Priority effects, taxonomic resolution, and the prediction of variable patterns of colonisation of algae in littoral rock pools

This study focuses on succession of macroalgae in littoral rock pools on th e west coast of Italy. Previous studies in this system indicated that eithe r canopy algae or turf-forming algae may dominate fate in succession. Prior ity effects and non-hierarchical interactions have been proposed as possibl e explanations for these patterns. From previous knowledge on the timing of reproduction and recruitment of the two groups of algae and their interact ions, I predicted that: (1) canopy algae would dominate patches of substrat um cleared during their main period of recruitment (between April and July) ; (2) the turf-forming algae, although initially present, would be replaced by canopies in these patches; (3) turf-forming algae would characterise bo th the early stages of colonisation and the mature assemblage in patches cl eared before or after the main period of recruitment of canopy algae, and ( 4) succession would be more consistent in space (i.e. canalised) in the pre sence of canopy algae than when the turf-forming plants achieve dominance. These predictions were tested in a multifactorial experiment where patches of substratum were cleared in three different periods (before, during and a fter the main period of recruitment of canopy algae), on three dates within each period and in two replicate pools in each date. Univariate and multiv ariate analyses indicated that variability at early stages of colonisation dictated much of the subsequent dynamics in this system. Predictions 1-3 we re supported by the results, but only at a gross level of taxonomic resolut ion Patterns of colonisation of individual species of turf-forming algae we re unpredictable due to large small-scale spatial and temporal variation in abundance. Prediction 4 was not supported by the results. This study indic ated that knowledge of the life-histories and ecology of individual populat ions is crucial to increase the accuracy and precision of ecological models that attempt to predict succession in variable systems.