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Professor Charles Birch was interviewed in 2008 for the Interviews with Australian scientists series. By viewing the interviews in this series, or reading the transcripts and extracts, your students can begin to appreciate Australia's contribution to the growth of scientific knowledge.
The following summary of Birch's career sets the context for the extract chosen for these teachers’ notes. The extract discusses his approach to the factors important in determining animal population size. Use the focus questions that accompany the extract to promote discussion among your students.
Louis Charles (Charles) Birch was born in Melbourne in 1918. His interest in biology began at an early age; he collected beetles as a child and took the subject at school. He studied at the University of Melbourne and received a BAgrSc in 1939. His agricultural studies covered a number of areas including soil science, climatology, chemistry, physics and physiology – all of which provided a good background for his ultimate interest in ecology.
After graduating, Birch became a research entomologist at the Waite Institute, University of Adelaide, where he worked from 1939 to 1945. His research projects included finding ways to stop grasshopper plagues and understanding how insects would affect stored wheat. He and a colleague, HG Andrewartha, began to understand that animal population numbers are largely determined by environmental factors such as the weather. Their theory was in opposition to the prevailing idea of the time that populations are self-regulating and population size is dependent on competition for resources. Together they wrote The Distribution and Abundance of Animals (published in 1954) which set out their conclusions.
Birch spent time overseas as a Research Fellow at the University of Chicago in 1946. In 1974 he was awarded a senior overseas CSIRO Research Scholarship and studied at the Bureau of Animal Population, Department of Zoological Field Studies, Oxford University.
For most of his career, Birch was at the University of Sydney. He was a senior lecturer in zoology (1948–1953), reader (1954–1960), Challis Professor of Zoology (1960–1963) and Challis Professor of Biology (1963–1983). He has been an emeritus professor of the university since 1983.
In addition to his population ecology research, Birch has a strong interest in science and religion and the philosophy of science. He has written widely on the relationship between the objective world of science and the subjective world of personal experience. His books include Confronting the Future (1975), The Liberation of Life (1981) and Science and Soul (2007). In 1990 he was jointly awarded the Templeton Prize for progress in religion.
In 2008, Birch was made a Member of the Order of Australia. He is a Fellow of a number of international associations including the American Association for the Advancement of Science, the British Ecological Society, the Ecological Society of America and the Academy of Environmental Biology of India.
Birch was elected a Fellow of the Australian Academy of Science in 1961.
It is interesting that you talk about the applied projects, because the science that I know you were involved with in Adelaide was really about the much more general questions and debates about density dependence and population regulation. How did the pure science come out of the applied?
Well, an attitude that Andrewartha and I had was that we wanted to work on animals that had some practical importance in terms of the economy, as far as that was possible, but to do it in such a way that at the same time we would be learning principles of ecology. Both of us came to the conclusion that the numbers of animals could be determined by almost any component of environment. One was sometimes more important than others but, in most of the cases that we studied, the numbers were determined very largely by the weather. If it was favourable, the insect population went up; if it was unfavourable, the population went down – a fairly simple proposition. We therefore didn’t put emphasis where the central emphasis had been in ecology of the numbers of animals, on the so-called density-dependent factors.
There was a thesis, opposed to ours, that all animal populations were self-regulating. That meant that, as the numbers went up under favourable conditions, the animals would become so crowded that the birth rate would drop, the death rate would go up and the numbers would go down. And so, if you asked the question, ‘What prevents the species from becoming extinct?’ the answer was density regulation: the numbers wouldn’t go right down because, as the animals got to a low density, the pressure on them was decreased.
We looked for density-regulating factors, however, and couldn’t find them! We were told that was because we always worked with animals which were on the edge of their distribution. That isn’t quite true, but it is true that we worked on animals where weather was a very controlling and important component.
In fact, Andrewartha and I didn’t persuade our colleagues that any component of environment can be important. That led us to study as many populations as we could find, and we wrote a book called The Distribution and Abundance of Animals. It contained mainly case histories, and we reckoned that there was no need to postulate density-regulating factors in any of these case histories. We tried to investigate studies which had been going on for a long time – thrips for about 20 years, grasshoppers for about 10 years – and we put them, and all those by other people that we studied, together into The Distribution and Abundance of Animals.
I think that had some influence, but we were always in a minority with our ideas of the controlling influences in ecology – and we still are. This is a dispute in ecology which to some extent has lost its kick, but it still goes on. The biggest exponent of the Andrewartha–Birch idea is a chap in the Waite Institute now, Tom White, who has written a couple of books on it. He is a very enthusiastic follower of Andrewartha and draws his inspiration from him.
It must have been pretty amazing for a couple of Australians, at the end of the world, to be major players in a major scientific controversy about paradigms in ecology.
Well, in a sense, Dr Nicholson, who was the Chief of the CSIRO Division of Entomology in Canberra, was a very potent exponent of the density-regulating school of thought. He worked on blowflies and regarded them as a sort of model. Of course, when you work on blowflies in the laboratory and give them a fixed amount of food every day, they do become density regulating. But we never saw a laboratory population as a model for what happens in nature. The important thing is that, if we ask the question, ‘What do your populations do in nature? Why don’t they become extinct?’ then the answer is that some populations do become extinct. For example, under very severe conditions of weather the whole population will indeed die out.
We introduced the concept of dispersion of a population, which are its spatial arrangements. One subpopulation of the species may be in a favourable environment while another is in an unfavourable environment and becomes extinct. But that area can be recolonised, because there always will be some parts of the dispersion of the animal that can help in repopulation. So extinction is not a problem for us. In fact, we realised that it is extremely difficult [laugh] to make any species extinct – which is what you want to do with a pest species, but who has ever been successful in doing that?
View the edited transcript of the full interview.
Select activities that are most appropriate for your lesson plan or add your own. You can also encourage students to identify key issues in the preceding extract and devise their own questions or topics for discussion.
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