The influence of physical factors and ornithogenic products on plant and arthropod abundance at an Inland Nunatak group in Antarctica

Summary

Robertskollen is a group of geologically similar nunataks in western Dronning Maud Land, Antarctica, with breeding colonies of snow petrels Pagodroma nivea at some of the nunataks. Transects determining macro-plant structure and cover were conducted along an a priori determined bird-influence gradient to assess the relative importance of ornithogenic products and physical factors on plant assemblages. Fine-scale (intra-transect) dispersion patterns of plants were determined primarily by physical factors affecting water availability (i.e. the amount of drift-snow available and the effects of shelter and shade on evaporation rates). Coarse-scale (inter-transect) analysis of plant dispersion patterns, however, showed significant responses along the bird-influence gradient, with consistent responses between nunataks. Plant cover was directly related to bird-influence, but was depressed within bird colonies, apparently due to excessive nutrient enrichment. Mites (Acari) were the only arthropods recorded at Robertskollen and total mite abundance was related to plant cover, although specific responses varied. Thallus diameters of the abundant lichen Umbilicaria decussata decreased with decreasing bird influence, suggesting that nutrients limit plant growth away from bird colonies. Soil concentrations of major plant nutrients, N, P and K, were significantly greater close to bird colonies. We conclude that nutrients in ornithogenic products have direct causal effects on the abundance and dispersion of the biota of inland Antarctic nunataks, and that the effects of nutrient enrichment are detectable at different spatial scales from the effects of physical factors.