Analysis of abrupt transitions in ecological systems

Mark D Ohman,Russell J Schmitt,Debra P C Peters,Kristen B Gorman,Finn C Pillsbury,Sapna Sharma,Brandon T Bestelmeyer,Christine M Laney,Andrew Rassweiler,Sally J Holbrook,Aaron M Ellison,William R Fraser

doi:10.1890/es11-00216.1

Abstract

The occurrence and causes of abrupt transitions, thresholds, or regime shifts between ecosystem states are of great concern and the likelihood of such transitions is increasing for many ecological systems. General understanding of abrupt transitions has been advanced by theory, but hindered by the lack of a common, accessible, and data-driven approach to characterizing them. We apply such an approach to 30–60 years of data on environmental drivers, biological responses, and associated evidence from pelagic ocean, coastal benthic, polar marine, and semi-arid grassland ecosystems. Our analyses revealed one case in which the response (krill abundance) linearly tracked abrupt changes in the driver (Pacific Decadal Oscillation), but abrupt transitions detected in the three other cases (sea cucumber abundance, penguin abundance, and black grama grass production) exhibited hysteretic relationships with drivers (wave intensity, sea-ice duration, and amounts of monsoonal rainfall, respectively) through a variety of response mechanisms. The use of a common approach across these case studies illustrates that: the utility of leading indicators is often limited and can depend on the abruptness of a transition relative to the lifespan of responsive organisms and observation intervals; information on spatiotemporal context is useful for comparing transitions; and ancillary information from associated experiments and observations aids interpretation of response-driver relationships. The understanding of abrupt transitions offered by this approach provides information that can be used to manage state changes and underscores the utility of long-term observations in multiple sentinel sites across a variety of ecosystems.

Highlights

Many ecological systems can exist in two or more states that differ in abundance or composition of species, rates of ecological processes, and ecosystem services provided by them (Beisner et al 2003, Suding et al 2004)
Data collected within the California Current System (CCS) provide an example of abrupt transitions with a linear tracking mechanism (Fig. 3)
These case studies illustrate that abrupt transitions and state changes can be identified, and can be understood via a suite of general concepts (Fig. 1) and relatively simple methods

Summary

Introduction

Many ecological systems can exist in two or more states that differ in abundance or composition of species, rates of ecological processes, and ecosystem services provided by them (Beisner et al 2003, Suding et al 2004). Gradual transitions between ecosystem states are unremarkable, occurring during succession or as ecosystems track gradually changing environmental conditions. Abrupt transitions between ecosystem states are typically unexpected and can have wide-ranging, negative impacts. Abrupt transitions happen either when the gradually changing environment passes a critical point or when discrete perturbations cause sudden changes in underlying environmental drivers. Abrupt and irreversible transitions are forecast to increase as climatic changes and depletion of natural resources both accelerate (Millennium Ecosystem Assessment 2005, Fagre et al 2009). Such forecasting, is difficult because there are many different causes of state changes (Hastings and Wysham 2010)

Methods

Results

Conclusion