Trade-off between competition and facilitation defines gap colonisation in mountains
Faculty of Sciences. Biology
Oxford :Oxford Journals on behalf of the Annals of Botany Company
AoB plants / Annals of Botany Company. - Oxford, 2009, currens
, 13 p.
University of Antwerp
Recent experimental observations show that gap colonisation in small-stature (e.g. grassland and dwarf shrubs) vegetation strongly depends on the abiotic conditions within them. At the same time, within-gap variation in biotic interactions such as competition and facilitation, caused by distance to the gap edge, would affect coloniser performance, but a theoretical framework to explore such patterns is missing. Here we model how competition, facilitation and environmental conditions together determine the small-scale patterns of gap colonisation along a cold gradient in mountains, by simulating coloniser survival in gaps of various sizes. Our model adds another dimension to the known effects of biotic interactions along a stress gradient by focussing on the trade-off between competition and facilitation in the within-gap environment. We show that this trade-off defines a peak in coloniser survival at a specific distance from the gap edge, which progressively shifts closer to the edge as the environment gets colder, ultimately leaving a large part of large gaps unsuitable for colonisation in facilitation-dominated systems. This is reinforced when vegetation size and temperature amelioration are manipulated simultaneously with temperature in order to simulate an elevational gradient more realistically. Interestingly, all other conditions being equal, the magnitude of the realised survival peak was always lower in large than in small gaps, making large gaps harder to colonise. The model is relevant to predict effects of non-native plant invasions and climate warming on colonisation processes in mountains.