Author: Oxford University Press
Category: Young Adult Nonfiction
My aim in this book is to investigate and celebrate the biology of animal architecture. I believe that by writing this comprehensive overview, it can be seen that this is a coherent biological topic which gives us important insights. I last did this 20 years ago (Hansell 1984), so it is interesting for me not only to see how much the subject has developed during that time, but also how my views have changed too. Animal builders are patchily distributed through the animal kingdom, but research effort is also unevenly distributed within that. Spiders in particular have received a lot of research attention, from the level of their building material to the functional design of webs and their foraging ecology. Bird nests still remain rather under-researched, but there is a flurry of exciting research on bowerbird displays. The book reveals a need for more information in a number of areas, for example, on the composition and properties of self-secreted building materials other than silk, and the mechanical properties of nearly all structures other than spider webs. On the other hand we now have a much better understanding of how simple organisms can build large complex structures, and there have been developments in the ecological and evolutionary concepts of niche construction and ecological inheritance to which studies of animal builders have contributed. This book recognises three broad categories of structure: homes, traps and displays. Chapter 1 looks at the functional role of these: homes to protect builders from the hostile forces of the physical and biological world, foraging and feeding assisted by burrowing or by the use of nets or webs, and structures for intraspecific communication, in particular the displays of bowerbirds. Chapter 2 tests predictions relating to building materials: that self-secreted materials will tend to be more standardised and more complex than collected materials and that, because of this, they will tend to be more characteristic of dynamic structures like traps than of static ones, exemplified by houses. In Preface ix fact, collected materials prove to be quite highly standardised, while the synthesis of self-secreted materials does show some flexibility. The process of building is examined in Chapters 3 and 4. Building anatomy is shown to be generally unspecialised for delicate manipulative skills but modified for power in many burrowing species. Building behaviour is found to be simple and repetitive. These findings support predictions I have previously made (Hansell 1984, 2000). The creation of very large and complex structures is shown to be possible largely through a dialogue between the builder and the developing structure in which building actions in response to local stimuli change the stimulus situation; complex architecture is an emergent property of self-organising processes. These principles apply equally well to building by large workforces of social insects as to single individuals. Animal tools are considered in the light of these findings, because they are generally regarded as important in the context of human evolution, in spite of being small and often of simple construction. Some tool makers are found to show evidence of advanced learning and cognition, but assessment of these attributes in builders generally suffers from lack of evidence. Mechanics, growth, and design are the subjects of Chapter 5. Animal homes show how building rules can be conserved while the structures grow with the size of the individual or colony occupying them. Spiders' webs provide models for the study of engineering in tension, while display structures, in particular those of bowerbirds, provide possible models for the investigation of the evolution of an aesthetic sense. In Chapter 6, the cost of home building and its trade-offs with other life history traits is examined using examples of birds' nests and caddis cases; on trap building costs and their consequences, spider webs again supply the majority of the evidence. Buildings change the world both for builders and organisms that associate with them. These are the themes of Chapters 7 and 8. Predictions (Hansell 1987a, 1993) that builders, as ecosystem engineers, will tend to stabilise habitats, resist extinction, and promote biodiversity are examined. The last of these is clearly supported, although this is found to be largely through facultative associations by organisms with constructed habitat niches. The limitations of animal built structures as evidence of phylogeny is discussed, and the concept of a key adaptation examined with the conclusion that arthropod silk has the strongest claim to this title. Evidence that building has contributed to social evolution (Hansell 1987a) is found to be inconsistent. Finally, builders are seen to alter the course of their own evolution through ecological inheritance, the passing on to their descendents of habitats that they have altered.