Habitat use and diet as biogeographic indicators for subantarctic Ectemnorhinini (Coleoptera: Curculionidae)

Abstract

Most of the species in the Ectemnorhinin are cryptogam feeders, angiosperm feeders representing a minority. It is hypothesized that this dearth of angiosperm feeders is due to previous climatic conditions, which precluded angiosperm herbivory, but allowed for the exploitation of a diverse cryptogamic flora, and that only with the post-glacial warm-up of the Subantarctic has angiosperm herbivory become possible. When examined in the light of the Quaternary history of the South Indian Ocean Province islands, evidence obtained from a study of the habitat use, diet and morphology of species within the tribe supports this hypothesis.

Habitat Specificity of Mites on Sub-Antarctic Marion Island

“…Higher altitude areas tend to be dominated by typically Antarctic fellÞeld, or wind desert areas, while the lowlands have closed, tundra-like vegetation (Gremmen 1981, Bergstrom and. On the basis of their histories, and lack of vascular vegetation, Chown (1989) grouped these fellÞeld habitats and the rocky shoreline areas characteristic of most of these islands (e.g., de Villiers 1976, Knox 1994) into a single, Ôepi-lithicÕ biotope. The habitats constituting this biotope are thought to have been continually present, even during the Neogene glacial maxima, when many of the islands had a substantial ice cover (Hall 1990, Chown 1994, Bergstrom and Chown 1999.…”

“…However, the extent of these habitats is thought to have varied in concert with climatic ßuctuations. However, the hab-itats characterized by vascular plants (i.e., those of the ÔvegetatedÕ biotope, Chown 1989) are thought to have been largely absent at the height of the Neogene glaciations, but more extensive during interglacial periods. In a few instances, vascular species such as those in the genera Lyallia and Azorella may have been present at the glacial maxima (Schalke and Van Zinderen Bakker 1971, Young and SchoÞeld 1973, Scott 1985.…”

Pachnobium dreuxin. g., n. sp., ses occurrences modernes et fossiles sur l’archipel Crozet (Coléoptère Curculionidae Ectemnorrhininae)

“…Selon le principe d'actualisme, les variations d'abondance des taxons dont l'écologie actuelle est connue permettent de reconstituer les environnements passés à une époque donnée. Ainsi, les espèces de charançons du genre Dusmoecetes Jeannel, connues pour être des consommatrices de plantes vasculaires, se trouvent dans des milieux riches en végétation (Chown 1989), comme les zones tourbeuses et les pentes à taux de recouvrement végétal élevé. De même, le staphylin Antarctotachinus crozetensis Enderlein est cité du même habitat que les taxons précédents (Davies 1973).…”

“…À l'inverse, Xanium vanheoff enianum Enderlein est un consommateur de cryptogames. On le trouve sous les pierres, dans les zones à faible couverture végétale, comme le «fellfi eld», zone pierreuse à végétation très clairsemée au-dessus de 100 m d'altitude (Chown 1989). Ces taxons sont donc de bons indicateurs des conditions écologiques passées, et les changements dans la composition des assemblages d'insectes au cours du temps sont un indice des changements environnementaux qui se sont succédés au cours de la période couvertes par la séquence sédimentaire.…”

Conclusion: change in terrestrial and marine systems

“…Early work (e.g. Chown 1989Chown , 1990a suggested that a major evolutionary signal in the insects, both on the Prince Edward Islands and on the other South Indian Ocean Province Islands, is a clear division between the eplithic (coastal, fellfield, rockface) and the vegetated (lowland vegetation communities) biotopes. The former biotope is home to speciose assemblages, which are thought to have survived and in some cases speciated during Quaternary glacial events, and whose species are reasonably habitat specific.…”