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Paul Hendricks.

Rediscovery of Discus brunsoni Berry, 1955 and Oreohelix alpina (Elrod, 1901) in the Mission Mountains, Montana : with comments on Oreohelix elrodi (Pilsbry, 1900) (Volume 1997?) online

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Online LibraryPaul HendricksRediscovery of Discus brunsoni Berry, 1955 and Oreohelix alpina (Elrod, 1901) in the Mission Mountains, Montana : with comments on Oreohelix elrodi (Pilsbry, 1900) (Volume 1997?) → online text (page 1 of 1)
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Rediscovery of Discus brunsoni Berry, 1955 and Oreohelix alpina (Elrod, 1901)

in the Mission Mountains, Montana,

With Comments on Oreohelix elrodi (Pilsbry, 1900)



Paul Hendricks

Montana Natural Heritage Program

1515 East Sixth Avenue

Helena, Montana 59620

and

909 Locust Street

Missoula, Montana 59802

(406) 543-0995

email: [email protected]



Rediscovery of Discus brunsoni Berry, 1955 and Oreohelix alpina (Elrod, 1901) in the Mission
Mountains, Montana, with comments on Oreohelix elrodi (Pilsbry, 1900)

ABSTRACT

During summer 1997, extant populations of the endemic land snails Discus brunsoni and
Oreohelix alpina were rediscovered near the type localities in the Mission Mountains, Montana;
last known collections were made 33 and 48 years ago, respectively. D. brunsoni and Oreohelix
elrodi (also endemic to the Mission Mountains and nearby Swan Range) were previously reported
to be sympatric in subalpine limestone talus. Both species were found in 1997 in diorite talus; the
latter species also occupied argillite talus with little, if any, limestone present at any site. Live D.
brunsoni (n = 8) were found near the talus surface only on bare rock or foliose lichen on rock
during cool, wet conditions. Live O^ elrodi were found near the talus surface on rock (n = 9) or
organic litter accumulations (n = 55) during all conditions, although in reduced number during
warmer and drier weather. Above treeline, live O. alpina were found exclusively in exposed
locations under limestone talus, sometimes attached to rock surfaces (n = 7) but more often
present in organic detritus (n = 10). Lack of collections of D. brunsoni and O. alpina in recent
decades probably resulted from 1) extremely restricted distributions, 2) limited knowledge of
habitat requirements, and 3) scarcity of active collectors in the region.
Key words : Discus brunsoni , Oreohelix alpina , Oreohelix elrodi , Montana, distribution, ecology.



INTRODUCTION

The Mission Mountains of northwestern Montana are recognized as an area of significant
snail endemicity in the Interior Columbia River Basin (Frest and Johannes 1995). The mountains
extend about 80 km north to south and 19 km east to west, rising abruptly from a base at 1036 m
in the Swan and Flathead valleys to a crest of nearly 3018 m. The range is composed of
Precambrian Belt rocks (mostly limestone and argillite) that were deeply dissected by alpine
glaciers during the Pleistocene (Alden 1953). The Mission Mountains still support small cirque
glaciers and permanent ice patches. The portion of the mountain range within Lake County
contains the type localities for three narrowly endemic terrestrial snail species, none of which has
yet been documented at more than two sites.

Oreohelix elrodi (Pilsbry, 1900) was discovered in 1899 in talus slopes between 1067-
1524 m above the north side of McDonald Lake (Pilsbry 1900, Elrod 1903a), where it was most
common, and also found rarely along the south side of the lake. The amphitheater around
McDonald Lake remains the only known locality for this species in the Mission Mountains, but it
has been found more recently above Lion Creek in the nearby Swan Range (Fairbanks 1984).
Oreohelix alpina (Elrod, 1901) was first found in 1900 on ASinyaleamin Mountain= (Elrod 1901,
1902, 1903b) and again later that year on the west ridge of McDonald Peak; both locahties were
above treeline between 2377-2743 m and remain the only sites where this species has been
located. Discus brunsoni Berry, 1955 was first encountered (a single shell) in 1948 in talus slopes
above the north side of McDonald Lake at an estimated elevation of 1067 m, with additional
material collected there in 1950 (Berry 1955, Brunson 1956). The type locality remains the only
known site for D. brunsoni . Interestingly, this talus slope is also the type locality for O. elrodi .



which had been collected several times between 1899 and 1948 (Branson 1956), but D. bransoni
was not discovered there until almost half a century later. Known localities for the three snail
species in the Mission Mountains are within the Mission Mountains Tribal Wildemess of the
Confederated Salish and Kootenai Tribes and are relatively secure from human disturbance. None
of the snail species has any special federal designation but all three are on the state list of Animal
Species of Special Concem maintained by the Montana Natural Heritage Program.

Live Oreohelix elrodi were reported at the type locality as recently as 1993 (Frest and
Johannes 1995). There are no known collections in recent years, however, for O. alpina and
Discus bransoni (Frest and Johannes 1995). Apparently, O. alpina was last collected on 2 August
1949 on McDonald Peak, and D. bransoni was last collected on 29 May 1964 at McDonald Lake
(R. B. Branson pers. comm. for both collections). Primary objectives of the study reported here
were to 1) revisit the type localities of Oreohelix alpina and Discus bransoni and, if possible,
locate extant populations of each species, and 2) supplement previous brief descriptions of the
habitats where each species is found.
STUDY SITES AND METHODS

I used a variety of sources to obtain relatively precise descriptions of type localities and
habitat use by Oreohelix alpina and Discus bransoni , including published literature and
conversations with Dr. R. B. Branson, who made the last known collections of each species. The
type locality of D. bransoni was easily identified. Berry (1955) provided a photograph of the site
and Branson (1956) added considerable detail of the conditions and physical setting where this
species was discovered. The site (Site 1) is an extensive talus slope on the north side of
McDonald Lake (T19N R19W SI 1) that is accessible by trail. Trips to Site 1 were made on 10



June, 1 July, 4 July and 10 July 1997. Rock at Site 1 was composed predominantly of blocks of
diorite about 1 m^ in size, with less than 5% argillite fragments intermixed. Neither rock material
effervesced in acid, indicating the absence of calcium carbonate. Canopy cover was 0% in the
search area, slope = 36" facing SSE. Forest at the margins of the talus slope was composed of
Douglas-fir ( Pseudotsuga menziesii ) and ponderosa pine ( Pinus ponderosa ). Pockets of water
birch (Betula occidentalis ), quaking aspen ( Populus tremuloides ) and mock orange ( Philadelphus
lewisii ) were scattered in and near the margins of the talus and comprised much of the organic
litter among the talus fragments. Talus was inspected to a maximum depth of 1 m in an area of 25
X 40 m. Additional searches during other visits to Site 1 were focused in this area. Site 2 (about
100 m east of Site 1) was composed of about equal amounts of smaller-sized diorite and argillite;
average talus fragment size was about 30 X 30 cm. Canopy cover (surrounding species
composition as at Site 1) was 0%, slope = 32" facing SSE, search area was 15 X 20 m. Site 3
was about 500 m east of Site 2. Search area at Site 3 was 10 X 25 m, rock was 100% argillite
with average fragment size about 10 X 20 cm. Slope, aspect, cover and surrounding vegetation
at Site 3 were similar to the other two sites.

Access to the historical sites of Oreohelix alpina was not so straightforward. Neither
location can be reached by trail. The McDonald Peak site is in the Grizzly Bear Conservation
Zone of the Mission Mountains Tribal Wilderness and closed to all recreational use from 15 July-
1 October. Snowpack often precludes trips into the alpine before mid- July, so the McDonald
Peak site was not visited in 1997. Elrod (1901, 1902, 1903b), Pilsbry (1939) and Frest and
Johannes (1995) describe the type locality as above treeline on ASinyaleamin Mountain. = There
is no Sinyaleamin Mountain on current U.S.G.S. topographic maps. Details of the 1900 trip on



which the species was discovered (Elrod 1902) indicate, however, that Sinyaleamin Mountain is
now known as East St. Marys Peak; O. alpina was collected by Elrod on the southwest ridge of
that mountain (T18N R18W S20).

I chmbed East St. Marys Peak on 27 August 1997 and searched for Oreohelix alpina at
two sites (Sites 1 and 2) on the southeast ridge (T18N R18W S21) and also the top of the
southwest ridge (Site 3), which included the summit. Site 1 was a broad level area atop the
southeast ridge at approximately 2637 m; the ground was covered with a variety of alpine forbs
and grasses (vegetation cover = 60-70%) in which were open patches of limestone scree
(fragment diameter about 2-4 cm). Site 2 was farther north about 1 km, where the ridge
narrowed between 2713-2774 m. Exposure at this site was to the southwest but near the ridge
crest. Shallow limestone talus became predominant with only scattered patches of alpine
vegetation present (cover = 85-95% rock). Plants in the area included snow cinquefoil ( Potentilla
nivea), mountain avens ( Dryas octopetala ), alpine sorrel (Oxyria digyna ) and moss campion
( Silene acaulis ). Site 3 included the summit (2873 m) and top of the southwest ridge. Plant
composition and percent cover at this site were similar to Site 2.

Time spent searching for each species was recorded as a measure of search effort (Ausden
1996); time of day refers to Mountain Daylight Time. The substrate on which each live snail was
found (Arock= or Aorganic litters) was noted, and shell diameter of live individuals was
measured with a dial caliper. Photographs of live snails and habitats for each species were taken
and are available from the Montana Natural Heritage Program, Helena, Montana. G-tests (Sokal
and Rohlf 1981) were used to analyze frequency distributions of substrate use; statistical
significance was assumed when P < 0.05.



RESULTS

Discus brunsoni and Oreohelix elrodi

Presence at different sites: Three talus sites within the general type locality of both species were

examined during four different visits (Table 1). All sites were at 1 128 m along the trail paralleling

McDonald Lake on its north side. On 10 June and 4 July, weather was sunny and warm (21-

1?PC) at the time of the searches (10:15-12:00); no precipitation had fallen in the previous 48

hours. On both dates only Site 1 was checked. Four live estivating Oreohelix elrodi and no

Discus brunsoni were found during 75 min of searching by two persons on 10 June. The 4 July

visit was devoted to study of the rocks and no live snails of either species were noted.

On 1 July weather was wet and cool (10"C) during the search period (10:00-13:00); the
area received steady precipitation during the previous 48 h. At Site 1 I found 20 live Oreohelix
elrodi and 5 live Discus brunsoni in 120 min. At Site 2 I found 110. elrodi and no D. brunsoni
during 60 min. Under similar conditions on 10 July (wet, 14-17" C) I found 19 live O. elrodi and
3 Uve D. brunsoni at Site 1 during 120 min (1 1:00-13:00). At Site 2 I found 7 live O. elrodi and
no D. brunsoni in 30 min (13:30-14:00). At Site 3 I found 7 live O. elrodi and no D. brunsoni in
15 min (15:35-15:50).

Substrate selection within talus: Substrate of occurrence (rock, organic litter) for live snails
found at all three sites was documented on 1 and 10 July. All (n = 8) live Discus brunsoni were
found on bare or lichen-covered rock. Nine of 64 live Oreohelix elrodi were found on similar
substrate, 55 were found on organic litter accumulations (bark, twigs, leaf fragments, needles) or
live moss among the talus. The difference between the two species in frequency of substrate
occurrence was statistically significant (G = 26.724, df = 1, P < 0.001).



Shell diameter: Discus brunsoni averaged 9.5 mm diameter and ranged from 6.7-10.5 mm (Table
1). For Oreohelix elrodi at Site 1, 28 (71.8%) of 39 live individuals were > 15 mm diameter. At
Sites 2 and 3 the respective numbers of live snails in this category were 6 (33.3%) of 18, and 2
(28.6%) of 7. Samples undoubtedly contained members of more than one cohort. The presence
of individuals < 7.5 mm diameter in each sample suggests reproduction is occurring at each site.
Oreohelix alpina

Presence at different sites and substrate selection: Weather on East St. Marys Peak was clear
and cool (12.5''C at the summit) on 27 August. I found no snails in 30 min (12:15-12:45) at Site 1
on the southeast ridge.

At Site 2 I found 16 live O. alpina in 45 min (13:30-14:15) in three areas searched along
300 m of ridge. All live snails were under limestone blocks about 20 X 30 cm square and 4-8 cm
thick. Six snails were attached to the undersides of limestone fragments or atop bare rock
beneath overlying blocks, one group of 10 live snails was found in leaf litter (area = 9 cm^)
accumulated near the base of snow cinquefoil. Some soil development was present at each site
where live snails were found. Dead shells were found with little effort on open ground.

I searched the summit area (Site 3) for 15 min (14:30-14:45) and found one live snail at
2865 m near the top of the southwest ridge. This individual was on bare rock under a limestone
block near a patch of snow cinquefoil.

Shell diameter: Mean (+ SD) diameter of live shells (n = 16) was 5.7 + 1.9 mm; range was 2.5-
8.5 mm. The smaller individuals indicate reproduction is probably occurring at this location.
Mean diameter of dead shells for which measurements were possible (n = 9) was 8.9 + 0.5 mm;
range was 8.0-9.6 mm.

8



DISCUSSION

Extant populations of Discus brunsoni and Oreohelix alpina were located in 1997 at or
near the type localities 33 and 48 years, respectively, after the last documented collections (R. B.
Branson pers. comm., T. J. Frest pers. comm.). The range in shell size of live individuals at each
site (including O. elrodi sites) indicates the presence of multiple cohorts and likelihood of
continuing reproduction. The sites where O. alpina was found on the southeast ridge of East St.
Marys Peak represent a slight range expansion at the type locality, where Elrod (1902) found
them on the southwest ridge. I have found no evidence that O. alpina has been collected on East
St. Marys Peak since 1900, when Elrod discovered the species. The last documented collection
of O. alpina (Branson specimen catalog) was made on McDonald Peak on 2 August 1949.
Correspondence from Stillman Berry (21 August 1951: Branson pers. comm.) indicates that
another collection may have been made on McDonald Peak in 1950 or 1951, but there is no
evidence of this in Branson=s catalog.

Several interacting factors probably contributed to the failure to find Discus bransoni and
Oreohelix alpina during the last several decades. First, I know of no active resident collectors of
terrestrial moUusks. Non-resident collectors passing through the area may have visited sites when
conditions were not especially favorable for finding these species {D. bransoni in particular) near
the surface of talus slopes. The nearly half-century span between first discoveries of O. elrodi and
D. brunsoni at the same site supports this contention. Differences in habitat selection may have
contributed to this lapse, as will be discussed below. Furthermore, it seems unlikely that very
many non-resident collectors would attempt to visit the relatively inaccessible localities of O.
alpina . Second, the known distributions of both species are quite restricted. It would be easy to



overlook them without clear knowledge of the geographical area. For example, it is impossible to
identify ASinyaleamin Mountain= or the exact location of O. alpina on this mountain or
McDonald Peak without a copy of Elrod=s (1902) description of his collecting trip. Third,
habitat requirements, especially for D. brunsoni , may be more narrow than previously appreciated.
Information gleaned from Berry (1955) and Branson (1956) suggests that D. bransoni and O.
elrodi are sympatric in talus slopes on the north side of McDonald Lake. However, it may be that
both species co-occur in only a very restricted zone defined by the narrower habitat preference of
D. bransoni . Evidence to date indicates that O. elrodi is significantly more widespread, even in
the McDonald Lake cirque.

AH three snail species favor exposed talus habitats. The type of talus in which each
species is found, however, appears to differ among species. Oreohelix alpina is found exclusively
above treeline in shallow limestone talus on mountain ridges. The descriptions provided by Elrod
(1901, 1902, 1903b) and Frest and Johannes (1995) agree generally to my findings in 1997.
Elrod (1902) commented that the snails were found among and under rocks with little vegetation
nearby. All live individuals I located were under the protection of stones in areas of scant
vegetation cover, but usually with some soil and litter accumulation nearby. Ten (62.5%) of 16
live individuals that I could measure (one shell was broken during handling) were smaller than the
minimum diameter (7 mm) described for this species (Elrod 1903b, Pilsbry 1939). However, size
range of empty shells found mostly on open ground closely matched the published range and
mean. Perhaps adults are more likely to be caught away from refuges in adverse conditions, and
fatalities washed onto open ground.

Discus bransoni and Oreohelix elrodi are found well-below treeline in talus slopes

10



surrounded by closed- and open-canopy forest (Branson 1956), but the rock types comprising the
talus inhabited by the snails are infrequently mentioned in published reports. Berry (1955) and
Frest and Johannes (1995) identified the talus as limestone; both Elrod (1901, 1902, 1903a) and
Branson (1956) failed to mention rock composition. I did not detect limestone at the three sites
where I found one or both species. D. bransoni was found exclusively in talus predominantly of
diorite boulders. O. elrodi was found at this site as well as in smaller-sized talus of argillite (Table
1). D. bransoni may be more of a habitat specialist than previously appreciated, associating with
only a subset of available rock types.

The biology and ecological requirements of Discus bransoni and Oreohelix elrodi remain
largely unknown, so explanations for patterns of presence or absence near the surface of talus
slopes are speculative. O. elrodi was more abundant (4-6 fold during my searches) than D.
bransoni near the surface of talus in wet and cool conditions, and a few individuals could be still
be found when it was warmer and drier. Several factors could contribute to this pattem. First,
absolute population size of O. elrodi at Site 1 may be greater than that of D. bransoni . Ratios of
each species near the talus surface could be representative for all depths in talus. Second, I found
significant differences between the two species in substrate use. Some D. bransoni were found on
foliose lichen (tentatively identified as Arctoparmelia subcentrifuga ) growing on the diorite, but
otherwise were on bare rock. In contrast, O. elrodi were most often found on organic litter and
vegetation. Preference by O. elrodi for organic litter may keep them nearer the surface of talus
slopes where litter accumulations are larger and apparently more numerous. Third, larger shell
size of O. elrodi might reduce its rate of desiccation by decreasing the surface area/volume ratio
(see Goodfriend 1986), allowing larger individuals to remain nearer the drier talus surface for

11



longer periods than D. brunsoni and small O. elrodi . The four live O. elrodi found on 10 June in
warm and dry conditions were 18-21 mm diameter and estivating at that time. Fourth, D.
brunsoni may tend to be nocturnal or crepuscular and make vertical migrations to the talus surface
during periods of activity (Branson 1956). Timing of my searches would not have detected this.
ACKNOWLEDGMENTS

Field work was generously supported by a Canon Exploration Grant administered by The
Nature Conservancy and Canon U.S.A., Inc. I benefited greatly from conversations with T. J.
Frest and especially R. B. Branson, whose knowledge and documentation of the snails of the
Mission Mountains were enthusiastically shared whenever requested. J. S. Marks and L. M.
Hendricks participated in the hunt for Discus brunsoni; T. Gignoux identified the rocks at the D.
bransoni site. T. Shreve visited the type locality of Oreohelix alpina with me. An earlier draft of
the manuscript benefited greatly from the comments of two anonymous reviewers. This paper is
dedicated to the memory of the late J. R. Reichel of the Montana Natural Heritage Program, who
supported my efforts even before this project was conceived.
LITERATURE CITED
Alden, W. C. 1953. Physiography and glacial geology of westem Montana and adjacent regions.

U. S. Geological Survey Professional Paper 231. 200 pp.
Ausden, M. 1996. Invertebrates. Pp. 139-177 In Ecological census techniques, a handbook (W.

J. Sutherland, ed.). Cambridge University Press, Cambridge.
Berry, S. S. 1955. An important new land-snail from the Mission Range, Montana. Bulletin,

Southem Califomia Academy of Sciences 54:17-19.
Branson, R. B. 1956. The mystery of Discus bransoni . The Nautilus 70:16-21.

12



Elrod, M. J. 1901. Montana shells. Rocky Mountain Magazine 2:691-697.

Elrod, M. J. 1902. A biological reconnoissance in the vicinity of Flathead Lake. University of

Montana Bulletin No. 10, Biological Series No. 3.
Elrod, M. J. 1903a. Notes on Pvramidula elrodi Pils. The Nautilus 16:109-112.
Elrod, M. J. 1903b. Montana shells- Pyramidula strigosa . The Nautilus 17:1-6.
Fairbanks, H. L. 1984. A new species of Oreohelix (Gastropoda: Pulmonata: Oreohelicidae)

from the Seven Devils Mountains, Idaho. Proceedings of the Biological Society of

Washington 97:179-185.
Frest, T. J., and E. J. Johannes. 1995. Interior Columbia Basin moUusk species of special

concern. Final Report to Interior Columbia Basin Ecosystem Management Project.

Deixis Consultants, Seattle. 274 pp.
Goodfriend, G. A. 1986. Variation in land-snail shell form and size and its causes: a review.

Systematic Zoology 35:204-223.
Pilsbry, H. A. 1939. Land moUusca of North America (north of Mexico), volume 1 part 1. The

Academy of Natural Sciences of Philadelphia, Monographs Number 3. Philadelphia. 573

pp.
Sokal, R. R., and F. J. Rohlf. 1981. Biometry, second edition. W. H. Freeman, San Francisco.

859 pp.



13



Table 1. Maximum diameter (in mm: mean + SD) of live Oreohelix elrodi and Discus brunsoni
in three talus sites on 1 and 10 July 1997, Mission Mountains, Montana. Sample sizes are in
parentheses.

Site 1 Site 2 Site 3



Rock type


diorite


diorite, argillite


argillite


Average fragment size


1.0 m'


0.09 m'


0.02 m'


0. elrodi








mean


16.2 ±4.5 (39)


14.0 ±4.7 (18)


12.0 ± 4.2 (7)


range


4.1-22.6


7.5 - 22.3


6.5 - 17.7



D. brunsoni



mean 9.5 ±1.4 (8)

range 6.7 - 10.5



14





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Online LibraryPaul HendricksRediscovery of Discus brunsoni Berry, 1955 and Oreohelix alpina (Elrod, 1901) in the Mission Mountains, Montana : with comments on Oreohelix elrodi (Pilsbry, 1900) (Volume 1997?) → online text (page 1 of 1)