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Keystone predators (eastern newts, Notophthalmus viridescens) reduce the impacts of an aquatic invasive species

  • Conservation Ecology
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Abstract

Predation, competition, and their interaction are known to be important factors that influence the structure of ecological communities. In particular, in those cases where a competitive hierarchy exists among prey species, the presence of certain keystone predators can result in enhanced diversity in the prey community. However, little is known regarding the influence of keystone predator presence on invaded prey communities. Given the widespread occurrence of invasive species and substantial concern regarding their ecological impacts, studies on this topic are needed. In this study I used naturalistic replications of an experimental tadpole assemblage to assess the influence of predatory eastern newts, Notophthalmus viridescens, on the outcome of interspecific competition among native and nonindigenous tadpoles. When newts were absent, the presence of the tadpoles of one invasive species, the Cuban treefrog, Osteopilus septentrionalis, resulted in decreased survival and growth rate of the dominant native species, Bufo terrestris, and dominance of the tadpole assemblage by O. septentrionalis. However, the presence of one adult newt generally reduced or eliminated the negative impacts of O. septentrionalis tadpoles, resulting in comparable survival and performance of native species in invaded and noninvaded treatments. Differential mortality among the tadpole species suggests that newts preyed selectively on O. septentrionalis tadpoles, supporting the hypothesis that newts acted as keystone predators in the invaded assemblage. The presence of nonindigenous larval cane toads, Bufo marinus, did not significantly affect native species, and this species was not negatively affected by the presence of newts. Collectively, these results suggest that eastern newts significantly modified the competitive hierarchy of the invaded tadpole assemblage and reduced the impacts of a competitively superior invasive species. If general, these results suggest that the presence of certain species may be an essential factor regulating the ecological impacts of biological invasions.

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Acknowledgements

I thank C. K. Dodd and A. C. Echternacht for guidance and support throughout this project. W. J. Barichivich, K. F. Noble, and J. S. Staiger provided significant logistic and personal support and assisted with field and laboratory work. L. I. Casey and J. E. Earl helped monitor the experiments and collect data. M. L. Beals, C. K. Dodd, A. C. Echternacht, M. S. Gunzburger, D. Simberloff, and two anonymous reviewers commented on the manuscript. Lerio Corporation donated the vinyl tanks used in this research. This research was funded primarily by a U.S. Geological Survey Cooperative Ecosystem Study Unit agreement grant. The University of Tennessee Graduate School and Department of Ecology and Evolutionary Biology provided additional financial support for this project. This research was conducted in accordance with all applicable laws and was approved by the University of Tennessee IACUC, protocol # 1246.

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Authors and Affiliations

  1. Department of Ecology and Evolutionary Biology, The University of Tennessee, 569 Dabney Hall, Knoxville, TN, 37996-1610, USA

    Kevin G. Smith

  2. Florida Integrated Science Center, United States Geological Survey, 7920 NW 71st St, Gainesville, FL, 32653, USA

    Kevin G. Smith

  3. Department of Zoology, School of Environmental Science and Development, North-West University, Private Bag X6001, 2520, Potchefstroom, South Africa

    Kevin G. Smith

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  1. Kevin G. Smith
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Correspondence to Kevin G. Smith.

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Communicated by David Post

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Smith, K.G. Keystone predators (eastern newts, Notophthalmus viridescens) reduce the impacts of an aquatic invasive species. Oecologia 148, 342–349 (2006). https://doi.org/10.1007/s00442-006-0370-y

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