Bonnie Lauck

Life history of the frog Crinia signifera in Tasmania, Australia

A pitfall-trap study was used to investigate the importance of body size, age, body condition (males only), season and growth history as determinates of male and female life-history fitness traits in a population of the frog Crinia signifera. Specimens were dissected to determine physiological characteristics and skeletochronology was used to determine age. Females lived longer and attained a larger size than males by delaying sexual maturity. Most females and males attained sexual maturity after three and two years, respectively; although eggs were found in females as young as one year old. Body size (but not age) was the primary determinant of fecundity, total reproductive output (clutch mass) and oviduct mass for females. Season was the predominant influence on egg size, with smaller eggs produced in summer than in other seasons. Direct investment in male gonads (testes size) was determined by body size and also by age. This, and the fact that sexual size dimorphism in amphibians is commonly female biased, suggests that male size is not necessarily the primary determinant of male reproductive success in C. signifera. Whereas selection on reproductive traits in females is likely to act predominantly on body size, selection in males is also likely to act on survival.

Association of common brown froglets, Crinia signifera, with clearcut forest edges in Tasmania, Australia

W e examined the response of the common brown froglet, Crinia signifera, to recently clearcut forest edges in Tasmanian wet Eucalyptus obliqua forest. We established transects of pitfall traps crossing coupe edges, within coupes, and within mature forest interiors (riparian and non-riparian) at three study sites. Pitfall captures of C. signifera were greatest at the immediate logged forest edge (which corresponded with a firebreak constructed as part of standard clearfell, burn and sow silvicultural practices in Tasmania). Capture rates were lower in both the coupe interior and the immediate unlogged forest edge and declined to negligible numbers in the unlogged forest interior. Edge penetration was estimated to be generally 50-100 m. We suggest that Tasmanias current management of wet forest may provide additional habitat for C. signifera by changing the age structure of the forest and providing additional forest edge/firebreak habitat. However, C. signifera is common and disturbance tolerant, and thus these findings should not be extrapolated to other Australian frog species that may be disadvantaged by current logging practices.

Fluctuating asymmetry of the frog Crinia signifera in response to logging

Fluctuating asymmetry has been proposed as an indicator of environmental stress and population health. However, a notable feature of research examining the relationship between fluctuating asymmetry and population fitness is that of inconsistency. Logging dramatically alters habitat and has the potential to increase or decrease environmental stress. To evaluate the response of fluctuating asymmetry to logging, I conducted research to determine whether fluctuating asymmetry differs in the frog Crinia signifera captured at logged and unlogged sites and if any differences were correlated with body size or body condition. There was a decrease in fluctuating asymmetry but also a decrease in body size and body condition as a result of logging. I also investigated whether any relationship existed between the subtle asymmetry of individuals and the following indicators of fitness: clutch size, clutch mass, average egg mass, testes size, body size and body condition. There was no significant relationship between subtle asymmetry and the fitness indicators.

Breeding site characteristics regulating life history traits of the brown tree frog, Litoria ewingii

Past research has determined the habitat requirements of amphibian species predominantly from presence/absence studies. This study tested the hypothesis that relationships between breeding site habitat components, life history traits and fitness may provide a higher resolution of biological data relating to the habitat requirements of amphibian species. We tested this novel approach by using Litoria ewingii as our model species. We correlated larval and metamorph life history traits with habitat variables at 28 small to medium sized ponds within a commercially logged forest in southern Tasmania, Australia. To avoid larval mortality due to pond desiccation, L. ewingii laid eggs and metamorphosed earlier in smaller ponds. Snout vent length at metamorphosis increased with elevation and metamorphosis was earlier in less shaded ponds. Breeding ponds that maximised the fitness of L. ewingii were higher elevation ponds with reduced shading, steeper bank slopes and reduced pond isolation. The findings of the study equip land managers with a greater ecological understanding of ecosystem function in relation to specific species. The methodological approach has broad application to conservation biology where an awareness of the specific habitat requirements of amphibians is critical to successful ecosystem management.

Impacts of Shading on Larval Traits of the Frog Litoria ewingii in a Commercial Forest, Tasmania, Australia

Abstract Removal of vegetation directly surrounding a breeding pond has the potential to significantly alter the environmental conditions experienced by larval amphibians during development and, therefore, may affect the life history of this and subsequent life stages. In this study, we investigated growth, development, and survivorship of Litoria ewingii as a result of different shading conditions in a commercially logged forest in Tasmania, Australia. We specifically investigated responses in two types of breeding ponds available to the species: permanent ponds, and smaller ephemeral ponds. Increased shading in permanent ponds resulted in reduced survival. Larval growth and development did not respond significantly to shading treatment in permanent ponds but were significantly affected by pond elevation. In ephemeral ponds, increased shading resulted in decreased developmental rate and a higher coefficient of variation for size at metamorphosis. Our findings suggest that the larval success of L. ewingii is not likely to be enhanced by vegetative buffer zones around permanent pond margins but may be enhanced by ensuring heterogeneity of shading conditions around ephemeral ponds.