Abstract
Disturbances can negatively affect multiple levels of biological organization. With human activities increasing the intensity of disturbance regimes, we need to understand when and where adverse effects of disturbance occur. Yet, how landscape heterogeneity (i.e., variation in local resource availability and meta-ecosystem resource flows) mediates the effects of disturbances remains poorly understood, despite the frequent occurrence of connected meta-ecosystems in nature. In this study, we assessed how disturbance intensity affects biomass (here: summed bio-area of all individuals in the community) and community dynamics of freshwater protist communities in connected ecosystems. We used highly replicated experimental microcosms to simulate two-patch meta-ecosystems varying in local resource availability (low versus high carbon release) and meta-ecosystem subsidy flow (movement of detritus and inorganic nutrients). We expected that a high-quantity flow of allochthonous subsidies would stabilize receiving communities in their response to disturbance and thus mitigate the negative effects of disturbance on community dynamics, but only when local resource availability was low. We found that the effects of disturbance depended on local resource availability and meta-ecosystem subsidy flow in our experiment. Irrespective of subsidy flow, high-resource ecosystems were unaffected by disturbance, resulting in overall higher community biomass of protist communities. In contrast, low-resource ecosystems showed a strong biomass decline in response to increased disturbance. These negative effects were partly mitigated when low-resource ecosystems received subsidy flow from a high-resource ecosystem. Our proof-of-concept approach confirms that the effects of disturbance can be context dependent. Including spatial heterogeneity in local resource availability and cross-ecosystem subsidy flow may be essential for understanding disturbance effects on communities. Further consideration of these factors is needed in management aiming to mitigate disturbances in natural ecosystems.