Can early loss of affiliates explain the coextinction paradox? An example from <Emphasis Type="Italic">Acacia</Emphasis>-inhabiting psyllids (Hemiptera: Psylloidea)

Recent models indicate that coextinction events should be numerous but empirical support for coextinction is paradoxically scarce. I investigated whether the coextinction paradox is due to affiliates becoming extinct well ahead of their hosts, with the disjunction masking the coextinction event. Using psyllids (Hemiptera: Psylloidea) on acacias (Mimosaceae: Acacia) in southern Sydney as an example system, I compared the density of affiliate species and the proportion of specialists on threatened versus secure hosts. I observed reduced psyllid species densities on the threatened hosts Acacia pubescens and A. prominens relative to common, sympatric acacias, consistent with the loss of affiliates ahead of host plant extinction. However, contrary to predictions, I found no support for reduced affiliate specialisation on the threatened hosts. Rather, proximity to closely related hosts may be a stronger determinant of the proportion of specialised psyllid species on a host. In addition, generalists, as well as specialists, may be lost from declining plants due to loss of familiarity with rarely-encountered host plants.