Ecological Entomology (2011), 36, 241–250 DOI: 10.1111/j.1365-2311.2011.01266.x Trophic-level responses differ at plant, plot, and fragment levels in urban native forest fragments: a hierarchical analysis FRANZ-RUDOLF SCHNITZLER, ∗ S T E P H E N H A R T L E Y and P H I L I P J.LESTER School of Biological Sciences, Victoria University of Wellington, Wellington, New Zealand Abstract. 1. Using a hierarchical generalised linear model we examined effects of landscape fragmentation (fragment area, isolation, and urbanisation of the surrounding matrix), within-fragment habitat quality (host plant abundance and plant species richness), and properties of the individual trees, on plant herbivore and parasitoid abundance. 2. The present study was conducted in 10 present-day fragments of native forest near Wellington, New Zealand ranging in size from 12 to 1068 ha. The tri-trophic 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). 3. Parasitism by Aleiodes declanae was significantly higher in more isolated fragments and was negatively correlated with parasitism rates by other species, and positively correlated with tree size. 4. Parasitism by Meteorus pulchricornis was not related to 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. 5. Herbivory was positively related to the local abundance of host plants, but was unrelated to the fragment-level properties. 6. 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. Key words. Braconidae, Geometridae, habitat fragmentation, herbivory, parasitoids, species biology, tri-trophic interaction, urban forest fragmentation. Introduction Human activities such as agriculture, deforestation and urban- isation have led to the fragmentation of natural environments. Fragmentation results in a reduction in habitat area and a decrease in habitat connectivity, both of which can reduce plant and animal species richness (Turner, 1996; Wood et al., 2000; Correspondence: Franz-Rudolf Schnitzler, School of Biological Sciences, Victoria University of Wellington, PO Box 600, Wellington 6140, New Zealand. E-mail: SchnitzlerR@landcareresearch.co.nz ∗ Current address: Landcare Research, Private Bag 92170, Auckland Mail Centre, Auckland 1142, New Zealand. Fahrig, 2003). Although habitat fragmentation is considered a threat to biodiversity worldwide, the mechanisms behind the decline of biological diversity are poorly understood. Insects are under as much threat as many other organisms (Samways, 2005). Several observational studies of arthropod communi- ties, as well as experimental evidence, have shown that species richness, community biomass, and biotic interactions are all influenced by the area and isolation of habitats in a frag- mented landscape (Didham et al., 1996; Collinge & Forman, 1998; Gonzalez & Chaneton, 2002). However, certain animals or plants might respond differently to fragmentation than oth- ers, and changes in community at lower trophic levels may result in indirect and cascading effects (Turner, 1996).  2011 The Authors Ecological Entomology  2011 The Royal Entomological Society 241