Taxonomic inventories and assessments of terrestrial snails on the ...

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MATERIALS AND METHODS Tinian, the third-largest isl<strong>and</strong> in the Mariana Isl<strong>and</strong>s, is located between latitude 14E55' N <strong>and</strong> 15E06' N <strong>and</strong> longitude 145E35' E <strong>and</strong> 145E40' E, some 8 km south southwest <strong>of</strong> Saipan <strong>and</strong> 128 km north <strong>of</strong> Guam (Figure 1). The isl<strong>and</strong> is about 20 km long on its north-south axis <strong>and</strong> 10 km wide on its east-west axis, with a l<strong>and</strong> area <strong>of</strong> about 102 km 2 . Basement Eocene volcanic rocks are overlain by Miocene <strong>and</strong> Plio-Pleistocene coral <strong>and</strong> algal limestone <strong>and</strong> Holocene raised beach <strong>and</strong> reef deposits. Doan et al. (1960) mapped <strong>and</strong> described five physiographic divisions <strong>of</strong> the isl<strong>and</strong>: 1) a high, southern ridge, where the isl<strong>and</strong>’s highest elevation (187 m) is located; 2) a low, median valley that bisects the isl<strong>and</strong> in a northeastsouthwest direction; 3) a large central plateau; 4) a small, north-central highl<strong>and</strong> with a maximum elevation <strong>of</strong> 166 m; <strong>and</strong> 5) a northern lowl<strong>and</strong> (Figure 2). Aguiguan is a small, steep-sided isl<strong>and</strong> <strong>of</strong> approximately 7.2 km 2 located 8 km southwest <strong>of</strong> Tinian at 14E51' N <strong>and</strong>145E33' E. The isl<strong>and</strong> is composed entirely <strong>of</strong> limestone <strong>and</strong> rises to an elevation <strong>of</strong> 157 m. Most <strong>of</strong> the coastline consists <strong>of</strong> sheer limestone cliffs rising abruptly from the sea in a series <strong>of</strong> eight separate terraces (Tayama <strong>and</strong> Ota, 1940). The terraces have been variously grouped into three (Butler, 1992) or four (Tayama <strong>and</strong> Ota, 1940) major terraces. The uppermost terrace forms a nearly flat, central plateau. There are no beaches or embayments (Figure 3). Terrestrial gastropod populations were surveyed by two methods. For arboreal species, a modification <strong>of</strong> the method used by Hopper <strong>and</strong> Smith (1992) was used. Thirty-minute visual surveys were conducted by observers in forested areas <strong>of</strong> the isl<strong>and</strong>s. Locations <strong>of</strong> sampling sites were determined by GPS (Garmin ® GPS 72). Presence or absence <strong>of</strong> <strong>snails</strong> was determined by examining leaves <strong>of</strong> broad-leaved tree species, including Hern<strong>and</strong>ia sonora, Guamia mariannae, Cynometra ramiflora, Neisosperma oppositifolia, Ochrosia mariannensis, Mammea odorata, <strong>and</strong> Aglaia mariannensis, which serve as host species for partulids in other Mariana Isl<strong>and</strong>s. Special emphasis was given to re-visiting sites in Aguiguan where Partula langfordi, an Aguiguan endemic, <strong>and</strong> Partula gibba were reported historically (Craig <strong>and</strong> Ch<strong>and</strong>ran, 1992; Smith, 1995; Kondo, unpublished data). These species were listed as C<strong>and</strong>idate Species for protection under the U.S. Endangered Species Act. No published records <strong>of</strong> partulid tree snail distribution in Tinian are known; Kondo (1970) reported Partula gibba from Tinian, but he did not provide locality data. When live arboreal <strong>snails</strong> were located within the visual census period, 25-m 2 plots were established under the densest understory, as determined by a spherical densiometer. During a 30-min search, all <strong>snails</strong> located to 2 m height within the plots were identified to species or collected <strong>and</strong> preserved in 75.5% ethanol for identification in the laboratory. Shell lengths <strong>of</strong> specimens were measured to the nearest 0.1 mm with sliding vernier calipers (Digimatic ® 500- 136, Mitutoyo Corp.) or with a Peak ® 10x Scale Loupe. Host tree species were recorded for each snail observed. Leaf litter was examined for 10 min in search <strong>of</strong> fresh partulid ground shells at each sampling site. Observations <strong>of</strong> dead ground shells were recorded. If no live <strong>snails</strong> or fresh 2
Figure 1. Map <strong>of</strong> the Mariana Isl<strong>and</strong>s. Inset shows the position <strong>of</strong> the Mariana Isl<strong>and</strong>s in relation to Asia <strong>and</strong> the western Pacific. Arrows indicate the location <strong>of</strong> Tinian <strong>and</strong> Aguiguan, south southwest <strong>of</strong> Saipan. 3
Page 1: Taxonomic
Page 4 and 5: CONTENTS Abstract iii Introduction
Page 8: Figure 2. Map of T
Page 11 and 12: Figure 4. An investigator collectin
Page 13 and 14: Figure 7. A “midden” of
Page 15 and 16: Table 1. Continued. Location GPS Ge
Page 17 and 18: Table 2. Species assemblage <strong
Page 19 and 20: Figure 8. Size-frequency distributi
Page 21 and 22: Figure 12. Size-frequency distribut
Page 23 and 24: Table 4. Summary of</strong
Page 25 and 26: Figure 18. Size-frequency distribut
Page 27 and 28: Figure 22. Mean shell sizes <strong
Page 29 and 30: young. By mid-1954, the population
Page 31 and 32: Table 6. Land snai
Page 33 and 34: conservation efforts should include
Page 35 and 36: Lydeard, C., R.H. Cowie, W.F. Ponde

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