Weak Competition between Coastal Insect Herbivores

Related communities of four to seven insect herbivore species commonly feed on each of the coastal plant species Borrichia frutescens (L.), Iva frutescens (L.), and I. imbricata Walt. which grow on spoil islands in west-central Florida. Most stems of these host plant species show no evidence of herbivory or of actively feeding herbivores. At the scale of within Iva bushes or Borrichia patches on islands, there were significantly fewer co-occurrences of herbivores on individual stems or terminals than expected, suggesting competition is important on a small scale in this system. However, at the scale of between patches of host plants, that is, between islands, there were no negative correlations between herbivores which suggests that competition is unimportant in influencing the distribution of these species at larger spatial scales. At large spatial scales, other phenomena such as host plant genotype or environmental (island) variability may be more important in influencing the distribution of herbivores.