Sources of Variation in Defensive Traits in Quercus Species: Insights Gained from Research Spanning Individuals to Communities and Local- to Broad-Scale Factors

Abstract

The genus Quercus (Fagaceae), commonly known as oaks, contains about 600 species of shrubs and trees distributed throughout the Northern Hemisphere. Along their distributions, oak species are attacked by a diverse fauna of vertebrate and invertebrate herbivores, and, concomitantly, produce a broad array of defensive traits against these enemies. These include physical traits such as toughness, fiber content, and trichomes, chemical traits including phenolic compounds, and phenological traits such as leaf longevity and timing of leaf senescence. Due to their high species diversity and broad distribution, oaks provide an ideal model to test predictions about biotic and abiotic control over plant defensive traits, as well as establish connections between oak chemistry, arthropod community structure, and ecosystem processes. Accordingly, research on oak anti-herbivore defences dates back to the last half century and spans more than 60 species, ranging from perennial shrubs to deciduous trees and from montane tropical forests to temperate deciduous forests or Mediterranean-type vegetation. In this chapter, we seek to summarize this rich body of research by describing the most relevant findings on patterns of variation in oak defences, ranging from individual- to community-level variation and spanning local-scale to broad-scale patterns. In each case, we analyse and synthesize the most important underlying biotic and abiotic factors presumably shaping (or at least associated with) these patterns, and, in doing so, aim to provide an integrative view of sources of variation shaping patterns of intra- and inter-specific variation in oak anti-herbivore defences. Finally, we also point at opportunities to study potential linkages in patterns of oak defence and herbivory across scales to advance our understanding of defence expression in oaks as well as other tree taxa.