Design, constraint and construction: essays and experiments on evolution and foraging

Abstract

This thesis is written as a series of journal articles and book chapters exploring the concepts of optimal design, constraint, and construction. It traces my own journey through evolutionary theory. Design, constraint, and construction are metaphors that shape, integrate, and propel what could crudely be regarded as three alternative research programmes within evolutionary biology -functionalism, structuralism, and constructionism. In the first chapter I introduce these alternative research programmes by outlining their histories and current positions. Chapter 2 is a critique of the most rigourous and well developed optimal design argument - optimal foraging theory. In this chapter I analyse the validity of optimal foraging theory's assumptions and review tests of one particular set of optimal foraging models - optimal diet theory. I conclude that optimal foraging theory has been nowhere near as successful as its proponents have claimed. However, this does not mean that optimal foraging theory is necessarily a complete waste of time. Its models can be used to organise research and to foster communication between behavioural ecologists and psychologists. In Chapters 3 and 4, I examine the utility of one optimal foraging model, the Ideal Free Distribution (IFD), in explaining and predicting the behaviour of a flock of captive house sparrows. Contrary to the claims of previous researchers, the initial model does not accurately predict the behaviour of the flock Modifications of the IFD that incorporate perceptual and social constraints are more realistic and accurate, but are less general and, thus, more difficult to test. While optimality models like the IFD often require the secondary incorporation of constraints in order to make accurate predictions, the factors that determine these constraints can be studied in their own right. In Chapter 5, I examine the effects of group level constraints on individual foraging behaviour. In Chapter 6, I develop and test a model that simulates the behaviour of the birds in the previous experiments. The model explores how the behaviour of individual birds constrains the behaviour of other birds in the flock. This model only makes accurate predictions when the effect of group cohesion is incorporated as an additional constraint At the end of this empirical investigation of the design and constraint viewpoints neither perspective emerges as unambiguously good or bad. Both have uses and limitations. One of the limitations of both the design and constraint perspectives is that they encourage static analyses of developmental and evolutionary phenomena. The constructionist perspective provides an alternative to both the design and constraint approaches. Chapters 7, 8, and 9 outline the relationship between the constructionist perspective and the design and constraint approaches. Chapter 7 is a short critique of recent attempts to promote "Structuralism" in biology. It deconstructs the structure/function or design/constraint dichotomy and draws on a resolution of the nature/nurture dispute to articulate an alternative constructionist perspective. In Chapter 8, I outline some of the methodological problems that arise from adopting the design approach and discuss the implications of the construction viewpoint for studies of foraging and evolution. In Chapter 9 I apply constructionist ways of thinking about explanations of stability and change to two highly polarised debates - the selection versus constraint and the ecology versus history controversies. The ability of the constructionist approach to provide a novel resolution of these long standing debates is, I think, a measure of its success.