Can early loss of affiliates explain the coextinction paradox? An example from Acacia-inhabiting psyllids (Hemiptera: Psylloidea)

Abstract

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.

The path to host extinction can lead to loss of generalist parasites

“…This result supports coextinction theory; however, the proportion of specialist parasites was not significantly different, suggesting that host declines lead to the loss of both specialist and generalist parasites. A similar result was found among acacias and the phytophagous insects that feed on them (Powell ). A recent study of fish parasites found that specialist parasites tend to use hosts with low vulnerability to extinction (Strona, Galli & Fattorini ), which may be additional support for the loss of specialist parasites from threatened hosts.…”

Parasites at Risk – Insights from an Endangered Marsupial

“…We predict that several parasites are at risk of extinction either during the decline of the host or during the conservation efforts to recover the host. [30,31]. These data indicate that factors other than host specificity may also be important determinants of extinction risk for parasites.…”

Coextinction dilemma in the Galápagos Islands: Can Darwin's finches and their native ectoparasites survive the control of the introduced fly Philornis downsi?

“…The ectoparasites' dependence on avian hosts implies that they are also coendangered and risk going extinct together with them. In addition, sustained parasite transmission requires a threshold host population size, meaning that some of Darwin's finch ectoparasite species might be already extinct, as parasite extinction could precede that of the hosts (Gompper & Williams, 1998;Altizer et al, 2007;Powell, 2011;Bush et al, 2013;R osza & Vas, 2015). The coextinction threat of a host-parasite system should be assessed on a case by case basis (G omez & Nichols, 2013) as it will depend on the host and the parasite ecology, phylogeny, and the parasite's host range and life cycle (G omez et al, 2012).…”