Distinguishing random environmental fluctuations from ecological catastrophes for the North Pacific Ocean

Abstract

The prospect of rapid dynamic changes in the environment is a pressing concern that has profound management and public policy implications. Worries over sudden climate change and irreversible changes in ecosystems are rooted in the potential that nonlinear systems have for complex and 'pathological' behaviours. Nonlinear behaviours have been shown in model systems and in some natural systems, but their occurrence in large-scale marine environments remains controversial. Here we show that time series observations of key physical variables for the North Pacific Ocean that seem to show these behaviours are not deterministically nonlinear, and are best described as linear stochastic. In contrast, we find that time series for biological variables having similar properties exhibit a low-dimensional nonlinear signature. To our knowledge, this is the first direct test for nonlinearity in large-scale physical and biological data for the marine environment. These results address a continuing debate over the origin of rapid shifts in certain key marine observations as coming from essentially stochastic processes or from dominant nonlinear mechanisms. Our measurements suggest that large-scale marine ecosystems are dynamically nonlinear, and as such have the capacity for dramatic change in response to stochastic fluctuations in basin-scale physical states.

Contingencies and compounded rare perturbations dictate sudden distributional shifts during periods of gradual climate change

“…Conversely, punctuated ecological change may be the result of sudden changes in forcing agents (e.g., climatic regime shifts) or the effects of gradual or stochastic changes that periodically, either acting independently or together, exceed some critical threshold or ''tipping point.'' In the case of tipping points, ecological change is rapid, temporally nonlinear, and difficult to anticipate, even when the underlying climatic change is gradual and temporally linear (5,6). Evidence for the importance of tipping points has been accumulating in a wide range of ecological systems and in organisms ranging from diatoms to copepods to salmon (6), and tipping points are often well described in ecological models (e.g., ref.…”

“…In the case of tipping points, ecological change is rapid, temporally nonlinear, and difficult to anticipate, even when the underlying climatic change is gradual and temporally linear (5,6). Evidence for the importance of tipping points has been accumulating in a wide range of ecological systems and in organisms ranging from diatoms to copepods to salmon (6), and tipping points are often well described in ecological models (e.g., ref. 7).…”

Wavelet analysis of correlation among Canary Islands octopus captures per unit effort, sea-surface temperatures and the North Atlantic Oscillation

“…The main requirement of many statistical tools for time series analysis (e.g., Fourier analysis) is stationarity (Priestley, 1981). However, environmental time series do not always satisfy this requirement, and growing evidence supports the need to consider the importance of transient dynamics in environmental process (Stenseth et al, 1998;Hsieh et al, 2005;Cazelles et al, 2008;Rouyer et al, 2008).…”

“…A simple approach to study environmental processes is to consider them as linear and stationary, although, non-linear, nonstationary, and multi-scale processes are the rule rather than the exception (Hsieh et al, 2005;Rouyer et al, 2008). The main requirement of many statistical tools for time series analysis (e.g., Fourier analysis) is stationarity (Priestley, 1981).…”

Anoxic sediments off Central Peru record interannual to multidecadal changes of climate and upwelling ecosystem during the last two centuries

“…Decadal variability may also modulate the frequency, intensity and timing of the ENSO cycle (Wang and 2004). These low frequency changes in the physical environment can result in large non-linear "regime shifts" in marine ecosystem structure in the Pacific Basin (Mantua and Hare, 2002;Schwartzlose et al, 1999;Hsieh et al, 2005). Within the HCE , two "anchovy regimes" (from the start of the fisheries until early 70s, and from early 90's until present) separated by a "sardine regime" (from mid 70's until early 90's) have been proposed (Chávez et al, 2003;Alheit andÑiquen, 2004).…”