Based on the adaptive syndrome of Euura lasiolepis, it is evident that the emergent properties of distribution, abundance, and population dynamics are all very dependent on the availability of suitable resources provided by the willow host population. These resources are highly variable in space and time, the critical factor being the local production of the rapidly growing, more juvenile type of shoots. These high-quality resources are generally in short supply, as illustrated for well-established clones in Figures 3.2 and 3.6. Therefore, an appreciation of willow module variation over a landscape is necessary to understand the ecology of the sawfly.

In Chapter 3 I emphasized the link between female ovipositional preference and larval performance. Understanding this close relationship was important for a mechanistic explanation of why females would be so selective, thereby resulting in severe limitation of resources to individuals and to the population at large. However, only female preference is critical to understanding the typically low carrying capacity in local willow populations and how resource supply can change in response to water availability to the willow host plants. Of course, when a female's choice is compromised by poor resources, the local result is observed as reduced larval survival.

RESOURCE VARIATION

Three main factors influence shoot module production: disturbance, water availability, and willow ramet and genet age. Erosion, flooding, fire, and snow damage all played their role in the dynamics of the willow populations.