Comparative nutritional ecology of bryophyte and angiosperm feeders in a sub‐Antarctic weevil species complex (Coleoptera: Curculionidae)

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Abstract
Highly productive and st,ructurally diverse angiosperm communities occur on sub‐Antarctic Marion Island, yet cryptogams are the main source of energy and nutrients for five of the six native weevil species (Curculionidae: Ectemnorhinini) that occur there. Previously it has been hypothesized that low‐temperature regimes, during the Pleistocene, precluded angiosperm herbivory. This hypothesis was based,inter alia, on the assumption that at low temperatures feeding on bryophytes is more nutritionally advantageous than feeding on vascular plants. This assumption was tested by comparing the consumption rate (CR) and approximate digestibility (AD) (mass and energy) of bryophytes and angiosperms in twoDusmoecetesspecies indigenous to Marion Island. The approximate digestibility ofBlepharidophyllum densifolium(Scapaniaceae) energy and dry mass were similar forD.marioniJeannel adults at 5°C and at 10°C.D.similis(C. O. Waterhouse) adults fedAzorella selagoHook (Apiaceae) leaves also had similar AD for food dry mass and energy at 5°C and at 10°C. However, the performance ofD.similisonA.selagoleaves and flowers at 5°C was better than that ofD.marionion bryophytes at both temperatures. Bryophyte feeding does not appear to be nutritionally more advantageous at low temperatures in the sub‐Antarctic, nor does angiosperm herbivory appear to be comparatively disadvantageous at low temperatures, althoughD.similisdoes not feed onAcaena magellanica(Lam.) (Rosaceae) at 5°C. It seems likely that moss‐feeding evolved in response to an absence of angiosperms during glacial periods, rather than because of a nutritional advantage associated with bryophagy at low temperatures.