Ecology of Sydney's urban fragments: has fragmentation taken the sting out of insect herbivory?
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Dieter F. Hochuli, Heloise Gibb, Susan E. Burrows, Fiona J. Christie, 2004. "Ecology of Sydney's urban fragments: has fragmentation taken the sting out of insect herbivory?", Urban Wildlife: More than meets the eye, Daniel Lunney, Shelley Burgin
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The urban remnants of Sydney support a unique and diverse fauna and flora. Many are of high conservation value, despite being subjected to a range of anthropogenic disturbances that seemingly compromise their biodiversity value. We tested a suite of hypotheses associated with habitat fragmentation and urbanisation. We found that the composition of invertebrate fauna of small remnants was significantly different to that in larger continuous areas of similar vegetation, with higher trophic levels (predators and parasitoids) being most affected. Subsequent surveys on Eucalyptus botryoides revealed higher levels of herbivory in urban remnants, consistent with the hypothesis that herbivores in these remnants were released from pressures of parasitism and predation. The importance of higher trophic levels in regulating herbivory was demonstrated in field experiments excluding avian and insect predators from branches being used by a dominant herbivore on E. botryoides, Doratifera casta (Lepidoptera: Limacodidae). The declining state of urban remnants may be linked to a disruption of ecological processes associated with the loss of species from higher trophic levels, releasing herbivore populations from pressures of predation and parasitism. While this may be perceived as compromising the ecological integrity of urban remnants, it may also be an unavoidable consequence of habitat fragmentation and a factor that needs to be incorporated in the future management goals of urban remnants.