Thresholds and Regime Shifts at Four LTER Sites (CCE, JRN, PAL, SBC) 1951-2009

The existence and causes of abrupt transitions, thresholds, or regime shifts between ecosystem states is of great concern because the likelihood of such transitions is predicted to increase. The science for measuring and responding to state changes, however, is not well developed. This limitation stems from a lack of data-supported case studies of abrupt transitions in all but a few well-studied ecosystems. We used 30-60 years of data on biological responses and putative drivers from ocean, coastal, polar, and dryland ecosystems to illustrate general approaches to analysis of abrupt transitions. The analyses indicate one case in which the state or response variable (krill abundance) tracked abrupt changes in the driver (Pacific Decadal Oscillation) in a linear fashion. Response variables in other cases (sea cucumber abundance, penguin abundance, and perennial grass production) exhibited hysteretic relationships to drivers (wave intensity, sea ice duration, and monsoonal rainfall amounts, respectively) through a variety of response mechanisms. The analyses illustrate that 1) a suite of common concepts and approaches can be used across disparate systems, 2) there are generally insufficient data for the use of leading indicators, particularly considering the abruptness of transition relative to the lifespan of long-lived organisms, 3) information on spatiotemporal context is useful for comparing transitions in similar systems, and 4) ancillary information from associated experiments and observations is critical for interpreting response-driver relationships.

生态系统状态间的突变转换、阈值效应及制度转移（regime shifts）的存在及其成因备受关注，因为此类转换发生的概率预计将有所上升。然而，用于监测与响应生态系统状态变化的相关科学体系尚未成熟完善。这一局限性源于：除少数已被充分研究的生态系统外，其余生态系统均缺乏基于数据支撑的突变转换案例研究。本研究采用了来自海洋、海岸、极地及旱地生态系统的、时长30至60年的生物响应数据与推定驱动因子数据，用以阐释突变转换分析的通用方法。分析结果显示，有一例中，状态变量或响应变量（磷虾丰度）以线性方式追踪驱动因子（太平洋年代际振荡（Pacific Decadal Oscillation））的突变变化。其余案例中的响应变量（海参丰度、企鹅丰度与多年生草本植物产量）则通过多种响应机制，与对应驱动因子（分别为波浪强度、海冰持续时长与季风降雨量）呈现滞后关联关系。本次分析表明：
1) 一系列通用的概念与方法可跨不同生态系统应用；
2) 总体而言，用于早期预警指标（leading indicators）分析的数据往往不足，尤其是考虑到相较于长寿生物的寿命而言，突变转换发生得十分迅速；
3) 时空背景相关信息可用于对比相似生态系统间的状态转换；
4) 来自相关实验与观测的辅助信息，对于阐释响应-驱动因子关联关系至关重要。