Trophic-level responses differ at plant, plot, and fragment levels in urban native forest fragments: a hierarchical analysis

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We examined the broad-scale (patch-level) influences of landscape fragmentation, the medium-scale (plot level) influences of within-fragment habitat quality and the fine-scale properties of individual trees, on the abundance of herbivores and their parasitoids. The study system consisted of the plant Macropiper excelsum, its main insect herbivore Cleora scriptaria, and two parasitoid wasps: the braconids Aleiodes declanae (endemic specialist) and Meteorus pulchricornis (exotic generalist). Parasitism by the endemic specialist was significantly higher in more isolated fragments and was negatively correlated with parasitism rates by other species, and positively correlated with tree size. Parasitism by the introduced specialist was not related to broad-scale landscape fragmentation, but was positively related to host larval densities measured at the individual plant‐level, and declined with increasing plant species richness at the plot‐level. Herbivory was positively related to the local (plot-scale) abundance of host plants, but was unrelated to the fragment‐level properties. Species showed individualistic associations to habitat fragmentation, with properties of within‐patch quality often proving to be more important to the abundance and composition of this tri‐trophic community. Parasitoids appear to display a variety of associations to fragmentation, rather than having a typical or general relationship as predicted by the trophic level hypothesis.

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