The effect of seasonal environment and fire on the ecology of frillneck lizards, Chlamydosaurus kingii, in the wet-dry tropics of northern Australia

摘要

A population of Chlamydosaurus kingii, in Kakadu National Park, Northern Territory, was studied between April 1991 and April 1994. This species is a large, arboreal and insectivorous agamid lizard which inhabits open forests and woodlands throughout northern Australia. The principal aims of the study were to examine the ecological relationships between this species and seasonal variation experienced in the wet-dry tropics, and the frequent annual fires in this region. Additional information on the population dynamics and the previously undocumented dry season ecology was also collected. The study involved the telemetry and mark-recapture of C. kingii in Eucalypt dominant tall open forest during the dry and wet seasons. All research was conducted within Kapalga Research Station, where a landscape scale fire experiment was in progress. Seasonal variation has a significant effect on the ecology of Chlamydosaurus kingii. Frillneck lizards show a clear response to the prolonged dry season. This includes a decrease in the volume of food taken, reduced activity and reduced seasonal growth. This coincides with the selection of large Eucalyptus trees. Termites are a substantial part of their diet during the dry season. The presence of termites in their diet is initially perplexing given the "sit and wait" foraging behaviour of frillneck lizards, but the unique foraging behaviour (above the ground during the day) exhibited by Australian Harvester termites (Drepanotermes) allows frillneck lizards access to them when other food resources are generally low. Growth is reduced in the dry season as a result of the lower volume of food ingested. There is a general trend of energy conservation in the dry season. Male frillneck lizards are able to maintain their body condition throughout the dry season, but their condition decreases at the commencement of the reproductive period. This presumably is due to the increased energy expenditure associated with defending home ranges and sexual activity. Females show considerably more variation in body condition, apparently related to the production of eggs. Fire is common throughout northern Australia. Frillneck lizards are able to survive fires lit in the first few months of the dry season by remaining perched in trees. A higher level of mortality occurs in the late dry season fires, along with a change in the behavioural response to fire by sheltering in either larger trees or in hollow termite mounds. Food is more accessible after fires due to the removal of ground vegetation. This is reflected in greater volume and diversity of prey in stomach contents after fires. This increase is more pronounced after late dry season fires, possibly due to the greater amount of ground vegetation removed by these more intense fires. During the dry season frillneck lizards prefer trees with a medium canopy cover located in an area with a low density of grass. Fire has an effect on this relationship. Habitat which has not been burnt for a number of years develops a denser layer of grass and possibly a more continuous tree canopy cover, compared to annually burnt habitat Frillneck lizards in habitats unburnt for a number of years tend to perch in trees with a smaller canopy. Diets are generally similar among the three fire treatments. In general, fire influences the habitat use of frillneck lizards by creating more heterogenous habitats, with more open areas. Frillneck lizards restrict their reproductive cycle to the wet season (summer months), as is common with other agamids. The reproductive season begins prior to the onset of monsoonal rains and the related increase in food availability. Hatchlings begin to emerge during the period of highest food availability, although some late hatchings occur, and they may experience greater difficulty in obtaining food. Male frillneck lizards grow faster than females and have a larger body size. Males also maintain larger home ranges than females in the dry season, which may ensure the presence of a number of females within their home ranges. Only large males actively defend their home ranges. The low densities of frillneck lizard in one site may be related to the absence of fire, and this may affect the long-term viability of populations.