Untangling mechanisms structuring insect diversity patterns in the Cape Floristic Region : the Restionaceae and their herbivores

[摘要] ENGLISH ABSTRACT: Research into the patterns and drivers of insect diversity in the Cape Floristic Region (CFR)lags far behind that of plants. Here I sample insect herbivore communities on a dominantplant family (Restionaceae), and use a spatially nested sampling design and network analysisto evaluate the association between plant and insect diversity in the CFR. I find that plantspecies richness predicts insect richness better than environmental factors. Turnover in insectcommunities is strongly associated with turnover in plant (both species and phylogenetic)communities at both local and regional sampling scales, suggesting insect host specificity.Plant communities unsurprisingly show significant turnover at small spatial scales (i.e.communities situated 0.1-3 km apart show significant turnover and may be tied to ecologicalniches). Insects show a similar pattern, but the decrease in community overlap is moregradual, suggesting many insects can utilise multiple (possibly closely related) hosts whileplants are tied to particular niches. The emergent structure of multiple interaction networks isspatially and temporally invariant, despite high compositional change. However, the internalstructure of the networks shows variation (i.e. interactions show spatial and temporalturnover). Seasonal interaction turnover is driven by a turnover in herbivores and byherbivore host switching. Spatially the turnover in interactions is driven by simultaneousturnover in both plants and insects, either suggesting that insects are host specific, or thatboth groups exhibit parallel responses to environmental gradients. Spatial interaction turnoveris also driven by a turnover in plants, showing that many insects can utilise multiple (possiblyclosely related) hosts and have wider distribution ranges than their host plants. Results pointtoward insect host specificity, but probably not at the species level, as the primary mechanismstructuring insect communities associated with the Restionaceae in the CFR.

[发布机构] Stellenbosch University