Daily and Seasonal Activity Patterns in Two Species of High Altitude Skink, Niveoscincus microlepidotus and N. metallicus, from Tasmania

-We studied the activity patterns of two species of viviparous lizards co-occurring in a harsh sub-alpine environment. Activity patterns were studied over the active period, October to March, to investigate differences between an alpine specialist species, Niveoscincus microlepidotus, and a lowland generalist species, N. metallicus, at its altitudinal limit. Distinct differences were found in emergence and retreat times, behavior during the day, activity between the seasons, and total activity over the summer period. Loglinear modeling clearly showed a relationship between sex, season and the behavior of the lizards. Niveoscincus microlepidotus exhibited more variable behavior than N. metallicus, with a capacity to shift from bimodal to unimodal diel activity. Diel and seasonal activity in N. microlepidotus was greatly extended, largely through the use of thigmothermy to supplement shuttling heliothermy. Activity patterns in heliothermic lizards are often determined by climate and weather, and particularly by contemporary levels of insolation (Avery, 1978; House et al., 1980). Because the body temperature of an ectotherm is a complex function of its biophysical environment (Grant and Dunham, 1988), thermoregulating lizards are constrained to occupy specific thermal activity windows. A lizard that can be active for longer periods will ultimately have more available energy. Assuming that food is readily available, daily energy assimilation should increase with activity time, because the rates of digestion and assimilation are temperature dependent (Van Damme et al., 1991) and are maximized at or near active body temperatures (Avery et al., 1982). At high altitudes lizards may be inactive for more than half the year. During this time they must survive on stored energy, particularly lipids, and these energy stores, built up over the warmer months, must be adequate for the duration of hibernation (Adolph and Porter, 1993). Consequently, an increased activity window during summer months, both on a diel and seasonal basis, may increase survivorship over the winter period. Time is therefore an important resource, and temporal partitioning may consequently be of great adaptive importance to species of lizards found at high altitudes (Simon and Middendorf, 1976; Toft, 1985). The two species chosen for this study were Niveoscincus microlepidotus, an alpine specialist, and N. metallicus, a species primarily associated with more temperate habitats; both are viviparous. Mating in N. microlepidotus may occur at any point during summer (DecemberFebruary) (M. Olsson pers. comm.). Females that mate early in the season usually carry their embryos through hibernation until the following spring; those that mate towards the end of summer ovulate in spring (September) after carar er months, must be adequate for the dution of hibernation (Adolph and Porter, 1993). sequently, an increas d activity window ring sum er months, both on a diel and seaal basis, may increas survivorship over the 29 This content downloaded from 207.46. 13.101 on Sat, 08 Oct 2016 06:08:15 UTC All use subject to http://about.jstor. org/terms J. MELVILLE AND R. SWAIN rying sperm through winter. In N. metallicus young are born in late summer, mating occurs in late autumn and females carry sperm through winter and ovulate in spring; some females mate again in September (Swain and Jones, 1994; Jones and Swain, in press). Our study was carried out at the tree line on Mt Wellington, southern Tasmania, where the two species co-occur. The site represents the upper and lower altitudinal limits on the mountain of N. metallicus and N. microlepidotus respectively. The climate is sub-alpine and, although strongly seasonal, rapid and substantial diel changes frequently occur. Snow may fall in any month of the year, but is most common during winter when the lizards hibernate. The active period for reptiles at this site is from spring (late September) to autumn (late April) (unpubl. data). High altitude Scelporus jarrovi exhibit both unimodal and bimodal activity patterns in response to variations in their thermal environment (Beuchat, 1989). Our study was undertaken to see if this occurs also in N. microlepidotus and N. metallicus, and to determine whether any differences in temporal partitioning that might exist between these species were relevant to their altitudinal distributions. MATERIALS AND METHODS The Study Sites. -Two adjacent but separate sites were chosen for this study to take account of clear differences in microhabitat preferences for the two species (unpubl. data). The total area was approximately 80 m x 50 m and the proximity of the sites meant that it was a matter of only a few steps to move from one to the other to make observations. The sites were within the sub-alpine to alpine transition zone at an altitude of 1080 m, on the eastern face of Mt. Wellington. Rainfall at the location is high, frosts are frequent, and glazing storms occur throughout the year, but snow cover is usually restricted to winter and early spring. The area consists of a mosaic of three distinct macrohabitats: subalpine woodland, alpine heath, and boulder fields. Niveoscincus metallicus were observed in open sub-alpine woodland which is their preferred habitat at this altitude; densities are in the range 10-20 in a 10 x 10 m square. Sub-alpine woodlands are typical of dolerite-capped mountains in the east of Tasmania and, on Mt. Wellington, this community type occurs between 1000 and 1100 m. Canopy coverage is <30%, allowing a vigorous understorey, up to about 1.5 m in height. In places litter layers, composed mainly of eucalypt debris, accumulate up to 30 cm in depth. Maximum canopy height is 10 m and is dominated by the snow gum, Eucalyptus coccifera. Alpine heaths occur in association with poorly drained, acidic peat soils. Trees are absent and the vegetation height does not exceed 1.5 m. The ground cover is low and dense and numerous alpine plant species are present. Low numbers of both species occur in this habitat, which was not utilised for this study. Niveoscincus microlepidotus were observed in a dolerite boulder field. In this habitat, vegetation is restricted to encrusting lichen and mosses on the surface of boulders, which range in diameter from 0.5-8 m. Lizard densities of 25-35 individuals 100 m-2 were present. Field Observations. -Early in spring, twelve individuals (4 male, 4 female, 4 juvenile) of N. microlepidotus and nine individuals (3 male, 3 female, 3 juvenile) of N. metallicus were captured, sexed, and tagged by a small (2 mm x 2 mm) piece of colored tape stuck to the dorsal surface. As an extra identification measure, each animal was also given a unique toe-clip. Weekly visits were paid to the study site to check on the condition of the tags; when necessary animals were recaptured and the tag replaced. Sexing was achieved by eversion of the hemipenes in males and by gentle palpitation to locate developing ggs or embryos in the females. In spring all female N. microlepidotus observed carried advanced embryos and the female N. metallicus all contained very early embryos. In summer, two of the four N. microlepidotus had well developed embryos, while all of the female N. metallicus were in this condition. In the autumn sample one N. microlepidotus was pregnant and all three N. metallicus were post partum. The 21 marked individuals were observed over a period of three days in each of late spring, mid-summer and autumn. Daily patterns of acivity were recorded for both species. Particular care was given to choosing days for observations in which similar weather conditions prevailed; warm sunny days with little cloud cover were chosen in order to minimize differences in behavior associated with heavy cloud, rain squalls or snow showers. Observations commenced at 0630 h (Local Summer Time), prior to emergence, and were continued until half an hour after the final retreat each day. At five minute intervals a record was made of all lizards visible and the activity of each lizard. Observations took approximately 5 min, after which the observer moved to the adjacent site; observations continued throughout the day and all were carried out by the same person (JM). Activity was recorded using the following behavior categories: overt basking-sitting in the full sun for extended periods of usually more than five minutes; body flattened, often with the legs held back against the side of the body; 30 This content downloaded from 207.46. 13.101 on Sat, 08 Oct 2016 06:08:15 UTC All use subject to http://about.jstor. org/terms ACTIVITY PATTERNS IN ALPINE SKINKS TABLE 1. Range of emergence and retreat times and air temperatures for Niveoscincus microlepidotus and N. metallicus. N values identify the number of times marked individuals (12 N. microlepidotus, 9 N. metallicus) were observed in a 3 day observation period. All times are Local Summer Time.