, Volume 158, Issue 4, pp 625–632 | Cite as

Impact of the invasive cane toad (Bufo marinus) on an Australian frog (Opisthodon ornatus) depends on minor variation in reproductive timing

  • Michael R. Crossland
  • Ross A. Alford
  • Richard Shine
Population Ecology - Original Paper


Invasive species are widely viewed as unmitigated ecological catastrophes, but the reality is more complex. Theoretically, invasive species could have negligible or even positive effects if they sufficiently reduce the intensity of processes regulating native populations. Understanding such mechanisms is crucial to predicting ultimate ecological impacts. We used a mesocosm experiment to quantify the impact of eggs and larvae of the introduced cane toad (Bufo marinus) on fitness-related traits (number, size and time of emergence of metamorphs) of a native Australian frog species (Opisthodon ornatus). The results depended upon the timing of oviposition of the two taxa, and hence the life-history stages that came into contact. Growth and survival of O. ornatus tadpoles were enhanced when they preceded B. marinus tadpoles into ponds, and reduced when they followed B. marinus tadpoles into ponds, relative to when tadpoles of both species were added to ponds simultaneously. The dominant tadpole–tadpole interaction is competition, and the results are consistent with competitive priority effects. However, these priority effects were reduced or reversed when O. ornatus tadpoles encountered B. marinus eggs. Predation on toxic toad eggs reduced the survival of O. ornatus and B. marinus. The consequent reduction in tadpole densities allowed the remaining O. ornatus tadpoles to grow more rapidly and to metamorphose at larger body sizes (>60% disparity in mean mass). Thus, exposure to B. marinus eggs reduced the number of O. ornatus metamorphs, but increased their body sizes. If the increased size at metamorphosis more than compensates for the reduced survival, the effective reproductive output of native anurans may be increased rather than decreased by the invasive toad. Minor interspecific differences in the seasonal timing of oviposition thus have the potential to massively alter the impact of invasive cane toads on native anurans.


Competition Density dependence Predation Recruitment Priority effects 



We thank Kay Bradfield for assistance with experimental work, the members of TeamBufo for encouragement and discussion, and the CSIRO Division of Wildlife and Ecology and the Australian Research Council for financial support. Ben Phillips helped us with statistical analyses. Comments from K. Smith and an anonymous reviewer helped improve an earlier version of this manuscript. The methods used in this study comply with current Queensland and Australian laws.


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Copyright information

© Springer-Verlag 2008

Authors and Affiliations

  • Michael R. Crossland
    • 1
  • Ross A. Alford
    • 2
  • Richard Shine
    • 1
  1. 1.School of Biological Sciences A08University of SydneySydneyAustralia
  2. 2.School of Marine and Tropical BiologyJames Cook UniversityTownsvilleAustralia

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