Browsing by Author "Haupt, Tanya Magdeleen"
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- ItemWandering albatross, Diomedea exulans, and the flightless moth, Pringleophaga marioni, on sub-Antarctic Marion Island : a case of thermal ecosystem engineering(Stellenbosch : Stellenbosch University, 2014-04) Haupt, Tanya Magdeleen; Chown, Steven L.; Sinclair, Brent J.; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.ENGLISH ABSTRACT: Recent work has shown that on sub-Antarctic Marion Island, caterpillars of the flightless tineid moth, Pringleophaga marioni, have much higher and considerably less variable populations in recently abandoned nests of the wandering albatross, Diomedea exulans, compared to old nests and other plant communities. Since no evidence for nutrient input was provided, it was hypothesised that wandering albatrosses serve as thermal ecosystem engineers by providing a warm microhabitat in which caterpillar growth and survival are improved. In this thesis, I used a multidisciplinary approach integrating physiology, ecology and behaviour, to better understand the reason for the high caterpillar biomass in nests, and explore the hypothesis of thermal ecosystem engineering. My first objective was to provide a more quantitative life-cycle estimate for P. marioni by rearing caterpillars at different temperature regimes, and in so doing estimate the effects of temperature on development and survival (Chapter 2). Contrary to previous estimates of 2-5 years, a year-long life cycle estimate was found, and although development was fastest at high temperatures of 15°C, caterpillars had low survival. Development time was similar at the fluctuating temperatures of 5-15°C and 10°C, with a longer duration at 5°C. By conducting a more extensive sampling effort of caterpillar biomass and temperature in nests (Chapter 3), I showed that recently abandoned nests had a significantly higher abundance of caterpillars compared to nests from which chicks had recently fledged, as well as older nests. Temperature data collected over a c. one year period showed that temperature in occupied nests remained high during the entire year of occupancy and events at which P. marioni experience chill coma were substantially reduced. Consequently, the effects of thermal acclimation on the physiological and behavioural responses of P. marioni caterpillars were explored. First, how temperature affects the metabolic rate of caterpillars was examined (Chapter 4). Metabolic rate was significantly higher at a low acclimation temperature of 5°C compared to 15°C, providing partial support for metabolic cold adaptation. No evidence was provided that caterpillars reduce their metabolic rates to conserve water, and caterpillars responded to fluctuating temperatures by depressing their metabolic rates. Second, the relationship between thermal preference and locomotor performance of caterpillars was examined (Chapter 5). A common assumption made is that animals will prefer temperatures that maximise performance. Preference was significantly lower (c. 8°C) compared to the optimum temperature for locomotion (c. 23°C), and it was suggested that caterpillars may prefer lower temperatures where survival or assimilation efficiency is maximised. Lastly, if nests provide a fitness advantage, either caterpillars or ovipositing female moths may likely seek out nests. Using choice experiments (Chapter 6), I showed that caterpillars are unlikely to use thermal or chemosensory cues to locate nests and showed a strong avoidance to high temperatures of 15°C. This latter response initially does not appear to fit with the idea that caterpillars favour warm nest temperatures. Although such high temperatures may occasionally be reached in wandering albatross nests, there is considerable daily fluctuation. Variable temperatures including high temperatures of 15°C did not have deleterious effects on caterpillar growth rates and survival, and development was fastest at the fluctuating temperature of 5-15°C compared to 5°C. Caterpillars may also experience chill coma events less often in warm nest environments. Collectively, these findings suggest that the thermal engineering by wandering albatross may indeed improve caterpillar growth and survival. Additional factors were also identified that may contribute to the high abundance of caterpillars in nests (e.g. differential mortality in and out of nests because of mouse predation; high temperatures enhance decomposition rates) (Chapter 7), therefore leaving much scope for future work to further explore this unique interaction between wandering albatross and flightless moth caterpillars.