MEPS 269:49-59 (2004)  -  doi:10.3354/meps269049

Allee effects in marine systems

Joanna Gascoigne1,2,*, Romuald N. Lipcius2

1Virginia Institute of Marine Science, College of William and Mary, Askew Street, Gloucester Point, Virginia 23062, USA
2Present address: School of Ocean Sciences, University of Wales Bangor, Menai Bridge, PO Box 1346, Anglesey LL59 5AB, UK

ABSTRACT: The fitness or population growth rate of populations with Allee effects increases with increasing population size or density up to a certain threshold. Allee effects are possible in marine populations, as they are less open than has been assumed and may have a metapopulation structure. We modelled the population consequences of Allee effects and show that increases in mortality interact with critical Allee thresholds, such that an Allee effect with no population consequences at low mortality can drive a population to extinction when mortality is increased. In heavily fished species, populations with strong Allee effects go extinct at lower levels of fishing mortality, or conversely as fishing mortality increases, weaker Allee effects can drive population to extinction. We found little empirical evidence in the literature for widespread Allee effects in marine populations, although we found some suggestive observations, particularly for broadcast spawners and in exploited populations This might be due to methodological problems or long time lags. Many marine species have components of their life history or ecology which could in theory generate Allee effects; however the population level consequences of these potential mechanisms remains virtually unexplored. We suggest that including Allee effects in models of vulnerable populations may be critical for the precautionary management of exploited and threatened marine species.


KEY WORDS: Allee effects · Positive density dependence · Inverse density dependence · Depensation


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