On signals of phase transitions in salmon population dynamics.
Critical slowing down (CSD) reflects the decline in resilience of equilibria near a bifurcation and may reveal early warning signals (EWS) of ecological phase transitions. We studied CSD in the recruitment dynamics of 120 stocks of three Pacific salmon (Oncorhynchus spp.) species in relation to critical transitions in fishery models. Pink salmon (Oncorhynchus gorbuscha) exhibited increased variability and autocorrelation in populations that had a growth parameter, r, close to zero, consistent with EWS of extinction. However, models and data for sockeye salmon (Oncorhynchus nerka) indicate that portfolio effects from heterogeneity in age-at-maturity may obscure EWS. Chum salmon (Oncorhynchus keta) show intermediate results. The data do not reveal EWS of Ricker-type bifurcations that cause oscillations and chaos at high r. These results not only provide empirical support for CSD in some ecological systems, but also indicate that portfolio effects of age structure may conceal EWS of some critical transitions.
Department of Ecology and Evolutionary Biology, University of Toronto, , 25 Willcocks St., Toronto, Ontario, Canada, , M5S 3B2, Department of Zoology, University of Otago, , 340 Great King Street, Dunedin 9016, New Zealand, Odum School of Ecology, University of Georgia, , 140 East Green Street, Athens, GA 30602-2202, USA, Department of Zoology, University of Oxford, , South Parks Road, Oxford OX1 3PS, UK.
Martin
M
Krkošek
John M
JM
Drake
D000818:Animals; D003247:Conservation of Natural Resources; D008954:Models, Biological; D017683:Oncorhynchus / Q000502:physiology*; D011157:Population Dynamics; D013045:Species Specificity
critical slowing down; early warning signals; phase transitions; portfolio effects; salmon; stochasticity