Spatial patterns in the microarthropod community associated with Azorella selago (Apiaceae) on the sub-Antarctic Prince Edward Islands

[摘要] ENGLISH ABSTRACT: The spatial distribution of animals and plants at different scales is a central theme inecology. Knowledge of biodiversity distribution is essential, especially with the currentthreat of climate change and invasion by alien species. Since the impact of climatechange and alien species will be, and has already been pronounced in polar regions,information on the current spatial distributions of biota in these regions is critical topredict the consequences of climate change and alien species on the future survival,distribution and abundance of indigenous biota. This study was conducted on the sub-Antarctic Prince Edward Islands (consisting of Marion Island and Prince Edward Island),which have experienced rapid climate changes over the past 50 years. Additionally, anumber of alien plant, vertebrate and invertebrate (also microarthropod) species havebeen introduced to these islands. Since microarthropods (mites and springtails) play anessential role in decomposition and mineralization of plant material on the islands, theloss of microarthropods from decomposer communities might have disastrous results forecosystem processes. Therefore it is essential to know the current distributions ofmicroarthropods in order to predict future distributions patterns in reaction to climatechange and invasive species. In this study, the spatial distribution of mites and springtailsinhabiting the cushion plant Azorella selago Hook, were examined at different scales ofobservation. Firstly, the microarthropod community was examined at a fine scale. Therelationship between microarthropod species richness and abundance and plant size,isolation, within-plant variability, grass cover and microclimate variables wereinvestigated. Thereafter, the spatial variability of microarthropod abundances wasexamined within stands of plants, with statistical methods using varying degrees oflocational information to determine if microarthropod abundance is random, regular oraggregated at this scale. Further, the spatial variability of microarthropod communities inA. selago at different altitudes and on different sides of Marion Island, i.e. island-widescale, was examined. The last scale of observation was the island-wide scale, in whichmicroarthropod assemblages were compared between Marion Island and Prince EdwardIsland, as well as in different plant species. Microarthropods showed spatialheterogeneity within A. selago plants (higher abundances in eastern and southern sides of plants), island-wide (lower springtail abundance on the eastern side of the island and athigh altitudes) and between islands (more alien species on Marion Island). In contrast,microarthropod abundance was not spatially heterogeneous within a stand of plants, i.e.mostly randomly distributed. The possible mechanisms responsible for these patternsdiffer between scales, and range from temperature and nutrient availability at the withinplant and island wide scale to alien species between islands. Climate change is likely toalter these distribution patterns of microarthropods, either directly (unfavourable climatefor indigenous species growth, development and dispersal) or indirectly (favouring alienmicroarthropod species; increase in grass cover on A. selago plants may alter communitystructure). The information presented here, is essential for predicting the possible impactsof climate change on microarthropods in fellfield ecosystems on sub-Antarctic islands.

[发布机构] Stellenbosch University