Project: Effects of Demography and Genetics on Extinction in Small Populations: Experiments with an Exploited Kelp

NSF Award Abstract:
The process of species extinction represents both a basic ecological and societal concern. Despite interest in extinction processes, there is little empirical information on mechanisms leading to extinction, particularly in marine systems, because extinction events involve small population sizes and are infrequent. Small population size is thought to increase the risk of extinction through several different mechanisms. Ecological mechanisms include increased variation in population growth rates due to chance events (demographic stochasticity), and positive density dependence (i.e., reduced population growth at low density). Genetic mechanisms include loss of favorable alleles due to chance events (genetic drift) and inbreeding depression.

This project will experimentally disentangle the effects of different mechanisms associated with small population size in a commercially-harvested marine kelp, the sea palm Postelsia palmaeformis. To test effects of genetic variation, experimental populations will be established from either a single founder, multiple founders from the same population, or multiple founders from different source populations. The genetic treatment will be combined with a density manipulation (large and small populations) to test for ecological effects of population size. Experimental populations will be monitored for times to extinction, and the underlying processes will be studied in detail by marking individual plants and measuring survival, fecundity, and growth rates. These data will be incorporated into a population model to determine the relative sensitivity of population growth to different effects of small population size and to different life stages. Concurrent monitoring of genetic structure of the experimental populations using AFLP fingerprinting techniques will provide an independent measurement of genetic dynamics and effects on population performance, and will validate basic assumptions of the study. The study will increase our understanding of the effects of small population size on extinction risk, help to characterize the life cycle of marine kelps, and provide important information for developing effective conservation and remediation strategies for exploited marine species.