positive distrust in simplicity--lessons from plant defences and from competition among plants and among animals

1. The address is concerned with the degree of complexity needed in a satisfying ecological theory. 2. Using the incidence of spines, it is argued that previous hypotheses intended to explain the development of anti-herbivore defences are inadequate, and a new «scarcity-accessibility» hypothesis is proposed instead. The variables that need to be considered are productivity, accessibility and proportion of the landscape covered, architecture, seasonal behaviour relative to neighbours, nutrient concentration relative to neighbours and kinds of herbivore present. The new hypothesis accounts for completely opposite kinds of plants being armed, for example, particularly slow-growing and particularly fast-growing plants, or the deciduous species in one system and the evergreen in another