A quantitative framework for analysis of regime shifts in a Galápagos coastal lagoon

Abstract

Regime shifts are often used to describe sharp changes between two or more ecological states, each characterized by their own dynamics, stochastic fluctuations, or cycles. Ecological theory indicates they can occur either as a result of an abrupt environmental forcing (extrinsic regime shift), or be indicative of complex responses to local-scale dynamics and thresholds (intrinsic regime shift). One important area of ecological research is to develop quantitative tools to analyze regime shifts, but there are few studies that have applied these methods to the long-term ecological record. In this study, we introduce a framework to investigate regime shifts in diatom assemblages and mangrove ecosystem dynamics in a coastal lagoon from the Gala´pagos Islands over the past 2600 years. The framework integrates a set of established statistical methodologies for investigating regime shift dynamics in long-term ecological records. We use these methods to (1) identify the presence of regime shifts; (2) test for a series of hypothetical relationships (i.e., linear through to threshold) between ecological response and environment using nonlinear regression; and (3) investigate the relative importance of intrinsic and extrinsic dynamics in response to environmental perturbations. The transitions in the diatoms closely track the sequence of disturbance, recovery, and habitat shifts that have occurred in the lagoon over the past 2600 years, demonstrating extrinsic responses to environmental forcing. In contrast, the shift from a mangrove-to a microbial mat-dominated system ;945 cal yr BP provides potential evidence of an intrinsic regime shift. Our framework enables robust interpretations into the underlying dynamics of regime shifts in the paleoecological record and is widely applicable for investigating abrupt ecological changes in a range of systems.

Extrinsic vs. Intrinsic Regimes Shifts in Shallow Lakes: Long-Term Response of Cyanobacterial Blooms to Historical Catchment Phosphorus Loading and Climate Warming

“…Once historical cyanobacterial groups were identified based on the regression tree, we quantified the trends in echinenone concentration across the transition corresponding to the timing of the catchment P load index (from 1871 to 2001) and the observational temperature record by fitting linear, unimodal, threshold and sigmoidal models to both the environment (catchment P load index and mean annual temperature) and response (echinenone concentration) series using generalized nonlinear least squares regression (Seddon et al, 2014). The best model for each variable was then identified using the Akaike Information Criterion (AIC).…”

“…A common thread among recent studies of regime shifts is the idea that an ecosystem may experience nonlinear dynamics in response to either extrinsic or intrinsic processes (Seddon et al, 2014). An extrinsic shift will occur in response to an abrupt change in an environmental driver, similar to the "driver threshold" scenario outlined in Andersen et al (2009) and Randsalu-Wendrup et al (2016).…”

Late Holocene regime shifts in moorland ecosystems: high resolution data from the Pennines, UK

“…Quantitative approaches are increasingly used to assess regime shifts (Scheffer et al 2009) and are also being applied to palaeoenvironmental data (Seddon et al 2014;Streeter and Dugmore 2014). However, rigorous data demands mean that a statistical approach will not be applicable to all datasets.…”

Simultaneous abrupt shifts in hydrology and fish assemblage structure in a floodplain lake in the central Amazon

“…1a, study area description is presented in the supplementary Material and Methods). We applied a statistical procedure25 that detects abrupt shifts and correspondence in paired time-series data (i.e., hydrology vs. fish assemblage structure), estimates response functions of shifts, and indicates whether shifts resulted from external or internal drivers.…”