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Professor Michael Bull

Population ecology of the sleepy lizard, tiliqua rugosa, at Mt Mary, South Australia

C. M. Bull. - Abstract A population of the sleepy lizard, Tiliqua rugosa, near Mt Mary, South Australia, was surveyed by random encounter captures along 42 km of transects over 10 y 1982 - 1991. Population size, estimated by the Jolly-Seber method, was lowest (724 adults) following the 1982/1983 drought, but then increased to a plateau (1500 - 1600 adults) which was maintained for 5 y. Densities in each 1 km segment of the transects varied from 0.3 - 5.5 lizards per ha. Adjacent segments of the transects varied more than two fold in lizard numbers, and those differences were consistent over time. Over all years, an estimated 16% of juveniles survived their first year, 42% of those survived a second year, and 62% of those survived a third year. By 3 y some juveniles had reached adult size, although others took more than 5 y to mature. Annual survival of adults of all ages, was 80 - 90%, whereas only 4% of juveniles reach adulthood. Cars killed an average 3% of the adult population each year, and were a major source of mortality. To sustain stable populations adults must live 20 - 50 y. This long-lived species has a population structure governed by low recruitment, but long survival of established adults. It differs from the rapid turnover dynamics reported for many other lizard species.

Mother-offspring recognition in two Australian lizards, tiliqua rugosa and egernia stokesii

Adam R. Main and C. Michael Bull. - Abstract. Kin recognition has been reported in many animal taxa, but rarely in lizards. Newly born clutches from two viviparous Australian skink species, Tiliqua rugosa and Egernia stokesii, were either left with their mothers, separated at birth and kept with a foster mother, or kept completely isolated from any adults. In experimental trials mothers were presented with their own and with non-related young in gauze bags, and their attention to each young lizard was measured by the number of directed tongue flicks and the time in contact. There was a consistent tendency in both species for mothers to direct more attention to their own young, whether they had been kept together or apart. Foster mothers directed more attention to their own non-familiar young than to their familiar foster young. In reciprocal experiments, young lizards of both species consistently directed more attention to their own mothers than to unrelated females, even when they had been isolated from their mothers from birth. Olfactory cues are probably important for recognition. Using these cues, lizards can recognise kin, and discriminate between kin and non-kin even if the latter have been in close association. It was not possible to determine if the discrimination was genetically based, or if it was acquired during or shortly after birth. The presence of mother-offspring recognition suggests that family groups may be a component in the social organisation of these species.

Ant distribution across a tick parapatric boundary in south Australia

Neil B. Chilton1 and C. Michael Bull- Abstract. Ants were sampled by pit trap at 85 sites, 0.5 or 1.0 km apart, along six transects across a parapatric boundary between the reptile ticks Aponomma hydrosauri and Amblyomma limbatum near Mt Mary in South Australia. There was no tendency for overall ant density, or for the distribution of any single species of ant, to be related to the tick distribution. Thus the survey found no support for the hypothesis that predation by ants was maintaining the boundary. Along the transects there were no correlations between ant and tick densities. Thus the survey found no support for the hypothesis that ant predation was a major factor controlling tick densities. These negative results provide further evidence that single, strong ecological processes cannot explain this well studied parapatric boundary.

Characteristics of the clutch of the gidgee skink, Egernia stokesii

Glen A. Duffield and C. Michael Bull - Abstract. The viviparous birth of Egernia stokesii, an Australian skink, is described. Data from 29 clutches over three years from a population near Hawker, South Australia are presented. Females produce an average 5.07 young per clutch in February or March. Clutches are produced over an average 2.8 days. New born juveniles weigh an average 8.15 g and have an average snout-vent length of 6.73 cm. Juveniles in larger clutches were smaller, when the effect of the size of the mother was taken into account. The average relative clutch mass was 16.5%. The data are discussed in the context of life history patterns of Australian skinks.

Food addition and home range size of the lizard tilqua rugosa

G. Dubas1 and C. M. Bull - Abstract. The Australian sleepy lizard, Tiliqua rugosa (previously Trachydosaurus rugosus), is a large, mainly herbivorous skink. Individuals of this species occupy overlapping home ranges. We conducted four experiments at Tickera, South Australia, in different seasons in 4 yr. We located individuals daily on two plots over 20 days, to estimate short term home ranges and mean daily distance between locations. In the second half of each experiment, abundant food was added to one of the plots while the other was left as a control. Home ranges were significantly influenced by season, being larger in the spring than in the summer or autumn. There were no differences between sexes. The change in home range size between the first and second halves of the experiments was no different on the experimental plots where food was added than on the controls. Food levels did not appear to influence home range size of Tiliqua rugosa at the time and place of these experiments.

Parturition in the Sleepy Lizard, Tiliqua rugosa

C. Michael Bull, Yvonne Pamula, and Lana Schulze - Abstract. Reproductive parameters were determined for the 23 juveniles from the 13 clutches (Table 1). Gravid mass was taken as the last measurement of female mass before parturition. Mean weight of juveniles on the day of birth was 106 g, and ranged from 60.8 - 139.0 g. There was no tendency for single young to be heavier than young from clutches of two (F1,12 = 0.01, P = 0.94), but total clutch mass (weight of all offspring from a female) was greater in females with clutches of two (F1,12 = 25.4, P <0.001). Gravid mass and snout-vent length were not significantly different between females producing clutches of one or two (F1,12="2.2," P="0.16" and F1,12="0.01," P="0.93)," but total offspring mass was positively correlated with female gravid mass (Pearson Correlation r="0.66," P < 0.01). Relative clutch mass, measured as the percentage of gravid mass lost during parturition, averaged 26.8%, and ranged from 16.6% to 34.8%. It was significantly higher in females with clutch size of two (F1,12="11.0," P < 0.01). Parturition of seven young from four clutches was directly observed.

Interactions between Introduced and Native Millipede Species in South Australia.

Tabatha T. Griffin and C. Michael Bull -Abstract. The Portugese millipede Ommatoiulus moreleti (Lucas) (Diplopoda: Julidae) has recently been introduced to South Australia where it has reached very high densities. In parts of the Adelaide Hills it now co-occurs with two native millipedes, Oncocladosoma clavigerum Jeekel (Diplopoda: Paradoxosomatidae) and Dimerogonus orophilus (Attems) (Diplopoda: Cambalidae). We attempted to show whether the introduced species, which has successfully invaded the detrivore community, has affected the ecology or behaviour of the native millipede members of that community. Experiments in laboratory and field arenas showed the three species overlap broadly in activity time and microhabitat. The two native species showed no significant difference in habitat choice or aggregating behaviour when alone or mixed with the introduced Ommatoiulus moreleti, and the natives commonly aggregated with the introduced species. Although Dimerogonus orophilus had reduced feeding activity in the presence of Ommatoiulus moreleti, neither native species rejected food that had been in contact with Ommatoiulus moreleti. We conclude that direct interactions between the introduced invader and the native species cause few behavioural or ecological changes within the detrivorous millipede community.

A model to explain ecological parapatry

by C. Michael Bull1 and Hugh Possingham -Abstract. Ecological parapatry, where pairs of largely allopatric taxa abut along common boundaries without hybridization, is often reported but seldom explained. A computer simulation model is developed which shows that parapatry between two species can be maintained by interspecific interaction on a cline of reducing ecological suitability for the competitively stronger species. In the model, a homogeneous environment requires much greater interaction strength to sustain parapatry than does a heterogeneous environment with alternate regions of favourable and poor habitat. The heterogeneous environment of the model is intended to mimic the environment near a well studied parapatric boundary between two reptile tick species.

Recognition of Offspring by Females of the Australian Skink, Tiliqua rugosa

C. M. Bull, M. Doherty, L. R. Schulze and Y. Pamula - There was variation between females in both the amount of time they attended each bag and the number of tongue flicks they directed at them. Females gave significantly more tongue flicks to bags with their own offspring, spent significantly more time directing attention to bags with their own offspring, and nosed and contacted bags containing their own offspring in significantly more trials (Table 1). The responses of females to clean paper and paper from their home cage were also variable. Females spent significantly more time still, and significantly less time in exploratory activity when presented with paper from their home cage (Table 2). Females also showed a tendency to tongue flick less with home cage paper (Table 2), although the result was not significant, presumably because of the low sample size. There was no trend for increased tongue flick rate in response to home cage cues. Female Tiliqua rugosa respond differently to their own offspring than they do to unrelated offspring. This implies that they can discriminate. They may either be recognizing their own offspring, or young that have been reared with them. The females were unlikely to be responding just to home cage cues. Lizards, including females in our experiment, typically show less exploratory behavior and reduced tongue flick responses to home cage cues compared to novel stimuli (DeFazio et al., 1977; Gove and Burghardt, 1983; Graves and Halpern, 1991). The increase in tongue flick rate to related offspring reported in our experiments is directly opposite to the predicted response to home cage stimuli.

Reproductive Interactions Between Two Australian Reptile Tick Species

C. M. Bull and D. Burzacott -abstract. In South Australia the two tick species Amblyomma limbatum and Aponomma hydrosauri share the same common reptile host species, but have allopatric distributions which abut along a narrow parapatric boundary. Reproductive interference is a mechanism that has previously been suggested could contribute to maintaining the boundary. Populations of each species were established in pens within the range of Ap. hydrosauri. Pens held either each species alone, or the two species together. The performance of females in those pens was monitored over 28 months. There was no indication that the proportion of attached females which mated and engorged was reduced by the presence of heterospecifics. There was no indication that the time taken to mate, engorge and detach was any longer in the presence of heterospecifics. The experiment did not support the hypothesis that reproductive interference contributes to maintaining the parapatric boundary. However Am. limbatum in the pens had a shorter season of reproductive activity, and achieved much smaller numbers of reproductive females. This may inhibit successful colonization of cooler habitats to the south of its distribution.

Investigations of the role of mucus and faeces in interspecific interactions of two land snails

C. M. bull, G. H. baker L. M. Lawson and M. A. Steeda - abstract. A previous report (Smallridge & Kirby, 1988) showed interspecific competition between the two land snails Theba pisana and Cernuella virgata and suggested the mechanism of competition may be that heterospecific mucus and excrement inhibits activity. We describe a series of experiments in which we could find no consistent evidence for any short-term inhibition of activity in the presence of heterospecific mucus. Furthermore snails did not consistently avoid mucus treated surfaces or mucus coated food. Cernuella stopped at and fed from snail faeces (both conspecific and heterospecific) more than did Theba. This suggests an alternate mechanism for interspecific competition.

Habitat Choice and Predator Avoidance in Tadpoles

Andrew G. Peterson, C. Michael Bull and Louise M. Wheeler - abstract.- Larvae of Ranidella signifera and Litoria ewingi are common members of the tadpole communities of temporary ponds in south-eastern Australia, where odonate larvae are the major predators. In field surveys, R. signifera was found more often on the pond substrate than was L. ewingi. This difference in habitat choice was documented further in laboratory aquaria, including a simulated pond edge. For both species, substrate use increased in the dark phase of a 12:12 photoperiod. In the laboratory, L. ewingi suffered heavier predation from the corduliid odonate Hemicordulia tau, a benthic predator, than did R. signifera. Predation on L. ewingi, but not on R. signifera, declined as water depth increased, implying that L. ewingi use the water column to escape benthic predators. Overall predation rate was greater in the dark phase when the predators were more active, and when tadpoles used the substrate more.

Population dynamics and pair fidelity in sleepy lizards

C. Michael Bull -Conclusions. Two conclusions emerge from this long-term study.

Explanations of the organization and dynamics of the population of Tiliqua rugosa cannot be derived from short-term studies. Long-term investigations comparing individual reproductive success, survival of offspring, and social position of individuals in the population, are needed to complement studies of population dynamics over varying environmental conditions. Similar long-term studies of other long-lived lizard species are needed to provide a richer perspective of lizard ecology.
Work to date has shown that reproduction in Tiliqua rugosa is not polygamous. There is a complex social organization, which features monogamy in a season and pair fidelity across years, and which implies long term individual recognition. Presumably, adult longevity coupled with stable population dynamics, allow development of this complex organization, while the low recruitment rate of juveniles to the population selects for behaviors leading to high quality young, rather than high numbers of young.

Any generalizations about lizard ecology must include data from long-lived species like Tiliqua rugosa, yet that group is generally under-represented in reviews. This continuing study of sleepy lizards contributes to lizard ecology by increasing the representation of that group.

The impact of tick load on the fitness of their lizard hosts

C. Michael Bull and Dale Burzacott - Summary. A survey was conducted of natural populations of the sleepy lizard Tiliqua rugosa in South Australia to determine whether infestation by ectoparasitic ticks reduced their fitness. Between 1982 and 1990 2183 captures of 824 individual lizards were made in an area where they were infested by the tick Aponomma hydrosauri, and 3668 captures of 586 individual lizards were made in an area where they were infested with the tick Amblyomma limbatum. Lizards with high tick loads in one year tended to have high loads the next year. Longevity of lizards in the study was either not correlated with tick load, or positively correlated. Size achieved was greater amongst lizards with greatest tick load, and lizards in mating pairs had higher tick loads than those never found in pairs. The data do not support the hypothesis that tick load diminishes host fitness.

How do sleepy lizards find each other?

C. Michael Bull, Gavin S. Bedford1, and Brigitte A. Schulz - abstract. During the spring, adult sleepy lizards (Tiliqua rugosa) form monogamous pairs that remain closely associated for extensive periods over an interval of 6-8 weeks. After natural separations of hours to days, pairs reform. This paper describes observations of natural pairs, and of natural and experimental separations in the field. Sleepy lizards appear to use three mechanisms to relocate their partners. They either follow trails, use airborne signals, or search familiar sites. It is usually the male that seeks to relocate the female, but in several cases, females were observed to relocate their male partners.

The Use of Resource Patches by Earthworms

M. S. Hughes1, C. M. Bull1 and B. M. Doube2 - Summary. A field experiment was established to assess the effects of additional organic matter on earthworm populations. Bags of soil (15 cm deep) were placed in a pasture at Balhannah, South Australia, at the beginning of autumn 1991. The bags were initially seeded with five individuals of Aporrectodea trapezoides, and 250 g of dried sheep manure was added to most bags. Manure was added either in pellet or milled form, and applied either on the surface, in the 5-10 cm layer, or evenly dispersed over 15 cm. In harvests at weeks 7, 9 and 11 after the start of the experiment, A. trapezoides and three other species, A. caliginosa, A. rosea and Microscolex dubius were recovered from the bags. Bags with added manure had significantly higher numbers of each species than bags with no manure. During the four week sampling period (weeks 7 - 11) the numbers of M. dubius recovered per bag decreased, while A. rosea per bag increased. Total earthworm numbers were not influenced by either the form or the location of application of the manure. Earthworms were sampled from three depths, 0 - 5, 5 - 10, and 10 - 15 cm. Both numbers and biomass of earthworms were positively correlated with the location of the manure. Cocoons of Aporrectodea species were more abundant when the manure was milled and evenly dispersed, and were consistently located in the lower soil layers, regardless of the form or location of manure.

The effects of sheep manure on the survival and growth of the earthworm Microscolex dubius (Annelida: Acanthodrilidae)

M. S. Hughes1, C. M. Bull1 and B. M. Doube2 -Abstract. Field and laboratory experiments were performed to determine the effects of varying the quantity of organic matter, in the form of sheep manure, on populations of the earthworm Microscolex dubius. In the field, bags of soil (15 cm deep) were placed in a pasture at Balhannah, South Australia, during winter, 1991. The bags contained varying quantities of sheep manure, making up 0 - 100% by volume. Twelve adult M. dubius were placed in each bag, and their survival and growth were assessed after 6 - 8 weeks. In the laboratory, pots of soil mixed with 0 - 100% manure, were used with five M. dubius from either large or small size classes. Their survival and growth were assessed after 40 days.In both experiments the proportion of added manure significantly affected both survival and growth of M. dubius. The earthworms grew and survived best at moderate levels of manure.

Host-seeking behaviour by australian ticks with differing host specificities

I. Belan1 and C.M Bull -abstract. Ticks generally detach from their hosts into sites where they are later exposed to host species which may or may not be suitable for infestation. The question of how four species of ticks, with differing specificities, behave towards such potential host species was examined. Observations of the generalists, Aponomma hydrosauri and Amblyomma limbatum and the specialists, Aponomma fimbriatum and Aponomma concolor showed that the generalists were attracted to a wider range of potential host species than the specialists and that the larval stages of all tick species, regardless of specificity, contacted more potential host species than the adults. The interspecific differences may be attributed to reliance on different sets of host cues, while the intraspecific differences may reflect the developmental state of the sensory system.

Microcosm investigations into the influence of sheep manure on the behaviour of the geophagous earthworms Aporrectodea trapezoides and Microscolex dubius

M. S. Hughes1, C. M. Bull1 and B. M. Doube2 -Abstract. A series of experiments was conducted over 96 h in 240 mm deep soil microcosms, to assess the effect of the presence and distribution of sheep manure over the soil surface on the vertical and horizontal distribution of burrows and numbers of the earthworms Aporrectodea trapezoides and Microscolex dubius. Within some microcosms the dung was placed on half of the soil surface and this caused aggregation with over two thirds of the earthworms being found in the soil directly under the manure. The presence of surface-applied sheep manure caused both species to aggregate in the surface soil. In contrast, without manure, A. trapezoides was evenly distributed throughout the soil profile while M. dubius aggregated in the deeper soil. The pattern of burrow construction was also influenced by the presence of surface manure. In the absence of manure, burrows of both species were evenly distributed through the soil, but in the presence of surface manure, M. dubius constructed proportionally more burrows close to the surface. Both species constructed approximately twice the burrow area in the absence than in the presence of surface manure. For both species the daily rate of burrow construction decreased over the experimental period. From these data we inferred that there was more widespread and active foraging behaviour in both species when organic food material was scarce. M. dubius differed from A. trapezoides in that it more strongly concentrated foraging activity in the vicinity of the manure food source.

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