Mammals of the San Gabriel Mountains of California Part 2

[Ill.u.s.tration: FIG. 1. Southern oak woodland a.s.sociation. The open leaf-strewn floor of the woodland lacks shelter for ground-dwelling rodents and the population of rodents is small. _Peromyscus boylii rowleyi_ is the commonest rodent. Photo March 10, 1952, in Evey Canyon, 2700 feet elevation.]

[Ill.u.s.tration: FIG. 2. Yellow pine forest a.s.sociation, composed largely of yellow pines, white fir, and black oak. Photo April 27, 1952, at Big Pines, 6800 ft. elevation.]

PLATE 3

[Ill.u.s.tration: FIG. 1. View of the sagebrush scrub a.s.sociation showing a nearly pure stand of basin sagebrush. _Dipodomys agilis perplexus_ and _Reithrodontomys megalotis longicaudus_ occur in this a.s.sociation, and _Peromyscus truei montipinoris_ is present where this a.s.sociation merges with the pinyon-juniper a.s.sociation. Photo April 27, 1952, in Swarthout Valley, 6200 feet elevation.]

[Ill.u.s.tration: FIG. 2. View of a pinyon pine woodland. This habitat const.i.tutes the upper part of the pinyon-juniper a.s.sociation, and is the habitat of _Neotoma fuscipes simplex_, _Peromyscus truei montipinoris_, and _Eutamias merriami merriami_. Photo April 27, 1952, in Sheep Creek Canyon, 5500 feet elevation.]

PLATE 4

[Ill.u.s.tration: FIG. 1. View of the juniper belt. This habitat forms the lower part of the pinyon-juniper a.s.sociation. _Perognathus fallax pallidus_, _Dipodomys panamintinus mohavensis_, and _Peromyscus truei montipinoris_ are typical of this area. Photo April 27, 1952, at Desert Springs, 4300 feet elevation.]

[Ill.u.s.tration: FIG. 2. Joshua tree woodland a.s.sociation. The characteristic mammals are _Dipodomys panamintinus mohavensis_, _D.

merriami merriami_, and _Onychomys torridus pulcher_. Photo January 4, 1952, 6 miles east and 2 miles south Llano, 3600 feet elevation.]

The biota of the washes that cut through the juniper belt in and below many of the larger canyons differs from that of the surrounding juniper-clad benches. Because the washes are in the same geographic area as the juniper belt they are discussed together. These washes on desert slopes are densely populated by rodents derived from adjacent areas, and support vegetation typical of higher floral belts in a.s.sociation with xerophytic, typically desert, species. In a sense, the washes serve to mix up the mammals of adjacent areas. For example, _Onychomys torridus pulcher_ and _Peromyscus eremicus eremicus_, which are mammals typical of the desert, were found in Mescal Wash above their usual desert range; and _Peromyscus californicus insignis_ and _Peromyscus boylii rowleyi_, which are chaparral inhabiting mammals, were found in the wash far removed from their chaparral environment. Washes are evidently effective agents in facilitating the dispersal of certain species of mammals. It is easy to envision a species crossing hostile habitats _via_ dry washes to invade suitable niches in an area which is geographically and ecologically isolated from the original home of the species.

Approximately 500 trap nights in Mescal Wash, at 4100 feet elevation, in the lower edge of the juniper belt, yielded the following mammals:

TABLE 8.--YIELD OF 500 TRAP-NIGHTS IN MESCAL WASH (DESERT SLOPE).

========================================================== | Number | Per cent | | of total --------------------------------------+--------+---------- Perognathus fallax pallidus | 5 | 4.5 Dipodomys panamintinus mohavensis | 43 | 38.7 Peromyscus californicus insignis | 3 | 2.7 Peromyscus truei montipinoris | 1 | .9 Peromyscus boylii rowleyi | 2 | 1.8 Peromyscus eremicus eremicus | 28 | 25.0 Peromyscus maniculatus sonoriensis | 23 | 20.5 Onychomys torridus pulcher | 4 | 3.5 Neotoma lepida lepida | 3 | 2.7 --------------------------------------+--------+----------

_Dipodomys panamintinus mohavensis_, _Neotoma fuscipes simplex_, and _Peromyscus truei montipinoris_ are probably the most characteristic mammals of the pinyon-juniper a.s.sociation.

Sagebrush Scrub a.s.sociation

MAJOR PLANTS

_Bromus sp._ _Artemisia tridentata_ _Chrysothamnus nauseosus_ _Purs.h.i.+a glandulosa_

This a.s.sociation is found on only the crest and desert slope of the range between 5000 and 8000 feet elevation. There it characteristically occupies flats and clearings in the yellow pine forest and pinyon-juniper woodland. The dominant plant of the a.s.sociation is basin sagebrush, and in many places this plant forms mixed growths with s...o...b..ush and _Haplopappus_. The low brush of this a.s.sociation is formed by closely s.p.a.ced bushes with gra.s.ses growing between.

Because of its limited occurrence in the San Gabriel Mountains, this a.s.sociation there has relatively little effect on mammalian distribution. Locally, nevertheless, the presence of this a.s.sociation governs the distribution of certain mammals. For example, on Blue Ridge, islands of sagebrush amid the conifers provide suitable habitat for _Dipodomys agilis perplexus_ and _Perognathus californicus bernardinus_; and in Swarthout Valley _D. a. perplexus_, _Reithrodontomys megalotis longicaudus_, and _Lepus californicus deserticola_ are seemingly restricted to the sagebrush flats.

Joshua Tree Woodland a.s.sociation

MAJOR PLANTS

_Yucca brevifolia_ _Lycium Andersonii_ _Eriogonum fasciculatum_ _Tetradymia spinosa_ _Ephedra sp._ _Larrea divaricata_

This a.s.sociation is on the piedmont that dips toward the Mojave Desert from the interior base of the San Gabriels. The widely s.p.a.ced Joshua trees with low bushes between, and the dry washes breaking the level terrain below the mouths of canyons are typical of this area. Field work was extended no farther down into the desert than about the 3500 foot level, where this a.s.sociation was still dominant.

Although the vegetation of this area is scattered and spa.r.s.e, presenting a barren and sterile aspect, the area supports a rather high population of rodents. The soil at the bases of many large box-thorn- and creosote-bushes is perforated by burrow systems of _Dipodomys panamintinus_ or _Dipodomys merriami_, and those burrows abandoned by kangaroo rats are used as retreats by _Onychomys torridus_ and _Peromyscus maniculatus_. The mammals of this a.s.sociation are all characteristic of the fauna of the Mojave Desert, with the ranges of such species as the coyote and jack rabbit extending well up the desert slope of the mountains.

The mammals listed below were taken in 1948 in roughly 400 trap nights in the Joshua belt, at an elevation of 3500 feet, one mile below the mouth of Graham Canyon.

TABLE 9.--YIELD OF 400 TRAP-NIGHTS IN THE JOSHUA TREE BELT.

====================================================== | Number | Per cent | | of total -----------------------------------+--------+--------- Dipodomys panamintinus mohavensis | 36 | 59.0 Dipodomys merriami merriami | 15 | 24.6 Onychomys torridus pulcher | 4 | 6.6 Peromyscus maniculatus gambeli | 6 | 9.8 -----------------------------------+--------+---------

Populations of _Dipodomys merriami_ and _D. panamintinus_ fluctuate widely, possibly in response to weather cycles. In November of 1948 trapping in the Joshua belt showed that _panamintinus_ outnumbered _merriami_ approximately three to one, whereas in December of 1951, after a succession of unusually dry years, _merriami_ was the more numerous. Further, _merriami_ occurred in the lower parts of the juniper belt in 1951 where in 1948 it seemed to be absent.

_Dipodomys merriami merriami_ and _Onychomys torridus pulcher_ are diagnostic of the Joshua tree woodland a.s.sociation in the San Gabriel Mountains area, since few individuals of either species occur outside of this a.s.sociation.

ACCOUNTS OF SPECIES

Family DIDELPHIDAE

=Didelphis marsupialis virginiana= Kerr

Virginia Opossum

The opossum is common in and near small towns and cultivated areas at the Pacific base of the mountain range and does not thrive away from human habitation; extensive trapping in the coastal sage and chaparral belts produced no specimens except immediately adjacent to citrus groves. Pequegnat (1951:47) mentions that opossums in the Santa Ana Mountains of southern California are in the lower parts of the larger canyons, especially near human habitation.

_Specimens examined._--Los Angeles County: Claremont, 1600 ft., 2 (PC).

Family TALPIDAE

=Scapa.n.u.s latima.n.u.s occultus= Grinnell and Swarth

California Mole

Workings of moles were found on the Pacific slope of the mountains from 1600 feet at Claremont up to 7500 feet on Blue Ridge, and on the Pacific slope beneath basin sagebrush in Cajon Canyon one mile from desert slope Joshua-tree flats, but not on the desert slope, although moles probably occur on that slope in some of the places where there is suitable habitat.

Near Camp Baldy in the sandy soil beneath groves of alders moles seemed to be especially abundant. Although common on the coastal face of the range, moles shunned compact, dry, or rocky soils. In the greasewood chaparral one-half mile west of the mouth of Palmer Canyon, where the soil was hard and rocky, mole tunnels were in soft soil that had acc.u.mulated at the edge of a fire road beneath a steep road cut. The a.s.sumption is that this acc.u.mulation contained insects attractive, as food, to the moles.

_Specimens examined_, 2: Los Angeles County: Camp Baldy, 4200 ft., 1(PC); Claremont, 1600 ft., 1(PC).

Family SORICIDAE

=Sorex obscurus parvidens= Jackson

Dusky Shrew

Jackson (1928:124) recorded a specimen from Camp Baldy, 4200 feet, San Antonio Canyon.