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1 2 Amphibians and Reptiles in Southwest Riparian Ecosystems '

Charles H. Lowe 3

Abstract.--Obligate riparian amphibians and reptiles in Arizona and Sonora, Mexico are discussed. Local population extinctions in Arizona are examined. Special status for obli­ gate riparian species is proposed.

Among the obligate riparian species that occur Local extinctions (extirpations) of populations both in southern Arizona and adjacent Sonora, Mexico of obligate riparian reptile species has been in there are two native turtles and four native snakes; progress in Arizona for about 20 years but are these riparian reptiles also have limited distribu­ essentially unrecorded. One of these extinctions is tions in adjacent southern New Mexico. All but one shown in Figs. 1 and 2 for T. marcianus on the have wider distributions in the Republic of Mexico former Santa Cruz River at Tucson, Arizona. The than in the United States. data are for a once robust population located on the western floodplain of the river between Grant Obligate Riparian Species Road and Sweetwater Drive. The density graphed is mean density per five-year period for transect obser­ Kinosternon flavescens Yellow Mud Turtle vations on the floodplain using Silverbell Road. Kinosternon sonoriense Sonoran Mud Turtle The last permanent water in the Santa Cruz River at Tucson was in 1941. Th~ last checkered garter snake Thamnophis eques Mexican Garter Snake was seen in the population in 1976. The survivor­ Thannophis cyrtopsis Black-necked Garter Snake ship curve in Fig. 2 is an extinction curve for Thannophis marcianus Checkered Garter Snake this population. The final cause of extinction was Thamnophis rufipunctatus Narrow-headed Garter Snake encroachment--agricultural followed by urbanization.

In spite of what may appear to be wide geo­ 15 1 graphic distributions, these species are riparian I obligates that have narrowly limited ecological I --?---1 distributions and low total species-population den­ . I I sities, however dense may be some of the local pop­ I ulations that remain. While strictly speaking they --7---'----? 10 • I · are not yet endangered as species, all~ clearly I I threatened species throughout their southwestern )- --7--+---7----.------.... 1- . I . distributions. Perhaps oddly, the two turtles have ;;; z I more robust populations in Arizona than do the UJ 0 I riparian snakes. Only one of four snakes -1 (I. ~I cyrtopsis) is dependably found when searched for -I in its old known localities and habitats in Arizona. :z:l~ While it remains among those obligate species some­ t-1 :li what less affected by riparian alterations in the -'I Southwest, during the 1980's it is also on the brink I of elimination from some riparian communities in 1940 Arizona where it is now seriously reduced in popu­ lation size. Fig. 1.--Thamnophis marcianus on the floodplain of the Santa Cruz River, northwest Tucson, Arizona. Local population extinction due to man-made encroachment. 1Paper presented at the first North American Riparian Conference, Tucson, Arizona, April 16-18, Native animal species that are obligate ripar­ 1985. ian species are usually the first to disappear from 2For discussions on amphibians and reptiles in the riparian community as the result of significant Southwest riparian ecosystems I thank William A. alterations to the environment. Important man-made Calder, Stephen F. Hale, Terry B. Johnson, Cecil R. perturbations causing riparian habitat alteration Sch~Jalbe, and William H. Woodin. and destruction in the Southwest &re given in Table 3Department of Ecology and Evolutionary Biology, 1. Documented cases of local population extinctions University of Arizona, Tucson, Arizona, 85721. of obligate riparian reptiles (3) and amphibians (1) in Arizona are given in Table 2.

339 Table 1.--Han-made perturbations causing riparian habitat alterations and 80 destruction in the North American Thomnophis morcionus Southwest, United States and Mexico.

P6 = 15.5078-0.1637 t 50 r = -0.998 Pump Down, Damming p <.001 Encroachment >- 20 Agr ic ul tur al ..... Reclamation :::i Urbanization ID <( et al. ID 0 5 a:: 0.. Pollution Acid Rain Pesticides Trace Metals et al.

0.1 Grazing, Woodcutting

Exotic Species

Fig. 2.--Probability on time for survivorship of Thamnophis marcianus, after 1960 to extinc­ tion; see Fig. 1. three are salamanders. All are riparian species and all but two are obligately so, for they must use surface water--permanent or temporary, running These extirpation events took place in the or standing--for reproduction. While we assume 1960's and 1970's. The local extinction of riparian that all of these species may not be equally amphibian and reptilian populations in Arizona is threatened in 1985, all are riparian species and clearly in process having been underway for a time thus are clearly threatened as we near the close equal to about one human generation. This is not of the century. They are threatened principally unexpected. Arizona is participating in the current by encroachment, pump down, and by pollution man-made global faunal mass extinction that was including acid rain and pesticides. accelerated earlier during this century. On what basis should we finally judge the AMPHIBIANS threatened status of Arizona's amphibian species? It is self-evident that the ranid frog (genus Rana) Our vertebrate amphibian fauna is far more populations in Arizona are threatened and 3 species diverse than many suspect. There are 24 species in are properly so listed (AGFD 1982). There is (was) Arizona and 31 in Sonora. Host of the amphibians a total of 5 native Rana species in Arizona, and in Arizona-Sonora are anurans (frogs and toads); in the longer run to the end of the century and

Table 2.--Local extinctions of obligate riparian populations of amphibians and reptiles due to man-made alteration and destruction of riparian habitats in Arizona.

Population Riparian Riparian Species Locality Decade Status Alteration Type

Thamnophis eques Rillito floodplain Extinction 1960 Encroachment xeror i par ian vicinity Tucson Urbanization Thamno_ehis marcianus Santa Cruz floodplain Extinction 1970 Encroachment xeroriparian vicinity Tucson Urbanization Thamnophis rufi,eunctatus Fort Valley Extinction 1960 Pump Down hydroriparian vicinity Flagstaff Ran a tarahumarae1 Santa Cruz County ( 6) Extinction 1970 Pollution mesoriparian

1 Species apparently eliminated from the fauna of Arizona; work in progress (S. F. Hale).

340 beyond they all are unquestionably in subequal tara frogs to succumb first, and the semiaquatic pip jeopardy with Rana tarahumarae the ~1adrean Tarahu­ frogs (that are periodically terrestrial) to be mara Frog which already may be completely eliminated eliminated at some intermediate time point. I.Je will, from Arizona's fauna by habitat pollution (Hale and of course, have to wait and see. It should not be a May 1983). long w'ait, particularly if the price for Arizona copper goes up substantially and/or the Nacozari What is the time frame that we have in mind? smelter goes into operation on schedule. What is our time perspective for threatened and endangered species? Is it this decade (?), next Whatever the lethal mechanism and wherever it decade (?), or the next century that is nmv less is mediated--in the water, soil, food, shelter, all than one human generation away? In talking to or other--the obligate riparian species we have variously concerned people interested in the subject left are threatened now (Table 1). In general, of threatened and endangered species in the South­ species are "threatened" in the "now" and \llest, both in Hexico and the United States, I find "endangered" in the "future;" they are finally that their time perspective on the subject is often doomed however when the time perspective is hazy or even unconsidered. inadequate in the now.

It is, of course, much later than we think. RECOMMENDATIONS For example, in Arizona during 1970-1980 the Tarahumara Frog was eliminated from 5 of the 6, or With regard to Arizona's riparian species, 6 of the 6, of its historically known populations several recommendations are made at this time for (see Hale and May 1983). Most or all of the other the current listing of Threatened Native Wildlife Rana species in Arizona, all four of which are in Arizona (AGFD); see Table 3. The listing of

Table 3.--Specific recommendations on obligate riparian species of amphibians and reptiles for Threatened Native Wildlife in Arizona by the Arizona Game and Fish Commission (see AGFD 1982).

&~HIBIANS, Obligate Riparian Sources of Alteration and Destruction Retain: All 7 species listed Add: Rana chiricahuensis Encroachment, Pollution Rana yavapaiensis Pump Down, Encroachment, Pollution TURTLES, Obligate Riparian Retain: Kinosternon flavescens Encroachment, Pollution Add: Kinosternon sonoriense Encroachment, Pollution, Pump Down SNAKES, Obligate Riparian Retain: Thamnophis eques Encr;achment, Grazing Thamnophis rufipunctatus Encroachment, Pump Down Add: Thamnophis cyrtopsis Encroachment, Grazing Thamnophis marcianus Encroachment, Pump Down

"pips" in the Rana J?.!.Eiens complex of leopard frogs, still additional threatened riparian species is are surely to follow the "taras" if, indeed, pollu­ appropriate and soon should be considered further. tion related to acid rain and/or trace metals is substantiated beyond reasonable doubt as a causal Regarding the field (status) investigations of factor in the extirpation of !· tarahumarae. Special Status Species, they should include for each known population and locality (i) the current age­ The case is particularly instructive. In specific population density, and (ii) an historic freshwater populations where the taras have been resume on presence, density, habitat condition, and eliminated (e.g., Sycamore Canyon, Santa Cruz Co., man-made perturbations affecting habitat alteration Arizona), the sympatric pips remain as do the native and quality at least since the turn of the half fish. If lethal pollutant toxin(s) is mediated century. partly or wholly through the stream water, we could be observing the beginning of a riparian community physiological extinction pattern in which LITERATURE CITED the aquatic-semiaquatic species with the highest physiological flushing rate is eliminated first; fluid flushing processes are but one of the possible Arizona Game and Fish Department. 1982. Threatened skin-related avenues for toxic poisoning in frogs. native wildlife in Arizona. Arizona Game and Because fishes are integumentally waterproofed Fish Commission, Phoenix, Arizona. (Hith lover urine flows and lower glomerular filtration rates), while frogs are integumentally Hale, S. F. and C. J. May. 1983. Status report for highly permeable to water (with higher urine flows Rana tarahumarae Boulenger. Report from Arizona and higher glomerular filtration rates), the fishes Natural Heritage Program, Tucson, to U. S. Fish would be expected to succumb last, the highly aquatic and \Vildlife Service, Albuquerque, New Mexico.

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