Density-dependent sex ratio adjustment and the allee effect: a model and a test using a sex-changing fish

Walker, Stefan P.W., Thibaut, Loïc, and McCormick, Mark I. (2010) Density-dependent sex ratio adjustment and the allee effect: a model and a test using a sex-changing fish. American Naturalist, 176 (3). pp. 312-321.

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Positive density dependence (i.e., the Allee effect; AE) often has important implications for the dynamics and conservation of populations. Here, we show that density‐dependent sex ratio adjustment in response to sexual selection may be a common AE mechanism. Specifically, using an analytical model we show that an AE is expected whenever one sex is more fecund than the other and sex ratio bias toward the less fecund sex increases with density. We illustrate the robustness of this pattern, using Monte Carlo simulations, against a range of body size–fecundity relationships and sex‐allocation strategies. Finally, we test the model using the sex‐changing polygynous reef fish Parapercis cylindrica; positive density dependence in the strength of sexual selection for male size is evidenced as the causal mechanism driving local sex ratio adjustment, hence the AE. Model application may extend to invertebrates, reptiles, birds, and mammals, in addition to over 70 reef fishes. We suggest that protected areas may often outperform harvest quotas as a conservation tool since the latter promotes population fragmentation, reduced polygyny, a balancing of the sex ratio, and hence up to a 50% decline in per capita fecundity, while the former maximizes polygyny and source‐sink potential.

Item ID: 15191
Item Type: Article (Research - C1)
ISSN: 1537-5323
Keywords: positive density dependence, polygyny, sexual selection, sex ratio adjustment, protogynous hermaphrodite, reef fish
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Reproduced with permission from the University Chicago Press (12 months embargo). Am. Nat. 2010. Vol. 176, pp. 312–321. © 2010 by The University of Chicago. 0003-0147/2010/17603-52068$15.00. All rights reserved.

Date Deposited: 13 Jan 2011 05:53
FoR Codes: 06 BIOLOGICAL SCIENCES > 0602 Ecology > 060202 Community Ecology (excl Invasive Species Ecology) @ 50%
06 BIOLOGICAL SCIENCES > 0602 Ecology > 060205 Marine and Estuarine Ecology (incl Marine Ichthyology) @ 50%
SEO Codes: 96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960808 Marine Flora, Fauna and Biodiversity @ 100%
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