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 frutes cens (L.), and I. imbricata Walt. which grow on spoil islands in west-centr al Florida. Most stems of these host plant species show no evidence of herb ivory or of actively feeding herbivores. At the scale of within Iva bushes or Borrichia patches on islands, there were significantly fewer co-occurren ces of herbivores on individual stems or terminals than expected, suggestin g 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 w ere no negative correlations between herbivores which suggests that competi tion is unimportant in influencing the distribution of these species at lar ger spatial scales. At large spatial scales, other phenomena such as host p lant genotype or environmental (island) variability may be more important i n influencing the distribution of herbivores.