One of the interesting things about the theory of population extinction is that despite widely differing processes for the cause of extinction (demographic stochasticity, environmental variability, environmental deterioration, extreme catastrophic events), virtually all models predict there to be a positive monotonic relationship between initial population size and extinction time. Although this is clearly a testable prediction, attempts at empirical demonstration have been equivocal. We hypothesized that this anomaly is due to the transient properties of ensembles of populations, such that many populations escape their initially vulnerable state to achieve a condition referred to as “quasi-stationarity” where effects of initial conditions are erased. It follows that extinction of populations initialized far from quasi-stationarity are exposed to a two-phase extinction hazard. We tested this prediction with experiments using Daphnia magna. Although observed results were subtle, statistical analysis showed that indeed a switch occurred so that early on in the experiment the extinction hazard was primarily due to the initial condition, whereas later the primary determinant of extinction time was habitat size. This result is potentially useful to understanding how and why extinctions occur in small populations in nature.
- Drake, J.M., J. Shapiro & B.D. Griffen. 2011. Experimental demonstration of a two-phase extinction hazard. Journal of the Royal Society Interface 63:1472-1479.