Ecological processes influencing the composition of subtidal marine hard-substrate communities

摘要

Ecological community composition is driven by complex processes which often operate simultaneously. Unravelling the mechanisms generating both small- and large-scale patterns in ecology remains a key challenge for ecologists. Of critical importance for ecology is the need to gather empirical data, to rigorously test long-standing ecological theories and inform their context specificity.The Biotic Interactions Hypothesis (BIH) proposes that biotic interactions, such as consumer pressure, vary along an environmental gradient and are stronger towards the tropics. Large consumer access to sessile communities was manipulated in a replicated exclusion study along the east coast of Australia. Contrary to the historical opinion, andin line with recent studies, consumers were generally no more important at low latitudes to sessile hard-substrate community diversity, evenness and richness. Another longstanding and intensely debated ecological theory is The Dynamic Equilibrium Model (DEM), which extends the Intermediate Disturbance Hypothesis by predicting a shifting position of peak diversity along a gradient of disturbance depending on the underlying productivity of the system. To examine the DEM, communities were repeatedly subjected to an experimental gradient of physical disturbance at multiple locations along the east coast of Australia. The results of this study partially supported the DEM, with evidence of positive disturbance-diversity relationships at low latitudes and negative disturbance-diversity relationships at high latitudes. Following disturbance, the identity of successful early colonists can determine the subsequent trajectory of community assembly. Recolonisation patterns of three solitary and three colonial groups were examined along a gradient of disturbance area at multiple time points and sites. The disturbance area-recolonisation relationship in these sessile invertebrate communities was highly variable among taxa, times and sites. Whilst disturbances that change resource availability are recognised as ecologically significant, the provision and characteristics of physical habitats at the local-scale also needs to be incorporated into ecological models. Through experimental manipulation of initial substrate complexity, using turfing algae mimics, this study found sessile invertebrates and mobile epibiota responded strongly, but in opposite directions, to habitat complexity. This thesis highlights the necessity of exploring the multiple ecological mechanisms which can influence communities through use of experimental manipulations conducted on appropriate scales.