The dynamics of mountain rock pools – Are aquatic and terrestrial habitats alternative stable states?

The theory of alternative stable states (ASS) proposes that ecosystems can exhibit multiple equilibria stabilised by positive feedback mechanisms. There are signs that terrestrial and aquatic habitats could exhibit ASS and we investigate this possibility in eroded basins on an isolated rock outcrop. The coverage of terrestrial and aquatic habitats on the Korannaberg Mountain in South Africa was quantified using GIS for three intervals between 1993 and 2011. Results confirmed that the proportional coverage of habitat states showed a consistent bimodal distribution over the study period, thereby supporting the ASS hypothesis. The depth of geological basins and the distance from the exposed cliff face were significantly associated with the proportion of aquatic habitat within the basins. These patterns were interpreted by hypothetical feedback mechanisms driven by basin inundation and wind erosion. Findings supported dual responses of habitat classes to basin parameters; a phenomenon often associated with ASS. Stability of aquatic and terrestrial habitats and the differential responses of these habitats to similar combinations of system parameters oppose the succession hypothesis and support the ASS hypothesis. These findings are consistent with unique diversity patterns demonstrated by previous studies and further justify the use of rock pools and vegetation patches as natural models in ecology and evolutionary biology research.