Greimler, Josef , López, Patricio , Reiter, Karl , Baeza, Marcelo , Peñailillo, Patricio , Gatica, Alejandro , Ruiz, Eduardo , Novoa, Patricio , Stuessy, Tod .
Assembly of the vegetation of the Robinson Crusoe Islands. What we know, and what we do not know.
We have investigated the vegetation of the Robinson Crusoe Islands based on nearly 200 releves and have produced two vegetation maps. These data, together with those collected ca. 100 years ago plus sediment core analysis on the island Alejandro Selkirk, allow some conclusions on vegetation dynamics in the late Quarternary (pre-human period) and the rapid changes since the first humans arrived on the archipelago in the 16th century. Regarding earlier stages of colonization and community assembly, we have only little and indirect evidence from phylogenetic analysis of endemic plants. There is ample room for speculation whether deterministic assembly or neutral assembly was more important. Classical niche concepts assume that community assembly should be neutral when competition is low in a friendly environment. Such conditions can be assumed in early stages of colonisation in oceanic islands, and we can therefore assume some neutrality in those early phases. Later on other stochastic (drift) or deterministic processes (selection) or both, e.g., in speciation by anagenesis or cladogenesis, act on the members of the establishing communities. Dispersal from a source area to the archipelago is probably a less severe filter for ferns as can be assumed from the distribution of some circumaustral lineages and the presence of an effective wind system. Ferns do play an important role in the extant vegetation of the archipelago and they were certainly among the first plants to colonize the islands. Within the angiosperms there are several species that show a high divergence from potential continental progenitors. Thus the progenitor of the endemic genus Robinsonia, which radiated into several species, and the two species of Myrceugenia that form forests on both islands may have been among the early colonizing angiosperms. It is, however, difficult to reconstruct the vegetation through the several million to hundred thousand years. The overall assemblage in the late Quarternary was probably not very different from what was there before the 16th century, with some shifting in dominance patterns due to climatic oscillations. Since then a dramatic change can be observed with an increase of the fern Histiopteris incisa indicating human disturbance as well as an increase in grasses (alien species added to the native flora) and alien herbaceous weeds that were not present before. The pattern of alien impact, however, differs widely between the two islands due to different geomorphology and levels of human intervention.
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1 - University of Vienna, Systematic and Evolutionary Botany, Rennweg 14, Vienna, Austria
2 - University of Vienna, Systematic and Evolutionary Botany, Rennweg 14, Vienna, A 1030, Austria
3 - University of Vienna, Department of Vegetation Ecology, Rennweg 14, Vienna, A 1030, Austria
4 - Universidad de Concepción, Departamento de Botánica, Concepción, Chile
5 - Universidad de Talca, Departamento de Biologia Vegetal y Biotecnologia, Talca, Chlie
6 - Universidad de Talca, Departamento de Biologia Vegetal y Biotecnologia, Talca, Chile
7 - Corporación Nacional Forestal, Jardin Botánico, Viña del Mar, Chile
8 - University Of Vienna, Systematic And Evolutionary Botany, Rennweg 14, Wien, N/A, A-1030, Austria, 43-1-427754140
Presentation Type: Oral Paper:Papers for Topics
Location: Franklin B/Hyatt
Date: Tuesday, July 10th, 2012
Time: 1:45 PM