Thomas Mitchell and the Wellington caves: The relationship among science, religion, and aesthetics in early-nineteenth-century Australia

THOMAS MITCHELL (1792–1855), explorer and Surveyor-General in New South Wales between 1828 and 1855, was a talented and competent draughtsman who was responsible for the original sketches and even some of the lithographs he used to illustrate his two journals of exploration, published in 1838 and 1848. In this paper, I will be concerned with the 1838 journal, entitled Three Expeditions into the Interior of Eastern Australia; with descriptions of the recently explored region of Australia Felix, and of the Present Colony of New South Wales. On the whole, it is a detailed and lavishly illustrated account of the land Mitchell encountered, along with its inhabitants and natural history. My particular interest is in offering an explanation for differences between a sepia sketch depicting a cave at Wellington, NSW, that Mitchell prepared as one of the illustrations for geological material included in this journal, and the final lithograph.

Costs of learning: the dynamics of mixed-prey exploitation by silver perch, Bidyanus bidyanus (Mitchell, 1838)

Although generalist predators have been reported to forage less efficiently than specialists, there is little information on the extent to which learning can improve the efficiency of mixed-prey foraging. Repeated exposure of silver perch to mixed prey (pelagic Artemia and benthic Chironomus larvae) led to substantial fluctuations in reward rate over relatively long (20-day) timescales. When perch that were familiar with a single prey type were offered two prey types simultaneously, the rate at which they captured both familiar and unfamiliar prey dropped progressively over succeeding trials. This result was not predicted by simple learning paradigms, but could be explained in terms of an interaction between learning and attention. Between-trial patterns in overall intake were complex and differed between the two prey types, but were unaffected by previous prey specialization. However, patterns of prey priority (i.e. the prey type that was preferred at the start of a trial) did vary with previous prey training. All groups of fish converged on the most profitable prey type (chironomids), but this process took 15-20 trials. In contrast, fish offered a single prey type reached asymptotic intake rates within five trials and retained high capture abilities for at least 5 weeks. Learning and memory allow fish to maximize foraging efficiency on patches of a single prey type. However, when foragers are faced with mixed prey populations, cognitive constraints associated with divided attention may impair efficiency, and this impairment can be exacerbated by experience. (c) 2005 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.