Catchment conversion to agriculture alters freshwater macroinvertebrate community responses to flow disturbance: results from a replicated in‐stream experiment

Anthropogenic stressors often co‐occur in ecosystems, but their combined impacts are rarely assessed using field experiments. Press disturbances particularly can reshape community dynamics, altering their capacity to withstand or recover from acute pulse disturbances by modifying response diversity. We assessed macroinvertebrate responses to co‐occurring anthropogenic disturbances by manipulating streamflow in eight Tasmanian streams along a gradient of upstream catchment conversion to agriculture (0–45%). Temporary half‐weirs created high‐ and low‐flow reaches, simulating pulse disturbances. Chao's species richness declined, and community composition was altered in sites with 0% agricultural conversion, but these recovered once normal base flows were restored. In comparison, under reduced flows, there was no change in Chao's species richness in sites with 33–45% agricultural conversion, but community composition was altered, with recovery indicated once base flows were restored. Under low flows in forested streams, response‐trait diversity declined but under higher proportions of agricultural conversion, response‐trait diversity declined minimally. Some single traits declined within high‐flow reaches only to recover after baseflow restoration. Catchment conversion to agriculture altered stream community response diversity, leading to differential responses to flow changes. Although agricultural land‐use altered the ability of communities to respond to pulse disturbances, the presence and direction of change for some treatments would have been difficult to predict a priori. Combined press‐ and pulse‐disturbances altered communities more than independently acting disturbances but the press disturbance (max 45% catchment area) was too weak to prevent recovery.