Page 119 - Land Snails of New Mexico

Bailey (1913) discerned only three life zones for the M o u n t
Pupilla (probably blandi) and a Vertigo (probably modesta) from 12,300 fton Lake Peak. At 11,880 fton SB, five species were taken: Vitrina pellucida, Columella columella, Discus w h i t n e y i , E u c o n u l u s f u l v u s , a n d V e r t i g o m o d e s t a . A t 1 1 , 6 0 0 ft, t h e f o l l o w i n g s p e c i e s w e r e a d d e d t o t h e h i g h e l e v a t i o n list: Discus shimekii (LP), Microphysula ingersolli (LP), and Pupilla blandi (SB), while Striatura meridionalis (MT) and V a l l o n i a c y c l o p h o r e l l a ( L P ) w e r e a d d e d a t 1 1 , 2 0 0 ft. N o n e o f theabove 10speciesisrestrictedtothehighelevationsofthe Arctic-Alpine and Hudsonian Zones. In fact, there seems to be no gastropod association restricted to highest peaks in N e w Mexico, likethose observed in some other groups of organisms, particularly in the herbaceous plants. Rather, the gastropod inhabitants of these highest zones can be regarded as tolerant species extending to high elevations, but better represented in
Taylor "Range". Upper Sonoran, Transition, and Canadian.
Along thetransect,fromLocs.MT-54 to-56,occurjunipers,
p i n y o n p i n e s , a n d l i v e o a k s t y p i c a l o f t h e U p p e r S o n o r a n L i f e
Z o n e . T h e T r a n s i t i o n Z o n e i n c l u d e s s c a t t e r e d p o n d e r o s a p i n e -
DouglasfirforestandpatchesofGambelOak,coveringmuch
of Locs. MT-57 to 63. Bailey (1913:59) observed that "The CanadianZoneareaissorestrictedandisolatedthatitseemsto
lack m a n y of the m a m m a l s and birds of the m o r e extensive areas tothenorthandsouth,..." Inthiszone,spruceandfir characteristically vegetate the uppermost stations (Locs. M T - 6 4 to 67), although open grasslands cover much of the upper southern slopes of M o u n t Taylor proper.
ALTITUDINAL DISTRIBUTION ALONGIGNEOUSROCKTRANSECTS
the Canadian and Transition Zones, below.
Proceeding downward, the boundary between the Hudsonian
I n d i s c u s s i n g a l t i t u d i n a l r e l a t i o n s h i p s , it s e e m s j u s t i f i a b l e t o make useofthelongstandinglife-zonescheme, employed above, that was defined and discussed for New Mexico by Bailey (1913) and which, during the past 80 years, seems not tohave been much improved upon. These zones have been discussed by Metcalf and Smartt (this volume).
and Canadian Zones seems to be clearly identifiable in comparing their respective gastropod faunas. As indicated in Table 2, no more than seven species were found at any elevation (combined for all transects) above 11,000 ft, whereas, 16 or more species were recorded from all elevations (combined t r a n s e c t s ) f r o m 1 0 , 8 0 0 d o w n t o 6 , 4 0 0 ft. N u m b e r s o f s p e c i m e n s taken per sample show a comparable marked decrease from Canadian to Hudsonian Zone localities as well (Table 2). It appears that this decrease in diversity and density is related to a timberline effect, as was discussed by Hoff (1962:62). Hoff noted that low winter temperatures and short growing seasons become increasinglyinimicaltothegrowthoftreesathigher elevations. He stressed that the upward decline in leaf-litter producing deciduous trees such as aspen, Gambel oak, and maples, was of critical importance to land snails in providing food (indirectly) and shelter. Both Hoff (1962) and Karlin
Since life zones tend to descend to lower elevations along mesic canyons than elsewhere, the lower elevations provided by Bailey for "cold" slopes are employed here. These include the:
1 ) H u d s o n i a n Z o n e , 1 1 , 0 0 0 - 1 2 , 0 0 0 ft; 2 ) C a n a d i a n Z o n e , 8 , 5 0 0 11,000 ft; 3) Transition Zone, 7,000-8,500 ft; and 4) Upper Sonoran Zone, 4,500-7,000 ft. The lowest three zones are roughly equivalent (Canadian to Upper Sonoran) to the Spruce Fir,PonderosaPine,andPinyon-JuniperZones ofsome authors. Species taken at all elevations sampled along the four transects are indicated in Table 1, except for the slug Deroceras laeve. Balds occur at highest elevations on the four peaks surveyed. They are in the uppermost Canadian, Hudsonian, or Arctic Alpine Z o n e of Bailey. In this study, highest collections w e r e not obtained above 12,000ft, thus were in the uppermost Hudsonian Zone. Bailey (1913) was not inclined to recognize a Hudsonian Zone on the summits of the Mogollon Mountains and Mount Taylor.However,invarioustableswe haveincludedthehighest locality on Mount Taylor (11,200 ft)in the Hudsonian Zone, in accordance with our arrangement noted above. The Hudsonian Z o n e is n a r r o w a n d is essentially a z o n e at a n d slightly a b o v e timberline,where thenumber ofspeciesoftreesbecomes greatly reduced, and where trees are usually dwarfed and gnarled. The m a i n c o n i f e r s a r e b r i s t l e c o n e p i n e , a l p i n e fir, a n d E n g e l m a n n spruce. Dwarf willows, gooseberries, and other shrubs are common here.Bailey(1913:50)notedthatthiszone (likeothers) may send"narrowtonguesdown steepgulches 1,000feetbelow normal." However,canyonsaregenerallynotwelldevelopedin the Hudsonian Zone, since, in progressing upward, canyons flattenout and ultimately merge with upper slopes on the balds. This produces more uniform habitats and biotas at the highest elevations than those at more biotically diverse, lower zones.
(1961) pointed out the special importance of stands of aspen to
In the Hudsonian Zone, collections were made as high on transects as 12,000 fton LP, 11,800 fton SB, and 11,200 fton MT. OnlyVitrinapellucidawastakenatthehigheststation (12,000ftonLakePeak).However,Hoff(1962)reporteda
Transition Zones. In general, a situation occurs in which diversity in land-snail species is less in the upper Canadian and lower Transition Zones, and becomes progressively richer towards elevations nearer the Canadian/Transition Zone
land snails and the concomitant decline observed in both aspens andsnailsatelevationsneartimberline.
In our transects, overall, as noted above, a considerable
increase in number of species is observed in descending from 11,200- to 10,800-ft elevations, which are considered here to
span the Canadian/Hudsonian boundary. However, almost all of thisincreaseiscontributedbytheSB transect.Taxaadditional to the 10 listed above for the Hudsonian Zone, which were recorded at 10,800 ft, include: Oreohelix nogalensis (SB), Pupilla muscorum (SB), Radiodiscus millecostatus (SB), Ashmunella rhyssa (SB), Gastrocopta quadridens (SB), Glyphyalinia indentata (MT), and Zonitoides arboreus (LP, MT).A preferenceforarborealhabitatsoftenhasbeennotedfor Z arboreus.Someoftheotherspeciesthatappearhere,below timberline,may alsorequireorpreferthepresenceoftrees.
In contrast to the rather clear-cut distinction observed
between the Hudsonian and Canadian Zones, a similar distinction is not evidenced between the Canadian and
boundary. The best-developed stands of deciduous trees occur at or near these elevations, and they are associated with and
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