Do invasive rodents impact endangered insular iguana populations?
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Ample evidence confirms that large invasive mammalian competitors and predators can devastate endangered insular iguana populations. However, the impact of invasive rodents, particularly rats (Rattus rattus), has remained elusive. Tail autotomy occurs frequently in lizards, often as an antipredator tactic, but sometimes from intraspecific aggression. Tail autotomy can incur substantial locomotor, behavioral, energetic, and survival costs. Furcation (i.e., dividing into branches) of regenerated tails may also result from attempted predation but occurs much more rarely, and with unknown costs. To evaluate the potential impact of invasive rodents—primarily rats—on West Indian rock iguanas (genus Cyclura), we compared tail-break and tail-furcation frequencies among 19 insular iguana populations (3,537 individuals) representing three species in the Bahamian Archipelago (including the Turks and Caicos Islands). The findings supported our three hypotheses: (1) that tail-break and tail-furcation frequencies are significantly higher in populations coexisting with invasive rodents; (2) that tail-furcation results primarily from failed predation attempts rather than intraspecific aggression; and (3) that frequencies of tail breaks and tail furcation are associated with each other, suggesting a degree of commonality in cause-effect (i.e., failed predation attempts). Tail furcation, in contrast to tail breakage, never occurred on islands lacking invasive mammalian predators. We conclude that invasive rodents, particularly rats, may have a greater impact on endangered insular iguana species than previously recognized.
KeywordsInvasive mammals Rats Lizards Tail autotomy Tail furcation Predation
We thank the many students and colleagues without whose support this work could not have been accomplished. Research by Hayes and Carter was supported by the Bahamas Ministry of Agriculture, Chicago Zoological Society, Denver Zoological Society, Disney Foundation, Insular Species Conservation Society, and International Iguana Foundation. Iverson’s studies were funded by the Test Fund, the Cope Fund, and the Professional Development Fund, all of Earlham College. Knapp’s work was funded by the John G. Shedd Aquarium’s citizen scientist iguana research program. All authors were also supported by their host institution(s), with research approved by their respective institutional animal care and use committees, and authorized by Bahamas research permits.
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