Bottom-up effects on gall distribution

Abstract

The global pattern of insect gall distribution predicts that the highest richness of such insect guild is found in hot, dry and nutritionally poor environments. In search for a mechanism for this pattern, most studies have focused on top-down effects, such as predation and parasitism, which could potentially be weakened in those stressful environments and favour gall survivorship. In this chapter, however, we examine bottom-up effects that could also be suppressed under environmental stress and, therefore, create suitable hosts for galling insects. We discuss how plants can defend against galling insects and the role of such defences in shaping the pattern of gall distribution.