LAUSR

Herbivorous insects that feed internally on plant tissues depend on their host plants as food resource and immediate habitat. The parasitoids of these herbivores, in turn, depend both on their host herbivores and on the herbivores' host plants. Thus, we may suppose that herbivores and parasitoids must be more affected by biotic interactions (the biotic filter) than their host plants. Also, resource specialisation can mediate the importance of hosts as biotic filters, since the distribution of specialised consumers is limited to sites occupied by their few host species. Plants and insects were sampled in remnants of the Brazilian Cerrado to address three questions: (i) Does beta‐diversity increase at higher trophic levels? (ii) Is host plant specialisation positively related to the beta‐diversity? (iii) Are trophic level effects on beta‐diversity mediated by host plant specialisation? Appropriate null models were employed to explore the importance of biotic filters associated with resources in explaining the beta‐diversity of higher trophic levels. Beta‐diversity and host plant specialisation were lower for parasitoids than for herbivores, and total beta‐diversity did not differ between herbivores and plants. Null models revealed that the presence of host plants did not constrain overall beta‐diversity patterns. Beta‐diversity of herbivores and parasitoids, however, increased with host specialisation. Our findings indicate that low beta‐diversity of basal trophic levels decreases the effect of biotic filters, allowing consumers to occupy several sites. We also show that the severity of biotic filters is higher for host specialists, which might explain the higher beta‐diversity of herbivores compared to parasitoids.