Regime shifts and hysteresis in the pitcher-plant microecosystem

Abstract

Changes in environmental conditions can lead to rapid shifts in ecosystem state ("regime shifts"), which subsequently returns slowly to the previous state ("hysteresis"). Large spatial and temporal scales of dynamics, and the lack of frameworks linking observations to models, are challenges to understanding and predicting ecosystem responses to perturbations. The naturally-occurring microecosystem inside leaves of the northern pitcher plant (Sarracenia purpurea) exhibits oligotrophic and eutrophic states that can be induced by adding insect "prey." Here, we further develop a model for simulating these dynamics, parameterize it using data from a prey addition experiment and conduct a sensitivity analysis to identify critical zones within the parameter space. Simulations illustrate that the microecosystem model displays regime shifts and hysteresis. Parallel results were observed in the plant itself after experimental enrichment with prey. Decomposition rate of prey was the main driver of system dynamics, including the time the system remains in an anoxic state and the rate of return to an oxygenated state. Biological oxygen demand influenced the shape of the system's return trajectory. The combination of simulated results, sensitivity analysis and use of empirical results to parameterize the model more precisely demonstrates that the Sarracenia microecosystem model displays behaviors qualitatively

Experimental support for alternative attractors on coral reefs

“…For example, Sirota et al (42) varied the amount of prey (organic matter) that entered the aquatic microecosystem that forms in the leaves of a carnivorous pitcher plant, and found that a modest enrichment of food induced a sudden transition of the pool from the initial aerobic state to an anaerobic state. Although subsequent modeling suggests the presence of hysteresis in this system (67), there was not an empirical test for discontinuity in the driver–response relationship by also evaluating whether the threshold for the pool to switch back to the aerobic state occurred at the same or lower level of enrichment as the switch to the anaerobic condition. Here, we tested explicitly for such initial state dependence of the driver–response relationship.…”

Ecosystem tipping points in an evolving world

“…increasing productivity, increasing mortality) to observe when the system transitions to a new state [48][49][50] . To test for hysteresis in the system, the environmental condition can then be reversed while tracking system recovery to the initial state 45,51 .…”

Diverse microbial communities hosted by the model carnivorous pitcher plant Sarracenia purpurea: analysis of both bacterial and eukaryotic composition across distinct host plant populations

“…Recent studies have linked enzyme activity to bacterial functions in nutrient cycling within S. purpurea pitchers (Luciano & Newell, 2017; Bittleston et al, 2018; Young, Sielicki & Grothjan, 2018). However, despite studies of bacterial diversity, characterization of bacterial enzyme functions, the critical importance of bacteria in prey digestion and thus carbon and nutrient supply to the food web, bacteria have only recently been considered as more than a ‘black box’ in food web models (Lau et al, 2018). It is unknown if the microbial functions of the pitcher plant detrital food web are similar to or distinct from other aquatic ecosystems.…”