National Recovery Plan for the Corangamite Water Skink Eulamprus tympanum marnieae Garry Peterson and Peter Robertson
|
|  Yüklə 0.7 Mb.
|
TaxonomyThe Corangamite Water Skink is currently recognised as a subspecies of the widespread, cool temperate Southern Water Skink (Eulamprus tympanum tympanum) (Hutchinson and Rawlinson 1995). It is distinguished morphologically from E. t. tympanum by very small mid-body and paravertebral scales, the black dorsal markings arranged as short irregular transverse bars and the bold ventral patterns of black longitudinal strips on a yellow background. The initial conclusion following the discovery of E. t. marnieae was that it represented a new species. Subsequent collections of individuals intermediate in both colour pattern and scalation, however, suggested that intergradation with E. t. tympanum had occurred (Hutchinson and Rawlinson 1995). The notion of intergradation was further supported with the recent discovery of additional morphologically intermediate populations (Peterson 1999; Robertson and Lowe 1999). Recent molecular analysis also did not support the view of a new species. To the contrary, this work revealed that E. t. marnieae as currently recognised, is comprised of populations from two distinct genetic groups, each with separate evolutionary origins (Scott and Keogh 2003). These independent origins are aligned with a deep genetic separation identified within E. t. tympanum in south-western Victoria (Scott and Keogh 2003). As a consequence, a revision of the taxonomy of E. t. marnieae and E. t. tympanum within south-western Victoria is required. DistributionThe Corangamite Water Skink is endemic to the Victorian Volcanic Plain IBRA bioregion in south-western Victoria, where it occurs as a number of isolated populations between Colac and Lake Bolac (Figure 1), over a maximum distance of about 100 km. Detailed maps showing the distribution of this taxon are available from the Department of Sustainability and Environment (DSE). 
Figure 1. Distribution of Corangamite Water Skink HabitatWithin the Victorian Volcanic Plain, the Corangamite Water Skink inhabits specific geological regions known as the Later Newer Basalts. Known colloquially as the ‘stony rises’, the Later Newer Basalts are geomorphic areas of extensive sheet basalt lava flows deposited over a period of 1.8 million years, from the late Tertiary to the Holocene (Joyce 1988). The rises are basalt ridges and boulder heaps often left by the collapse of lava tunnels (Skeats and James 1937; Ollier and Joyce 1964). Prior to European settlement, these Later Newer Basalts were broadly vegetated by Stony Knoll Shrubland, Stony Rises Woodland, Plains Grassland and Plains Grassy Woodland vegetation communities and their associated mosaics, on shallow stony loams and dark clay soils (Willis 1964; Ross 1999; NRE 2003). Localities occupied by E. t. marnieae consist of large deeply fissured basaltic flows or outcrops, remnant vegetation and adjacent permanent or ephemeral wetlands (Peterson 1997; Robertson and Lowe 1999; Peterson 2000). The remnant vegetation generally comprises native plants such as Scrub Nettle (Urtica incisa), Variable Groundsel (Senecio pinnatifolius), Tall Sedge (Carex appressa) and Tree Violet (Melicytus dentata) (Peterson 1997). At most sites, the understorey consists largely of exotic pasture grasses, a legacy of its past agricultural history. Water bodies associated with E. t. marnieae sites include freshwater meadows, deep freshwater marshes, permanent open freshwater lakes, semi-permanent saline marshes and permanent saline lakes. At the microhabitat level, E. t. marnieae selectively occupy moist and cool microenvironments in areas of high shrub density, large rock aggregations with numerous fissures and close to water (Peterson 1997; 2001). Individuals were observed foraging relatively infrequently in vegetation or in shallow water along the lake’s edge (Malone and Peterson (in prep). Juveniles occur around small scattered rocks and dense vegetation cover, suggesting an element of microhabitat partitioning between adults and juveniles (Peterson 2001). The deeply fissured rock piles provide cool and humid refuges during the warm dry summer months when conditions elsewhere in the basalt plains environment would be intolerable to water skinks (Hutchinson and Rawlinson 1995). Proposed recovery actions include the determination of habitat critical to survival of E. t. marnieae. Important PopulationsThe Corangamite Water Skink is currently known from 30 sites that represent 11 discrete populations (Table 1). Most sites support extremely small populations (as few as four adults), although some sites may have up to 430 adults (Peterson 2000), with population size correlating to habitat availability and complexity (G. Peterson unpubl. data 2009). The small number of fragmented, extant populations of E. t. marnieae and their unique genetic lineages, combined with the decline of the subspecies and its grassland/wetland habitat indicate that all populations are extremely important for the survival of the taxon.
Table 1. Population information for Corangamite Water Skink |