Biological Invasions

, Volume 15, Issue 5, pp 1005–1015 | Cite as

Road transect surveys do not reveal any consistent effects of a toxic invasive species on tropical reptiles

  • Gregory P. Brown
  • Matthew J. Greenlees
  • Benjamin L. Phillips
  • Richard Shine
Original Paper

Abstract

Effects of perturbations to wildlife often are measured by changes in rates of encounter with animals during standardised surveys, such as along roads. Previous work has predicted that the invasion of toxic cane toads (Rhinella marina) through the Australian tropics will cause massive mortality of anuran-eating snakes, and influence abundances of other native species. We surveyed three adjacent road transects for nocturnal snakes and lizards, beginning shortly before toads arrived at this site near Darwin, in the Northern Territory. In the wet-seasons of four successive years, we conducted surveys on 591 nights; on 302 of these nights, all three transects were surveyed. We recorded 8,880 live cane toads and 3,365 live reptiles. Toad numbers increased over time on all three transects but encounters with 13 species of native reptiles varied inconsistently. Eight of the 13 species of native reptile showed no significant change in encounter rates following the arrival of toads. Of the five species that did change in encounter rates, only one taxon (the bluetongue skink, Tiliqua scincoides intermedia) declined across all three transects. Encounter rates of the other four species often increased on at least one transect but decreased on at least one other. Thus, either the impact of cane toads on counts of reptiles differed between nearby sites, or (more likely) other factors had more influence on reptile numbers. A consistent decrease in reptile numbers on the busiest road over the study period suggests that local snake populations were affected more by road-kill than by invasive toads. Without spatial replication, this decrease could have been interpreted as an impact of toad invasion.

Keywords

Abundance Alien species Bufo marinus Ecological impact Predator–prey Surveys 

References

  1. Brown GP, Shine R (2002) The influence of weather conditions on activity of tropical snakes. Austral Ecol 27:596–605CrossRefGoogle Scholar
  2. Brown GP, Phillips BL, Shine R (2011) The ecological impact of invasive cane toads on tropical snakes: field data do not support predictions from laboratory studies. Ecology 92:422–431PubMedCrossRefGoogle Scholar
  3. Caughley G (1977) Analysis of vertebrate populations. Wiley, New YorkGoogle Scholar
  4. Doody JS, Green B, Sims R, Rhind D, West P, Steer D (2006) Indirect impacts of invasive cane toads (Bufo marinus) on nest predation in pig-nosed turtles (Carettochelys insculpta). Wildlife Res 33:49–54CrossRefGoogle Scholar
  5. Doody JS, Green B, Rhind D, Castellano CM, Sims R, Robinson T (2009) Population-level declines in Australian predators caused by an invasive species. Anim Conserv 12:46–53CrossRefGoogle Scholar
  6. Dubey S, Brown GP, Madsen T, Shine R (2009) Sexual selection favours large body size in males of a tropical snake (Stegonotus cucullatus, Colubridae). Anim Behav 77:177–182CrossRefGoogle Scholar
  7. Griffiths AD, McKay JL (2007) Cane toads reduce the abundance and site occupancy of freshwater goannas Varanus mertensi. Wildlife Res 34:609–615CrossRefGoogle Scholar
  8. Hagman M, Phillips BL, Shine R (2009) Fatal attraction: adaptations to prey on native frogs imperil snakes after invasion of toxic toads. Proc R Soc B 276:2813–2818PubMedCrossRefGoogle Scholar
  9. Jackman S (2011) pscl: classes and methods for R developed in the political science computational laboratory, Stanford University. Department of Political Science. R package version 1.04.1, Stanford, California. URL:http://pscl.stanford.edu/
  10. Letnic M, Webb JK, Shine R (2008) Invasive cane toads (Bufo marinus) cause mass mortality of freshwater crocodiles (Crocodylus johnstoni) in tropical Australia. Biol Conserv 141:1773–1782CrossRefGoogle Scholar
  11. Lever C (2001) The cane toad. The history and ecology of a successful colonist. Westbury Academic and Scientific Publishing, Otley, West YorkshireGoogle Scholar
  12. Llewelyn J, Phillips BL, Shine R (2009) Sublethal costs associated with the consumption of toxic prey by snakes. Austral Ecol 34:179–184CrossRefGoogle Scholar
  13. Madsen T, Ujvari B, Shine R, Olsson M (2006) Rain, rats and pythons: climate-driven population dynamics of predators and prey in tropical Australia. Austral Ecol 31:30–37CrossRefGoogle Scholar
  14. Nakagawa S (2004) A farewell to Bonferroni: the problems of low statistical power and publication bias. Behav Ecol 15:1044–1045Google Scholar
  15. O’Donnell S, Webb JK, Shine R (2010) Conditioned taste aversion enhances the survival of an endangered predator imperiled by a toxic invader. J Appl Ecol 47:558–565CrossRefGoogle Scholar
  16. Phillips BL, Shine R (2007) When dinner is dangerous: toxic frogs elicit species-specific responses from a generalist snake predator. Am Nat 170:936–942PubMedCrossRefGoogle Scholar
  17. Phillips BL, Brown GP, Shine R (2003) Assessing the potential impact of cane toads Bufo marinus on Australian snakes. Conserv Biol 17:1738–1747CrossRefGoogle Scholar
  18. Phillips BL, Brown GP, Webb JK, Shine R (2006) Invasion and the evolution of speed in toads. Nature 439:803PubMedCrossRefGoogle Scholar
  19. Phillips BL, Brown GP, Greenlees M, Webb JK, Shine R (2007) Rapid expansion of the cane toad (Bufo marinus) invasion front in tropical Australia. Austral Ecol 32:169–176CrossRefGoogle Scholar
  20. Phillips BL, Greenlees MJ, Brown GP, Shine R (2010) Predator behaviour and morphology mediates the impact of an invasive species: cane toads and death adders in Australia. Anim Conserv 13:53–59CrossRefGoogle Scholar
  21. Pramuk J (2006) Phylogeny of South American Bufo (Anura: Bufonidae) inferred from combined evidence. Zool J Linn Soc 146:407–452CrossRefGoogle Scholar
  22. Price-Rees SJ, Brown GP, Shine R (2010) Predation on toxic cane toads (Bufo marinus) may imperil bluetongue lizards (Tiliqua scincoides intermedia, Scincidae) in tropical Australia. Wildlife Res 37:166–173CrossRefGoogle Scholar
  23. Shine R (2010) The ecological impact of invasive cane toads (Bufo marinus) in Australia. Q Rev Biol 85:253–291PubMedCrossRefGoogle Scholar
  24. Shine R, Brown GP (2008) Adapting to the unpredictable: reproductive biology of vertebrates in the Australian wet-dry tropics. Phil Trans R Soc B 363:363–373PubMedCrossRefGoogle Scholar
  25. Ujvari B, Madsen T (2009) Increased mortality of naïve varanid lizards after the invasion of cane toads (Bufo marinus). Herpetol Conserv Biol 4:248–251Google Scholar
  26. Ujvari B, Shine R, Madsen T (2011) Detecting the impact of invasive species on native fauna: cane toads (Bufo marinus), frillneck lizards (Chlamydosaurus kingii), and the importance of spatial replication. Austral Ecol 36:126–130CrossRefGoogle Scholar
  27. Woinarski JCZ, Milne DJ, Wanganeen G (2001) Changes in mammal populations in relatively intact landscapes of Kakadu National Park, Northern Territory, Australia. Austral Ecol 26:360–370CrossRefGoogle Scholar
  28. Woinarski JCZ, Armstrong A, Price O, McCartney J, Griffiths AD, Fisher A (2004) The terrestrial vertebrate fauna of Litchfield National Park, Northern Territory: monitoring over a 6-year period and response to fire history. Wildlife Res 31:587–596CrossRefGoogle Scholar
  29. Zuur AF, Ieno EN, Walker NJ, Saveliev AA, Smith GM (2009) Mixed effects models and extensions in ecology with R. Springer, New YorkCrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media Dordrecht 2012

Authors and Affiliations

  • Gregory P. Brown
    • 1
  • Matthew J. Greenlees
    • 1
  • Benjamin L. Phillips
    • 1
    • 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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