The effects of logging on amphibian life history

I assessed the value of life history studies as an approach to evaluating the impact of recent clearfell logging on pond breeding frogs. I conducted a number of distinct studies investigating different aspects of amphibian life history in response to logging using Crinia signifera and Litoria ewingii as my model species.

Life history studies were successfully able to:

• assess breeding site suitability for ewingii by correlating habitat components with life history traits and fitness. Breeding ponds that maximised the fitness of L. ewingii were higher elevation ponds with reduced shading, steeper bank slopes and reduced pond isolation. The outcomes of the study enabled me to provide management guidelines for the construction of ponds designed to maximise the fitness of target species.
• determine the consequences of decreased shading associated with vegetation removal around permanent and ephemeral ponds for larval fitness in L. ewingii. Increased shading around permanent ponds resulted in reduced survival. Increased shading in ephemeral ponds resulted in decreased developmental rate and a higher variation in size at metamorphosis. The outcome of the study provided guidelines for vegetation management around breeding sites
• investigate landscape use of the commercially managed forest by Crinia signifera in order to determine the fraction of the forest used as habitat, the effect of logging upon movement through the forest, and the consequences for reproductive output. Crinia signifera was distributed widely throughout the forest landscape for up to 500 m around each permanent breeding site. Ponds surrounded by unlogged forest were colonized almost two times faster than ponds surrounded by logged forest. As a result, total reproductive output at unlogged ponds was double that of ponds surrounded by recently logged coupes.
• demonstrate that logging can affect maternal reproductive investment and offspring fitness in both Crinia signifera and Litoria ewingii. Eggs were collected from ponds located in either logged or tmlogged forest and raised to metamorphosis under common laboratory conditions. Egg size was greater at unlogged than logged sites for both species. For L. ewingii, size at hatching was also greater at unlogged sites; but for C. signifera size at hatching was independent of logging treatment. For L. ewingii, survival to metamorphosis was greater at logged sites. For C. signifera survival at metamorphosis did not differ with logging treatment despite greater survival at hatching in eggs from logged sites.
• confirm that fluctuating asymmetry has limitations as an indicator of ecosystem stress and the population health of C. signifera in response to logging. The findings indicate a decrease in fluctuating asymmetry (and implied environmental stress) but also a decrease in body size and body condition (i.e. fitness) as a result of logging. There was no significant relationship between the levels of subtle asymmetry in individuals and the following life history traits: clutch size, clutch dry mass, average egg dry mass, oviduct dry mass, testes size, age, body size and body condition.

My research confirms that logging significantly influences the life history of L. ewingii and C. signifera. I argue that, by linking changes in life history traits with assessments of fitness, life history studies can be used to understand why species respond to logging in the ways they do. In this way, life history studies can provide data on which to base constructive, defensible recommendations for the ecologically sustainable management of commercial forests with regard to the frog species that use them. Life history studies are a valid experimental approach that can be used to redress the data deficit relating to the impact of logging on amphibians in Australia.