Page 124 - Land Snails of New Mexico

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Table2. Numbersofspeciesandnumberofspecimens(standardizedmathematicallytoa3-literstandard,seetext)takenalongeach offourtransectsinNew Mexico. Theslug,Deroceraslaeve,observedatsomelocalities,isomitted. Transectsareabbreviatedasin text and Table 1. Horizontal lines indicate boundaries between lifezones as in Table 1.
Elevation Number ofSpecies
Number ofSpecimens
SB LP MT Total
40 40 39 39 19 67 86 53 44 58 155
10 239 109 219 577
(feet) WB SB
LP MT Total WB
12,000
11,880
11,600
11,200
10,800
10,400
10,000
9,600
9,200
8,800
8,400
8,000
7,600
7,200
1 1 5 5 3 46 3 45 7
1 13 45 16
7 13 45 17 11 8 88 20 11 11 96 2] 15 11 128 26 11 15 10 10 26
10 22 147 27 10 19 196 28 14 16 108 24 12 16 34 22
105 1537 766 1934 356 1355 254 1594
1017 2010
80 2121
96 2138 157 1820 146 872
878 1070 29446 340 135553 688
Microphysula ingersolli, and Vertigo gouldii. InNewMexico,theUpperSonoranZoneisoftenreferredto
as a Pinyon-Juniper Zone. Especially along canyons, trees such
as various live oaks, Arizona walnut, lance-leaf cottonwood, b o x
elder,hackberry, mulberry, and species of ash and willow occur
together with conifers. Shrubs such as mountain mahogany,
silktassel, and species of Rhus may be common. There are
present, then, a number of deciduous species that can provide some leaflitter.
Although not as well-defined as the boundary between the Hudsonian and Canadian land-snail associations, there is a
discernible and progressive decrease in land snail taxa in proceeding from the Transition Zone down through the Upper Sonoran Zone. As indicated in Table 2, at the four Upper Sonoran stations from 6,800 to 5,600 ft, there is a progressive decrease in numbers of species (transects combined) through 25,
18,12,and9.
Precipitation decreases at lower elevations, just as
temperature increases, and, in turn, increases evaporation. A decrease in montane land snails dependent on moist conditions mightbeexpected,andisseeminglybeingobservedhereinthe upper Sonoran Zone. A comparable increase in arid-adapted
6,800
6,400 6,000113 5,60082
451 392 35 999 49 22
13 21 6 25 16 5 318
12 9
seem to provide favorable habitats for land snails. In Table 2, consideringstationsfrom7,200to10,800fttobecomprised in the Canadian-Transition Zones, greatest species diversity is found in the medial part of this series of localities, from 8,000 to 9,200 ft (26 to 28 species, all transects included). Greatest densitiesofspecimens(calculatedtothreeliters),consideringall four transects, were found (1,355 to 2,138 per sample) from 7 , 6 0 0 t o 1 0 , 4 0 0 ft, w h i c h e n c o m p a s s e s m o s t o f t h e t w o z o n e s combined. Thus, in these transects, and probably in canyons of New Mexicomountains,ingeneral,landsnailsflourishbestat elevations comprising the middle Transition to middle Canadian zones, or from approximately 7,500 to 10,000 ft. Several species were found to be restricted mainly to the Canadian and Transition Zones. With all transects considered, these include the following: Ashmunella thomsoniana, Gastrocopta quadridens, Nesovitrea hammonis electrina, all species of Oreohelix except O. barbata, Punctum minutissimum, Pupilla muscorum, and Radiodiscus millecostatus. In addition, several species are mainly restricted to the Transition and Canadian Zones, except for extending to lower elevations along the W B transect, where special, locally mesic habitats prevail (discussed below). These include Euconulus fulvus, Hawaiia minuscula,
76 1208 148 400 445 323 474 204 321 627 271 442
103 482 408
231 912 898 219 1306 517 867 679 117 232 486 8