Literaturdatenbank
Literaturdatenbank |
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Lovich, J. E., & Meyer, K. (2002). The western pond turtle (clemmys marmorata) in the mojave river, california, usa: highly adapted survivor or tenuous relict? Journal of Zoology, London, 256, 537–545.
Added by: Admin (14 Aug 2008 20:35:29 UTC) Last edited by: Beate Pfau (23 Dec 2009 10:05:36 UTC) |
| Resource type: Journal Article BibTeX citation key: Lovich2002b View all bibliographic details  |
Categories: General Keywords: Actinemys, Actinemys marmorata, Clemmys, Emydidae, Habitat = habitat, Nordamerika = North America, Schildkröten = turtles + tortoises Creators: Lovich, Meyer Collection: Journal of Zoology, London |
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| Abstract |
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The western pond turtle Clemmys marmorata is protected by the State of California and recent surveys have confirmed that many populations have been extirpated or are declining, particularly in southern California. Threats to the continued survival of the species include habitat modification/destruction, grazing, commercial harvest, vehicle-related mortalities, and competition from exotic species. Over 90 percent of the wetland habitats within the historic range of the species in California have been eliminated due to agricultural development, flood control and water diversion projects, and urbanization. Little is known of the ecology of C. marmorata relative to other species of North American turtles, and nothing has been published on the ecology of relict, morphologically and genetically distinct populations in the Mojave River of California. A significant portion of the historical range of the turtle in the Mojave River occurs at the Afton Canyon Area of Critical Environmental Concern (ACEC) administered by the Bureau of Land Management (BLM). Populations in this area and nearby Camp Cady, administered by the California Department of Fish and Game, are small and tenuous. Much of the Mojave River flood plain has been infested with the exotic pest plant saltcedar (Tamarix ramosissima), replacing an estimated 70 percent of the native riparian vegetation in the ACEC. The changes in channel morphology and hydrology associated with saltcedar invasion in the Mojave River have degraded what little western pond turtle habitat exists in this arid region. The BLM is the lead agency in the preparation of the West Mojave Coordinated Management Plan, an ambitious effort aimed at protecting biodiversity in the increasingly urban western Mojave Desert. The western pond turtle is one of many species for which data are critically needed to ensure that they are adequately protected under the developing Plan. The objectives of our study are as follows: 1) to determine the distribution and status of populations in the West Mojave Planning Area (WMPA); 2) to elucidate the demographic structure (adult sex ratios, size- age-class distributions, and population density/biomass) of C. marmorata in the WMPA; 3) to determine clutch size and clutch frequency of females; and 4) to examine seasonal changes in habitat use in this uncharacteristically harsh portion of the western pond turtle's range. Preliminary data show males have an average carapace length of 13.1 cm, while females are slightly larger at 14.5 cm. Average weight of adult males and females is 400 and 525 g, respectively. The adult sex ratio at two study sites (n=34) is biased at 1.3 males per female. Egg laying occurs in late May and early June. Clutch size for 5 gravid females ranged from 4-6 eggs with an average of 4.8. Several animals were equipped with radio transmitters to monitor movements. Small movements between adjacent ponds and wetlands have been observed on several occasions. Aspects of the ecology of populations of the western pond turtle Clemmys marmorata were investigated in the Mojave River of the central Mojave Desert, California, U.S.A. One population occupied man-made ponds and the other occurred in natural ponds in the flood plain of the Mojave River. Both habitats are severely degraded as a result of ground water depletion from human activities along the river and one is infested with the exotic shrub saltcedar Tamarix ramosissima. Mean female carapace length (CL) was significantly greater (14.4 cm) than that of males (13.7 cm). Live juveniles were not detected during the period of study. Shelled eggs were visible in X-radiographs from 26 May to 14 July. Mean clutch size was 4.46 and ranged from 3 to 6 eggs. Clutch size did not vary between 1998 and 1999 but was significantly correlated with CL for both years combined, increasing at the rate of 0.548 eggs/cm CL. Gravid female CL ranged from 13.3-16.0 cm. Some females nested in both years. Mean X-ray egg width (21.8 mm) was not significantly correlated with CL or clutch size. X-ray egg width differed more among clutches than within, whether including CL as a co-variate or not. Nesting migrations occurred from 6 June to 8 July with minimum round trip distances ranging from 17.5-585 m with a mean of 195 m. Mean estimated time of departure as measured at the drift fence was 18:13. Most females returned to the ponds in the early morning. Nesting migrations required females to be out of the water for estimated periods of 0.83 to 86 h. The destination of nesting females was typically fluvial sand bars in the channel of the dry riverbed. Overall, the ecology of C. marmorata in the Mojave River is very similar to that reported for populations in less severe habitats along the west coast of the United States. Notable exceptions include long nesting migrations to sandbars in the dry river channel, a possible result of human modifications to the environment, and an apparent lack of terrestrial overwintering behaviour in Mojave River populations. The general similarity of desert and coastal populations is possibly a reflection of their recent geographic separation. Overall, populations in the Mojave River exhibit few obvious adaptations to living in the desert and are considered to be tenuous relicts of the Pleistocene. The small size and tenuous status of these populations suggests that immediate conservation action is needed, including establishment of satellite populations as a hedge against extirpation.
Added by: Admin Last edited by: Beate Pfau |