Identifying and Managing Threatened Invertebrates through Assessment of Coextinction Risk

Abstract

Invertebrates with specific host species may have a high probability of extinction when their hosts have a high probability of extinction. Some of these invertebrates are more likely to go extinct than their hosts, and under some circumstances, specific actions to conserve the host may be detrimental to the invertebrate. A critical constraint to identifying such invertebrates is uncertainty about their level of host specificity. We used two host-breadth models that explicitly incorporated uncertainty in the host specificity of an invertebrate species. We devised a decision protocol to identify actions that may increase the probability of persistence of a given dependent species. The protocol included estimates from the host-breadth models and decision nodes to identify cothreatened species. We applied the models and protocol to data on 1055 insects (186 species) associated with 2 threatened (as designated by the Australian Government) plant species and 19 plant species that are not threatened to determine whether any insect herbivores have the potential to become extinct if the plant becomes extinct. According to the host-breadth models, 18 species of insect had high host specificity to the threatened plant species. From these 18 insects, the decision protocol highlighted 6 species that had a high probability of extinction if their hosts were to become extinct (3% of all insects examined). The models and decision protocol have added objectivity and rigor to the process of deciding which dependent invertebrates require conservation action, particularly when dealing with largely unknown and speciose faunas.

Australian spiny mountain crayfish and their temnocephalan ectosymbionts: an ancient association on the edge of coextinction?

“…We then estimated temnocephalan coextinction, given the extinction of a certain proportion of host species, based on repeated random sampling of hosts (without replacement and with 500 replicates) [9,11]. Because symbiont extinction risk may be affected by host extinction probabilities [4], patterns of coextinction were compared under equal versus weighted host extinction probabilities. Weighted probabilities were based on the assessed IUCN Red List conservation status, as described above.…”

“…However, very few studies have reconstructed the shared histories of associated clades through deep time, during which extensive environmental change may have profoundly affected their evolution, both separately and jointly [3]. Furthermore, there is an urgent need for information on the specificity of interspecies associations in cases where the host is of conservation concern [4], because the extinction risk for symbionts (non-free-living organisms [5]) may be closely linked to that of their hosts [6][7][8]. Adaptation to new host species (host switches) may reduce the risk of symbiont coextinction (in this case, defined as the extinction of a symbiont species owing to the extinction of its hosts [9,10]).…”

“…In the face of these narrow ranges, and possible anthropogenic threats, the majority of Euastacus have been assessed by the International Union for Conservation of Nature (IUCN) [38] as endangered or critically endangered, including all northern Australian species included in this study (figure 2). Concomitantly, these threats may apply to their temnocephalan symbionts [4] especially where alternative hosts are limited or unavailable. Coextinction risk for Australian temnocephalans has, however, never been formally assessed [7,38].…”

A new species of mealybug (Hemiptera: Pseudococcidae) from critically endangered Banksia montana in Western Australia

“…This conclusion is supported by applying the decision framework for cothreatened taxa of Moir et al (2011). It should be noted that populations of B. montana may survive, but still result in the extinction of the mealybug.…”

Description of three new species of Ceratocader (Hemiptera: Heteroptera: Tingidae) from Western Australia

“…au/browse/profile/20507 and Chandler et al 2002). Therefore, C. coatesi may be restricted in range due to the small range of the host plant and could require conservation itself (co-threatened: Moir et al 2011). However, no conclusion is possible as yet because only one specimen has been found.…”