LAUSR

Individuals differ! This observation goes already back to Aristotle almost 2500 years ago, but individual differences are nowadays still highlighted in various areas of social and natural sciences. Almost every day, new fascinating layers of this variation, with their intriguing causes and consequences for species interactions, are discovered. Likewise, variation within and among plant individuals and across landscapes are critical for plant–herbivore interactions, but not fully explored. Microor macro-scale spatial heterogeneity in the abiotic and biotic environment can generate significant withinand among-plant variation (e.g., Schaeffer et al. 2018), and recent studies have provided novel insights into how plant chemistry impacts herbivores, microbes and natural enemies (Albrectsen et al. 2018; Calf et al. 2018; Coley et al. 2018; Cuny et al. 2018). Moreover, the effects of plant chemical traits are often considered in isolation, but they may act together with other features of growth and defense to form distinct trait combinations or syndromes (Coley et al. 2018; Kergunteuil et al. 2018; Tewes and Müller 2018). Yet it is important not to just focus on plant traits, as environmental change such as habitat fragmentation and climate change also alter the relative abundances of herbivores and predators (van der Putten 2012; Genua et al. 2017). In this special topic, stimulated by the Plant–Herbivore Interactions Gordon Conference of 2017, we invited a series of reviews and empirical studies that build on recent advances to examine the drivers and importance of variation within and among plants at the microand macro-scale for the interactions among plants, herbivores and other organisms. The studies of this special topic cover a broad range of plant life forms, from marine algae in an aquatic system (Ledet et al. 2018) to terrestrial herbs (Calf et al. 2018; Chiriboga et al. 2018; Cuny et al. 2018; Howard et al. 2018; Humphrey et al. 2018; Kergunteuil et al. 2018; Quintero and Bowers 2018), to shrubs (Nell et al. 2018; Ochoa-López et al. 2018), to long-lived trees (Albrectsen et al. 2018; Bagchi et al. 2018; Cipollini and Peterson 2018; Coley et al. 2018; Falk et al. 2018; Lämke and Unsicker 2018). In twelve case studies and four review papers, selected aspects of the huge variation in phenomena and underlying mechanisms are highlighted and new research questions opened, which may inspire further research in this exciting field. Below we highlight some of the key findings of these papers.