Herbivore-induced responses and patch heterogeneity affect abundance of arthropods on plants

1. Plants respond to herbivore damage by inducing defences that can affect the abundance of herbivores and predators. These tritrophic interactions may be influenced by heterogeneity in plant neighbourhood. 2. In the present study, the effects of induced responses on the abundance of herbivores (flea beetles and aphids), omnivores (pirate bugs and thrips), and predators (lady beetles and spiders) on individual plants and their neighbours between and within patches composed of three tomato plants was investigated. 3. Herbivore damage was manipulated to create homogeneous patches where either all or none of the plants had defences induced by herbivore damage, and heterogeneous patches where only one of the plants was induced. 4. Arthropod abundance on plants at different scales was compared by testing between patch effects (patch level), for neighbourhood effects at the plant phenotype level (neighbourhood level), and between near and far plants (within patch position). 5. At the patch level, plants in homogeneously induced patches contained fewer flea beetles and pirate bugs, but more lady beetles, compared with homogeneously non-induced patches. There was no effect of patch type on the abundance of aphids, thrips, and spiders on plants. 6. At the neighbourhood level, induced plants in heterogeneous patches contained more flea beetles and pirate bugs compared with induced plants in homogeneous patches, indicating that the abundance of some herbivores and omnivores on induced plants varied depending on the phenotype of the other plants within the patch. Within patch position, there was no evidence that the abundance of herbivores or predators on non-induced plants was affected by proximity to an induced plant. 7. Therefore, variation in plant neighbourhood generated by induced plant responses affected the abundance of three arthropods from three feeding guilds.