Odysseys in Pastryland – a bird’s eye view of microevolution

Colin McHenry, Geoff R. MacFarlane

Abstract


Theory based models of microevolutionary processes are difficult to test in the wild, because the data relating to the specific predictions of the model must be disentangled from the complexity of the species’ overall ecology. Since the 1960s some evolutionary ecologists have been using field experiments involving artificial prey and wild predators – the ecology of the ‘prey’ is under the control of the experimenter, which greatly simplifies the logistics of testing specific microevolutionary models. So far, this technique – typically using prey ‘worms’ made from pastry and wild passerine birds as predators – has been used to test theoretical models of crypsis, directional vs. stabilising selection, apostatic selection, polymorphism, and mimicry systems (Allen, Cooper, Hall, and McHenry 1993). To date, the ‘Pastryland’ technique has been used by ecologists at the Universities of Reading and Southampton in the UK.Because it is a simple model of microevolution in the real world, and because individual experiments rarely require more than a few days to complete, ‘Pastryland’ has also been used to demonstrate the process of natural selection to tertiary science students (Allen, Cooper, Hall, and McHenry 1993). Natural selection is a powerful but very subtle theory, and is hard to grasp without some sort of real world demonstration or example. The logistics of Pastryland experiments mean that it can easily be performed as part of a tertiary field-based activity, with students intimately involved with the running of the experiment. Students are immersed in evolution by taking an active role in the process. Although the pastry ‘prey’ are artificial, the technique relies ultimately on the behaviour of wild predators, as a ‘real’ selective pressure, enhancing student concept acquisition in evolutionary theory.

Pastryland was trialed as a group field project for third year ecology undergraduates at the University of Newcastle. They tested a specific prediction about the dynamics of mimicry systems that has not yet been tested experimentally. This was the first time (to our knowledge) that Pastryland has been used within a teaching context in Australia, and we adapted the technique to make use of common wild birds in Australian urban environments. In the UK, the most important predator was the blackbird (Turdus merula) – in coastal NSW, the main predators are noisy miners (Manorina melanocephala), magpies (Gymnorhina tibicen), and currawongs (Strepera graculina). Students also modified the experimental design to improve controls, and involved local high schools in the hope that the technique would ‘catch-on’ with science teachers.

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