The recent paper by Hanna Kokko and Graeme D. Ruxton (2000), "Breeding suppression and predator-prey dynamics" [Ecology 81(1):252-260], presents a model of adaptive changes in population dynamics. The equations used for fitness (equations 2a and 2b) should read as follows:
[V.sub.X] = [S.sub.X](X,Y,[m.sub.X]) + [m.sub.X][S.sub.x](X,Y,[m.sub.X])(2a)
[V.sub.Y] = [S.sub.Y](X,Y,[m.sub.Y]) + [m.sub.Y][s.sub.y](X,Y,[m.sub.Y]). (2b)
The original equations incorrectly scaled the reproductive value increase that parents obtain by producing offspring by 1/2. While this is true for each offspring in a diploid species, Eqs. 2a and 2b refer to female-to-female reproduction only. Since (assuming a 1:1 primary sex ratio) the production of females is associated with production of an equal number of males, the fitness benefit from each brood doubles, thus canceling the diploidy scaling. The corrected equations above match Fisher's (1930) formulation where only same-sex offspring add to the parent's fitness, unsealed by relatedness. In a treatment that explicitly includes both sexes, sex-specific reproductive values would have to include genetic relatedness (e.g., Taylor 1988).
This correction removes the factors 2 and 0.5 from Eqs. 4, 5a, and 5b. Maximizing [V.sub.X] and [V.sub.Y], under the correction, will always tend to increase rather than decrease population growth rates (though this may again be violated in an age-structured model where parents may have higher reproductive values than new recruits). The main conclusions of the paper, concerning the range of possible effects on dynamics, however, are not altered by the corrected equations. The shape of the new density dependence can still vary in ways that either promote or destroy population stability (see online Appendix: Fig. 1.). Therefore, while parameter values at which specific examples are generated will differ from those presented in Kokko and Ruxton (2000), equivalent examples can be generated. As an example, in the online Appendix, Fig. 2 presents an analogous example to Fig. 4 of Kokko and Ruxton (2000), showing predator-induced oscillations.
Fisher, R. A. 1930. The genetical theory of natural selection. Clarendon, Oxford, UK.
Kokko, H., and G. D. Ruxton. 2000. Breeding suppression and predator-prey dynamics. Ecology 81:252-260.
Taylor, P. D. 1988. Inclusive fitness models with two sexes. Theoretical Population Biology 34:145-168.
The two figures illustrating points made in the above errata are available in ESA's Electronic Data Archive: Ecological Archives E081-012.