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

Abstract

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 two Dusmoecetes species indigenous to Marion Island. The approximate digestibility of Blepharidophyllum densifolium (Scapaniaceae) energy and dry mass were similar for D.marioni Jeannel adults at 5°C and at 10°C. D.similis (C. O. Waterhouse) adults fed Azorella selago Hook (Apiaceae) leaves also had similar AD for food dry mass and energy at 5°C and at 10°C. However, the performance of D.similis on A.selago leaves and flowers at 5°C was better than that of D.marioni on 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, although D.similis does not feed on Acaena 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.