Costs of dispersal alter optimal offspring size in patchy habitats: combining theory and data for a marine invertebrate

Authors

  • Scott C. Burgess,

    Corresponding author
    1. CSIRO Marine and Atmospheric Research, Cleveland Qld, 4163, Australia
    Current affiliation:
    1. Centre for Population Biology, University of California Davis, Davis, California, USA
    • School of Biological Sciences, University of Queensland, Brisbane Qld, 4072, Australia
    Search for more papers by this author
  • Michael Bode,

    1. School of Botany, University of Melbourne, Melbourne Vic, Australia
    Search for more papers by this author
  • Dustin J. Marshall

    1. School of Biological Sciences, University of Queensland, Brisbane Qld, 4072, Australia
    Current affiliation:
    1. School of Biological Sciences, Monash University, Clayton, Melbourne, Victoria, Australia
    Search for more papers by this author

Correspondence author. E-mail: scburgess@ucdavis.edu

Summary

  1. Much of the theory on offspring size focuses on the effects of habitat quality on the relationship between offspring size and fitness. Habitat spacing may be another important factor that affects selection on offspring size when offspring disperse prior to colonization and accrue deferred costs that are mediated by offspring size.

  2. We developed a theoretical model, based on a well-known optimality model, of how selection on offspring size changes with dispersal distance. The model assumes that offspring fitness depends on both offspring size and dispersal duration and that dispersal time and distance are positively related. Such assumptions are based on thousands of marine invertebrate species with non-feeding larvae, but our model also applies more generally to any organism where offspring size modifies the energetic costs of dispersal, and there is a positive relationship between dispersal duration and distance.

  3. Our model predicts that, even when habitat quality does not vary, more isolated habitats may favour the production of fewer, larger offspring if smaller offspring incur greater deferred costs of dispersal. We then empirically demonstrate that offspring size and dispersal duration have interactive effects on post-settlement survival in a marine invertebrate (Bugula neritina), and such size-dependent deferred costs of dispersal are of a magnitude sufficient enough to potentially favour larger offspring in isolated habitats.

  4. Together, our results indicate that the spatial pattern of suitable habitat could impose very different selective regimes on offspring size compared with the effects of habitat quality. Furthermore, our predictions contrast to those predicted for seed size and dispersal in plants, where the production of smaller, more numerous seeds is often a more efficient way for mothers to access distant, suitable habitat.

Ancillary