Page 116 - Land Snails of New Mexico

110
ProvinceinNew Mexicoexhibitdistributionaltrendsrelatedto
Sample sites were confined to areas of relatively uniform vegetation and physical features within a square 30x30 meters. Within this area, larger snails were hand-collected for 30 minutes, paying particular attention to logs, talus, and other
elevation. Despite this, there are few published data detailing
such patterns in specific mountain ranges. Karlin (1961) m a d e
Some general observations concerning altitudinal distribution in
theRockyMountainregion.Hoff(1962)collectedlandsnails microhabitats.Litterwascollectedinsmallamountsfromareas incidentally to a study of pseudoscorpions in northern and
central N e w Mexico, noting elevations and major vegetation types of localities. Metcalf (1984) reported on the altitudinal distribution of land snails in the San Andres and Organ Mountains of south-central N e w Mexico.
Two groupsofmontanetransectsaresummarizedherein.
The more extensive survey, by Dillon, was carried out along
montane canyons in areas of igneous bedrock in four different
areasofNewMexico.TwotransectsweresurveyedbyMetcalf
along valleys with Paleozoic sedimentary bedrock in the Sacramento Mountains of south-central N e w Mexico.
TRANSECTS IN CANYONS WITH IGNEOUS BEDROCK
The collections analyzed in this study were made in the summer of 1986. Transects were selected with regard to their elevation (peaks higher than 10,000 ft/3,050 m), geography (spaced nearly equidistant on two north-south axes), geology (igneous bedrock), and accessibility (mostly public lands with foot trails). T h e localities surveyed were along generally east westoriented canyons, which drained westward off north-south oriented mountain ranges. Localities were situated at400-ft (122 m ) increments along canyons. Because the designations in feet a r e i n 1 0 0 ' s , a n d t h e a v a i l a b l e t o p o g r a p h i c m a p s w e r e c a l i b r a t e d in feet, these U.S. designations, rather than metric ones, will be used hereafter.
judged to be typical of the site, to total at least 3 liters volume. This was bagged, returned to the laboratory, and allowed to air dry.Litterwasthenpassedthroughcoarseandfinemesh sieves and was exhaustively hand-picked for shells, dead and living (usually dormant), under bright lights and with magnification. This method istime-consuming, but effective in revealing small specimens, and was considered to be the leastbiased of several methods evaluated by Waldén (1981).
For quantitative analysis, numbers of snails were standardizedvolumetricallyinthemannerofWäreborn(1969) and Waldén (1981). Volumes ofleaflitter,afterdrying,ranged from 1.00 to 4.00 liters with an average of 2.35 liters. As Wäreborn(1969)did,thenumberofsnailsobtainedwasthen evaluatedtocorrespondto3.00liters.Thoughnonrandom samplingandstandardizationofnumbers ofsnailsinthemanner noted above must be considered as less than ideal, Waldén (1981:353) observed that "the quantitative results probably do not deviate very much from those which would have been achieved by a strictly randomized sampling ...."
The four transects surveyed--with the mountain ranges, highest peaks, highestelevations at which collections were m a d e (in parentheses), and canyons involved were as follows. In the southwest: the Mogollon Mountains, Whitewater Baldy (10,800 ft), Whitewater Creek Canyon, in the southeast: the Sierra B l a n c a M o u n t a i n s , S i e r r a B l a n c a P e a k ( 1 1 , 8 8 0 ft), S o u t h F o r k and Three Rivers Canyons, in the northeast transect: Sangre de CristoMountains,LakePeak(12,000ft),RioenMedioCanyon,
KiLOMETERS '=====
CONTOUR INTERVAL 250 meters 250m =(820ft)
Figure1.TopographyoftheWhitewaterBaldytransectandlocationsofcollectingstationsWB1 toWB16.
3287. li- llow Mountuin
9000
(2)
Q.S9.", Whitewater
N,
\. &# Q
>,
{($
&
S S'N
3' \.
°oo
\\| * N: