key: cord-103294-1lrfna4v
authors: Northrop, Amanda C.; Avalone, Vanessa; Ellison, Aaron M.; Ballif, Bryan A.; Gotelli, Nicholas J.
title: Clockwise and counterclockwise hysteresis characterize state changes in the same aquatic ecosystem
date: 2020-05-02
journal: bioRxiv
DOI: 10.1101/2020.05.01.073239
sha: 
doc_id: 103294
cord_uid: 1lrfna4v

Incremental increases in a driver variable, such as nutrients or detritus, can trigger abrupt shifts in aquatic ecosys-tems. Once these ecosystems change state, a simple reduction in the driver variable may not return them to their original state. Because of the long time scales involved, we still have a poor understanding of the dynamics of ecosys-tem recovery after a state change. A model system for understanding ecosystem recovery is the aquatic microecosystem that inhabits the cup-shaped leaves of the pitcher plant Sarracenia purpurea. With enrichment of organic matter, this system flips within 1 to 3 days from an oxygen-rich state to an oxygen-poor (hypoxic) state. In a replicated green-house experiment, we enriched pitcher plant leaves at different rates with bovine serum albumin (BSA), a molecular substitute for detritus. Changes in dissolved oxygen ([O2]) and undigested BSA concentration were monitored during enrichment and recovery phases. At low enrichment rates, ecosystems showed a substantial lag in the recovery of [O2] (clockwise hysteresis). At intermediate enrichment rates, [O2] tracked the levels of undigested BSA with the same profile during the enrichment and recovery phases (no hysteresis). At high enrichment rates, we observed a novel response: changes in [O2] were proportionally larger during the recovery phase than during the enrichment phase (counter-clockwise hysteresis). These experiments demonstrate that detrital enrichment rate can modulate a diversity of hysteretic responses in a single aquatic ecosystem. With counter-clockwise hysteresis, rapid reduction of a driver variable following high enrichment rates may be a viable restoration strategy.

matter to pitchers causes an abrupt increase in BOD resulting from decomposition 22, 32 by carbon-limited 33 bacteria. Pitchers 99 in all enrichment treatments saw an rapid decline in [O 2 ] following the initial enrichment phase, suggesting that BOD in-100 creased rapidly (Fig. 2) . This rapid change in BOD may have contributed to clockwise hysteresis at low levels of enrichment, 101 but doesn't account for the counterclockwise hysteresis at high enrichment levels. In other systems, clockwise hysteresis is 102 generally the result of positive feedback loops 34 .

shallow lakes, a simple reduction in phosphorus input does not lead to a proportional recovery in macrophyte cover 10 or 105 community structure 12 . Further, these communities do not fully recover in the time frames in which they are studied 12 106 and may effectively remain permanently degraded. These examples and our work highlight the importance of applying a 107 dynamic regime concept 35 to ecosystem management and restoration. Such an approach would include testing for hysteresis, 108 characterizing feedbacks that maintain undesirable regimes, and identifying if and how system variables change as a result of 109 a regime shift 36 .

In ecosystems where hysteresis is counter-clockwise, rapid reduction in a driver variable from high to low levels may be 111 a successful restoration strategy. In contrast, systems that have experienced chronic low-levels of enrichment may exhibit 112 clockwise hysteresis that requires more extreme reductions of the driver variable, or alternative restoration strategies 36 , to 113 restore. Although there is still an important need for early warning signals, past histories of high versus low enrichment may 114 dictate different restoration strategies for collapsed ecosystems. 

Efficiency of insect capture by sarracenia purpurea (sarraceniaceae), the northern pitcher plant

Preparation and purification of DNA from insects for AFLP analysis