Experimental separation of genetic and demographic factors on extinction risk in free-living populations of an exploited species

Background/Question/Methods

Understanding the roles of key processes governing species extinction is essential for implementing strategies to conserve biodiversity, but studying these is challenging.  When populations reach small sizes, genetic (inbreeding depression, genetic drift) and ecological (demographic stochasticity, Allee effects, environmental fluctuation) processes may create an extinction risk vortex.  The relative contribution of these processes to extinction in wild populations is unknown, but has important implications for how endangered species are managed.  We established experimental field populations of a harvested kelp, the sea palm Postelsia palmaeformis, in which we independently varied initial genetic diversity (completely inbred, control, outbred) and population size, and monitored subsequent extinction rates over 12 years.

Results/Conclusions

Ecological processes dominated the risk of extinction, whereas genetic effects were weak and statistically not significant.  Across all experimental populations, annual extinction risk declined sharply between 10-100 individuals.  While demographic stochasticity and Allee effects made large contributions at very small (<10) population sizes, environmental variability determined extinction risk over most population sizes. Our results suggest that detailed ecological studies and management strategies to increase population size should be given primacy over descriptions of genetic structure and management emphasizing genetic diversification to most effectively conserve an at-risk species.