Erosion of compensatory processes and the loss of resistance to climate variability

Communities persist via processes that counter (resistance) or recover from disturbance (resilience). Where communities resist disturbance, compensatory mechanisms can absorb the effects of disturbance so that no overall... [ view full abstract ]

Communities persist via processes that counter (resistance) or recover from disturbance (resilience). Where communities resist disturbance, compensatory mechanisms can absorb the effects of disturbance so that no overall structural change occurs. Whilst compensatory processes increase in strength to counter the net effects of multiple disturbances, we have limited understanding of how compensatory processes may respond to extreme short-term disturbance events. Using a model kelp forest system, we assess the strength of compensatory responses to heatwaves under both contemporary and near-future ocean warming and acidification. In this system, gastropod grazers compensated for increased expansion of algal turfs under accumulating disturbances, except under heatwaves in a warmer ocean. These latter conditions stimulated the greatest rates of expansion of turfs, but strongly suppressed consumption so that herbivores were unable to counter the ecological effects of the extreme event. Whilst communities show some degree of resistance to future disturbance, extreme events may erode compensation where the pace and size of environmental change is greater than what compensatory processes can absorb. Such abrupt failure of compensation may account for the surprisingly rapid shifts of communities to contrasting states.