, vol. 40, no. 3, pp. 309–322, 2006 copyright 2006 society ... · mount rainier national park,...

56437238, 56440. Plectrohyla cyanomma: MEX: OAX-ACA: Sierra de Juarez, 1.2 km north of crest of CerroPelon, UTA A-5731, 5735. Plectrohyla mykter: MEX:GUERRERO: Sierra Madre del Sur, 0.8 km southwestof Omilteme, UTA A-4108211. Plectrohyla psarosema:

MEX: OAXACA: Sierra Mixes, 5.8 km (by road) westof Totontepec, UTA A-5782 (holotype), UTA A-5771,5776, 5783 (paratypes). Plectrohyla sabrina: MEX:OAXACA: Sierra de Juarez, 11.1 km south of VistaHermosa, UTA A-52810 (paratype).

Journal of Herpetology, Vol. 40, No. 3, pp. 309–322, 2006Copyright 2006 Society for the Study of Amphibians and Reptiles

Associations of the Van Dyke’s Salamander (Plethodon vandykei) withGeomorphic Conditions in Headwall Seeps of the Cascade Range,

Washington State

AIMEE P. MCINTYRE,1,2 RICHARD A. SCHMITZ,3 AND CHARLES M. CRISAFULLI4

1Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon 97331, USA; E-mail:

[email protected] of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon 97331, USA; E-mail:

[email protected] States Forest Service, Pacific Northwest Research Station, Olympia, Washington 98512, USA; E-mail:

[email protected]

ABSTRACT.—We explored the association between Van Dyke’s Salamander (Plethodon vandykei) and

hydrologic condition, geomorphology, and vegetation structure in headwall seeps in the Cascade Range of

Washington State. After conducting salamander surveys and measuring habitat characteristics at 40 seep sites

from July to August of 2002, we modeled occurrence of P. vandykei at three site scales: between seeps, within

seeps, and between microhabitat sites. We ranked a priori models using Bayesian Information Criterion

(BIC). Using logistic regression, with presence and absence as the response, we found best approximating

models for the occurrence of P. vandykei at the three site scales is predicted by hydrological and geological

habitat characteristics. Between seeps, the probability of the occurrence of P. vandykei increased with

increasing proportions of seep face having both dry and sheeting hydrology, and increasing proportions of

seep face . 5 m high. Within seeps, the probability of the occurrence of P. vandykei was negatively

associated with seeps where total overhead cover was . 25%. Between microhabitat sites, the probability of

the occurrence of P. vandykei was positively associated with increases in the percent cover of small cobble,

small gravel, and bedrock. P. vandykei appears to be associated with habitats that maintain cool thermal and

hydric conditions favorable for a species that is sensitive to heat and desiccation due to physiological

constraints.

The Van Dyke’s Salamander (Plethodon van-dykei), endemic to Washington State, is oftenconsidered more closely associated with waterthan any other western Plethodon species (Bro-die, 1970), with the possible exceptions of theDunn’s Salamander (Plethodon dunni) and thecoeur d’Alene Salamander (Plethodon idahoensis;Leonard et al., 1993). Plethodon vandykei is foundin three disjunct population centers in Wash-ington State: the southern and central Cascades(the area included in this study), the WillapaHills, and the Olympic Peninsula (Leonard et

al., 1993). The restricted range of P. vandykeisuggests that it has relatively sedentaryhabits or narrow ecological tolerances (Wilsonet al., 1995). Respiratory requirements mayinfluence life history characteristics of Plethodonsalamanders (Feder, 1983), which lack lungs(Noble, 1931) and rely on moist permeableskin to respire (Gatz et al., 1974). Plethodonspecies appear to have narrow physiologicaltolerance limits as a result of their lunglessness,making them susceptible to heat and drying(Feder, 1983; Stebbins and Cohen, 1995). Thus,they are frequently associated with cool, moisthabitats.

Plethodon vandykei has been documentedalong high-gradient streams, in the splash zonesof waterfalls, and in seeps (Nussbaum et al.,

2 Corresponding Author. Present address: Washing-ton Department of Fish and Wildlife, 600 Capitol WayNorth, Mailstop 43200, Olympia, Washington 98501-1091, USA

NEW PLECTROHYLA FROM OAXACA 309

1983; Leonard et al., 1993; Wilson, 1993; Jones,1999). Zones of saturated overland flow occurwhere soils thin over impermeable bedrock(Ziemer and Lisle, 1998); they can occur whenthe soil becomes fully saturated and subsurfaceflow emerges on the surface (Ziemer and Lisle,1998). This often occurs when water percolatesthrough coarse substrates until it reachesimpermeable bedrock of a cliff face, formingwhat we referred to as headwall seeps (Fig. 1A).

Although habitat associations have beenexplored for P. vandykei along high-gradientstreams in the southern and central CascadeRange of Washington State (McIntyre, 2003), nostudies have explored the relationship of P.vandykei with headwall seep habitats. McIntyre(2003) found that habitat characteristics influ-enced by geomorphic and hydrologic condi-tions were indicators of the occurrence of P.vandykei at stream sites in the Cascade Range.The probability of the occurrence of P. vandykeialong streams was positively associated withsteep, vertical and V-shaped valley walls thatlacked soil and were unable to support woodyvegetation, high-gradient stream channels dom-inated by bedrock and boulders (. 256 mmdiameter), availability of small cobble (65–128 mm diameter) presumably used as cover,and the presence of valley wall seeps.

We designed this current study to assesswhether the habitat characteristics that arepredictive of the occurrence of P. vandykei atstream sites were similar to the habitat char-acteristics associated with the occurrence of P.vandykei at headwall seep sites in the CascadeRange. We developed resource selection modelsfor P. vandykei in headwall seeps and assessedthe influence of habitat characteristics on theoccurrence of P. vandykei at multiple site scales:between seeps, within seeps, and microhabitatsites. Plethodon vandykei is rare within its range,and exploring the importance of quantifiablehabitat characteristics in headwall seeps mayenable us to better understand the underlyinggeophysical and ecological processes that de-termine the occurrence of P. vandykei.

Plethodon vandykei are difficult to detectbecause of their rarity and temporally restrictedsurface activities that are influenced by weatherconditions. Habitat models provide a means forpredicting suitable habitats, and can be used asa tool for narrowing the search for this speciesto areas that are more suitable. Although ourresearch specifically addresses habitat modelingfor P. vandykei, the tools that we present may beused to aid in the conservation and identifica-tion of suitable habitats for other species. Thesetools may prove to be particularly useful forspecies that share characteristics similar to P.

vandykei, including other plethodontid salaman-ders, or species that are difficult to detect.

STUDY AREA

Our study area included lands in the south-ern and central Washington Cascade Range,from the Muddy River drainage in SkamaniaCounty, north to the Carbon River drainage inMount Rainier National Park, Pierce County.Sample sites were headwall seeps located in theGifford Pinchot National Forest and MountRainier National Park. The area has beenmanaged for multiple purposes including tim-ber harvest, protection of ecological and geo-physical conditions, research, education, andrecreation. These lands have been affected bya variety of natural and anthropogenic distur-bances, and ranged from old-growth coniferousforest to extensively managed young stands,and included areas impacted by the 1980eruptions of Mount St. Helens. Headwall seeplocations ranged in elevation from 450–1550 m.

Seeps were located in the western hemlockand Pacific silver fir forest zones of the southernand central Cascade Range (Franklin and Dyr-ness, 1973). The western hemlock zone of thesouthern Cascade extends from 150–1000 m inelevation and is typified by a wet, mild,maritime climate. Precipitation occurs mainlyduring the winter and averages 1500–3000 mmper year. Summers are relatively dry with only6–9% of the total annual precipitation. NeitherJanuary nor July temperatures are extreme, withmean annual temperatures averaging 8–9uC.The Pacific silver fir zone occurs at elevationsfrom 900–1300 m on the western slopes of thesouthern Washington Cascade Range. This zoneis wetter and cooler than the adjacent westernhemlock zone. It receives considerably moreprecipitation, often in the form of snow, whichmay accumulate in winter snowpacks as deepas 1–3 m. Mean annual temperatures average5–6uC.

Much of the landscape supported late-seralforest dominated by Douglas-Fir (Pseudotsugamenziesii), western hemlock (Tsuga heterophylla),Pacific silver fir (Abies amabilis), western redcedar (Thuja plicata), and western white pine(Pinus monticola). Dominant shrubs includedsalmonberry (Rubus spectabilis), swamp goose-berry (Ribes lacustre), stink currant (Ribes brac-teosum), vine maple (Acer circinatum), sitka alder(Alnus crispa), and devil’s club (Oplopanaxhorridus). Dominant herbaceous plants presentat seeps were those primarily associated withwet habitats and included wood saxifrage(Saxifraga mertensiana), heart-leaved saxifrage(Saxifraga punctata), Alaska saxifrage (Saxifragaferruginea), smooth alumroot (Heuchera glabra),

310 A. MCINTYRE ET AL.

goat’s beard (Aruncus dioicus), tall bluebells(Mertensia paniculata), red columbine (Aquilegiaformosa), Pacific bleeding heart (Dicentra for-mosa), and maidenhair fern (Adiantum pedatum),along with various grasses, sedges, and bryo-phytes. Our study included naturally occurringheadwall seeps. Roadcut sites were not in-cluded because of the difficulty with assessinghabitats that are highly altered by the presenceof a road, which often truncate seeps unnatu-rally.

MATERIAL AND METHODS

Site Selection.—Five seeps where P. vandykeiwas known to occur prior to our study wereincluded. It was necessary to identify additionalseeps where the salamander had not previouslybeen documented to identify both undocument-ed seeps where the salamander was present, aswell as seeps representing unoccupied habitatwhere the salamander was not detected. Weused topographic maps and aerial photos tofind high-gradient areas that were consideredpotential seeps. We also relied on local expertswithin Mount Rainier National Park to help uslocate seeps. We then visited potential seeplocations to determine if they were suitable foruse in our study. Suitable sites were those areaswhere subsurface waters were forced to thesurface creating a seepage that was moist tosaturated. Seep faces were often composed ofvertical bedrock, with rocks accumulated alongthe base (Fig. 1A).

Because P. vandykei rely on moist conditions,we sampled only the wetted area of each seep.Consequently, the total area sampled amongseeps varied. We placed transects along the baseof the seep and parallel to the seep face (Fig. 1B).Transects were 1 m wide, and ran the entirelength of the wetted area. When the wetted areaof the seep extended down from the seep base .1 m, additional downslope transects were placedparallel and contiguous with the original transectuntil the wetted area was covered. Subsequentdown-slope transects were often not the samelength as the first transect, because the wettedarea tapered. Each transect was divided into 2 mlong sampling units, where animal surveys wereconducted. Habitat characteristics were mea-sured at equidistant points along the seep face.When seeps measured 30 m or less in totallength, measures were taken at three equidistantpoints along the seep face (e.g., a 20-m seepwould have equidistant point measures at 5, 10and 15 m). Seeps . 30 m long had additionalequidistant point measures, with one moreequidistant point for each additional 10 m intotal length (e.g., a 40-m seep would have fourequidistant points).

Salamander Surveys.—Salamander surveyswere conducted at each seep in July and August2002. Sites were surveyed after snowmelt andrain, when conditions were favorable for thedetection of P. vandykei. Animal surveys wereconducted only when substrates were moist,wet, or saturated and ground temperatures hadnot dropped below freezing for at least the 72-hperiod prior to sampling (Jones, 1999). Transectswere divided into 1 3 2 m sampling units,which were searched for salamanders by turn-ing all available surface cover objects (e.g.,rocks, wood, and bryophytes). Animal surveyswere conducted immediately prior to thecollection of habitat measures, with care takento replace all cover objects to their originalposition.

Habitat Measures.—We recorded measures ofcurrent hydrologic condition, geomorphology,and vegetation structure. Habitat measureswere recorded concurrent with animal surveys.The between-seep analysis compares habitatcharacteristics of seeps where P. vandykei wasand was not detected, and included variablesrecorded once for each seep. Measures ofhydrologic condition included the presence orevidence of any stream channel(s) associatedwith the seep (located within 10 m of the wettedarea of the seep), the current hydrologiccondition of those streams (dry, moist, wet,trickling, sheeting, or rushing), and the length(cm) of the seep face dominated by eachhydrologic condition (same categories asabove). A measure of geomorphology was thetotal length of the seep (m) (the length of thetransect placed along the seep base). A measureof vegetation structure was the dominant seralclass in the vicinity of the seep (nonvascular,grass-forb, forb-shrub, shrub-sapling, sapling-pole, young forest, mature forest, or old-growthforest). Measures of current hydrologic condi-tions allowed us to assess the species’ associa-tion with moisture conditions. We were in-terested in the total length of the seep becausewe posit that P. vandykei might be associatedwith longer seeps that provided more suitablehabitat. We included a measure of vegetationstructure to evaluate association with seralclass. P. vandykei is currently considered anold-growth associate, federally listed as a ‘‘Sen-sitive’’ species (USDA and USDI, 2004a,b).

The within-seep analysis examined the differ-ences between areas where the salamander didand did not occur within seeps. Habitat char-acteristics were measured at equidistant pointsalong the seep face. The same measures taken atequidistant points were also recorded at pointspositioned at the seep base directly above eachP. vandykei animal capture location. Summaries

ASSOCIATIONS OF PLETHODON VANDYKEI WITH HEADWALL SEEPS 311

of equidistant point measures at each site werealso included in the between-seep analysis.

At each equidistant point we measured seepface and seep base characteristics including:total overhead cover (%), height of the seep face(m), slope of the seep face (degrees), and slopeof the seep base (degrees). The total overheadcover was an ocular estimate including thecover contributed by over- and under-storycanopy, and the seep face. Estimates of totaloverhead cover were measured by holding armsup at a 45u angle, forming a circle withoutspread arms. The percentage of the circlecovered by vegetation and seep face wasrecorded. Ocular overhead cover estimates wererecorded using modified Daubenmire coverclasses of 0, . 0–5, 6–25, 26–50, 51–75, and 76–100% (Daubenmire, 1959). The height of theseep face was estimated as one of four classes(0–5.0, 5.1–10.0, 10.1–20.0, and . 20.0 m). Seepface slope was an ocular estimate recorded asone of four classes (20–40, 41–60, 61–80, and. 80u). Seep base slope was measured usinga clinometer, recorded to the nearest degree. Wepredicted that P. vandykei would be positivelyassociated with seep face and base charactersthat minimized sun and wind exposure, such asan increase in overhead cover, taller seep face,and steeper seep face.

The microhabitat site analysis focused on thedifference between locations where the sala-mander did and did not occur and includedonly seeps where P. vandykei had been detected.Square quadrats measuring 0.5 m2 were sys-tematically placed in the center of all 1 3 2 msampling units. We alternated the position ofthe quadrat between flush with the upslope orthe downslope edge of the transect. The totalnumber of systematically placed quadrats wasbased on the number of 1 3 2 m sampling unitsand therefore varied between sites. Quadratsrepresenting microhabitat sites where the sala-mander was detected were centered on eachcapture location. Because we were interested ina comparison between microhabitats where thesalamander was and was not detected, system-atic quadrats that overlapped those centered onanimal capture locations were not included inour analysis. A single measure of hydrologiccondition was the dominant hydrology withinthe quadrat (dry, moist, wet, trickling, sheeting,or rushing). Measures of geomorphology in-

cluded the percent of the quadrat covered bysubstrate types (soil, sand, small gravel, largegravel, small cobble, large cobble, boulder, andbedrock). We measured vegetation structure asthe percent cover of vegetation lifeform (tree,shrub, forb, bryophyte, and graminoid), wood,branch, logs, and litter. We predicted that theoccurrence of P. vandykei would be positivelyassociated with large substrates (bedrock, boul-der, large cobble, and small cobble), sheetinghydrology, and early succession vegetation.

Statistical Analysis.—Resource selection mod-els (Manly et al., 1993) compared habitatcharacteristics of seeps with the occurrence ofP. vandykei at each of three site scales. Occur-rence of P. vandykei was a binary response ofdetected versus not detected, and modeledusing logistic regression (SAS Institute, 2000).Salamander detection was used as a surrogatemeasure of occurrence, with the recognition thatsalamanders may not have been detected atsites where they did occur. An a priori list ofcandidate models was developed at each of thethree site scales and best approximating modelsfor the odds of the occurrence of P. vandykeiwere selected (Burnham and Anderson, 1998).Results of logistic modeling after back-trans-formation from odds refer to the probability ofthe occurrence of P. vandykei.

Categorical Variable Selection.—Seven of thehabitat characteristics measured were categori-cal variables (e.g., measure of seep face height,where possible categories were 0–5.0, 5.1–10.0,10.1–20.0, and . 20.0 m), with some of thecategorical factors having up to eight categories.When there were more than two possiblecategories for a single measure of habitat,categories were collapsed into a single binomialindependent variable in a multiple logisticregression analysis that gave the greatest de-viance reduction (Tables 1, 2, 3) followingRamsey et al. (1994). For example, seep faceheight (SEEP FACE HEIGHT) in the within-seep analysis was collapsed into a single bi-nomial independent variable representing seepfaces that were either # 10 or . 10 m high. Inthe between-seep analysis, we used the samedeviance reduction method, except we furthersummarized binomial independent variablesinto a proportion of all equidistant pointmeasures within a seep. For example, SEEPFACE SLOPE in the between-seep analysis is

r

FIG. 1. (A) View of a headwall seep in the Cascade Range, Washington. Photo C. M. Crisafulli, (B) Transectdesign at a headwall seep surveyed for Plethodon vandykei. Cascade Range, Washington, 2002. Transects were1 m wide; sampling units were 2 m long. Habitat characteristics were measured at equidistant points along theseep face.


TABLE 1. Variables used in the between-seep, within-seep, and microhabitat site analyses of the occurrence ofPlethodon vandykei at seep sites located in the Cascade Range, Washington, 2002. Independent variables are eithercontinuous (C) or binomial (B).

AnalysisHabitat

characteristic VariableVariable

type Definition

Betweenseep

Hydrologiccondition

STREAMPRESENCE

B Presence or absence of a stream within 10 m ofthe seep face, where presence was an incisedstream channel or evidence of scouring and/or deposition.

STREAMHYDROLOGY

B Indicator of seeps that have a stream channelwith a current hydrology of rushing or moistversus dry, wet, trickling, or sheeting. Moist isdefined as substrate that contain water butlack beaded water on surfaces or filling smalldepressions; rushing is water flow that issignificant and rapid; dry is substrate surfacesthat lack water; wet is surfaces with waterpooled in small surface depressions; tricklingis visible water flowing over uneven rockysurfaces, where the unevenness of the rockcauses turbulence in the flow of water;sheeting is water flow over smooth rocksurfaces.

SEEPHYDROLOGY

C Proportion of seep face with both a dry andsheeting flow.

Geomorphology SEEP LENGTH C Total length of the wetted area along the seepbase (m).

SEEP FACESLOPE

C Proportion of equidistant point measures withina seep that have a seep face slope . 60u.

SEEP BASESLOPE

C Average seep base slope within a seep (degrees).

SEEP FACEHEIGHT

C Proportion of equidistant point measures withina seep that have a seep face height of . 5 m.

TOTALOVERHEADCOVER

C Proportion of equidistant point measures withina seep that have a total overhead cover of 0–5% (includes crown and under-story speciesas well as cover contributed by the seep face).

Vegetationstructure

SERAL CLASS B Indicator of seeps that have a forb-shrub ormature forest seral class versus nonvascular,grass-forb, shrub-sapling, young forest, or oldgrowth forest.

Withinseep

Geomorphology SEEP FACESLOPE

C Proportion of equidistant point measures withina seep that have a seep face slope . 80u.

SEEP BASESLOPE

C Seep base slope (degrees).

SEEP FACEHEIGHT

B Indicator of equidistant point measures that havea seep face height . 10 m versus , 10 m.

TOTALOVERHEADCOVER . 25%

B Indicator of equidistant point measures that havea total overhead cover .25% versus ,25%(includes crown and under-story species aswell as cover contributed by the seep face).

Microhabitatsite

Hydrologiccondition

HYDROLOGY B Indicator of a sheeting hydrology present withina quadrat, versus dry, moist, wet, trickling, orrushing hydrology. Hydrology categories asdefined for between-seep analysis.

Geomorphology SOIL C Percent (%) quadrat covered with soil (e.g.,mineral soil, volcanic ash, and organic soil).

SAND C Percent (%) quadrat covered with sand (, 2 mmin diameter, excluding soil).

SMALL GRAVEL C Percent (%) quadrat covered with small gravel(2–32 mm in diameter).

LARGE GRAVEL C Percent (%) quadrat covered with large gravel(33–64 mm in diameter).


the proportion of equidistant point measureswithin a seep that have a seep face slope . 60u.

Model Development.—Prior to analysis wedeveloped a suite of candidate models de-scribing the occurrence of P. vandykei at eachof three site scales. Our lists of a priori modelsrepresent hypotheses (Burnham and Anderson,1998) that are based on known biology ofplethodontid salamanders, along with personal

experience with P. vandykei. To account formulticollinearity, variables with correlations. 0.5 were not included in the same model.

We identified measures of hydrologic condi-tion, geomorphology and vegetation structurethat we felt were the most important in de-termining occurrence of P. vandykei at each ofthe three site scales. In the between-seepanalysis we identified three measures of hydro-logic condition, five measures of geomorpholo-gy, and a single measure of vegetation structure(Table 1). In the within-seep analysis we iden-tified four measures of geomorphology (Ta-ble 1). In the microhabitat site analysis weidentified one measure of hydrologic condition,eight measures of geomorphology, and ninemeasures of vegetation structure (Table 1).

In the between seep analysis of hydrologiccondition, we hypothesized that the odds of theoccurrence of P. vandykei would increase withthe presence of stream channels associated withseeps, streams with a currently moist or rushinghydrology, and seeps that had a greater pro-portion of both sheeting and dry seep facehydrology. In the microhabitat site analysis, wehypothesized that the presence of sheetinghydrology within a quadrat would increasethe odds of the occurrence of P. vandykei.

Models that consider the influence of geo-morphology on the odds of the occurrence of P.

TABLE 1. Continued.

AnalysisHabitat

characteristic VariableVariable

type Definition

SMALL COBBLE C Percent (%) quadrat covered with small cobble(65–128 mm in diameter).

LARGE COBBLE C Percent (%) quadrat covered with large cobble(129–256 mm in diameter).

BOULDER C Percent (%) quadrat covered with boulder(.256 mm in diameter).

BEDROCK C Percent (%) quadrat covered with bedrock.Vegetation

structureSHRUB C Percent (%) quadrat covered with shrubs (woody

plant species, nontree).FORB C Percent (%) quadrat covered with forbs

(herbaceous plant species).BRYOPHYTE C Percent (%) quadrat covered with bryophytes

(moss and lichen species).GRAMINOID C Percent (%) quadrat covered with graminoids

(grass species).LITTER C Percent (%) quadrat covered with litter (e.g.,

leaves, small twigs , 30 mm in diameter, andconifer needles).

WOOD C Percent (%) quadrat covered with wood (allnonround wood including bark, slabs andcourse woody debris).

BRANCH C Percent (%) quadrat covered with branches(round wood 30–101 mm in diameter).

LOG 1 C Percent (%) quadrat covered with logs, size class1 (round wood 101–500 mm in diameter).

LOG 2 C Percent (%) quadrat covered with logs, size class2 (round wood .501 mm in diameter).

TABLE 2. Coefficients in best approximatingmodels selected using BIC and fitted by logisticregression for the detection of Plethodon vandykei inseep habitats at three site scales. Cascade Range,Washington, 2002. Parameter estimates are log-oddsratios of occurrence.

VariableParameterestimate SE 95% C.I.

Between seepSEEP HYDROLOGY 7.32 2.76 2.60, 13.61SEEP FACE HEIGHT 2.64 1.41 0.32, 6.16

Within seepTOTAL OVERHEAD

COVER . 25%21.25 0.49 0.31, 2.23

Microhabitat siteSMALL COBBLE 0.11 0.03 0.06, 0.17SMALL GRAVEL 0.06 0.02 0.02, 0.09BEDROCK 0.05 0.01 0.02, 0.08


vandykei included seep length, seep face andbase slopes, seep face height, the total overheadcover, and substrate types. We hypothesizedthat the odds of the occurrence of P. vandykei inthe between- and within-seep analyses wouldincrease with longer seeps, steeper seep faces,taller seep faces, and greater overhead cover. Inthe microhabitat site analysis, we hypothesizedthat an increase in the amount of large rockysubstrates (bedrock, boulder, large cobble, andsmall cobble) would increase the odds of theoccurrence of P. vandykei.

The importance of vegetation structure, as-sessed as dominant seral class, was explored inthe between-seep and microhabitat site analy-ses. Although P. vandykei is currently consid-ered an old-growth forest obligate species, wehave detected it under a range of seral classesranging from forb-shrub dominated (in the 1980

blast area of Mount St. Helens) to old-growthforest. Thus, we hypothesized that abioticfactors such as dominant substrate and seepmorphology would have a greater influence onthe odds of the occurrence of P. vandykeibetween seeps, than biotic factors such asvegetation. In the microhabitat site analysis,models evaluated the importance of vegetationtype and vegetation litter (e.g., wood andbranch). We hypothesized that the occurrenceof P. vandykei would be positively associatedwith the presence of early seral class vegetation(bryophytes and graminoids), and negativelyassociated with the presence of vegetation litter.

A priori candidate models were limited tothose with no more than three variables tomaintain parsimony, and to ensure biologicallyinterpretable models. We included models in-volving habitat measures from more than one

TABLE 3. Rankings based on BIC for a priori models used in the between seep, within seep, and microhabitatsite analyses relating the occurrence of Plethodon vandykei to habitat features in seeps. Cascade Range,Washington, 2002. (Meaningful models within DBIC 4.0 and null models shown).

Analysis Rank Model ln(L) K BIC DBICPosterior

probability R2

Betweenseep

1 SEEP HYDROLOGY +SEEP FACE HEIGHT

34.54 3 45.53 0.00 0.621 0.470

2 SEEP HYDROLOGY 39.68 2 47.01 1.48 0.142 0.3443 SEEP HYDROLOGY +

STREAMHYDROLOGY

36.88 3 47.87 2.34 0.060 0.415

4 SEEP HYDROLOGY +SERAL CLASS

34.13 3 47.87 2.34 0.060 0.415

5 SEEP HYDROLOGY +SEEP FACE HEIGHT+ SEEP BASE SLOPE

34.39 4 48.79 3.25 0.024 0.480

6 SEEP HYDROLOGY +SEEP FACE HEIGHT+ SEEP FACE SLOPE

38.27 4 49.05 3.51 0.018 0.474

7 SEEP HYDROLOGY +STREAM PRESENCE

38.40 3 49.26 3.73 0.015 0.380

8 SEEP HYDROLOGY +TOTAL OVERHEADCOVER

34.80 3 49.39 3.86 0.013 0.377

9 SEEP HYDROLOGY +STREAMHYDROLOGY +TOTAL OVERHEADCOVER

39.00 4 49.45 3.92 0.012 0.464

29 Null 50.92 1 54.58 9.05 ,0.001 0.000Within seep 1 TOTAL OVERHEAD

COVER . 25%98.79 2 107.58 0.00 0.844 0.116

2 Null model 105.67 1 110.06 2.49 0.070 0.0003 SEEP BASE SLOPE 102.41 2 111.20 3.62 0.023 0.0564 TOTAL OVERHEAD

COVER . 25% + SEEPFACE SLOPE

98.14 3 111.33 3.75 0.020 0.126

Microhabitatsite

1 SMALL COBBLE +SMALL GRAVEL +BEDROCK

151.02 4 173.48 0.00 0.969 0.213

23 Null model 180.77 1 186.38 12.90 , 0.001 0.000


group (e.g., hydrologic condition and geomor-phology) to explore the possibility that one ormore types of habitat measure may concurrent-ly predict the occurrence of P. vandykei. Wedeveloped a total of 57 candidate models for thebetween-seep analysis (N 5 39), 16 for thewithin-seep analysis (N 5 81), and 86 for themicrohabitat site analysis (N 5 274).

Model Selection.—We used an informationtheoretic approach to rank a priori candidatemodels at each spatial scale. We used BayesianInformation Criterion (BIC), which tends tofavor lower-dimensional models more thanAkaike’s Information Criterion (Schwarz, 1978)and decreases the chances of nonsignificantvariable coefficients in top models:

BIC ~ {2ln (L) z K : ln (N)

where ln (L) denotes the maximum value of thenatural logarithm of the likelihood function; K isthe number of estimable parameters in a givenmodel; and N is the number of valid observa-tions.

The best approximating model at each of thethree site scales was the model with the mini-mum BIC value. Delta (D) BIC values were usedto identify competing models. Delta BIC isa measure of the difference in BIC rank betweenthe top and current models. Competing modelswith a DBIC , 2.0 were likely to describe thegiven data equally as well as the top model.Models with a DBIC , 4.0 were consideredmeaningful but not as descriptive as those withinDBIC 2.0 (Burnham and Anderson, 1998). Weassessed model selection uncertainty amongcompeting models by calculating posterior prob-abilities, or the probability of a model given thedata. In the absence of a reason to believe that anysingle candidate model may be better thananother, all prior probabilities were consideredto be equal (Ramsey and Schafer, 2002). Wereport maximum rescaled adjusted generalizedcoefficients of determination (R2) as an evalua-tion of the proportion of the response variationexplained by each model (Nagelkerke, 1991):

R2 ~ 1 { fL (0)=L (b )g2=n,

max (R2) ~ 1 { L (0)2=n, and

R2

~ R2=max (R2) ,

where L ( b ) and L (0) denote the log likelihood ofthe fitted and null models, respectively.

RESULTS

During July and August 2002 we recorded P.vandykei at 15 of 40 seeps surveyed (Fig. 2). We

documented the salamander in 10 of 35 (28.6%)seep sites at which the salamander had neverbeen recorded. Thirty-two P. vandykei werecaptured, with the total number detected ata seep ranging from 1–3 individuals. The meannumber of P. vandykei captured within the 15seeps was two individuals (SE 5 0.59), and themedian was 1. Only 9.6% of captured individ-uals were adults (with males and femalesreaching maturity at . 44 and 47 mm SVL,respectively [Petranka, 1998]).

Between Seep.—We used 39 seeps in thebetween-seep analysis, 14 seeps with P. vandykeidetected and 25 seeps with P. vandykei notdetected. One seep where P. vandykei had beenpreviously recorded was excluded from thisanalysis because at the time of animal surveysand habitat characterization the seep face haddried completely and no longer resembleda seep as defined for the purpose of this study.Nine measures of habitat were included in thisanalysis (Table 1).

The best approximating model selected usingBIC and relating detection of P. vandykei tohabitat characteristics in the between-seep anal-ysis included two measures of habitat (Model[SEEP HYDROLOGY + SEEP FACE HEIGHT];Table 2). The probability of the occurrence of P.vandykei increased as the proportion of the seepface with a dry and sheeting flow increased, andwith an increase in the proportion of equidistantpoint measures of seep face height . 5 m(Fig. 3). A single variable model (Model [SEEPHYDROLOGY]) was a competing model withDBIC 1.48 (Table 3). However, the top rankedmodel had a posterior probability of 0.621versus 0.142 for the competing model, suggest-ing that the top model is more than four timesas likely to explain the variability in the data.

Within Seep.—We conducted the within-seepanalysis using the 15 seeps at which P. vandykeioccurred. There was a total of 81 equidistantpoint measures included in the analysis, 29representing P. vandykei capture locations, and52 representing systematic measures of unusedhabitat. Four measures of habitat were includedin this analysis (Table 1).

The top model selected using BIC and re-lating the detection of P. vandykei to habitatcharacteristics in the within-seep analysis in-cluded one measure of habitat (Model [TOTALOVERHEAD COVER . 25%]; Table 2). Theprobability of the occurrence of P. vandykeidecreased as total overhead cover . 25%increased. When TOTAL OVERHEAD COVER. 25% was absent, the probability of occurrenceof P. vandykei was 0.531. When TOTAL OVER-HEAD COVER . 25% was present, the prob-ability of occurrence of P. vandykei dropped to


0.245. There were no competing models withinDBIC 2.0 (Table 3).

Microhabitat Site.—For the 15 seeps where P.vandykei occurred there was a total of 274quadrats, 28 representing microhabitat siteswhere P. vandykei was detected and 246 repre-senting microhabitat sites where P. vandykei wasnot detected. Eighteen measures of habitat wereincluded in the analysis (Table 1).

The top model selected using BIC and re-lating the occurrence of P. vandykei to habitatcharacteristics in the microhabitat site analysisincluded three measures of habitat (Model[SMALL COBBLE + SMALL GRAVEL + BED-ROCK]; Table 2). The probability of the occur-rence of P. vandykei increased with an increasein small cobble, small gravel, and bedrocksubstrates (Fig. 4). There were no competingmodels within DBIC 2.00 (Table 3).

Because the top model in the microhabitat siteanalysis included three variables, we exploredthe possibility that there may be more variablesthan can be represented by a three variablemodel important in predicting the occurrence ofP. vandykei at this spatial scale. Post prioriforward selection was performed from the topmodel to see if any additional variables would

be identified. Habitat characteristics chosenwith forward selection, in addition to thosealready represented in the top model, would beconsidered important for predicting P. vandykeidetection. Because forward selection from thetop model in microhabitat site analysis didnot yield additional variables, variables in thetop model best explain the variability in thedata.

DISCUSSION

Our results show that geomorphology andhydrology are indicative of, and possibly aid inthe maintenance of, habitat conditions thatpredict the occurrence of P. vandykei at seepsites in the Cascade Range. Indicators of suit-able habitat for P. vandykei included exposedbedrock, small cobble, and early seral classvegetation, in combination with hydrologicconditions that allow the salamander to remaincool and moist.

FIG. 3. Probability of the occurrence of Plethodonvandykei and two measures of habitat indicated by thebest approximating model in the between seepanalysis. Cascade Range, Washington, 2002. SEEPFACE HEIGHT is the proportion of equidistant pointmeasures within a seep that have a seep face height. 5 m. SEEP HYDROLOGY is the proportion of theseep face with a hydrology of dry or sheeting.

FIG. 4. Probability of the occurrence of Plethodonvandykei and three measures of habitat indicated bythe best approximating model in the microhabitat siteanalysis. Cascade Range, Washington, 2002. SMALLCOBBLE is the percent area of a 0.5-m2 quadratcovered by small cobble substrate (65–128 mm indiameter). SMALL GRAVEL is the percent area ofa 0.5-m2 quadrat covered by small gravel substrate (2–32 mm in diameter). The two surfaces show maxi-mum and minimum values of BEDROCK, which isthe percent area of a 0.5-m2 quadrat covered withbedrock (solid rock surface).

rFIG. 2. Location of seeps surveyed for Plethodon vandykei in the Gifford Pinchot National Forest and Mount

Rainier National Park, Cascade Range, Washington, 2002. Some sites were located close enough that a singlesymbol represents more than one site.


The occurrence of P. vandykei was positivelyassociated with specific hydrologic conditionsin the between-seep analysis. It was not thepresence of dry or sheeting hydrology alone,but the combination of the two that was anindicator of the occurrence P. vandykei. Theseconditions along the seep face and seep basecreate a moisture gradient along the seep fromdriest to wettest. A moisture gradient along theseep allows salamanders to move into areas thatare wet but not inundated with water, becauseseeps expand during wet periods and contractduring dry periods (Ziemer and Lisle, 1998).Sheeting hydrology probably indicates seepsthat are more likely to maintain wet, favorableconditions for plethodontid salamanders duringdry summer months. Most Plethodons have beenshown to exhibit a strong preference for moistsubstrates (Taub, 1961; Sugalski and Claussen,1997; Moore et al., 2001), while avoidingstanding water altogether (Taub, 1961). How-ever, P. idahoensis has been observed partiallysubmerged in water (Wilson and Larsen, 1988).

Between seeps, the occurrence of P. vandykeiwas positively associated with seep face heights. 5 m. In the within-stream analysis conductedby McIntyre (2003), vertical or V-shaped valleywalls were important in predicting the proba-bility of the occurrence of P. vandykei withinstreams. Just as deeply incised stream channelsmay insulate salamanders from seasonal differ-ences by sheltering them within the largerlandscape (Moore et al., 2001), taller seep facesmay provide a more thermally stable environ-ment, protecting P. vandykei from sun and windexposure. Tall seep faces may provide salaman-ders with more habitat and offer more refugefrom seasonal disturbances associated withincreased water flows experienced duringspring snowmelt and fall rains, as well asincrease the area influenced by the spray zone,further enhancing habitat.

In the within seep analysis, the occurrence ofP. vandykei was negatively associated with totaloverhead cover . 25%. We hypothesized thatsalamanders would be associated with seepsthat provide a greater protection from wind andsun exposure, and thought this would bereflected in more overhead cover. In our studyof P. vandykei along streams (McIntyre, 2003),the correlation between salamanders and a lackof over-story tree species was attributed togeomorphology (bedrock substrates and steepvalley walls) and hydrology that preventedwoody vegetation from establishing. We believethat geology and hydrology characteristics thatmaintain exposed bedrock and steep seep facesare responsible for a lack of over-story canopyat seep sites where P. vandykei occurs, asevidenced by a lack of soil substrates and the

presence of rock accumulations that are satu-rated with water. The salamander was alsoprevalent within the 1980 blast area of Mount St.Helens, where it has survived and persisted inlocations denuded by the 1980 eruption (Crisa-fulli et al., 2005). Seeps as defined in this studyare typically characterized by cool runningwater and are topographically shielded fromsun and wind exposure. In these habitats over-story cover is not necessary to maintain cool,moist conditions. Additionally, a thick herba-ceous layer of plants often grows at the base ofseeps, further ameliorating conditions that maycause desiccation.

Certain substrates were important to theoccurrence of P. vandykei in the microhabitatsite analysis, specifically an increase in smallcobble, small gravel, and bedrock. Similarassociations were observed at larger spatialscales among P. vandykei in streams. McIntyre(2003) found small cobble to be important inpredicting the occurrence of P. vandykei betweencapture locations along high-gradient streams,and bedrock was positively associated with thisspecies between and within streams. Smallcobble and small gravel provide high-qualitycover objects frequently utilized by P. vandykei.Accumulations of small cobbles may increasethe amount of interstitial space important fora subterranean species (Welsh and Ollivier,1998). Exposed bedrock helps to maintainheadwall seeps by forcing subsurface flows tothe surface.

Our results are consistent with those found inour concurrent study (McIntyre, 2003), in whichhydrologic conditions influenced the occurrenceof P. vandykei along high-gradient streams in thesame systems. An increase in the number ofside streams, or areas of actively flowing waterentering the stream channel, resulted in anincrease in the probability of the occurrence ofP. vandykei. In the same study, the presence ofseeps along the stream valley wall was posi-tively associated with the occurrence of P.vandykei. The presence of actively flowing waterprovides a source of moisture for salamandersthat rely on moist permeable skin in order torespire (Gatz et al., 1974). The microhabitatscreated by these hydrological characteristicsallow Plethodon salamanders to absorb waterdirectly from substrates through their perme-able skin (Spotila, 1972), thus preventing desic-cation.

It appears that the habitat characteristicsinnately present in headwall seeps are the samecharacteristics that P. vandykei is associated within streams. The salamander is well adapted tothe unique habitat characteristics provided byseep habitats. Our results indicate that P.vandykei may actually occupy proportionately


more seeps than high-gradient streams locatedin the Cascade Range. We documented thesalamander in 10 of 35 (28.6%) seep sites atwhich the salamander had never been recorded,as compared to two of 26 (7.7%) stream sites atwhich the salamander had never been recorded(McIntyre, 2003).

However, headwall seeps appear to berelatively rare on the landscape as comparedto high-gradient streams. We hypothesize thatthe rarity of P. vandykei is largely due to a limitin suitable habitat within its range. Although wedid not quantify seep density, we found thatsuitable seep habitats for P. vandykei were rare.Even so, it appears that these seeps oftenprovide the conditions necessary for the occur-rence of P. vandykei. We suggest that headwallseep environments are providing thermal andhydric stability, in addition to adequateamounts of cover objects.

Seeps may act to diffuse harsh conditions byproviding hydric and thermal stability (Huheeyand Brandon, 1973; Hynes, 1970) necessary forP. vandykei survival. Huheey and Brandon(1973) attributed use of seep habitats by theAllegheny Mountain Dusky Salamander (Des-mognathus ochrophaeus) to the stability of mois-ture and temperature that seep habitats provide.Plethodon idahoensis are tolerant to more severeenvironments where they occupy wet seepmicrohabitats (Wilson and Larsen, 1988). Tum-lison and Cline (1997) propose that seep habitatsprovide underground corridors to isolated sites,facilitating passage of the Oklahoma Salaman-der (Eurycea tynerensis) among habitat patchesthrough areas that would otherwise be unsuit-able.

Headwall seeps may be a source of connec-tivity for P. vandykei, facilitating movementbetween stream habitats for a species withrelatively low mobility (McIntyre, 2003). Thisconnectivity may be important for dispersingindividuals, especially over landscapes withrelatively low canopy cover. However, P.vandykei was found in low abundances at allseeps surveyed, with no more than 3 individ-uals captured at a seep, and adult salamanderswere not often encountered (representing only9.6% of individuals captured). A greater pro-portion of adult salamanders (33.7%) was foundassociated with streams in the Cascade Range(McIntyre, Schmitz, and Crisafulli, unpubl.data). The low number of individuals observedat seeps, in conjunction with the small pro-portion of adult salamanders, leads us tospeculate that the ephemeral nature of someseeps may be creating habitats that are unsuit-able for P. vandykei over longer time periods.Although P. vandykei may be highly adapted tohabitat characteristics common in seeps, they

may be unlikely to persist in seeps that areprone to seasonal drying, resulting in popula-tion sinks at these sites.

The study area is strongly influenced byvolcanoes, most notably Mount St. Helens,which has had an active history of violenteruptions (Lipman and Mullineaux, 1981).Areas adjacent to the three volcanic peaks(Mount Rainier, Mount Adams and Mount St.Helens) are generally mantled with pumicedeposits of variable age, origin and thickness(Mullineaux, 1996). During this study andothers (Crisafulli et al., 2005), we observed P.vandykei in seeps within areas severely dis-turbed by the 1980 eruption of Mount St.Helens. The deep tephra deposits overlyingbedrock in this area makes this landscape andthe hydrologic processes unique. Pumice depthand corresponding soil structure may promotea rapid downward movement of water thatflows comparatively unimpeded along bedrock,emanating from valley walls as seeps. Wespeculate that seeps may be more common,and have different flow regimes, than in areaswithout tephra. Therefore, the presence andactivity of volcanoes may aid in the mainte-nance of suitable habitat for P. vandykei withinthe Cascade Range.

Acknowledgments.—U.S. Fish and WildlifeService, Olympia, WA; U.S. Forest Service Re-gion 6 and Bureau of Land Management,Survey and Manage Program, Pacific North-west Research Station, Olympia, WA; GiffordPinchot National Forest; and Mount RainierNational Park provided funding and servicesthat supported this research. We thank R.Anthony, J. Li, F. Ramsey, and F. Swanson forproviding suggestions and support. We aregrateful to M. Erhart, H. Purdom, and J.Tagliabue for their help collecting data in thefield. We thank K. Ronnenberg for preparingfigures.

LITERATURE CITED

BRODIE, E. D. J. 1970. Western salamanders of thegenus Plethodon: systematics and GeographicVariation. Herpetologica 26:468–516.

BURNHAM, K. P., AND D. R. ANDERSON. 1998.Model Selection and Inference: A Practical In-formation Theoretic Approach. Springer-Verlag,New York.

CRISAFULLI, C. M., L. S. TRIPPE, C. P. HAWKINS, AND J. A.MACMAHON. 2005. Amphibian responses to the1980 eruption of Mount St. Helens. In V. H. Dale, F.J. Swanson, and C. M. Crisafulli (eds.), EcologicalResponses to the 1980 Eruption of Mount St.Helens. Springer-Verlag, New York.

DAUBENMIRE, R. F. 1959. A canopy-coverage method ofvegetational analysis. Northwest Science 33:43–64.


FEDER, M. E. 1983. Integrating the ecology andphysiology of plethodontid salamanders. Herpe-tologica 39:291–310.

FRANKLIN, J. F., AND C. T. DYRNESS. 1973. Naturalvegetation of Oregon and Washington. U.S. ForestService, Pacific Northwest Research Station, Port-land, OR.

GATZ, R. N., E. C. J. CRAWFORD, AND J. PIIPER. 1974.Respiratory properties of the blood of a lunglessand gill-less salamander. Respiration Physiology20:33–41.

HUHEEY, J. E., AND R. A. BRANDON. 1973. Rockfacepopulations of the Mountain Salamander Desmog-nathus ochrophaeus, in North Carolina. EcologicalMonographs 43:59–77.

HYNES, H. B. N. 1970. The Ecology of Running Water.University of Toronto Press, Toronto, ON, Canada.

JONES, L. L. C. 1999. Survey protocol for the VanDyke’s Salamander (Plethodon vandykei). In D. H.Olson (ed.), Standardized Survey Protocols forAmphibians under the Survey and Manage andProtection Buffer Provisions. Version 3.0,pp. 201–252. USDA Forest Service; Pacific North-west Research Station, Olympia, WA.

LEONARD, W. P., H. A. BROWN, L. L. C. JONES, K. R.MCALLISTER, AND R. M. STORM. 1993. Amphibians ofWashington and Oregon. Seattle Audubon Society,Seattle, WA.

LIPMAN, P. W. AND D. R. MULLINEAUX, editors. 1981. The1980 eruptions of Mount St. Helens, Washington.U.S. Geological Survey Professional Paper 1250.U.S. Government Printing Office, Washington, DC.

MANLY, B., L. MCDONALD, AND D. THOMAS. 1993.Resource Selection by Animals: Statistical Designand Analysis for Field Studies. Chapman Hall,London.

MCINTYRE, A. P. 2003. Ecology of Populations of VanDyke’s Salamanders in the Cascade Range ofWashington State. Unpubl. master’s thesis. OregonState University, Corvallis.

MOORE, A. L., C. E. WILLIAMS, T. H. MARTIN, AND W. J.MORIARITY. 2001. Influence of season, geomorphicsurface and cover item on capture, size and weightof Desmognathus ochrophaeus and Plethodon cinereusin Allegheny Plateau riparian forests. AmericanMidland Naturalist 145:39–45.

MULLINEAUX, D. R. 1996. Pre-1980 tephra-fall depositsfrom Mount St. Helens, Washington. U.S.Geological Survey Professional Paper 1563.U.S. Government Printing Office, Washington,DC.

NAGELKERKE, N. J. D. 1991. Miscellanea: a note ona general definition of the coefficient of determi-nation. Biometrika 78:691–692.

NOBLE, G. K. 1931. The Biology of the Amphibia.McGraw Hill, New York.

NUSSBAUM, R. A., E. D. BRODIE, AND R. M. STORM. 1983.Amphibians and Reptiles of the Pacific Northwest.University of Idaho Press, Moscow.

PETRANKA, J. W. 1998. Salamanders of the United Statesand Canada. Smithsonian Institution Press, Wash-ington, DC.

RAMSEY, F. L., AND D. W. SCHAFER. 2002. The StatisticalSleuth: A Course in Methods of Data Analysis.Duxbury Press, Belmont, CA.

RAMSEY, F. L., M. MCCRACKEN, J. A. CRAWFORD, M. S.DRUT, AND W. J. RIPPLE. 1994. Habitat associationstudies of the Northern Spotted Owl, Sage Grouse,and Flammulated Owl. In N. Lang (ed.), CaseStudies in Biometry, pp. 189–209. John Wiley andSons, Inc., New York.

SCHWARZ, G. 1978. Estimating the dimension ofa model. Annals of Statistics 6:461–464.

SPOTILA, J. R. 1972. Role of temperature and water inthe ecology of lungless salamanders. EcologicalMonographs 42:95–125.

STEBBINS, R. C., AND N. W. COHEN. 1995. A NaturalHistory of Amphibians. Princeton UniversityPress, Princeton, NJ.

SUGALSKI, M. T., AND D. L. CLAUSSEN. 1997. Preferencefor soil moisture, soil pH, and light intensity by thesalamander, Plethodon cinereus. Journal of Herpe-tology 31:245–250.

TAUB, F. B. 1961. The distribution of the Red-BackedSalamander, Plethodon c. cinereus, within the soil.Ecology 42:681–698.

TUMLISON, R., AND G. R. CLINE. 1997. Further notes onthe habitat of the Oklahoma Salamander, Euryceatynerensis. Proceedings of the Oklahoma Academyof Science 77:103–106.

USDA AND USDI. U.S. Department of Agriculture andU.S. Department of Interior. 2004a. Final Supple-mental Environmental Impact Statement to Re-move or Modify the Survey and Manage Mitiga-tion Measure Standards and Guidelines. Portland,OR.

———. 2004b. Record of Decision to Remove or Mod-ify the Survey and Manage Mitigation MeasureStandards and Guidelines in Forest Service andBureau of Land Management Planning Documentswithin the Range of the Northern Spotted Owl.Portland, OR.

WELSH, H. H. J., AND L. M. OLLIVIER. 1998. Streamamphibians as indicators of ecosystem stress: a casestudy from California’s redwoods. EcologicalApplications 8:1118–1132.

WILSON, A. G. J. 1993. Distribution of Van Dyke’sSalamander, Plethodon vandykei Van Denburgh.Unpubl. Ph.D. diss., Washington State University,Pullman.

WILSON, A. G. J., AND J. H. J. LARSEN. 1988. Activity anddiet in seepage-dwelling Coeur d’Alene salaman-ders (Plethodon vandykei idahoensis). NorthwestScience 62:211–217.

WILSON, A. G. J., J. H. J. LARSEN, AND K. R. MCALLISTER.1995. Distribution of Van Dyke’s Salamander(Plethodon vandykei Van Denburgh). AmericanMidland Naturalist 134:388–393.

ZIEMER, R. R., AND T. E. LISLE. 1998. Hydrology. In R. J.Naiman and R. E. Bilby (eds.), River Ecology andManagement, pp. 43–68. Springer-Verlag, NewYork.

Accepted: 20 April 2006.
