Variation in herbivore density among host plants and its consequences for community structure

Abstract

The densities of four species of gall-forming sawflies were found to vary significantly among willow host plant clones. Two of the speices varied among host plants at four sites in each of three years. The other two species varied in density among host plants at most of the sites in two of the three years. Total sawfly density also varied significantly among clones. Individual species densities on willow clones were significantly positively correlated between years when all sites were combined and frequently when sites were considered separately. Most pairwise species combinations were independent in density between years, but some negative correlations existed between the stem galler and the leaf galler. Gall-former densities also were largely independent among clones within years with all sites combined and with sites considered separately. The significant correlations were nearly all positive. At all four sites the combination of significant variation in sawfly densities among willow clones in the field and independence of species densities among clones resulted in significantly different communities (relative abundance of species) among willow clones in three years. Although sawfly abundances differed substantially among the four sites, this remained true. It is argued that the pattern of community structure among clones is the result of variation in host plant quality of clones. We propose an hypothesis to account for patterns of herbivore species associations based on intrapopulation host plant variation.

Interactions of gall-forming species at different plant spatial scales

“…Therefore, our results do not fully support reciprocal positive (facilitation) or negative effect (competition) of one species on another gall inducing species. On the other hand, these finding are partially consistent with those of Fritz et al (1987a), who showed that sawfly species were also independently or positively (2002, 2003 and 2004) combined in each category associated among willow host plants (Fritz et al 1987b). However, competition was demonstrated in that system.…”

Community structure of insect herbivores in a hybrid system: examining the effects of browsing damage and plant genetic variation

“…Similarly, Fritz (1992) demonstrated that differing genotypes of S. sericea (one of the species used in this study) varied in the structure of their insect communities. Variation in community structure among host plants has also been detected in field populations of willows (Fritz et al, 1987;Boecklen & Price, 1989), but genetic variation was not distinguished from environmental variation in those studies. More research using non-Salix populations is needed to determine the prevalence of plant genetic variation as the framework upon which arthropod communities are structured.…”

Aphid infestation promotes survival of a seed predator: observations and experiments on a tritrophic community module

“…Seed mass is an important plant fitness component, and it is influenced by plant genotype, soil conditions, micro-and large-scale climatic trends (cf. Fritz et al 1987). Seed mass seemed to be a variable character in L. anagyroides (Tables 2, 3), although its importance in influencing seedling survival is not known.…”