Tyler James Butts , Robert A Johnson, Michael Weber, Grace Marie Wilkinson 

   Food web structure may mediate the resistance and resilience of ecosystems to increasingly frequent and intense disturbances driven by climate change. In aquatic ecosystems, greater food web complexity is theorized to generate more pathways for nutrients and energy to flow as well as strengthen top-down control. As such, we predicted greater food web complexity would increase the resistance (longer response time) and resilience (shorter recovery time) of aquatic primary production to pulse disturbances and reduce the chance of a critical transition (passing a threshold). To test this prediction, we experimentally simulated two storm-induced pulse disturbances by adding N and P (~3% and ~5% increase in ambient concentrations) to three ponds with food webs of low, intermediate, and high complexity and compared to three reference ponds with matching food web structures. We evaluated the primary production response time (resistance) and recovery time (resilience) following each nutrient pulse using a response detection algorithm and evaluated evidence of a critical transition with online dynamic linear modeling (resilience). Chlorophyll-a concentrations never exceeded the response threshold in the high complexity pond following either nutrient pulse whereas the threshold was exceeded after 18 days in the intermediate and 24 days in the low complexity ponds following the first pulse. There was evidence of a critical transition in the low complexity pond following the first pulse. After the second nutrient pulse, chlorophyll-a exceeded the response threshold again in both the low and intermediate ponds, but the response was 12 days faster in the low complexity pond compared to the intermediate complexity pond. Recovery time increased by 14 days after the second pulse in the low complexity pond and was on track for a faster recovery time in the intermediate pond before the end of the experiment. These results support our prediction that greater food web complexity confers greater resistance and resilience of phytoplankton to repeated pulses of nutrient loading. This experiment provides empirical support that biodiversity and food web structure can help buffer aquatic ecosystems to increasing and intensifying disturbances.