Additional Studies on Pseudomyrmex Apache (Hymenoptera: Formicidae)

Psyche: A Journal of Entomology, Sep 2019

William S. Creighton

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Additional Studies on Pseudomyrmex Apache (Hymenoptera: Formicidae)

International Journal of Psyche 0 0 BY WILLIAM S. CIEIGHTON Department of Biology, City College , New York , USA ADDITIONAL STUDIES ON PSEUDOMYRMEX APACHE (HYMENOPTERA FORMICIDAE) When Pseudomyrmex apache was described in this Journal in 1952 (1), the writer called attention to the fa.ct that the incidence of this ant appeared to be gre,atest in the mountains of southeastern Arizona and that the incidence seemed to decrease sharply in areas south of that region. Additional field work in northern Mexico during the spring of 1953 has shown that this view is correct. Moreover, these studies indicate that the range of apache does not enter the tropics at all. This is a noteworthy distribution for a member of the genus Pseudomyrmex. The maj.ority of the species in that genus are strictly confined to the Neotropical region and the ew species which range into the southern United States are usually more abundant south o the Tropi.c of Can.cer than north of it. The unique geographical position of Ps. apache is, therefore, a matter of unusual interest. The new recor.ds for apache are presented below, together with a map showing the known range o.f this species" TEXAS" Arsarca Canyon, Chinati Mts., (4800') oe. colony Quercus grisea. - [M,,rch west of General Trias, none of the stations in Chihuahua yielded more than a. single colony. Many of the oak groves in Chihuahua, particularly those near the larger towns, have been denuded by wood-cutters. Despite t’his there are numerous areas where the groves are untouched. Those south of Parral are as extensive as any that the writer has encountered. Since apa.che will nest in at least three of the oaks present in this region, it follows that there are abundant nest sites available for it in .central and southern Chi huahua. Yet the in.cidence of apache in these groves is low, In many groves the writer failed to find any specimens of apache and the few .colonies which were secured are th.e result of repeated visits to the sta.tion at which they were finally taken. It may be recalled that identical collecting procedure in the oak groves of southeastern Arizona often produced from three to ten. colonies per station. The survey whi.ch gave the above records was carried south into Jalisco and Guanajuato and west through the Sierra Madre Occidental in Durango to the eastern border of Sinaloa. Except for the single, record from Villa Ocampo, a small town five miles south of the Durango,-Chihuahua border, no colonies of apache were taken south of the state of Chihuahua. The three southernmost records for apache, Villa Ocampo (Durango), China (Nueva Leon) and Monte Alto (Texas) are all near Latitude 26 China lies about twenty-one miles to the south of the parallel, the other two stations lie a little to the n.orth of it. Hence, there is a distance of at least one hundred and fifty miles between ea.ch of these stations and the Tropic of Cancer. The writer has repeatedly .collected in the region between Latitude 26 and the Tropic of Cancer. The eighty-nine stations which have been visited extend from Tamaulipas through Nuevo Leon and southern Coahuila to the western border of Durango. Oaks were present at many of the stations and these oaks. frequently contained arboreal ants. But the only record for apache coming from this region is he China record cited above. It is certain, therefore, that the incidence of apache south of Latitude 26 is even lower than it is in Chihuahua and it is probable that this ant is absent over much of the region between Latitude 26 and the tro’pics. There are now en.ough records to show that apache occurs in a comparatively narrow band of territory, about twelve hundred miles long, which extends, northwestward from the mouth of the Rio Grande River to southern California. Because of the skew .of this band to the northwest it is difficult to give satisfa,ctory northern and southern limits for the range of apache. If only latitude is considered the range runs from Lat. 33 25’ to Lat. 25 48’, a north, south extent .of approximately 512 miles. But this, method of delimiting the range is confusing, for it leaves, out of account the fa.ct that at any point along the east-west axis the width of the range is much less than five hundred miles. Indeed, in most places the band seems to be n.o more than tw,o hundred miles wide and its maximum width does not ex.ceed 370 miles. The distribution o.f apache throughout this long, narrow band is not uniform. The figures below show the total number of stations and colonies in ea.ch of the states where apache occurs. Stations Colonies California 1 2 Arizona 11 39 Chihuahua 5 10 Texas 3 4 Nuevo Leon 1 1 Durango 1 1 The very marked abundance of apache in the region near the southeastern border of Arizona is even more striking when it is considered that half of the ten colonies secured in Chihuahua came from a station in the extreme northwestern corner of the state (Nogales Ranch) which is only about thirty miles south of the U. S.-Mexico border. Since the most favorable part of the range of apache appears to be the region at the northern end of the Sierra Madre Occidental, it is instructive to consider the environmental conditions in this area. The maj.ority of the Arizona records for apache come from what Shreve (2) has called the "western xeric evergreen forest where oaks are dominant." This association is closely similar to LeSeur’s (3) "santaclarensis consociation" in Chihuahua. There seems to be no essential climatic difference in the two biomes, the principal distinction being the dominant oak involved. In Arizona this is Q. emoryi, in Chihuahu it is Q. santaclarensis. Bo.th these oak associations appear to reach their maximum development in areas where the average minimum annual temperature is not less than 15F..or more than 20F. In such areas light winter .snows are not uncommon and minimum January temperatures as low as -6F. have been recorded at several weather stations (4). The average annual rainfall in such areas is from 15 to 20 inches. Of this total more than hal2 2alls during the period fr.om the first of July to the middle of September. Spring rains are exceptionally light, seldom comprising more than 10% of the total annual rainfall. Over most of the year there is a difference of at least 40F. between the daily minimum and maximum temperatures. The humidity is low and the evaporation rate very high, since the area has an unusually large percentage of cloudless days. It seems .clear from the above data that apa.che can tolerate lower temperatures than most .of the other species of Pseudomyrmex which occur in the southern United States. For the range of Ps. elongata is confined to areas where the average annual minimum temperature is 30F. or more (southern Florida). That .of Ps. gracilis mexicanum is limited to areas where the above temperature is 25F. or more (southern Texas). Ps. brunnea is restricted to areas where the average annual minimum temperature does not go below 20F., hence, while it occurs as far north as the Car.olinas and thence south through the Gulf States into Mexico, it does not occur in southern Aizona. Only Ps. pallida, whose tolerance for low temperatures is equal to that of apache, does so, and palida occurs through the Gulf States and north to the Carolinas. The question immediately arises as to why, since apache can tolerate low temperatures as well as pallida, does not apache occupy the same area as the latter species. The restricting factor in this case appears to be rainfall rather than temperature. Although apache can live in areas where the average annual rainfall is as low as ten inches, it has never been taken in an area where the annual average rainfall is more than twenty-four inches. Beginning in west Texas (10 inches) and running east to Alabama (65 inches) there is a gradient of rainfall which increases to the east. It is interesting to note that the line which marks the area where the average annual rainfall passes 25 inches lies only a few miles north and east of the known. eastern limit of the range of apache. It is further interesting to note that there is a comparable gradient of rainfall which increases southward from the Rio Grande Valley down the coastal plain of Mexico. This gradient begins with 25 inches in the Brownsville area, rises to 45 inches at Tampico and reaches 64 inches at Vera Cruz. As has been noted elsewhere, apache .appears to be absent in this. area. This might be expected if the ant is unable to tolerate an average annual rainfall in excess of 24 inches. If, as seems to be the case, it is rainfall rather than temperature, which plays the. major part in determining the range of apache, some interesting speculations .can be advanced as to how apache reached its present geographical position. It may be taken as axiomatic that apache came to southern Arizona from tropical sources. Since three of the species vf Pseudomyrmex which occur in the southern. [March United States also occur along the coastal plain of eastern Mexico, this region has served as a pathway for northern migration of some members of this genus. It is possible that apache might have come north by this route a.nd reached southern Ariz.ona by turning west up the Rio Grande Valley. But if this. has. been the case then the climatic conditions along the eastern coastal plain in Mexico must ha.ve been different from what they are now or apache must have acquired its low tolerance for annual rainfall after it turned west from the coastal plain. In either case. it is difficult to see why apache should ha.ve stopped its migration along the coastal plain at the Rio Grande River. For, on either count, areas north of the Rio Grande along the Gulf Coast should have been available to it. It can be argued that subsequent climatic .change eliminated apache from the Gulf Coast except for the narrow strip ,of arid territory in the Rio Grande Valley area. The writer finds it difficult to believe that there would not be some tra.ces of ap.ache left in other parts, of the Gulf Coast region under such cir.cumstances. A much more acceptable explanation of the present range of apache can be made if it is assumed that the insect migrated north along the Mexican Plateau. The tra.ces of this northern progress are present along the western edge of the Platea.u, for the decreasing incidence of apache south through Chihuahua may be regarded in this light. There is additional evidence from the. responses of apache that it has had a long and extensive acquainta,nce with conditions on the Plateau. It has been shown elsewhere (1) that apache customarily nests in sizeable limbs .or the trunk of the tree, a.nd that it rarely, if ever, nests in hollow twigs as do many species of Pseudomyrmex. It has also been shown (5) that larger limbs, parti,cularly those stubs which point upward, accumulate much moisture after a rain fall. It seems clear that apache has lived under arid conditions long enough to have restricCed its nesting habits to the parts of the tree which provide the maximum conservation of moisture. Coupled with this is the large tolerance of apache for various sorts of trees as nest sites. To date this ant has been taken from six species of evergreen oak, two species of deciduous oak and mesquite. It is interesting to note that there is a succession of different species of oaks from north to south along the Plateau and that these oaks by no means form a continuous belt throughout this region. There are many areas where the oaks are replaced by mesquite. It may be no more than a coincidence that apache accepts several species of ,oaks. as well as mesquite as nest sites but, at least, this behavior is precisely what would be expected if apache had migrated north along the Mexican Plateau. Peptides Advance s in Hindawi Publishing Corporation ht p:/ www.hindawi.com Submit your manuscr ipts BioMed Hindawi Publishing Corporation ht p:/ www.hindawi.com Research International Stem Cells International Hindawi Publishing Corporation ht p:/ www.hindawi.com Zoology International Journal of Journal of Signal Hindawi Publishing Corporation ht p:/ www.hindawi.com Transduction Genetics Research International Hindawi Publishing Corporation ht p:/ www.hindawi.com Anatomy Research International Hindawi Publishing Corporation ht p:/ www.hindawi.com Biochemistry Research International Advances in Bioinformatics Hindawi Publishing Corporation ht p:/ www.hindawi.com Hindawi Publishing Corporation ht p:/ www.hindawi.com Enzyme Research International Journal of International Journal of Genomics Hindawi Publishing Corporation ht p:/ www.hindawi.com Journal of Nucleic Acids The Scientiifc World Journal LITERATURE CITED 1 . Creighton , W. S. , Psyche , Vol. 59 , No. 4 , p. 141 , December , 1952 . 2. Shreve , F. , in Kearney and Peebles, U.S.D.A. Misc . Pub. No. 423 , My 1942 . 3 . LeSeur, H., Univ. Texas Publication No. 4521 , June 1945 . 4. Smith , H. V. , Univ. Ariz. Agric. Exp. Sta. Bull . 197 , July 1945 . 5 . Creight.on. W. S.. Psyche . Vol. 59 , No. 4 .. p. 161 , December 1952 .


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William S. Creighton. Additional Studies on Pseudomyrmex Apache (Hymenoptera: Formicidae), Psyche: A Journal of Entomology, DOI: 10.1155/1954/29461