A DISJUNCT POPULATION OF CICINDELA FORMOSA SAY IN SOUTHWESTERN MONTANA, U.S.A. (COLEOPTERA: CICINDELIDAE)

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1 A DISJUNCT POPULATION OF CICINDELA FORMOSA SAY IN SOUTHWESTERN MONTANA, U.S.A. (COLEOPTERA: CICINDELIDAE) Paul Hendricks 1 and Peter Lesica 2 1 Montana Natural Heritage Program, Natural Science Room 205, University of Montana, 32 Campus Drive, Missoula, MT phendricks@mt.gov 2 Conservation Biology Research, 929 Locust Street, Missoula, MT ABSTRACT: A population of Cicindela formosa Say was discovered in the late 1980 s in the Centennial Sandhills of Beaverhead County, southwestern Montana. The sandhills locality is about 400 km south and west from the nearest collection sites for this tiger beetle species in Montana. The population continued to persist, and was especially robust in the more sparsely vegetated western portions of the sandhills, during subsequent floral and faunal surveys in 1995 and The Centennial Sandhills population of C. formosa is intermediate in appearance between C. f. formosa Say and C. f. gibsoni Brown. The Montana location is geographically intermediate between the C. f. gibsoni populations in Saskatchewan and Colorado, and with further study may shed light on the relationship between C. f. gibsoni and C. f. formosa. During the late 1980 s, the junior author noted the presence of a large and colorful tiger beetle in portions of the Centennial Sandhills, Beaverhead County, Montana, about 80 km west of Yellowstone National Park. The Centennial Sandhills are small and generally stabilized dunes covering an area 14 km long and 2-3 km wide between N, W and N, W, at a mean elevation of 2030 m adjacent and north of Upper and Lower Red Rock Lakes near the head of the Centennial Valley. Early-seral sandhills vegetation is dominated by grasses (Agropyron dastachyum, Stipa comata), forbs (Lupinus argenteus, Psoralea tenuiflora, Opuntia fragilis), and shrubs (Artemisia tripartita, Chrysothamnus nauseosus, C. viscidiflorus). While conducting a study of succession and disturbance of the sandhills vegetation in 1995 (Lesica and Cooper 1999), the junior author collected vouchers of the tiger beetle, which were later deposited at Cornell University and Montana State University (MSU), Bozeman, and identified as Cicindela formosa Say. Based primarily on the presence of expanded ivory maculations on the elytra, the voucher at Cornell was tentatively determined as C. f. manitoba Leng (Lesica and Cooper 1999). 1

2 Subsequently, the senior author collected additional vouchers during a faunal survey of the sandhills in 1999 (Hendricks and Roedel 2001); specimens of all tiger beetle species observed during the 1999 survey were also deposited in the MSU collection. All of the C. formosa vouchers from the Centennial Sandhills housed in the MSU collection were recently diagnosed to fit the description of C. formosa gibsoni Brown. Those specimens, and two in the senior author s possession, lack the coppery reflections on the sternum of C. f. manitoba (Wallis 1961), and the dorsum is darker reddish or purplish-red rather than reddish-brown. The ivory maculations on the elytra are often similar in development to C. f. manitoba, although some individuals show expanded maculations similar to C. f. gibsoni depicted in Figure 3b of Plate 7 in Pearson et al. (2006) and Figures of Plate 1 in Wallis (1961). However, most specimens appear at best as intermediate between C. f. gibsoni and C. f. formosa Say, with the ivory maculations not expanded to the extent of C. f. gibsoni. Cicindela formosa Say is widely distributed in the United States and extreme southern Canada east of the Rocky Mountains (Pearson et al. 1997, Acorn 2001, Pearson et al. 2006). Montana occurs on the northwestern edge of the species global range, with the Montana distribution restricted, as understood until now, to the prairies in the eastern third of the state, and extending farther west in the north along the Canadian border with Saskatchewan and Alberta; the range margin within Montana is closer to that shown in Pearson et al. (1997) than the later version (Pearson et al. 2006). The population of C. formosa in the Centennial Sandhills of Beaverhead County is separated from the nearest Montana collection localities (in Garfield, Powder River, and Toole counties) by about 400 km, occupies a significant hiatus in the northwest portion of the global range, and lies almost equidistant between the two widely disjunct populations of C. f. gibsoni, in the Great Sandhills of southwestern Saskatchewan and the Maybell Sand Dunes of Moffat County, northwestern Colorado (Pearson et al. 2006). With additional study, the Centennial Sandhills population of C. formosa may help shed light on the evolution of C. f. gibsoni, which is currently explained by some authors as adaptation to similar habitat in two isolated areas, with coincidental convergence on a similar phenotype (Pearson et al. 2006). 2

3 The Centennial Valley is oriented east-west and flanked by mountain ranges exceeding 3000 m elevation, with the Continental Divide running along the crest of the Centennial Mountains to the south. The Centennial Mountains form a significant barrier to the dispersal of Cicindela formosa, as the species has yet to be documented in the St. Anthony Dunes in Idaho 64 km south, or at any other Idaho location (Shook 1984, Pearson et al. 1997, Pearson et al. 2006). Other tiger beetle species collected during 1999 in the Centennial Sandhills included, in order of relative abundance, C. decemnotata Say (in early seral sandhills, blowouts, and sandy roads), C. tranquebarica kirbyi LeConte (in sedge-grass sand flats, and sandygravelly roads with a shallow water table), and C. nebraskana Casey (in sandy trails in more stabilized grassy sites). Cicindela formosa was easily the most abundant tiger beetle in 1999 in the western portion of the sandhills (Tepee Creek roughly divides the sandhills into eastern and western portions), where early seral habitat was also more available. During a 25 May traverse of the sandhills about 5.5 km west of Tepee Creek, the senior author counted about 160 C. formosa and two C. decemnotata in 14 blowouts and deposition sites. C. decemnotata was most abundant east of Tepee Creek, where the dunes tend to be lower and more stabilized, and where C. formosa was relatively uncommon. Six C. decemnotata and two C. nebraskana were counted on 27 May during a traverse of the sandhills about 4 km east of Tepee Creek. Road transects of 100 m length also showed a similar pattern of relative abundance of these two tiger beetle species within the sandhills. During late morning on 27 May (ambient temperature = 21 C), 19 C. formosa and no C. decemnotata were counted in 5 min during a transect of sandy road in the area of the 25 May traverse, whereas seven C. decemnotata and three C. formosa were counted in 10 min during a transect of sandy road 3.2 km east of Tepee Creek. Also on 27 May, 23 C. tranquebarica were counted in 10 min during a road transect adjacent to Tepee Creek. All three species were observed copulating on this date as well as into early July. The senior author set drift fence arrays and pitfall trap lines for small mammals in late May 1999 (Hendricks and Roedel 2001) and left these in 3

4 place during the summer. About 140 Cicindela formosa were captured in these traps during June and July, only in the sandhills 5 km west of Tepee Creek. During the same time period about 30 C. decemnotata were captured, only in the sandhills about 3.5 km east of Tepee Creek. This distribution pattern for C. formosa and C. decemnotata within the sandhills was similar to the results of the walking surveys and road transects. The Centennial Sandhills are of conservation interest because they harbor plant communities, four species of plants, and two small mammal species considered rare in Montana (Povilitis and Mahr 1998, Lesica and Cooper 1999, Hendricks and Roedel 2002). Some of these plants and plant communities rely on disturbance (fire, drought, wind, burrowing, grazing) to maintain the early-seral conditions and habitats, such as blowouts, they require. Cicindela formosa adults and larvae favor sandy habitats throughout their range, including sand dunes, sandhills, blowouts, and road cuts with loose and well-drained sandy soil, all of which are sparsely vegetated and in the early stages of stabilization (Larochelle and Larivière 2001); populations of C. formosa tend to decline as sites proceed through succession and become more densely vegetated and stabilized (Pearson et al. 2006). Thus, planned management activity in the Centennial Sandhills designed to maintain early-seral sandhills vegetation (Nathan Korb [The Nature Conservancy] personal communication) should also benefit the sandhills population of C. formosa. 4

5 ACKNOWLEDGMENTS We thank James Leibherr (Cornell University), Mike Ivie and Mike Kippenhan (Montana State University), and David L. Pearson (Arizona State University) for verifying our tiger beetle species determinations, sharing data on prior Montana collection localities of Cicindela formosa, and/or making subspecific determinations of the Centennial Sandhills C. formosa. Our field work, shared with Steve Cooper and Mike Roedel, was funded by cost-share agreements with the Montana Office and Dillon Field Office of the Bureau of Land Management, and Red Rock Lakes National Wildlife Refuge. LITERATURE CITED Acorn, J THE TIGER BEETLES OF ALBERTA. University of Alberta Press, Edmonton, Canada. 120 pp. Hendricks, P. and M. Roedel A FAUNAL SURVEY OF THE CENTENNIAL VALLEY SANDHILLS, BEAVERHEAD COUNTY, MONTANA. Unpublished report to the U.S. Bureau of Land Management and U.S. Fish and Wildlife Service. Montana Natural Heritage Program, Helena. 44 pp. Hendricks, P. and M. Roedel Preble s shrew and Great Basin pocket mouse from the Centennial Valley Sandhills of Montana. NORTHWESTERN NATURALIST 83: Larochelle, A. and M-C. Larivière Natural history of the tiger beetles of North America north of Mexico. CICINDELA 33: Lesica, P. and S. V. Cooper Succession and disturbance in sandhills vegetation: constructing models for managing biological diversity. CONSERVATION BIOLOGY 13:

6 Pearson, D. L., T. G. Barraclough and A. P. Vogler Distributional maps for North American species of tiger beetles (Coleoptera: Cicindelidae). CICINDELA 29: Pearson, D. L., C. B. Knisley and C. J. Kazilek A FIELD GUIDE TO TIGER BEETLES OF THE UNITED STATES AND CANADA. Oxford University Press, New York, USA. 227 pp. Povilitis, T. and M. H. Mahr Montana s Centennial Valley: natural diversity hot spot and wildland corridor. NATURAL AREAS JOURNAL 18: Shook, G. A Checklist of tiger beetles from Idaho (Coleoptera: Cicindelidae). GREAT BASIN NATURALIST 44: Wallis, J. B THE CICINDELIDAE OF CANADA. University of Toronto Press, Toronto. 74 pp. 6