Legacy effects and memory loss: how contingencies moderate the response of rocky intertidal biofilms to present and past extreme events

Abstract

Understanding how historical processes modulate the response of ecosystems to perturbations is becoming increasingly important. In contrast to the growing interest in projecting biodiversity and ecosystem functioning under future climate scenarios, how legacy effects originating from historical conditions drive change in ecosystems remains largely unexplored. Using experiments in combination with stochastic antecedent modelling, we evaluated how extreme warming, sediment deposition and grazing events modulated the ecological memory of rocky intertidal epilithic microphytobenthos (EMPB). We found memory effects in the non-clustered scenario of disturbance (60 days apart), where EMPB biomass fluctuated in time, but not under clustered disturbances (15 days apart), where EMPB biomass was consistently low. A massive grazing event impacted on EMPB biomass in a second run of the experiment, also muting ecological memory. Our results provide empirical support to the theoretical expectation that stochastic fluctuations promote ecological memory, but also show that contingencies may lead to memory loss.

Temporal clustering of extreme climate events drives a regime shift in rocky intertidal biofilms

“…Based on the results of a previous study (Dal Bello et al. ), we anticipate that the vegetated state would correspond to the biomass in the controls, while the semi‐bare state would reflect reduced biofilm biomass in the clustered perturbation scenario. This is expected because extreme events clustered in time may push the system below a threshold biomass value, impairing the ability of biofilm to recover to the vegetated state.…”

“…During the experiment, however, grazing pressure over biofilm assemblages was nearly absent (Dal Bello et al. ).…”

“…, Dal Bello et al. ). Although alterations of disturbance scenarios are already receiving a great amount of attention in the ecological literature, how variation in the regime of pulse perturbations affects regime shifts has been largely neglected.…”

“…, Dal Bello et al. ). We used photosynthetic biofilms primarily because it is a tractable system for field experiments, being the result of the activity of fast‐growing organisms, which display rapid responses to perturbations (Christofoletti et al.…”

“…Moreover, recent studies showed that changes in the temporal clustering of extreme events, that is the degree of separation between consecutive instances, can modulate ecological memory of microbial assemblages (Dal Bello et al. ) and regulate the onset of regime shifts in tropical ecosystems (Holmgren et al. ).…”