysis.sWater depth gauges were installed at the deepest point at each research site insMarch 2000. Maximum depth...

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...tiple competing hypotheses rather than selecting a single best model.sAdditionally, it is more conservative and less prone, than many traditional data analysissmethods, to producing spurious results (=-=Anderson et al. 2001-=-).sWe limited our analyses to include 15 predictor variables (Table 1.2) thatsrepresent local pond conditions and landscape-scale wetland characteristics in a beaver-smodified wetland landscape. We te...

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...al.s1983). In contrast, unburned areas are dominated by spruce-fir coniferous forests. Sincesaspen, birch and other early successional tree species are a favored food source for beavers(Jenkins 1979, =-=Johnston and Naiman 1990-=-b, Fryxell and Doucet 1993), forestsregeneration in the burned area provided an abundant food supply that would favorsbeaver population growth.sBeaver Colonization PatternssBeaver colonized pre-existi...

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...ibution and communitysstructure of a variety of animal taxa (including fish, birds, reptiles, mammals, and aquaticsinvertebrates) have been conducted (McDowell and Naiman 1986, Remillard et al. 1987,s=-=Dubuc et al. 1990-=-, Brown et al. 1996, McCall et al. 1996, Snodgrass and Meffe 1998).sHowever, studies examining relationships between beaver activity and amphibian speciessrichness and distribution have been limited, ...

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...urned areas are dominated by spruce-fir coniferous forests. Sincesaspen, birch and other early successional tree species are a favored food source for beavers(Jenkins 1979, Johnston and Naiman 1990b, =-=Fryxell and Doucet 1993-=-), forestsregeneration in the burned area provided an abundant food supply that would favorsbeaver population growth.sBeaver Colonization PatternssBeaver colonized pre-existing ponds previous to, and ...

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...HIBIAN SPECIES DISTRIBUTIONSsIntroductionsBeaver (Castor canadensis Kuhl) were historically widespread and abundantsthroughout North America but were locally extirpated in many areas due to trappings(=-=Ruedemann and Schoonmaker 1938-=-, Jenkins and Busher 1979, Naiman et al. 1988).sBeaver are known ecosystem engineers, impounding streams to create and modifyswetlands (Jones et. a1 1994). Beaver dams retain sediments, modify nutrien...

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...st known for foraging on the inner bark of small diameter earlyssuccessional tree species, beaver will forage preferentially on aquatic macrophytes,sparticularly during the summer months (Bradt 1938, =-=Svendsen 1980-=-). In large wetlandsswith abundant resources, a beaver colony might be sustained almost exclusively bysresources found within the pond (Howard and Larson 1985). Colonization of these sitessrepresents ...

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...and species richness havesreceived little attention.sThe effect of beaver on the landscape, and their ability to drastically modifysstream and wetland habitat, is well documented (Naiman et al. 1988, =-=Hammerson 1994-=-,sMuller-Schwarze and Sun 2003). Beaver activity varies spatially and temporally, therebyscreating a shifting mosaic of wetlands and an increase in wetland heterogeneity at theslandscape scale (Naiman...

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...to inconsistent efforts among sampling personnel and differencessin catchability and microhabitat use among species, they are an effective method forsestablishing amphibian species breeding presence (=-=Shaffer et al. 1994-=-). Due tosdifferences in the life history strategies of the studied species, larval sampling was thesonly method we used that could potentially document the breeding presence of allsspecies.sWe used d...

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...otographs and long-termsinvestigations of beaver colonization and landscape changes due to wetland creation andsmodification by beaver are made possible by interpreting historical aerial photographss(=-=Howard and Larson 1985-=-, Remillard et al. 1987, Johnston and Naiman 1 WOa, Lisles1994).sWe used aerial photographs to study wetland creation and modification by beaversat Acadia National Park, Mount Desert Island, Maine bet...

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...rze and Sun 2003). Beaver activity varies spatially and temporally, therebyscreating a shifting mosaic of wetlands and an increase in wetland heterogeneity at theslandscape scale (Naiman et al. 1986, =-=Remillard et al. 1987-=-, Naiman et al.1988, Snodgrasss1997). Studies assessing the spatial and temporal dynamics of beaver disturbance onsplant community composition and structure, and on the distribution and communitysstru...

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...eaver are most known for foraging on the inner bark of small diameter earlyssuccessional tree species, beaver will forage preferentially on aquatic macrophytes,sparticularly during the summer months (=-=Bradt 1938-=-, Svendsen 1980). In large wetlandsswith abundant resources, a beaver colony might be sustained almost exclusively bysresources found within the pond (Howard and Larson 1985). Colonization of these si...

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...chness may not takesinto account the varying life histories of individual pond-breeding species. For example,swood frogs (Rana sylvatica) are known to breed primarily in temporary, fishless wetlandss(=-=Hunter et al. 1999-=-). Adults and juveniles are terrestrial, spending most of the year insadjacent uplands, seasonal pools, and forested wetlands where they forage andsoverwinter. In contrast, bullfrogs (Rana catesbeiana...

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...ariety of animal taxa (including fish, birds, reptiles, mammals, and aquaticsinvertebrates) have been conducted (McDowell and Naiman 1986, Remillard et al. 1987,sDubuc et al. 1990, Brown et al. 1996, =-=McCall et al. 1996-=-, Snodgrass and Meffe 1998).sHowever, studies examining relationships between beaver activity and amphibian speciessrichness and distribution have been limited, and have not shown strong relationships...

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...tysstructure of a variety of animal taxa (including fish, birds, reptiles, mammals, and aquaticsinvertebrates) have been conducted (McDowell and Naiman 1986, Remillard et al. 1987,sDubuc et al. 1990, =-=Brown et al. 1996-=-, McCall et al. 1996, Snodgrass and Meffe 1998).sHowever, studies examining relationships between beaver activity and amphibian speciessrichness and distribution have been limited, and have not shown ...

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...n size and <2 m maximum depth at low water, Cowardin et al. 1979) comprises32% of the total wetland area and over 40% of the 9,000 wetland units represented bysNational Wetlands Inventory (NWI) maps (=-=Calhoun et al. 1994-=-).sBeaver, although historically present on Mount Desert Island, were extirpated duesto trapping in the 1 9'h century (Bailey 1925). Reintroductions began with foursindividuals in 192 1 and population...

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...iables in predicting amphibiansspecies richness in agricultural, urban and developing landscapes (Richter and Azouss1995, Hecnar and M'Closkey 1998, Kolozsvary and Swihart 1999, Lehtinen et al. 1999,s=-=Findlay et al. 2001-=-, Guerry and Hunter 2002). Similar multiple-scale studies are absentsfrom regions where direct anthropogenic disturbance, in the form of habitat loss andsfragmentation, is minimal. North American beav...

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...roductionsBeaver (Castor canadensis Kuhl) were historically widespread and abundantsthroughout North America but were locally extirpated in many areas due to trappings(Ruedemann and Schoonmaker 1938, =-=Jenkins and Busher 1979-=-, Naiman et al. 1988).sBeaver are known ecosystem engineers, impounding streams to create and modifyswetlands (Jones et. a1 1994). Beaver dams retain sediments, modify nutrient flow, andschange ripari...

Citation Context

...d all methods were repeated in 2001.sWe conducted egg mass surveys at all sites in April to document the breedingspresence of wood frogs (Rana sylvatica) and spotted salamanders (Ambystomasmaculatum)(=-=Crouch and Paton 2000-=-). We waded the perimeter of each site (up to onesmeter in depth) and identified and counted all visible egg masses. Surveys were onlysdone when visibility was not affected negatively by wind or rain....

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...ained (Fahrig and Merriams1985).sOur findings contrast with previous studies where significant differences insamphibian species richness in relation to beaver disturbance were not found (Suzukis1992, =-=Russell et al. 1999-=-). Study design may partially explain differences in our results.sFor example, rather than comparing impounded and unimpounded stream reaches, wesobserved beaver-modified and unmodified palustrine wet...

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...rge number of sites and provides an active approach tossampling various microhabitats and the opportunity to capture both fast-moving andscryptic species (Shaffer et al. 1994, Fellers and Free1 1995, =-=Thoms et al. 1997-=-). Thesentire perimeter of each wetland (up to 1 m in depth) was sampled once in both June andsJuly 2000 and 2001. This sampling schedule overlapped with the larval stages of allsexpected pond-breedin...

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...). Reintroductions began with foursindividuals in 192 1 and population numbers likely remained low prior to a large fire ins1947, which burned 6,800 ha on the eastern side of the island (Bailey 1925, =-=Baird 1964-=-,sPatterson 1983). The resulting change in forest composition, particularly the dominancesof early successional species preferred by beaver, such as aspen (Populus spp.) and birchs(Betula spp.), creat...

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...early half of the 28 1 km' area of thesisland (Patterson et al. 1983). The study area is at the transition zone between spruce-firsforests to the north and northeastern hardwood forests to the south (=-=Davis 1966-=-).sConiferous forests are dominated by white spruce (Picea glauca), red spruce (Piceasrubens) and balsam fir (Abies balsamea). Deciduous forests are characterized by birchs(Betula spp.), aspen (Populu...

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... NationalsPark, personal communication). While present throughout the island, beaver-createdswetlands (both active and abandoned) continue to be much more prevalent on the easternsside of the island (=-=Muller-Schwarze 1979-=-, JMC personal observation).sStudy SpeciessEleven pond-breeding amphibian species (8 anuran and 3 salamander species)shave been reported historically on Mount Desert Island (Manville 1939, Davis 1958,...

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... units represented bysNational Wetlands Inventory (NWI) maps (Calhoun et al. 1994).sBeaver, although historically present on Mount Desert Island, were extirpated duesto trapping in the 1 9'h century (=-=Bailey 1925-=-). Reintroductions began with foursindividuals in 192 1 and population numbers likely remained low prior to a large fire ins1947, which burned 6,800 ha on the eastern side of the island (Bailey 1925, ...

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... JMC personal observation).sStudy SpeciessEleven pond-breeding amphibian species (8 anuran and 3 salamander species)shave been reported historically on Mount Desert Island (Manville 1939, Davis 1958,s=-=Coman 1987-=-, Hunter et al. 1999; Table 1.1). While gray treefrogs (Hyla versicolor) andsnorthern leopard frogs (Ranapipiens) have been noted in the past (Manville 1939, Daviss1958, Coman 1987), there have been n...

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...hwarze 1979, JMC personal observation).sStudy SpeciessEleven pond-breeding amphibian species (8 anuran and 3 salamander species)shave been reported historically on Mount Desert Island (Manville 1939, =-=Davis 1958-=-,sComan 1987, Hunter et al. 1999; Table 1.1). While gray treefrogs (Hyla versicolor) andsnorthern leopard frogs (Ranapipiens) have been noted in the past (Manville 1939, Daviss1958, Coman 1987), there...

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...sites. A 68% decreasesin median inter-wetland distance due to beaver disturbance has been documented in asMaine watershed with a beaver recolonization history similar to that of Acadia NationalsPark (=-=Lisle 1994-=-).sBeaver activity is dependent on having stream corridors (connectivity) in whichsbeaver may build dams to create or modify wetlands. Many of the wetlands we surveyedswould not exist or would not pro...

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...ies in Oregon and South Carolina found no significant difference in amphibiansspecies richness or diversity between beaver-occupied and unoccupied stream reaches, orsbetween new and old beaver ponds (=-=Suzuki 1992-=-, Russell et al.1999).sHydroperiod is a major determinant in structuring amphibian communities, withslonger hydroperiod wetlands supporting more diverse amphibian populations (Wellbornset al. 1996, Sn...